EGAN 2011 Workshop

26 Jun 2011, 18:30 → 30 Jun 2011, 19:00 Europe/Rome

Sala Polivalente (Centro Culturale Altinate, Padova, Italy)

Andres Gadea (CSIC, Valencia, Spain), Silvia Monica Lenzi (PD)

First Workshop of the European Gamma and Ancillary Detectors Network (EGAN) of ENSAR. The aim of the EGAN 2011 Workshop is to present the status of the gamma-spectroscopy research in Europe and to discuss its perspectives. Sessions will be dedicated to the presentation of recent theoretical studies, the latest results obtained at the gamma-ray facilities in Europe, and to the discussion on the challenges of the future research, the experimental campaigns and technical developments within gamma-ray techniques. The main topics to be discussed at the workshop are: • shell structure far from stability • isospin degrees of freedom • high spin structure • superheavy nuclei • nuclear astrophysics • collective excitations • nuclear moments • spectroscopy with radioactive ion beams • gamma-ray detectors technology • complementary instrumentation Annual Open Meeting of the AGATA Collaboration: Thursday 30th June will be dedicated to the annual open meeting of the AGATA collaboration organized by the AGATA Collaboration Council where the status, results and plans of the AGATA project will be discussed. Meetings of the EGAN Working Groups: Friday 1st July will be devoted to the meetings of the EGAN Scientific Committee and of the Working Groups coordinating the ancillary instrumentation developments.

Detailed Padova Map Padova_Map.pdf

EGAN compact programme EGANcompact2A4.pdf

EGAN2011 places map EGAN2011_infoMap.pdf

First Circular First_Circular.pdf

Photographs Egan2011_a.jpg Egan2011_b.jpg

Poster EGAN2011 (high res) Poster_EGAN2011_HR.pdf

Poster EGAN2011 (low res) Poster_EGAN2011_LR.jpg

Second Circular Second_Circular.pdf

Third Circular Third_Circular.pdf

Sunday 26 June

Welcome Cocktail

Monday 27 June

Welcome

1 The European Gamma and Ancillary detectors Network

Slides Lenzi-EGAN2011.pdf

Nuclear Theory

2 Nuclear Energy Density Functionals

Energy density functionals (EDF) have become a standard tool for nuclear structure calculations, providing a complete and accurate, global description of nuclear ground states and collective excitations. Guided by the density dependence of nucleon self-energies in nuclear matter, semi-empirical functionals have been adjusted to the equation of state and to bulk properties of finite nuclei, and applied to studies of arbitrarily heavy nuclei, exotic nuclei far from stability, and even systems at the nucleon drip-lines. EDF-based structure models have also been developed that go beyond the static mean-field approximation, and include collective correlations related to restoration of broken symmetries and to fluctuations of collective variables. These models are employed in analyses of structure phenomena related to shell evolution, including detailed predictions of excitation spectra and electromagnetic transition rates.

Speaker: Dario Vretenar (University of Zagreb)

Slides Vretenar.pdf

Jurogam

3 Present and future of JURO-spectroscopy at JYFL

The interplay between single-particle motion, collectivity and pairing in nuclei is seen as a rich tapestry of exotic excitations when systematic spectroscopic studies are extended to nuclei at the extremes of neutron and proton numbers. Excited states of nuclei at the proton drip line and in the region of super-heavy elements can be populated in fusion-evaporation reactions with stable-ion beams available from the JYFL accelerator system. Coupling of various spectrometer systems to the RITU gas-filled recoil separator at JYFL has enabled the first observation of excited states in 57 very-neutron deficient and heavy nuclei. Detailed nuclear structure studies have been carried out in nuclei with mass numbers from around 70 to 255. In these studies the backbone in gamma-ray detection is formed by former Euroball detectors. The present JUROGAM II array is comprised of 24 Eurogam Clovers and 15 Eurogam Phase 1 or Gasp detectors (eff. 6.2% at 1.3 MeV). Fully-digital electronics and TDR acquisition allow higher counting rates to be used. Research highlights and future perspectives for lowering the spectroscopic limit in various types of tagging experiments at the upgraded JYFL accelerator laboratory will be discussed.

Speaker: Rauno Julin (Department of Physics, University of Jyväskylä)

Slides Julin.pdf

4 Measurements of transition probabilities with JUROGAM and MINIBALL

The region of the nuclear chart around neutron-deficient Pb nuclei is of great interest in modern nuclear structure physics as intriguing phenomena such as coexistence of multiple shapes have been observed. The relation between these configurations and fundamental nucleon-nucleon interactions can be studied in detail by measuring transition probabilities between the coexisting structures. In nuclei close to the Z=82 shell gap and the neutron mid shell at N=104, large valence neutron space together with the relatively small proton shell gap provides us with an excellent laboratory for such studies [1,2]. Recoil distance Doppler-shift lifetime measurements have been carried out in the neutron-deficient Hg[3], Pb[4] and Po[4,5] nuclei close to the neutron mid shell at the Accelerator Laboratory of the University of Jyväskylä utilising the JUROGAM γ-ray spectrometer, the Köln plunger device and the RITU gas-filled recoil separator together with the selective tagging methods. Complementary Coulomb excitation measurements of neutron-deficient Pb beams in inverse kinematics have been carried out at ISOLDE at CERN utilising the MINIBALL γ-ray spectrometer. Experimental methods and the results of these studies will be discussed. [1] J. L. Wood et al., Phys. Rep. 215, 101 (1992). [2] R. Julin, K. Helariutta, and M. Muikku, J. Phys. G, 27, R109 (2001). [3] T. Grahn et al., Phys. Rev. C 80, 014324 (2009). [4] T. Grahn et al., Phys. Rev. Lett. 97, 062501 (2006). [5] T. Grahn et al., Phys. Rev. C 80, 014323 (2009) .

Speaker: Tuomas Grahn (University of Jyväskylä)

Slides Grahn.pdf

5 SAGE spectrometer status and first results

In-beam γ-ray and electron spectrometers have long been used as tools to probe the structure of atomic nuclei. However, if used separately they can provide only partial information of the nuclear de-excitation processes and consequently of nuclear structure. This becomes increasingly problematic in heavy nuclei, especially at low transition energies and high multipolarities, where internal conversion competes strongly with γ-ray emission. The SAGE spectrometer [1] allows efficient cross-coincidence measurements between γ-rays and conversion electrons by combining the JUROGAM II germanium detector array with a highly segmented silicon detector and a solenoid electron transfer system. It employs digital front-end electronics and is coupled with the RITU gas-filled recoil separator and the GREAT focal-plane spectrometer for Recoil-Decay Tagging studies. SAGE is primarily employed in the study of superheavy nuclei in the quest of finding the “Island of Stability” and the next closed spherical shells. Experiments studying shape coexistence in the light lead region have also been performed. The SAGE spectrometer has been successfully commissioned in the University of Jyväskylä in 2010. The setup will be described and results from the first in-beam measurements showing the performance of the spectrometer will be presented. 1. P. Papadakis et al., AIP Conf. Proc., 1090(2009) 14

Speaker: Philippos Papadakis (University of Liverpool)

Slides Papadakis.pdf.pdf

6 In-beam spectroscopy in the region of ²⁵⁴No at JYFL

Nuclei in the neighbourhood of 254No are the heaviest nuclei, which have been studied by in-beam spectroscopic methods, and in which the decay paths of several K isomers have be delineated. These nuclei can be produced with relatively high cross section due to favourable projectile-target combinations, and give valuable information on single-particle and collective properties in a region just below the heaviest elements which have been produced in laboratory. This region is therefore an important testing ground for the predictions of state-of-the-art models describing superheavy elements. JUROGAM is an array of Compton-suppressed HPGe detectors at JYFL, which was upgraded to JUROGAM II in 2008. JUROGAM II has improved efficiency and can handle higher count rates because of the use of digital electronics. In combination with the gas-filled recoil-separator RITU and the focal-plane detector set-up GREAT, it is a powerful tool to make in-beam studies of very heavy nuclei with the help of the so-called Recoil-Decay Tagging (RDT) technique. Recently, ground-state bands could be established or extended in 246,248,250Fm. The results extend the systematics of nuclei in this region in terms of moment of inertia and excitation energies of rotational states. The results give as well a proof of principle, that other ground-state bands in the region (such as 256Rf) will be available for spectroscopy in the future, as new cross section limits have been reached. The spectroscopy of odd-even nuclei is more challenging due to the highly-fragmented spectra. Nevertheless, two rotational bands could be established in 255Lr, which is the heaviest nucleus so far to be studied in-beam. The level scheme at lower excitation energy is still under debate, and future in-beam and focal-plane studies will shed light on the exact positioning and spins of these bands.

Speaker: Steffen Ketelhut (Department of Physics, University of Jyväskylä)

Slides Ketelhut_EGAN2011.pdf

Nuclear Theory

7 Nuclear forces and spectroscopy

I will discuss some aspects of nuclear spectroscopy in the relation to the evolution of the structure of exotic nuclei by nuclear forces. There are several distinct components in nuclear forces in nuclei. Among them, the tensor force and the three-body force show visible effects on this evolution, as well as the major part of the central force. The shell evolution is, in fact, widely observed phenomena with many evidences. But it affects strongly the nuclear deformation which is nothing but a Jahn-Teller effect. I will sketch some examples from different angles, together with some basic arguments as to why particular patterns of the evolution are expected to occur. Examples will be discussed by including recent experiments on exotic oxygen, silicone, tin and other heavier nuclei.

Speaker: Takaharu Otsuka (University of Tokyo, Japan & MSU, US)

Slides Otsuka.pdf

Ancillaries

8 Status and perspectives of detector arrays of LaBr3:Ce

In the most recent years large volume LaBr3:Ce crystals have become available. The interest of the scientific community toward such kind of crystals is connected to its excellent scintillation properties. In fact, the LaBr3:Ce is an inorganic material which, when doped with 5% Cerium, shows the best energy resolution among all scintillators (2.7% a 661 keV) and an excellent subnanosecond time resolution. The LaBr3:Ce effective atomic number is high because of Lanthanum (Z=57) and its density is 5.1 g/cm3 which has to be compared with that of NaI (3.67 g/cm3), BGO (7.13 g/cm3) and HPGe (5.32 g/cm3) [1-3]. In addition, the crystal shows good temperature stability [4] and linearity in the production of scintillation light [5]. The first cylindrical 3" x 3" crystals have been produced in 2006 while in 2007 it was possible to reach the size of 3" x 6". In 2008 the first 3.5" x 8" detector has been delivered to Milano. Up to now we have received 6 large volume 3.5”x8” LaBr3:Ce crystals and for the end of the year an array of 10 of such detectors is planned to be ready to measure. Such a system can be coupled to an HPGe array either to significantly increase its coincidence efficiency keeping a selectivity in -rays energy or in a standalone mode in case peak density is low enough or background it extremely high. An overview of the R&D activity for the optimization of the performances of these detectors, of the tests with high energy g-rays and its expected performances will be given.

