Nuclear Structure Physics with Advanced Gamma–Detector Arrays (NSP13)

9 Jun 2013, 08:45 → 12 Jun 2013, 16:00 Europe/Rome

Archivio Antico and Aula Nievo (Palazzo del Bo', Padova, Italy)

Nuclear Structure Physics with Advanced Gamma-Detector Arrays

The Symposium "Nuclear Structure Physics with Advanced Gamma–Detector Arrays" (NSP13) marks 20 years from the first successful experimental campaigns with the gamma–ray spectrometer GASP and 10 years from the previous conference on “Nuclear Structure Physics with large gamma arrays” held in Legnaro–Padova. NSP13 is organized by INFN Padova, Laboratori Nazionali di Legnaro and the Department of Physics and Astronomy of the University of Padova.

The focus of the Symposium will be on the latest experimental results, theoretical challenges and the perspectives of nuclear structure physics with the modern gamma–ray Ge detectors, including the large gamma–ray detectors with AC shields and the most recent tracking arrays such as the AGATA demonstrator and GRETINA. Also the development of the many associated complementary detectors for gamma rays, neutrons, light and heavy-ions will be discussed.

The following main topics will be addressed during the discussions:

• Nuclear structure at extremes of isospin, mass, angular momentum and excitation energy
• Collective phenomena and symmetries
• Exotic decay modes
• Challenges in modern nuclear theory
• Aspects of nuclear astrophysics
• State of the art detectors

The Symposium is organized as a satellite event of the 25^th International Nuclear Physics Conference (INPC2013) to be held June 2–7, 2013 in Firenze.

Book of abstracts NSP13-book-of-abstracts.pdf

Concise Map of Padova Small_Map_of_Padova.pdf

First Announcement nsp13-firstAnnouncement.pdf

First circular NSP13-FIRST-CIRCULAR_16.pdf

Group Photo Photo-NSP13-1.jpg

Poster poster_NSP2013_v8_web.pdf

Scientific program Scientific_Program.pdf Scientific_Program-rev.pdf

Second circular NSP13-SECOND-CIRCULAR.pdf

Slides logo_bottom.jpg

Third circular NSP13-THIRD-CIRCULAR.pdf

Sunday, 9 June

Welcome Cocktail and Registration

Monday, 10 June

Registration

Session 1

Convener: Angela Bracco (MI)

1 Welcome

Speakers: Francesca Soramel (PD), Mauro Mezzetto (PD)

2 In Memoriam of Enrico Farnea

Speaker: Dino Bazzacco (PD)

Slides BazzaccoDino.pdf

3 Gamma-ray spectroscopy at GANIL

The EXOGAM array is a high efficiency germanium-array installed at GANIL since 2001. It is heavily used to study the structure of exotic nuclei produced in heavy-ion induced reactions. Most of the time, the array is coupled to other ancillary detectors, and in particular to the VAMOS large acceptance spectrometer. Another key setup is the combination of EXOGAM, the Neutron Wall –a large array of liquid scintillator to measure neutrons- and DIAMANT, a light-charged particle CsI multidetector. In this talk some examples of studies of neutron-rich nuclei around 68Ni performed with VAMOS will be shown. This includes some lifetime measurements as well as the combined prompt and delayed gamma-ray spectroscopy of nuclei produced in deep-inelastic reactions. The coupling of EXOGAM with the Neutron wall and DIAMANT is designed to study neutron deficient nuclei. This has been done in the region below 100Sn, for N~Z nuclei located close to the proton line. The results obtained for the self-conjugate N=Z=46, 92Pd seem to underline the role of the isoscalar T=0 neutron-proton pairing in the profound modification of the low-lying level scheme. As a by-product, a full characterization of EXOGAM as a Compton polarimeter has been performed and the structure of 91Ru has been studied in great details.

Speaker: Dr Gilles de FRANCE (GANIL)

Slides DeFranceGilles.pdf

4 The N=20-28 and N=40 islands of inversion: The physics picture.

The physics underlying the appearance of the so called "islands of inversion" will be described in the framework of large scale shell model calculations, with special emphasis in the structure and correlation energies of the intruder states. Evidences will be presented suggesting the merging of the N=20 and N=28 islands in the Magnesium isotopes.

Speaker: Prof. Alfredo Poves (Departamento de Fisica Teorica, UAM, Madrid)

10:30 Coffee Break

Session 2

Convener: Dr Georgi Georgiev (CSNSM)

5 The PRESPEC-AGATA in-beam spectroscopy campaign at GSI

The goal of the PRESPEC-AGATA project is to investigate the structure of exotic nuclei by performing in-beam gamma-spectroscopy experiments employing the SIS-FRS accelerator complex at GSI. The experimental set-up currently includes 19 AGATA high-resolution tracking gamma detectors providing about 10% full energy efficiency at 1 MeV. A set of advanced heavy ion detectors is used identification and tracking of exotic nuclei selected and transported through the fragment separator FRS. An active target and the heavy ion calorimeter and ToF detector LYCCA-1 complete the arrangement. The set-up constitutes the first full implementation of the HISPEC experiment for NUSTAR at the future FAIR facility. After successful commissioning, a first series of relativistic Coulomb excitation and secondary fragmentation experiments were performed in Autumn 2012. They dealt with the determination of B(E2) values in neutron-rich unstable Pb, Hg and Pt isotopes, fine structure of the pygmy resonance in 64Fe, Coulomb excitation of yrast-trap states in 52Fe and life times in neutron-rich Zr and Mo nuclei. First results show an unrivaled sensitivity of the set-up, surpassing the predecessor experiment RISING by at least one order