Speaker: Franco Camera (INFN and Univ. of MI)

Slides Camera.pdf

9 Overview of the PARIS Project

With the next generation of radioactive beams, rich research programs in nuclear physics could be addressed. However, they require efficient and dedicated detection systems. In particular, letters of intent for SPIRAL2 have shown the necessity to build a new calorimeter for medium and high-energy gamma-rays. The PARIS (Photon Array for the studies of Radioactive and Ion Stable beams) array should have the required characteristics through the exploitation of the novel scintillator LaBr3 (produced by Saint Gobain) that has an energy resolution of about 3% at 662 keV with excellent time response. A wide range of physics cases are envisaged from discrete gamma-ray spectroscopy (up to 15 MeV, at low multiplicity) to studies of giant resonances (up to 50 MeV) and reaction dynamics (sum-spin spectrometer for medium gamma-ray energies). To fulfil such a program, PARIS should be highly flexible, modular, allowing synergies with other arrays such as GASPARD and/or AGATA. The main characteristics of the PARIS array are given in this talk with highlights on the developments made to try and keep the excellent intrinsic LaBr3 properties. An overview of the current status and plans up to the first SPIRAL2 beams are also presented. On behalf of the PARIS collaboration

Speaker: Olivier Stezowski (IPN Lyon)

Slides Stezowski.pdf

12:45 Lunch break

Exogam

10 EXOGAM: recent results and near future perspectives

The EXOGAM array is installed at GANIL since 2001. During these ten years, it has been extensively used in various experimental areas of the laboratory, under many different configurations and attacking several physics problem. On average, the EXOGAM detectors are present in the experimental setups in more than half of the beam time. The physics outcome of such an intense use is vast and covers many facets of both nuclear structure and reaction mechanism studies. In this talk, some of the latest results obtained with the array will be presented. This will cover the physics along the N=Z line studied using fusion-evaporation reactions as well as some examples obtained via deep-inelastic reactions in the region of neutron rich nuclei around 68Ni. In most of the time, and in the examples which will be mentioned in the talk, EXOGAM was coupled to another set of detectors: either the large acceptance VAMOS spectrometer or the Neutron Wall and the DIAMANT charged particle array. In 2012, the array will be moved to the ILL for an experimental campaign of about four months (two reactor cycles). The physics programme of this campaign will be briefly described. Finally, after these ten years of exploitation, it is time for the EXOGAM array to be upgraded by equipping the Clover detectors with a new full digital electronics. This is the purpose of the EXOGAM2 project which is currently developing. The status of this development will be given.

Speaker: Gilles de FRANCE (GANIL)

Slides DeFrance.pdf

11 Structure of the N=Z nucleus ⁹²Pd: Evidence for an isoscalar spin-aligned neutron-proton coupling scheme

In nuclei with equal neutron and proton numbers (N=Z), the unique nature of the atomic nucleus as an object composed of two distinct types of fermions can be expressed as enhanced correlations arising between neutrons and protons occupying orbitals with the same quantum numbers. Such correlations have since several decades been predicted to favour a new type of nuclear superfluidity; isoscalar neutron-proton pairing, in addition to normal isovector pairing which dominates the structure of most known nuclei. Despite many experimental efforts these predictions have not been confirmed. N=Z nuclei with mass number > 90 can only be produced in the laboratory with very low cross sections. The related problems of identifying and distinguishing such reaction products and their associated gamma rays from the vast array of N>Z nuclei that are present in much greater numbers from the reactions used have prevented observation of their low-lying excited states until recently. In the present work the experimental difficulties have been overcome through the use of a highly efficient, state-of-the-art detector system and a prolonged experimental running period. Gamma-ray transitions from excited states in 92Pd were identified at the Grand Accelerateur National d'Ions Lourds (GANIL), France, using a combination of state-of-the-art high-resolution gamma-ray, charged particle, and neutron detector systems: The EXOGAM HPGe detector array coupled to the Neutron Wall liquid scintillator detector array and the DIAMANT CsI(Tl) charged particle detector system. The results have revealed evidence for a transition from normal superfluidity and seniority coupling, to an isoscalar spin-aligned coupling scheme in the ground states and low-lying excited states of the heaviest N=Z nuclei [1]. This new neutron-proton “paired phase” is different from the earlier predictions of a neutron-proton BCS type of pairing condensate and is predicted to have a considerable impact on the level structures and ground state properties of the heaviest N~Z nuclei. The talk will mainly focus on data analysis aspects and the experimental results. 1. B. Cederwall et al., Nature 469, 68 (2011)

Speaker: Farnaz Ghazi Moradi (The Royal Institute of Technology-KTH)

12 Prompt and delayed spectroscopy in the vicinity of ⁶⁸Ni at VAMOS-EXOGAM

Excited states in a wide range of neutron rich nuclei around 68Ni have been studied using the EXOGAM array in coincidence with the VAMOS large acceptance spectrometer. The nuclei of interest were produced via multi nucleon transfer reactions in inverse kinematics using a 238U beam at an energy around 16% above the Coulomb barrier. In nuclei located below 68Ni, a recent experimental work revealed the possible appearance of a third island of inversion. A sudden increase of collectivity from 62Fe to 64Fe has been observed and indicates a weakness of the N=40 subshell gap. The comparison with shell model calculations, show that the neutron g9/2 and d5/2 orbitals become active below N=40 when removing protons from the 68Ni core. Above 68Ni, the first 7/2\- state observed in the structure of copper isotopes can be interpreted as one proton in the p3/2 orbital coupled to the first 2+ state in nickel isotones. Similarly, as suggested by D. Pauwels et al, a one proton hole in the f7/2 orbital coupled to the first 2+ state in nickel isotones should induce some collectivity in the cobalt isotopes. The question of the nature of the low lying states in neutron rich Co isotopes therefore arises and it is the focus of this paper to discuss the structure of some nuclei in this mass region. To this end, we performed two complementary experiments at GANIL which aimed at 1) measuring the evolution of collectivity and 2) searching for the presence of isomers. In the first experiment, the lifetimes of the low-lying 9/2\- and 3/2\- excited states in 63,65Co have been measured for the first time using the recoil-distance Doppler shift method and the associated B(E2) transition probabilities extracted. The data from this experiment have been compared with large scale shell model calculations performed with the ANTOINE code using different interactions. A detailed analysis of the wave functions describing the states of interest in cobalt isotopes toward N=40 will be discussed. The results seem to indicate a different behavior as compared to what has been observed in the iron chain. The main goal of the second experiment we performed in this mass region was to perform the combined prompt and delayed gamma-ray spectroscopy using EXOGAM and the VAMOS spectrometer in a solenoid configuration. Preliminary results on new isomers and prompt decays will be presented.

Speaker: Aurore Dijon (GANIL)

Slides Dijon.pdf

Eagle

13 Central European Array for Gamma Levels Evaluation (EAGLE) - status report 2011

on behalf of the EAGLE collaboration The EAGLE multidetector gamma-ray spectrometer [1], installed at the Heavy Ion Laboratory, University of Warsaw, will soon enter the second phase of its development. 20 Phase-I detectors loaned by GAMMAPOOL will complement the present configuration of the system (EAGLE I), which consists of 12 HPGe ACS detectors that may be coupled to various auxiliary devices. Depending on type of measurements performed, these include a 4 π Si-Ball consisting of 30 individual Si detectors, an electron conversion spectrometer, a COULEX scattering chamber containing 48 PIN-diodes and a multiplicity filter consisting of 60 BaF2 crystals. The EAGLE-GAMMAPOOL campaign is scheduled for years 2011-2013: the full array will be used to study nuclear structure and reactions using beams from the Warsaw U-200P cyclotron. The current status of preparations for this campaign will be presented: \- mechanical frame \- liquid nitrogen transport line and automatic filling system \- Ge detectors annealing stands \- test experiments on EAGLE I, including studies of chirality by DSAM lifetime measurements, K-isomers, COULEX and Incomplete Fusion Reaction measurements. [1] see http://www.slcj.uw.edu.pl/eagle

Speaker: Julian Srebrny (Heavy Ion Laboratory, University of Warsaw)

Slides Srebrny.pdf

14 Dynamics of Incomplete Fusion Reaction - the first experiment on EAGLE array

The 20Ne+122Sn reaction was studied with the EAGLE [1] spectrometer, consisting of 12 Ge detectors and 30 elements Si-ball. The reaction mechanism was analyzed by an angular distribution of alpha particles, gated by gamma transitions characteristic for final reaction products. The data from our experiment, as well as 12C+160Gd [2] and 12C+51V [3] reactions, were interpreted in terms of a new model describing the dynamics of the Incomplete fusion reaction (ICF). Our model is a development of Sum Rule Model [4]. It is based on an assumption, that incomplete fusion is a two stage process. In the first stage, the projectile breaks apart before colliding with the target. In the second stage the projectile residue fuses with the target while the rest escapes in some effective potential. The escaping („projectile like”) fragment is emitted in forward angles, usually observed at θ<60 degrees in laboratory frame. ICF influence on high spin states population was shown [5], nevertheless so far proposed models don't handle the dynamics of the process - the creation of the compound nuclei and a „projectile like” fragment emission. Recently γ-ray fold distributions measured with the γ-detector array GASP [6], have been compared to the predictions of our model. We would like to briefly present the basics of the model as well as its software implementation – the COMPA code. It works in event by event mode, gives a complete information on the reaction products: spin and excitation energy of the recoil, reaction point coordinates, directions and velocities of the recoil and emitted light particles. The stopping of the reaction products in the passive elements of the setup, like support, target and backing, is taken into account. This way COMPA allows easy comparison with the experimental results. Bibliography [1] - J. Mierzejewski et al. submitted to Nucl. Instr. and Meth. A [2] - K. Siwek-Wilczyńska et al. Phys. Rev. Lett. 42, 1599(1979) [3] - D. J. Parker et al. Phys. Rev. C30, 143(1984) [4] - J. Wilczyński et al. Phys. Rev. Lett 45, 606 (1980) [5] - Pushpendra P. Singh et al. Phys. Rev. C 80, 064603 (2009) [6] - R.M. Lieder et al. submitted to Eur. Phys. J. A

Speaker: Jan Mierzejewski (Heavy Ion Laboratory, University of Warsaw)

Slides Mierzejewski.pdf

16:35 Coffee break

Nuclear Theory

15 Shell model calculations along Z=28 and N=50 shell closures

Recent progress in experimental techniques allows to study very exotic systems like neutron rich nuclei in the vicinity of Ni78. The spectroscopy of this region can be nowadays studied theoretically in the large scale shell model calculations. In this talk, I will report on the shell model developments leading to a unified description of neutron-rich nuclei between N=40 and N=50. In particular, I will discuss the evolution of the Z=28 and N=50 gaps as well as comment on the rigidity of neutron-rich Ni78 and proton-rich Sn100 nuclei.

Speaker: Kamila Sieja (IPHC STRASBOURG)

Instrumentation & Methods

16 Pulse Shape Analysis with the AGATA Demonstrator

AGATA (Advanced GAmma Tracking Array) is a new type of spectrometer using gamma ray Tracking. The principle of tracking bases strongly on the high segmentation of these detectors in combination with digital electronics. This allows to obtain online position information for the individual gamma interactions within the germanium shell with a resolution much beyond the physical segmentation volume of the detectors. A short introduction will be given on how the pulse shape analysis for AGATA is working. Some novel techniques on the characterization of these detectors will be presented as required for PSA. Finally it will be shown how position information is helpful to correct for neutron damage.

Speaker: Bart Bruyneel (CEA Saclay)

Slides Bruyneel.pdf

17 Gamma calorimeters for experimental studies relevant to explosive nucleosynthesis

A new method employing a large-volume NaI crystal was developed for cross-section measurements of astrophysically relevant capture reactions on medium-mass nuclei. The response function of such a 4 pi calorimeter enables the summing of all capture events. As a result, a single peak, the so-called sum peak, arises in the spectra. Its intensity can be used to obtain very low cross sections of capture reactions with unknown multiplicities. The method enables to first determine these multiplicities, which are then used to derive the corresponding efficiency of the sum peak by means of Monte Carlo simulations. Cross sections are finally obtained from the sum-peak intensity with an average uncertainty of approx.15%. Due to the unique features of the new method, coined 4pi-gamma-summing, a new large NaI detector (12inch x 24inch) was recently purchased with funds of the FP7/LIBRA project. In the present contribution, severe examples of cross section measurements relevant to explosive nucleosynthesis studies will be presented. In addition some interconnections to future arrays like PARIS or AGATA will be discussed.

Speaker: Sotirios Harissopulos (NCSR "Demokritos" - Athens)

Slides Harissopulos.pdf

18 FIssion Detector In AStrophysics (FIDIAS)

Time Projection Chambers are widely used since many years for tracking and identification of charged particles in high energy physics. The feasibility of using a low-cost and "mobile" instrument of this kind to count the recoils, instead of the gammas, emitted by a capture reaction in inverse kinematics is investigated. This approach would provide a breakthrough for cross section measurements of astrophysical relevance. Such a detector has been constructed at the Institute of Nuclear Physics of NCSR Demokritos in collaboration with the CEA, Irfu, Centre de Saclay. Some preliminary results from the first tests that have been performed with this detector will be presented, together with the future prospects of the project.

Speaker: Michail Axiotis (INP, NCSR "Demokritos")

Slides Axiotis.pdf

19 Gamma ray spectroscopy studies in Bucharest

A recent commissioned array that combines the excellent energy resolution of 8 HPGe detectors with the timing properties of 8 LaBr(3) scintillators was used in gamma-ray spectroscopy studies at the Bucharest FN tandem. The array's flexibility makes it suitable for lifetime measurements by In-Beam Fast Timing, Doppler Shift Attenuation Method and, in combination with a plunger device by Recoil Distance Method. Recent results will be presented for each of the methods mentioned.

Speaker: Constantin Mihai (IFIN-HH)

Slides Mihai.pdf

Welcome

20 The European Gamma and Ancillary detectors Network

Slides Lenzi-EGAN2011.pdf

Tuesday 28 June

Nuclear Theory

21 Correlations versus shell evolution in the Nuclear Shell Model

New trends in nuclear structure focus on the evolution of the spherical mean-field all over the nuclear chart. In a shell model context, occurence of magic numbers or development of regions of deformation result as a delicate balance between the monopole field and the residual correlations. We will illustrate the interplay between spherical shell gaps and deformation quadrupole correlations in several regions of the chart of nuclides. We will focus on the transitions from sphericity to deformation in neutron rich system at N=20 and N=40 and discuss the nature of strong correlations in proton rich systems at the N=Z line. In particular, the isoscalar versus isovector nature of correlations in paladium, cadmium and xenon self-conjugate systems will be discussed.

Speaker: Frederic Nowacki (Institut Pluridisciplinaire Hubert Curien, Strasbourg)

Slides Nowacki.pdf

Miniball

22 Gamma-ray Spectroscopy far from Stability with MINIBALL

The MINIBALL spectrometer utilizes successfully the huge variety of post-accelerated radioactive ion beams provided by REX-ISOLDE at CERN. In-beam -ray spectroscopy after Coulomb excitation or transfer reactions is performed with two optimized setups of ancillary detectors for particle detection. Details of the actual MINIBALL setup, including beam monitoring devices and methods to deal with beam contamination, will be presented. The physics program is covering a wide range of shell model investigations from the light sd-shell nuclei up to the Pb region. Especially the enlarged availability of exotic heavy ion beams enables unique studies of collective properties up to the actinide region. In future the HIE-ISOLDE project will provide promising perspectives for new MINIBALL experiments.

Speaker: Peter Reiter (IKP University of Cologne)

Slides Reiter.pdf

23 Coulomb Excitation of Isomeric states of ⁷⁰Cu

Extensive studies on Cu neutron-rich isotopes have been performed in recent years at REX-ISOLDE in the aim to investigate the nuclear structure in the vicinity of the N=40 sub-shell closure. In particular the study of odd-odd 68,70Cu nuclei was reported in [1] where for the first time low-energy Coulomb excitation measurements with isomeric radioactive post-accelerated beams were performed. For the case of 70Cu, a Iπ = 6- isomeric beam was used to study the multiplet of states (3-, 4-, 5-, 6-) arising from the π2p3/2⊗μ1g9/2 configuration. The isomeric nature of the 6- and 3- states was experimentally determined in previous work [2]. The beam was produced at ISOLDE, CERN by selective laser ionization technique and then post-accelerated by REX-ISOLDE to about 2.8 MeV/ nucleon. Gamma rays were detected with the MINIBALL high resolution Ge detector array. The 4- state of the multiplet was populated by Coulomb excitation and the reduced transition probability B(E2, 6-→4-) value was determined. The remaining member of the multiplet, the 5- state, was not observed in this experiment . To provide complementary information about the energy levels and reduced transition probabilities of the connecting transitions within the states of the multiplet, a new experiment was performed using a Iπ = 3- isomeric beam. Besides the known transition deexciting the 4- state [1], gamma rays of 511 keV were observed for the first time and were unambiguously associated to the 5- state deexcitation. This observation fixes the energy, spin and parity of this state, completing the low-energy level scheme of 70Cu. Moreover B(E2) values for all the possible E2 transitions within the multiplet are now precisely measured and will be compared with extensive shell-model calculations to get additional information on the underlying structure of the π2p3/2⊗μ1g9/2 multiplet. [1] I. Stefanescu et al. PRL98, 122701 (2007) [2] J. Van Roosbroek et al. PRC69, 034313 (2004)

Speaker: Elisa Rapisarda (IKS Katholieke Universiteit Leuven)

Slides Rapisarda.pdf

24 Evolution of nuclear deformation in the neutron-rich Kr isotopes

Nuclei in the neutron-rich A&asymp100; mass region are well suited for the understanding of the development of collectivity. By adding only a few neutrons to the N=50 shell closure, collective effects can quickly occur. For the Z=40 (Zr) isotopes, N=56 becomes an effective shell closure, so that 96Zr is quoted as a doubly-magic nucleus. Adding only a few neutrons more, the Zr-isotopes get strongly deformed. This behaviour indicates a shape phase transition at N=60 from spherical to deformed shapes. For the Z=38 (Sr) and Z=42 (Mo) isotopes the systematics show a similar behavior, whereas for the Z=44 (Ru) isotopes, this rapid change of the shape seems to be attenuated. The aim of our work was to investigate the behaviour of the Z=36 (Kr) isotopes in this phase transition region by determining the energies of the 2+1 states and their E2 decay transition strengths to the ground state in 94Kr (N=58) and 96Kr (N=60). Therefore, we performed two experiments at REX-ISOLDE at CERN in 2009 and 2010. We utilized the high-efficiency MINIBALL gamma-ray spectrometer to analyse the emitted gamma-rays and scattered particles after Coulomb-excitation. We will show and discuss the preliminary results. This work was supported by BMBF under Grant 06KY205I and 06KY9136I.

Speaker: Michael Albers (Institut für Kernphysik, Universität zu Köln)

Slides Albers.pdf

25 Single Particle states in ⁶⁷Ni

The interest in the structure of nuclei around 68Ni has been triggered long ago by the observation of the high excitation energy of the first 2+ in this nucleus [1]. Combining this observation with the fact that a minimum is reached in the systematic of B(E2;2+ -> 0+)-values at N=40 in the neutron rich nickel chain has lead to interpretations in terms of a harmonic oscillator subshell closure resulting in extensive theoretical studies [2]. The excitation spectrum of odd mass nuclei in the direct neighborhood of closed shells is usually governed by single particle excitations. One-neutron transfer reactions are a useful tool to fix spins and parities of excited states and determine spectroscopic factors which can be compared to shell model predictions. Recent large scale shell model calculations have shown the sensitivity of certain nuclear parameters in this region to the size of the N=40 and N=50 shell gaps [3]. By measuring effective single-particle energies these shell gaps can be fixed and serve as valuable input for various nuclear models. In this case the excitation spectrum of 67Ni was studied by performing the 66Ni(d,p)67Ni reaction in inverse kinematics with an energy of 3 MeV/u at the REX-ISOLDE radioactive ion beam facility in CERN using the MINIBALL setup in combination with the T-REX particle detection array [4]. The extracted angular distributions of the protons -based on particle-gamma coincidences- can be compared with DWBA calculations in order to determine spin and parity of the excited states as well as spectroscopic factors. Population of levels with excitation energy up to 6 MeV has been observed, an preliminary angular distributions indicate that levels above the N=50 shell gap are populated. An overview of the latest results will be given, including preliminary angular distributions. [1] R. Broda et al. Phys.Lett.B 113, 279 (1982) [2] O. Sorlin et al. Phys.Rev.Lett. 88, 092501 (2002) [3] K. Langanke et al. Phys.Rev.C 67, 044314 (2003) [4] V. Bildstein et al. Prog.Part.Nucl.Phys 59, 386 (2007)

Speaker: Jan Diriken (IKS - KU Leuven)

Slides Diriken.pdf

10:55 Coffee break

Nuclear Theory

26 Nuclear structure of ¹³²Sn neighbors across the N=82 shell closure

The evolution of nuclear structure for nuclei with an extreme ratio of neutrons to protons is an outstanding problem in modern nuclear structure physics. A relevant role in this study is played by nuclei in the vicinity of doubly closed shells since they offer the opportunity for a direct test of the single-particle properties as well as of the nucleon-nucleon interaction. In this context, a key region is that of exotic 132Sn, which has been the subject of great experimental and theoretical interest during the last decade. In recent years we have studied neutron rich nuclei around 132Sn [1,3] aimed at explaining the available data as well as to make predictions that may be verified in a not too distant future. All these studies have been performed within the framework of the shell model with realistic two-body effective interactions, namely derived microscopically from the free nucleon-nucleon (NN) potential. In this kind of calculations, only the valence nucleons are treated as active particles while the core polarization effects are taken into account perturbatively in the derivation of the effective interaction Veff. More precisely, starting from the CD-Bonn NN potential [4] we construct a low-momentum potential Vlow−k that preserves the deuteron binding energy and scattering phase shifts of the original potential up to a certain cutoff momentum [5]. This Vlow-k is a smooth potential which, summed to the Coulomb force for protons, is used to derive Veff though the folded diagram method [6]. In our calculations we assume 132Sn as a core and take all single-particle or single-hole energies of the shell-model Hamiltonian from the experimental spectra of nuclei with one-valence nucleon, while the two-body matrix elements are derived by the procedure mentioned above. The results obtained for 132Sn neighbors compare well with the available experimental data. Here, we report selected results focusing attention on how some properties change when crossing the N=82 shell closure. In particular, we discuss proton-neutron mixed-symmetry 2+ states in N=80 and 84 nuclei, which allow us to investigate the interplay between identical particles and neutron-proton correlations. References [1] L. Coraggio, A. Covello, A. Gargano , and N. Itaco, Phys. Rev. C 80 061303(R) (2009), and references therein. [2] L. Coraggio, A. Covello, A. Gargano , and N. Itaco, Phys. Rev. C 80 021305 (2009), and references therein. [3] A. Covello, L. Coraggio, A. Gargano , and N. Itaco, J. Phys. : Conf. Ser. 267, 012019 (2011). [4] R. Machleidt, Phys. Rev. C 63, 024001 (2001). [5] S. Bogner, T.T.S. Kuo, L. Coraggio, A. Covello, and N. Itaco, Phys. Rev. C 65, 051301(R) (2002). [6] L. Coraggio, A. Covello, A. Gargano , N. Itaco, and T.T. S. Kuo, Prog. Part. Nucl. Phys. 62, 135 (2009) .

Speaker: Angelina Gargano (INFN NA)

Slides Gargano.pdf

Orgam

27 Gamma Spectroscopy at IPN Orsay

The Orsay Gamma Array (ORGAM) is presently installed and running in the Orsay Tandem since 2009. A large amount of beam time has been devoted to gamma ray spectroscopy between 2009 and 2011 for ORGAM campaigns. Current Jully, 2011, part of the ORGAM array will be moved to Warsow, Poland, for the EAGLE campaign. This motivated us to plan for an ORGAM phase2 campaign and think of an optimum way to continue having an important gamma ray spectroscopy program at the IPNO Tandem, either on neutron rich nuclei by deep inelastic collisions or on N=Z nuclei. A configuration with EUROBALL cluster and coaxial detectors is presently under study. This configuration should be compatible with different ancillary detectors, like FAZIA or PARIS demonstrators. I’ll present the status of ORGAM campaigns, of the mid-term (ORGAM phase2) and long-term future of gamma spectroscopy at the IPNO Tandem.

Speaker: Iolanda MATEA (IPN Orsay, France)

Slides Matea.pdf

28 Nuclear moment studies in transfer reactions with the ORGAM spectrometer

Experiments to study nuclear moments in single and multi-nucleon transfer reactions have been carried out at the Tandem-ALTO facility of Orsay using the ORGAM spectrometer. Quadrupole moment measurement of the 6- isomeric state in 66Cu has been measured in a single nucleon transfer on a Cu2O host. As this state results from a week coupling between the πp3/2 and the ν g9/2 orbitals, leading to sizable deformation at oblate and prolate shapes in the 68Ni region, we have observed the interplay between these two different deformation-driving orbitals [1]. Furthermore, we have investigated the possibility of using multi-nucleon transfer reactions for the population and nuclear moment studies of isomeric states in 66Cu and 63Ni [2]. These studies could not only serve as a base for the determination of the unknown electric-field gradient of Cu in Zn e.g. via a quadrupole moment measurement, but would also allow the determination of the nuclear-spin orientation in these reactions. Therefore, investigations of this type open possibilities to employ nuclear moment measurements and transfer reactions to both on the neutron-deficient and neutron-rich side of the nuclear chart. [1] R. Lozeva et al, Phys. Lett. B 694 (2011) 316–321 [2] R. Lozeva et al, AIP Conf. Proc. 1224 (2010) p.143-150

Speaker: Radomira Lozeva (IPHC, CNRS/IN2P3)

Slides Lozeva.pdf

29 Tetrahedral Symmetry in the Actinides: the ELMA Project

During the last few years the TetraNuc collaboration has launched a series of experiments in the Rare-Earth region to possibly demonstrate the existence of high-rank symmetries in subatomic physics focused on the tetrahedral symmetry [1]. Meanwhile an important progress has been made on the theory side. Some suggestions strongly indicate that the Actinides region may be of particular interest because of the role of the octahedral symmetry. Our analysis clearly points out that some light uranium isotopes are among the most interesting experimental candidates [2]. The studies of high-rank symmetries will focus in the future on the measurement of the gamma decay branching ratio of the candidate states but also on the B(E2) and B(E1) transition probabilities. One has to remind that in the exact static limit of the tetrahedral symmetry, both the static quadrupole moment and the dipole moment must vanish and hence both transition probabilities are expected to be small. In the uranium isotopes strong experimental hints comes from the excited negative parity bands that are reported in the literature with no or extremely weak E2 in-band transitions; this fact might sign weak B(E2) but also large B(E1). To go further experimentally, we need to measure the candidate states-lifetimes in the uranium isotopes of interest. Unfortunately, it is far from being an easy task for these nuclei because of the limited existing production possibilities: most of them preclude the lifetime measurements to be performed based on the available Doppler methods. This motivates us to develop the ELMA project (Electron for Lifetime Measurements in the Actinides). In this talk I will present a brief overview of the current experimental knowledge and develop the ideas on how to search for the symmetries in the Actinide region as well. The results* of an early ELMA test experiment run at IPN-Orsay with the ORGAM array and a 232Th target from the IPNO target laboratory will also be presented. * Analysis by G. Lehaut (IPN-Lyon) and L. Sengelé (IPHC-Strasbourg) [1] D. Curien et al. J.of Phys. CS 205, 012034 (2010) [2] D. Curien et al. Int. J. of Mod. Phys. E 20, 219 (2011)

Speaker: Dominique CURIEN (IPHC-DRS, Strasbourg)

Slides Curien.pdf

13:00 Lunch break

New Gamma-arrays

30 GRETINA: Status and Future Plans

The gamma ray tracking technique uses highly segmented Ge detectors, and measures pulse shapes from each of the segments using fast digital electronics. These pulses are analyzed, in a procedure called signal decomposition, to determine energy, time, and three-dimensional positions of all gamma-ray interactions. This information is then used, together with the characteristics of the Compton and pair-production processes, to group and sequence the interactions points and determine the scattering path of the original gamma-rays. A 4π detector array based on this novel technique would provide high efficiency (~40% for 1 MeV gamma rays), excellent peak-to-total ratio (~0.6), and accurate position resolution (~2mm), increasing the detection sensitivity of the spectrometer by several hundreds compared to current arrays used in nuclear physics research. GRETINA, a first implementation of such an array using coaxial crystals (6x6 segments) and covering 1π solid angle, was completed in March 2011 at LBNL. A similar system developed in Europe, the AGATA demonstrator, is currently running a campaign at Legnaro. In this talk, we will review the basic principles of gamma ray tracking and the measured performance of GRETINA with radioactive sources and in-beam experiments. Besides their intrinsic value as demonstrators of the tracking technique, these instruments provide unique physics opportunities in nuclear structure: we will discuss some examples and present the plans for commissioning runs and first research campaigns. This work is supported by US-DOE under contract number DE-AC02-05CH11231.

Speaker: Augusto Macchiavelli (Lawrence Berkeley National Laboratory)

31 Gamma-ray spectroscopy experiments at RIKEN

In the Radioactive Isotope Beam Factory (RIBF) stable primary beams of energies up to 345 MeV/nucleon are used to produce radioactive isotope beams via in-flight separation with the BigRIPS fragment separator. For gamma-ray spectroscopy experiments these radioactive beams are either incident on a secondary target for in-beam experiments or stopped to measure isomeric or beta-delayed gamma-emission. In my presentation I will report on the results obtained from the first gamma-ray spectroscopy experiments performed at the RIBF. For stopped-beam experiments neutron-rich nuclei in the mass region A=110 were investigated after fission of a 238U primary beam. In this mass region, shape transitions around the Zr isotopes were studied. The first in-beam gamma-ray experiments targeted the "Island of Inversion", a region in which the standard ordering of shells is disturbed by neutron intruder configuration across the N=20 shell gap. Besides showing the results from these first experiments an outlook on future gamma-ray spectroscopy campaigns at the RIBF will be given.

Speaker: Pieter Doornenbal (RIKEN)

Slides Doornenbal.pdf

32 The GALILEO project at LNL

The GALILEO project has the goal to build of a 4pi high-resolution gamma-ray array by combining the GASP tapered detectors with the Gammapool Cluster detectors. The array will be located at the National Laboratories of Legnaro and will take advantage of the stable beams provided by the Tandem-ALPI-PIAVE accelerator complex and, in the future, of the exotic radioactive ion beams provided by SPES. One of the objectives of the project is to rearrange the original EUROBALL 7-capsules clusters into triple clusters. The triple cluster detectors will be placed at 90 degrees while the GASP tapered detectors will cover the forward and backward angles symmetrically. Several R&D activities are ongoing to develop a complete cryostat for the new triple cluster detector and to build the corresponding anti-Compton shields. The development of the front-end, digital sampling, pre-processing and readout electronics take advandage of the recent achievements of the AGATA project in these fields. A strong physics case was made for the building of the GALILEO array based on Letters of Intent submitted by several research groups from all over the world. The research topics expressed in the Letters of Intent cover a wide range of challenging nuclear structure physics issues to be investigated by means of gamma-ray and particle spectroscopy. They cover the study of nuclei from one edge of stability at the N=Z line to the other edge in neutron-rich regions. Experiments include full spectroscopy of the nuclei of interest, lifetime measurements via Doppler shift or fast timing techniques, g-factor, quadrupole moments and transition probabilities measurements in Coulomb excitation and multi-nucleon transfer reactions. Many of the proposed experiments are challenging and require the coupling of the gamma-array to state-of-the-art ancillary detectors, such as the EUCLIDES light charged particle detector, the DANTE MCP array, the RFD recoil detector, the Cologne plunger, the TRACE E-DE Si pixel detector, neutron detectors (n-Ring, N-Wall, NEDA), the LUSIA array of DSSSD detectors, arrays of MW-PPAC. The holding structure of the GALILEO array is designed in such a way to allow an easy coupling to a wide range of ancillary detectors. In the present talk the status and perspectives of the GALILEO project will be discussed.

Speaker: Calin Alexandru Ur (INFN PD)

Slides Ur-EGAN-pub.pptx

Instrumentation & Methods

33 Fast timing using the Mirror Symmetric Centroid Difference Method.

The newly developed Mirror Symmetric Centroid Difference (MSCD) Method [1,2] will be presented. Applications using electron-electron, electron-gamma and gamma-gamma coincidences using a double-Orange spectrometer [3] and LaBr3(Ce) demonstrate the high potential of this new method. This work was supported by the BMBF under contract 06KY9136I and GSI F&E under contract KJOLIE. [1] J.M. Régis, G. Pascovici, J. Jolie, M. Rudigier, NIM A 622 (2010) 83. [2] J.M. Régis, PhD thesis, University of Cologne (2011). [3] J.M. Régis, et al. NIM A 606 (2009) 466. [4] J.M. Régis, Th. Materna, G. Pascovici, S. Christen, A. Dewald, C. Fransen, J. Jolie, P. Petkov, K.O. Zell Review of scientific instruments 81 (2010) 113505.

Speaker: Jan Jolie (Institut für Kernphysik, Universität zu Köln)

Slides Jolie.pdf

16:35 Coffee break

Contributions

34 RDDS lifetime measurements of yrast states in ¹⁸⁶Hg

In light, even-mass Hg isotopes, a weakly deformed oblate ground state band is found to coexist with a more deformed prolate band. To investigate the nuclear structure in more detail a recoil-distance Dopplershift (RDDS) experiment has been performed to determine absolute transition strengths in 186Hg. These transition strengths provide information on the level mixing amplitudes of the two involved collective excitations. The experiment was carried out using the GAMMASPHERE HPGe-Array at the Argonne National Laboratory and the Cologne coincidence Plunger, equipped with a Ta-backed 150Sm target and a gold stopper foil. The beam was 40Ar at 184 MeV. We will present first results of the experiment. Supported by DFG, DE 1516/1-1

Speaker: Matthias Hackstein (Institut für Kernphysik, Universität zu Köln)

Slides Hackstein.pdf

35 Angular Correlations for Triaxial Nuclear Molecule ²⁸Si-²⁸Si

High-spin resonances well above the Coulomb barrier in 24Mg+24Mg and 28Si+28Si systems exhibit many narrow and prominent peaks correlated among the elastic and inelastic channels, which suggest rather long-lived compound systems and offer intriguing subjects in nuclear physics. Angular correlation measurements for 28Si+28Si made with 4π gamma detectors have provided crucially important information on resonances. Characteristic features of the experiments are following three points; 1) the resonance at Ecm=55.8MeV decays to the inelastic channels as single and mutual 2+ even more strongly than the elastic one. 2) angular distributions in those channels indicate a dominance of a single orbital angular momentum L=J=38. 3) the angular correlations of the fragments 28Si and γ-rays emitted from the fragments indicate that the intrinsic spins of the constituent nuclei are in the reaction plane. The latter two show a dis-alignment between the orbital angular momentum and the fragments spins. By using a molecular model the authors investigated an equilibrium configuration of interacting two oblate nuclei, and showed it to be the equator-equator one. Couplings among various molecular configurations are taken into account by the method of normal mode around the equilibrium, which gives rise to the molecular modes of excitation such as butterfly motion. These excitations exist over the range of spin J=34~40 in which the equator-equator onfiguration is stable, and are expected to be the origin of the narrow resonances. Decay properties of the molecular states including spin alignments have been investigated to know which kinds of the molecular modes are consistent with the resonances observed. At the resonance energy Ecm=55.8MeV, very strong excitations are seen in both the single 2+ and mutual 2+ excitations. However the normal-mode excitations exhibit strong yields to the mutual 2+ channel, but weak enhancements to the single 2+ channel, and thus do not fit well. Only the molecular ground state appears to follow those decay characteristics. Since the equilibrium configuration is triaxial, rotations of the total system induce mixing of K-quantum numbers, which is consistent with the angular correlations measured as well as the dis-alignments. At a given angular momentum J, this configuration rotates in a triaxial way preferentially about the axis corresponding to the largest moment of inertia in the state with the lowest energy. Therefore the whole system rotates about the normal to the plane defined by the two pancake-like 28Si nuclei. The spins of the 28Si fragments are thus in this plane since no rotation can occur about the symmetry axes of 28Si. Thus the angular correlations are very well reproduced with the molecular ground state as well as the fragment angular distributions. In conclusion, study of the 28Si+28Si system by the dinuclear molecular model gives variety of molecular states. In them the molecular ground state with J=38 is a candidate for the resonance at Ecm=55.8MeV. For systematic study for excitations of the molecular modes, the same kind of information on the other nearby resonances of 28Si+28Si is strongly called for.

Speaker: Eiji UEGAKI (Dept. of Mech. Engineering, Akita Univ., Japan)

Slides Uegaki.pdf

36 Interplay between single-particle and collective excitations in argon isotopes populated by transfer reactions

Multinucleon transfer reactions have been investigated in 40Ar+208Pb via particle-gamma coincidences with the Prisma+Clara set-up. New states have been identified and the strongly populated states have been discussed and compared with the sd-pf shell model calculations. In odd Ar isotopes, we identified a significant population of 11/2- states, reached via neutron transfer. Their structure matches a stretched configuration of the valence neutron coupled to the vibration quanta. This fact has been used to consistently follow the evolution of deformation in odd Ar isotopes.

Speaker: Suzana Szilner (Ruder Boskovic Institute)

Slides Szilner.pdf

37 Transfer Experiments at REX-ISOLDE

T-REX is an ancillary detector device for the MINIBALL setup at REX-ISOLDE, CERN. It consists of eight position sensitive silicon barrel detectors as well as a DSSSD CD-detector. This allows to cover a large range of scattering angles, what gives the possibility to determine spins and relative spectroscopic factors after transfer reactions using RIBs. We will introduce the T-REX setup and discuss the technical status and discuss some aspects of its future development, especially with respect to the HIE-ISOLDE project. We give an overview on results in the region of the "Island of Inversion" and highlight the importance of transfer reactions at T-REX. We also show recent data from a two-neutron transfer reaction towards Ar-46 to discuss the evolution of the N=28 shell gap below Ca-48. Finally, we mention first steps to study the isospin dependence of the symmetry energy using T-REX. Similar studies at future next-generation RIB facilities may give important information on systems with extreme values of isospin, like neutron stars.

Speaker: Dennis Mücher (Physics Department E12, TU Munich)

Slides Muecher.pdf

38 Gamma decay of giant resonances within the Skyrme framework

A microscopic formalism that allows the calculation of the gamma decay of nuclear excited states has been developed. In particular, it has been applied to the direct gamma decay of the Isoscalar Giant Quadrupole Resonance in 208Pb to the ground state and to the lowest low-lying octupole state, as well. The phonons are calculated within fully self-consistent RPA, while the calculation of the gamma decay width is performed at the lowest contributing order of perturbation theory within the framework of the Nuclear Field Theory (NFT), including consistently the whole effective Skyrme interaction in the particle-vibration coupling (PVC) vertex. The resulting decay width to the lowest 3- state is only a few percent of the decay width to the ground state, as indicated by the experiment.

Speaker: Marco Brenna (INFN MI)

Slides Brenna.pdf

39 Octupole Collectivity: Coulomb Excitation of ²²⁴Ra at ISOLDE-CERN

There is considerable theoretical and experimental evidence that atomic nuclei can assume reflection asymmetric shapes that arise from the octupole degree of freedom. From a microscopic point of view, the wave functions of low-lying 3- octupole excitations must contain components which include the intruding unique parity state ( _l_ , _j_ ). Because of the nature of the octupole-octupole interaction in nuclei, strong octupole correlations arise when the Fermi level lies between this intruder subshell and a subshell with Δ _j_ , Δ _l_ =3, giving rise to [ _l_ , _j_ ; _l_ -3, _j_ -3] particle-hole configurations at relatively low excitation energies. The strongest correlations occur near the proton numbers _Z_ = 34, 56 and 88 and the neutron numbers _N_ = 34, 56, 88 and 134 where, for the heaviest nuclei, an octupole deformation can occur in the ground state. Indeed, at these values of _Z_ and _N_ , nuclei exhibit phenomena associated with reflection asymmetry such as odd-even staggering of the positive- and negative-parity yrast bands in even-even nuclei, parity doublets in odd mass nuclei, and enhanced _E_ 1 moments due to a division of the centre of charge and centre of mass. The only observable that provides unambiguous and direct evidence for enhanced octupole correlations in nuclei is the _E_ 3 matrix element, and the measure of octupole correlations in the ground state is the B( _E_ 3; 0+ → 3-). In the mass region where octupole correlations are expected to be largest, i.e. at _Z_ = 88 and _N_ = 134, there is a lack of spectroscopic data on _E_ 3 moments. So far, only for 226Ra, with its comparatively long half life of 1600 years, has it been possible to measure the B( _E_ 3) strength using Coulomb excitation. This talk will present the current status and the first results from the recent Coulomb excitation the post-accelerated 224Ra beam at REX-ISOLDE facility, CERN, using the MINIBALL setup.

Speaker: Liam P. Gaffney (University of Liverpool)

Slides EGANJun2011_Gaffney.pdf

40 Yrast structure of the proton-particle three-neutron-hole nucleus ²⁰⁶Bi

The 206Bi nucleus is a one-proton-particle, three-neutron-hole system with respect to the doubly magic 208Pb core. Its low-energy structure arises from 1p-3h couplings involving 1h9/2, 2f7/2, and 1i13/2 proton particles, and 3p1/2, 2f5/2, 3p3/2 and 1i13/2 neutron holes. The 206Bi ground state, with spin-parity Jπ=6+, is of πh9/2νf5/2-1 character, with the isomeric (T1/2=7.7 μs) Jπ=4+ member of the πh9/2νp1/2-1 multiplet lying only 60 keV above it. At higher excitation energies, two other isomeric states have been identified in an earlier study with the 205Tl(α,nγ) reaction[1]. These are the 10- state at 1045 keV with T1/2=0.89 ms and an assigned πh9/2νi13/2-1 configuration, and the 15+ excitation at 3147 keV, with a 15.6 ns half-life of πh9/2ν(p1/2)-1(i13/2)-2 character. The highest yrast states known thus far in 206Bi, i.e., 17+ and 18+ levels at 3604 and 4305 keV have been located in the 205Tl(α,nγ) work as well. An experiment performed recently at Argonne National Laboratory, USA, in which gamma rays emitted during reactions induced by a 76Ge beam on a thick 208Pb target were measured with the Gammasphere array, showed that deep-inelastic processes populate relatively high-spin states in nuclei located "north-west" of 208Pb. One of the intense products was 206Bi. We analyzed the spectra of delayed gamma rays (emitted between beam bursts separated by ca. 412 ns) by requiring coincidences with the known 206Bi yrast transitions. A series of higher-lying gamma rays, deexciting two previously unknown 206Bi isomers, have been found. Inspection of the double gates set on these newly discovered transitions, allowed us to extend the 206Bi level scheme up to an isomeric level with the half-life >1 μs located at approximately 10 MeV. For the lower isomer, a half-life of 155(15) ns was established . With the help of the in-beam gamma-ray angular distributions and the extracted conversion coefficients we obtained information on multipolarities of some strong transitions. We have been able to propose spin and parity assignments for the new states up to 23+, based on their decay pattern and on comparisons with the shell model calculations. For higher lying states, spin and parity assignments were done on the basis of the extracted transition multipolarities. As the result, the spin of Jπ=32+ was proposed for the higher isomer what makes it one of the longest-lifetime isomers known with spin above 30 ħ. The yrast excitations located at energies up to approx. 7 MeV can be described in terms of the 1p-3h couplings. Higher lying yrast states, including the two new isomers, must involve neutron excitations across the N=126 shell gap.

Speaker: Natalia Cieplicka (Institute of Nuclear Physics, Polish Academy of Sciences, Krakow)

Slides Cieplicka.pdf

41 NEDA – NEutron Detector Array: Performance of different configurations

This work includes the simulations performed in order to design a new neutron detector array NEDA (NEutron Detector Array). NEDA will address the physics of neutron-rich as well as neutron deficient nuclei, mainly in conjunction with gamma-ray detectors arrays like AGATA, EXOGAM2 and PARIS. The geometry of NEDA is being optimized using Geant4 and ROOT analysis codes. Different size of the unitary cells as well as two materials (BC501A and BC537) are considered to study the neutron efficiency and the cross talk between the detectors. Two main geometries have been considered: 1- Flat hexagonal prisms to form a wall or spherical like shapes; 2- Full spherical geometries.

Speaker: Tayfun Huyuk (IFIC (CSIC - Universidad de Valencia))

Slides Huyuk.pdf

42 The Genesis of NEDA (NEutron Detector Array): Characterizing its Prototypes

In nuclear-structure physics, especially while exploring unknown regions of the chart of nuclides, the experimenter needs to carefully address the identification of the products from nuclear reactions. The reaction channel selectivity can be achieved through the detection of all, or at least as many as possible, of the emitted light particles (mainly neutrons, protons, and/or α particles). However, since the neutrons are more challenging to deal with, a clean and efficient detection of the number of emitted neutrons in each reaction is a critical matter. To this end, a new, neutron-detector array (NEDA) has been realized, based on the previous knowledge acquired by its predecessor (the Neutron Wall). NEDA will be made of a large number of closely-packed liquid-scintillator detectors suitable for detection of neutrons, in the energy range 0.1−20 MeV. NEDA will be coupled to γ-ray germanium arrays such as AGATA, EXOGAM2, and GALILEO for γ-ray spectroscopic studies. The goal is to design and build an array with the highest possible neutron detection efficiency, excellent discrimination of neutrons and γ rays, and a very small neutron-scattering probability. At LNL-INFN, we have been testing two types of prototype detectors. The first type involves detectors with the traditional BC501A scintillator liquid, whereas the second type consists of detectors made of the deuterated scintillator liquid BC537. Procatarctic results regarding the performances of these detectors will be presented.

Speaker: Akis Pipidis (INFN, Laboratori Nazionali di Legnaro, Legnaro (Padova), Italy)

Slides Pipidis.pdf

43 Gamma-ray spectroscopy of ³⁶Cl nucleus.

In the present work, structure of the 36Cl nucleus has been studied using Compton-suppressed GASP array. Medium-spin states in the 36Cl nucleus have been populated in the 24Mg(14N,2p) fusion-evaporation reaction at Elab = 31 MeV. Fifteen new excited levels decaying through more than 40 gamma transitions have been assigned to this nucleus. The branching ratios and angular distributions have been measured to assign spin and parity of newly identified levels. The level scheme of 36Cl has been extended up to the 9+ state at 7476 keV excitation energy, and up to the 11− state at 10296 keV excitation energy. Experimental results are interpreted in context of the Shell Model calculations using two different configuration spaces for positive and negative parity states. Present results are found to be in good agreement with the shell model predictions for both excitation energies and decay patterns.

Speaker: Sezgin AYDIN (Department of Physics, University of Aksaray, Aksaray, Turkey)

Slides Aydin.pdf

Wednesday 29 June

Ancillaries

44 Exploring exotic nuclei via transition probabilities using the plunger technique

Aside from energy spectra absolute electromagnetic transition probabilities are important observables for the investigation of nuclear structure. With the advent of radioactive beam experiments as well as experiments employing specific nuclear reactions by which nuclei far from the valley of stability can be investigated with the methods of gamma ray spectroscopy, e.g. deep-inelastic reactions, nuclear structure investigations of exotic nuclei became possible. Consequently efforts are made to adapt the experimental techniques which were successfully used in the past for less exotic nuclei to the needs of the new type of experiments. This applies also for the Recoil Distance Doppler Shift Method, also called plunger method which is well suited to measure level lifetimes in a direct manner. So far this method has been successfully applied after Coulomb excitation and particle transfer reactions at energies of 50-100 MeV/u. Also deep inelastic reactions have been used to perform plunger experiments. Each of the different reactions put specific demands on targets and plunger devices used as well as on the data analysis. In this contribution the status of actually used plunger techniques will be presented. In order to demonstrate what can be achieved by the plunger technique some recent results will be presented. In addition ongoing developments will be described.

Speaker: Alfred Dewald (Institut für Kernphysik, Universität zu Köln)

Slides Dewald.pdf

45 Neutron Wall and NEDA: status and perspectives

The status of the Neutron Wall and recent results obtained at GANIL will be reviewed. Perspectives and status of the R&D for the next generation neutron detector array NEDA will be presented.

Speaker: Johan Nyberg (Uppsala University)

Slides Nyberg.pdf

46 Gamma ray and recoil coincident measurements , application in lifetime determination of a short-lived nuclear state

A considerable improvement of measured &gamma-spectra can be achieved when &gamma-rays are detected in coincidence with fusion-evaporation reaction residues selected by the Recoil Filter Detector (RFD). RFD provides a velocity vector of fast recoils and allows for significant Doppler broadening minimization. This unique feature of RFD permits as well to evaluate a lifetime-&tau of an excited state. If &tau is comparable to or shorter than the transit time of the recoil through a target material it can be deduced from the intensity distribution of the gamma transition emitted promptly inside the target, thus giving rise to a tail of the &gamma-line. In the talk examples of lifetime measurements with the use of RFD coupled to gamma ray arrays as EUROBALL and GASP will be given. In particular, results concerning SD bands in the A~70 mass region will be presented. Perspectives of using such a device at radioactive beams with the AGATA gamma-ray spectrometer will be discussed.

Speaker: Piotr Bednarczyk (IFJ-PAN)

Slides Bednarczyk.pdf

47 New Silicon arrays for reaction studies at future facilities

In view of new generation facilities such as SPIRAL2 and FAIR, a new instrumentation has to be developed in order to perform reaction studies in optimum conditions. For this purpose, the GASPARD and HYDE projects aim to combine large solid-angle, high granularity Silicon Stripped detector arrays with the forthcoming major gamma arrays as AGATA or PARIS. The use of Digital electronics is foreseen in order to implement Pulse shape analysis techniques for improving particle identification. A good transparency to low energy gamma-rays is mandatory. While making use of pad detectors, the TRACE Silicon array is persuing similar technical objectives. After a short review of some physics cases that are envisioned with such detectors, I will present their status and perspectives.

Speaker: Didier Beaumel (IPN Orsay)

Slides Beaumel.pdf

48 Planned upgrades of the DIAMANT light charged particle array

DIAMANT is a light charged particle detector system of CsI(Tl) scintillators having a nearly 4π solid angle coverage. It has been developed in a collaboration by ATOMKI (Debrecen), CENBG (Bordeaux) and the University of Napoli (Naples). It has been used within the gamma-ray spectrometer arrays EUROBALL, EXOGAM and AFRODITE, as an ancillary detector to select or reject coincidence events including emitted charged particles, mainly protons and alphas. Recently it was mainly used within EXOGAM, at GANIL, the present VXI electronics of which is to be replaced by digital signal processing (DSP) electronics - the aim of the EXOGAM2 collaboration. The planned modernization of that electronics and the experience collected during the experiments done within the last decade motivated a feasibility study the aim of which is the possible upgrade of DIAMANT. In this contribution we give a report on the ongoing developments as for test measurements using avalanche photodiode (APD) readout instead of the present pin-photodiode readout of the scintillation light. Results on the use of a new, low-consumption preamplifier, and a prototype 4-channel DSP electronics developed at ATOMKI will also be presented. If test measurements using proton and alpha beams of our cyclotron can be completed in time, a comparison of performance between APD-based and pin-PD based detectors will also be discussed, besides tests done with radioactive sources. The particle discrimination capabiility of the detectors will also be compared when using NIM-based and DSP-based electronics.

Speaker: Barna Mátyás Nyakó (Institute of Nuclear Research of HAS)

Slides Nyako.pdf

11:05 Coffee break

Prespec/Despec

49 Status and perspectives of the PRESPEC campaigns

PRESPEC is a collaborative European project to construct and operate detector set-ups at the SIS/FRS facility at GSI for nuclear spectroscopy. It builds upon the successful RISING project and employs equipment that was used in RISING as long as is appropriate. It is also aimed at preparing for the spectroscopy to be carried out with HISPEC/DESPEC at NUSTAR/FAIR by commissioning and employing components developed for HISPEC/DESPEC already at the SIS/FRS facility. The just finished first PRESPEC campaign dealt with In-beam spectroscopy at relativitic energies using 105 EUROBALL Ge detectors and the HISPEC particle calorimeter LYCCA. Preparations have started to replace the Ge detectors by the AGATA array for another in-beam campaign which will start in 2012. A third campaign is planned around 2014 dealing with decay gamma spectroscopy. First results of the previous campaign and the perspectives for the future campaigns will be presented.

Speaker: Juergen Gerl (GSI)

Slides Gerl.pdf

50 Shell evolution in the newly-explored neutron-rich region around Z=82 and far beyond N=126

The study of exotic nuclei has shown that significant changes of the well known shell structure along the stability valley occur, especially for very neutron-rich nuclei with mass numbers below 100. The two most accessible doubly-magic nuclei above A=100 are 132Sn (Z=50, N=82) and 208Pb (Z=82, N=126). Both of them are very neutron rich but the second one is nonetheless stable. The evolution of the Z=50 shell above N=82, and in general the structure of nuclei around 132Sn, is nowadays an object of intense research at radioactive beams facilities accelerating fission fragments around A=140. On the other side, little is known on the evolution of Z=82 shell closure beyond N=126 and on the neutron-rich nuclei around 208Pb, because of the experimental difficulties to reach such nuclei. The study of these heavy nuclei is relevant also for nuclear astrophysics, since the measurement of their β-decay half lives will improve the understanding of the r-process stellar nucleosynthesis in heavy nuclei. Neutron-rich nuclei around 208Pb were populated by using a 1 GeV*A 238U beam at GSI and their study was made possible by the presence of long-lived isomeric states that were indeed expected by shell-model calculations. The resulting fragments were separated and analysed with the FRS-Rising setup. Many neutron-rich isotopes were identified for the first time. A significant number of new isomers were hence discovered. The new exotic isotopes observed, extend up to 218Pb along the Z=82 shell closure and up to N=134 and N=138 for the proton-hole and proton-particle Tl and Bi nuclei, respectively. The very exotic 210Hg nucleus was also produced and studied. In our talk, these experimental results will be discussed within state-of-the-art shell-model calculations. The significant discrepancies between the experimental findings and the behaviour expected from the usual seniority scheme will be pointed out, presenting the possible required modifications to nuclear models in this region.

Speaker: Andrea Gottardo (LNL, INFN)

Slides Gottardo.pdf

51 Tz=-1 -> 0 beta decays and the DeltaT=0, M1 transition "quasi-rule"

We have studied the Tz = -1 → 0 beta decays of 42Ti, 46Cr, 50Fe and 54Ni to the self-conjugate nuclei 42Sc, 46V, 50Mn, and 54Co respectively. The nuclei of interest were produced in the fragmentation of a 58Ni beam of 680 MeV/nucleon from the SIS-18 synchrotron at GSI. The ions produced and separated using the Fragment Separator (FRS) were identified by Z and A on an event-by-event basis. The selected heavy ions (HI) were implanted into a DSSSDs detector surrounded by RISING CLUSTAR array. In the analysis of the HI-beta or HI-beta-gamma correlations it was possible to a) measure the beta-decay half-lives with one order-of-magnitude better accuracy than the values existing in the literature, b) establish decay schemes, c) determine the direct ground state to ground state feeding in the decays, d) measure the decay intensity to the 1+ states populated in the daughter and hence the B(GT) values for the Gamow-Teller beta decays. The B(GT) values are of importance in terms of comparison with the analogous (3He,t) reactions on the mirror nuclei (Fujita et al.,PRL95(2005)212501). An interesting observation in these experiments is the predominant M1 decay of the T=0, 1+ states populated in the beta decay to the T=1, 0+ g.s. No M1 gamma transitions were observed to any other T=0, 1+ excited states. This is consistent with the absence of the IV term in the M1 transition probability here since it cannot connect states with T=0, in contrast with the general case where the IV dominates the M1 transition probability. This selection rule, called a “Quasi-rule” by Warburton and Weneser (D.H. Wilkinson “Isospin in Nuclear Physics”, 1969, SBN 7204 0155 0) is observed for the first time in the fp shell nuclei.

Speaker: Berta Rubio (IFIC CSIC Valencia)

Slides Rubio.pdf

12:40 Lunch break

Boat trip along the Piovego Canal in Padova

Guided walking tour to discover the Padova of Galileo

Social Dinner

Thursday 30 June

Introduction

AGATA Campaigns

52 Recent results using the AGATA Demonstrator at LNL

The expected experimental conditions at the planned future facilities for radioactive ion beams and for high-intensity stable beams are extremely challenging, requiring unprecedented levels of efficiency and sensitivity, which cannot be reached with the conventional 4π arrays of Compton-suppressed high-purity germanium detectors. The approach pursued in the past few years implies covering the full 4π solid angle with germanium detectors only, and maximising the photopeak efficiency and the peak-to-total ratio through the identification of the interaction points of the photons within the germanium crystals (pulse shape analysis) and a software reconstruction of the trajectories of the individual photons (γ-ray tracking). The major advantage with respect to the present generation arrays is arguably the excellent spectra quality provided up to relativistic beam velocities, where the Doppler broadening correction is dominated by the position resolution within the individual crystals rather than by the finite opening angle of the detectors. Presently, two projects aim to build an array based on the concepts of pulse shape analysis and γ-ray tracking: AGATA in Europe and GRETA in the United States. Both instruments are expected to play a major role in the future nuclear structure studies at the very limits of nuclear stability. This contribution will focus on the status of the AGATA project. A subset of the whole array, known as the AGATA Demonstrator Array, is operating since 2009 at the Laboratori Nazionali di Legnaro, where it is installed at the target position of the magnetic spectrometer PRISMA. The Demonstrator is presently composed of four triple clusters, with a photopeak efficiency ranging from 2.5% to 6% for single 1 MeV photons depending on the target-detector distance. The fifth AGATA triple cluster is expected to be installed soon with an overall increase of relative efficiency of approximately 25%. Following the commissioning runs, the experimental campaign has started at the beginning of 2010 and it will continue until the end of 2011. Most of the performed and of the proposed experiments aim to study neutron-rich nuclei using AGATA in coupled operation with PRISMA, although also experiments studying proton-rich nuclei in standalone operation are also foreseen. Preliminary results from the experiments performed so far will be presented.

Speaker: Enrico Farnea (INFN PD)

Slides Farnea.pdf

53 Installation of the AGATA Demontrator and commissioning experiments at LNL.

The future progress of gamma-ray spectroscopy studies relies on the capabilities of powerful devices based on the novel techniques of pulse shape analysis and gamma-ray tracking. The foreseen enhancement in performance compared to the present generation arrays depends on the capability to determine the amount of energy deposited in each interaction point of the photons and the position as well. This information is used to measure the energy of the photons through the reconstruction of their scattering sequence. This requires the digitization of the signals of each electrode of hundreds of segmented HPGe detectors and the use of powerful algorithms for the online data analysis. Such a technological effort was carried out in the last decade by two major collaborations, namely AGATA and GRETA. Extensive Monte Carlo simulations suggest that the performance of such instruments will strongly depend on the accuracy in localizing the interactions. The installation of the first phase of AGATA, namely the AGATA Demonstrator, is ongoing in LNL. The commissioning experiments focus on the estimation of the position resolution through a measurement of the Doppler correction capability the first detector. The first results obtained will be presented together with the procedure used to analyze the data. The value estimated for the position resolution is in good agreement with the basic design assumptions of AGATA. This confirms the feasibility of a gamma-ray tracking array, which will certainly have a large impact on a wide variety of physics.

Speaker: Francesco Recchia (University of Padova)

Slides Recchia.pdf

54 The AGATA-PreSpec campaign at GSI

The AGATA spectrometer will move to GSI at the of this year for a series of in-beam experiments at the GSI Fragment Separator (FRS) as part of the PreSpec campaign. The status of the AGATA set-up for the GSI campaign and the preparation of the experimental program will be presented.

Speaker: Wolfram KORTEN (IRFU, CEA/Saclay)

Slides Korten.pdf

55 Status of AGATA at Ganil

In this presentation, the possible physics programs that can be pursued combining the AGATA demonstrator with the existing detection systems at GANIL will be presented. The possible programs best utilizing the various facets of GANIL range from the spectroscopy of transuranium elements using fusion evaporation, the characterization of exotic nuclei from deep inelastic collisions using the high intensity stable beams, gamma spectroscopy with reactions at intermediate energies, exotic shapes at high angular momentum and the studies of high spin structure of neutron deficient nuclei produced using RIB at the Coulomb barrier. In order to better focus and increase the productivity of the AGATA demonstrator while at GANIL, this proposal will concentrate on its coupling with the VAMOS spectrometer and the EXOGAM g-ray array. In several cases, the addition of other auxiliary devices will be highlighted. This can be later broadened to other combinations depending on the focus of the research anticipated in the year 2014 when the demonstrator is proposed to be at GANIL. Technical issue will be also addressed.

Speaker: Emmanuel Clement (GANIL)

Slides Clement.pdf

10:40 Coffee break

First results & experiment status

56 Coulomb excitation of the ⁴²Ca with AGATA Demonstrator.

The Coulomb excitation experiment to study electromagnetic properties of low-lying states in 42Ca with a focus on a presumably superdeformed band was performed at the Laboratori Nazionali di Legnaro in Italy using the γ - ray spectrometer AGATA Demonstrator coupled to the DANTE charged particle detector array. Current status of the data analysis will be presented.

Speaker: Katarzyna Hadynska-Klek (University of Warsaw)

Slides Hadyńska.pdf

57 Lifetimes of excited states in ⁷²Zn and ⁷⁴Zn with the RDDS technique and the AGATA demonstrator

Radioactive nuclei provide unique opportunities to investigate the nuclear-structure properties as a function of isospin. This work is focused on the region of neutron-rich nuclei at about N=40 and the development of collectivity towards N=50. 68Ni presents a large E(2+) and a small transition probability B(E2), signs of a shell closure. However, recent experiments point towards a rapid onset of collectivity and deformed shapes for Cr, Fe, Zn and Ge isotopes. Along the Iron chain, E(2+) becomes very low and the B(E2) value increases suddenly near N=40. For the Zinc isotopes, the E(2+) continuously decreases from N=38 to N=44. Coulomb-excitation measurements of 74-80Zn at REX-ISOLDE indicate a maximum of collectivity for 74Zn [VdW]. This work aims at measuring the lifetime of low-lying states in the neutron-rich Zn isotopes and investigating how the residual interaction between the valence nucleons polarizes the 68Ni core. As the electromagnetic transition rates and quadrupole moments are sensitive to these effects, they are ideal observables to constrain theoretical nuclear structure models. Refined lifetime measurement of the first excited states in 72,74Zn have been performed through a recoil-distance Doppler shift method (RDDS) in order to obtain a direct measurement of B(E2) values. These informations couple with previous Coulomb excitation experiment allows an estimation of the 74Zn quadrupole moment. The experiment has been performed at Legnaro in Italy, with the AGATA demonstrator (composed of 4 triple clusters) and the PRISMA spectrometer. A 76Ge beam at 577 MeV impinging on a 238U target has been used to produce the Zinc isotopes from deep-inelastic scattering. First results for the measured transition probabilities and comparison to theoretical calculations will be shown. [VdW] J. Van de Walle et al., Phys. Rev. C 79 014309 (2009)

Speaker: Corinne Louchart (CEA Saclay, Service de Physique nucléaire)

Slides Louchart.pdf

58 Lifetime Measurements in Neutron-rich Cu isotopes

In this work, we present the preliminary results obtained in the experiment of “Lifetime Measurements in Neutron-rich Cu isotopes” performed at Laboratori Nazionali di Legnaro (Italy) in June 2010. The aim of the experiment has been to measure lifetime of excited states in neutron-rich nuclei in the region of 78Ni, in particular Ni and Cu isotopes, using the recoil distance Doppler shift method (RDDS). The states have been populated in a multi-nucleon transfer reaction between a Ge76 beam of 577 MeV energy and a U238 target of 1.5 mg/cm2 together with a 1.4 mg/cm2 thick Ta backing. The target was mounted together with a Nb degrader foil of 4.2 mg/cm2 thickness in a compact Plunger device, provided by the University of Cologne. The projectile-like reaction partners have been identified using the PRISMA magnetic spectrometer, which was positioned at 55º with respect to the beam axes, close to the grazing angle, while γ rays were detected by the AGATA Demonstrator located at backward angles sensitive to their Doppler shift. Only four of the five clusters were available for the experiment. There fore the efficiency of the system was about 3-4%. The results of the work will be discussed in detail at the talk.

Speaker: Maria Doncel (University of Salamanca)

Slides Doncel.pdf

59 Neutron-rich nuclei studied in the ¹³⁶Xe +²⁰⁸Pb deep-inelastic reaction

A deep-inelastic reaction experiment with a 136Xe beam impinging on a 208Pb target was performed. Gamma rays were detected with the AGATA demonstrator. The beam-like fragments were identified with the PRISMA spectrometer on even-by-event basis. The DANTE heavy ion detector array was also used, with the aim of increasing the overall statistics of the reaction. Doppler corrected gamma-ray spectra were obtained for both the identified beam-like nuclei and for the target-like binary partners. Preliminary results will be presented.

Speaker: Zsolt Podolyak (University of Surrey)

Slides Podolyak-Valiente.pdf

60 Lifetime measurements on neutron-rich isotopes

In the region right below the neutron-rich Ni isotopes, there is an increase of collectivity produced mainly by the monopole part of the tensor interaction of the nuclear force: the interaction between f{7/2} protons and both f{5/2} neutrons (attractive) and g{9/2} neutrons (repulsive) weakens when the proton f{7/2} orbital is not fully filled, and therefore the gap between the neutron orbitals f{5/2} and the g{9/2} decreases. This mechanism will favor particle-hole excitations across N=40 subshell closure and therefore the g{9/2} orbital will play an important role in driving the nucleus towards deformation. An increase in collectivity in neutron-rich Cr isotopes towards N=40 is expected while observing the decrease in excitation energies of the first 2+ states as we increase the neutron number above the subshell closure at N=32. The cromium isotopes from N=28 up to N=38 undergo a shape transition from spherical (N=28, {52}Cr) to deformed in {60,62}Cr, with a 4{+}/2{+} typical of a γ-soft rotor. This kind of transition has been described within the framework of IBM and the critical-point where the phase transition is described by the E(5) symmetry (from spherical vibrator U(5) to a γ-soft rotor O(6)). The expected behaviour in the excitation energies (energy spectrum) of the E(5) symmetry was observed in the N=34 Cr isotope ({58}Cr). The shape evolution along the Cr isotopic chain will be studied in terms of measured B(E2) relative values of electromagnetic transitions in 58Cr and 60Cr. To this purpose, the nuclei of interest were populated as products of a multinucleon-transfer reaction with a 64Ni beam at an energy of 460 MeV, directed onto a {238}U target. Lifetimes of first excited states of 58,60Cr will be measured by using the Recoil Distance Doppler Shift method (RDDS) with the AGATA Demostrator-PRISMA setup. Preliminary results will be presented.

Speaker: Víctor Modamio (LNL, INFN)

Slides Modamio.pdf

61 Characterization of new structures in octupole-deformed radium and thorium nuclei

An experiment was performed using AGATA to characterise new structures observed in the octupole-deformed light-actinide nuclei 220Ra and 222Th. The primary goal of the experiment was to measure the linear polarizations of transitions linking new (unpublished) rotational-like structures to the yrast octupole bands in these nuclei, and in the case of 222Th, to measure the linear polarizations of inter-band dipole transitions in the new structure. AGATA was used with the 18O (95 MeV) + 208Pb fusion-evaporation reactions. It is intended that the gamma-ray interaction positions within the AGATA detectors will be used to reconstruct the scattering angles of the transitions of interest, and hence determine their linear polarizations. Establishing whether inter-band dipole transitions in the new structure in 222Th are E1 or M1 is crucial to its possible interpretation as an excited alternating-parity octupole band. Although the gamma-ray spectra will be dominated by gamma rays from fast fission, the fission background can be effectively removed by gamma-ray gating. The data are presently in the early stages of analysis.

Speaker: John F. Smith (UWS)

Slides Smith.pdf

13:00 Lunch break

First results & experiment status

62 Study of High-Lying States in ²⁰⁸Pb with the AGATA Demonstrator

An AGATA-Demonstrator (AD) experiment to study the gamma decay from giant resonances at zero temperature has been performed in June 2010 at LNL. The giant resonance modes have been excited by inelastic scattering of 17O at 20 MeV/A (the highest energy available at LNL) on a series of targets, such as 208Pb, 90Zr and 140Ce. The scattered ions have been detected by two E-∆E Si telescopes of the TRACE project, while the γ-decay have been measured by the AD coupled to an array of large volume scintillator detectors (BaF2 and LaBr3:Ce). The experiment aimed at the measurement of a known case first, 208Pb, but with improved experimental conditions, in particular concerning the energy resolution of the gamma detection. In contrast to the existing measurement concentrating mainly on the γ decay of the giant quadrupole resonance (GQR) in the 10-13 MeV range, the experiment aimed also at the measurement of the lower excitation energy region between 5 to 10 MeV, where pygmy dipole structures exist but not all of them are yet well identified. Preliminary results of the analysis will be shown.

Speaker: Roberto Nicolini (Università degli Studi di Milano and INFN, sezione di Milano)

Slides Nicolini.pdf

63 Study of the Order-to-Chaos transition in ¹⁷⁴W with the AGATA-Demonstrator

The transition between order and chaos is studied in the warm rotating nucleus 174W by gamma-spectroscopy, focusing on the conservation of selection rules of the K quantum number with the excitation energy. The 174W nucleus was populated at high spins by the fusion-evaporation reaction of 50Ti (at 217 MeV) on a 128Te backed target. The measurement was performed in July 2010 at Legnaro National Laboratory of INFN using the AGATA Demonstrator HPGe-array coupled with an array of 27 BaF2 scintillator detectors. Preliminary results of the data analysis will be presented. In particular, we will concentrate on double gamma-coincidence matrices selecting the gamma-decay flow populating low-K and high-K structures of 174W.

Speaker: Valeria Vandone (Università degli Studi e INFN - Milano)

Slides Vandone.pdf

64 Measurement of 15 MeV gamma rays with the AGATA cluster detectors

In many in-beam gamma spectroscopy experiments the detection of high-energy gamma rays in the range up to 10-20 MeV is of primary importance. The performance of AGATA detectors in this energy range has, however, never been studied in detail. A measurement of the response to 15.1 MeV gamma rays has therefore been performed using two HPGe triple clusters of the AGATA Demonstrator array, operating at LNL. This study represents a crucial test of the AGATA detectors for the measurement of high-energy gamma rays, in terms of detection efficiency, energy resolution, tracking and performance of the pulse shape analysis (PSA) algorithms. The status of the experiment will be presented and first results will be shown.

Speaker: Fabio Crespi (Università di Milano - INFN)

Slides Crespi.pdf

65 Test of AGATA modules as polarization analyzers

We have investigated the ability of AGATA modules to measure the linear polarization of gamma rays, exploiting the dependence of the Compton scattering differential cross section on the azimuthal angle. To this purpose, enriched targets of 104 Pd, 108 Pd were bombarded by a 32MeV 12 C beam. Partially polarized gamma rays have been produced by Coulomb excitation of the first excited states of 104Pd and 108Pd, which deexcite by emission of gamma rays of 555.8 keV and 433.9 keV, respectively. Two of the AGATA demonstrator modules were positioned in such a way as to select gamma rays at angles not far from 90 degrees to the beam direction. The azimuthal distributions, with respect to the plane defined by the beam and the gamma directions, of the first Compton scattering of these gamma rays have been evaluated and compared to the corresponding distribution for the unpolarized 661 keV gammas from a 137Cs source. The instrumental distortions in the measured distributions appear to partially compensate in the ratio of the COULEX data to those of the 661 keV gammas, and a clear signal of linear polarization becomes apparent. This result opens the way to a possible measurement of the relative polarization of entangled gamma rays from singlet positronium decay and also to the measurement of the linear polarization of gammas from nuclear reactions. In the latter case, a careful calibration with radioactive sources would be necessary for each AGATA module.

Speaker: Barbara Melon (INFN FI and Università di Firenze)

Slides Melon.pdf

66 Confirmation of the molecular structure of excited bands in ²¹Ne

AGATA in conjunction with the TRACE charged particle detector, has been used to study the 16O(7Li, n p)21Ne* reaction. This experiment aims to measure both in-band transitions and transition rates in the excited cluster bands of 21Ne. A further goal is to identify the 'missing' K = 1/2, Iπ = 5/2− level, to resolve a long running discrepancy in the understanding of 21Ne. By facilitating the extraction of the dipole moments and moments of inertia for the K = 1/2 cluster bands, the molecular structure for the excited bands can be assigned. A brief status of the experiment and data will be given.

Speaker: Carl Wheldon (University of Birmingham)

Slides Wheldon.pdf

16:30 Coffee break

First results & experiment status

67 The neutron-gamma discrimination using ²⁵²Cf source with four AGATA triple clusters

A test experiment was performed at LNL (Padova) with four AGATA Triple cluster (ATC) detectors and a 60 kBq 252Cf source placed at a distance of about 50 cm from the ATC:s. Gamma rays from the spontaneous fission decays were measured by 16 HELENA BaF2 detectors which were used for hardware triggering and as a time reference for the time-of-flight (TOF) measurement. The aim of the experiment was to investigate the possibilities of discriminating neutrons and gamma rays in AGATA, for example by differences in TOF or pulse shapes, as well as to study the effect of neutrons on gamma-ray tracking. The preliminary results show that the neutron background can be suppressed by tracking, in agreement with our earlier simulation results. The neutron background may become a serious problem in future experiments with neutron-rich radioactive ion beams and in experiments where low background in the cleanness of the gamma-ray spectra is of utmost importance. Preliminary results from the analysis of the data obtained in the experiment will be presented.

Speaker: Menekse Senyigit (Ankara University)

Slides Senyigit.pdf

68 Lifetime measurement of the 6.792 MeV state in ¹⁵O with the AGATA Demonstrator

The results from the lifetime measurement of the first 3/2+ state in 15O are discussed. This state corresponds to a sub-threshold resonance in the 14N(p,γ)15O reaction, the slowest one of the CNO cycle. The accurate determination of the width of this resonance is of paramount importance in the evaluation of the astrophysical factor and the derived cross section [1]. For this purpose, an experiment was performed to measure the lifetime of the first 3/2+ state in 15O, decaying by a 6.792 MeV E1 transition to the ground state, by means of the Doppler Shift Attenuation method. Gamma rays were detected by the AGATA Demonstrator, placed close to the beam line, providing a continuous angular distribution of the emitted gamma rays. The first excited states in 15O (and 15N) were populated via nucleon transfer and fusion-evaporation reactions of 14N on 2H (implanted at the surface of a ~4 mg/cm2 Au layer) at 32 MeV beam energy, provided by the XTU Tandem at LNL. The procedure and steps followed in the data analysis are described together with some results of the high-energy gammas calibration. Spectra of several high- energy gamma rays de-exciting 1-10 fs lifetime levels in the populated nuclei will be shown and compared with the result of detailed simulations. [1] C. Peña-Garay and A. M. Sereneli, in preparation (2008) and arXiv: 0811.2424v1 [astro-ph]

Speaker: Rosanna Depalo (INFN LNL)

Slides Depalo.pdf

69 &gamma; -ray counting rate measurements for the Agata-Prisma plunger experiments

A. Goasduff1,2 , S. Courtin1,2, F. Haas1,2, G. Duchêne1,2, F. Didierjean 1,2, G. de Angelis3, J.J. Valiente-Dobòn3, A. Gottardo3, D. Montanari3, D.R. Napoli3, A. Pipidis3, E. Sahin3, R. Chapman4, J.F. Smith4, A. Andreyev4, D. Mengoni4, K. Spohr4, A. Gadea5, T. Huyuk5,D. Verney6, F. Ibrahim6,A. Dewald7, Th. Pissulla7, W. Rother7, M. Hackstein7, C. Fransen7,O. Moeller8, S. Lunardi9, D. Bazzacco9, E. Farnea9, S. Lenzi9, R. Menegazzo9, C. Michelagnoli9, F. Recchia9, C. Ur9. 1 Université de Strasbourg, IPHC, 23 rue du Loess 67037 Strasbourg, France. 2 CNRS, UMR7178, 67037 Strasbourg, France. 3 INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. 4 University of the West Scotland, Paisley, U.K. 5 IFIC, CSIC, Valencia, Spain. 6 Institut de Physique Nucléaire, IN2P3-CNRS/Université Paris-Sud, Orsay, France. 7 Institut für Kernphysik, Universität Köln, Germany. 8 Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany. 9 Dipartimento di Fisica and INFN, Sezione di Padova, Padova, Italy. To prepare the approved Agata-Prisma lifetime experiments (PAC n° 10.30, 10.44 and 10.45), we have performed in March 2011 γ-ray counting rate measurements using beams of 32S (Elab=190 MeV) and 58Ni (Elab=250 MeV) on different targets: Mg, MgO, Ni, Nb, Ta and Pb. The results of this experiment (PAC n° 11.02) will pe presented and discussed.

Speaker: Florent HAAS (IPHC Strasbourg)

Slides Haas.pdf

ACC Meeting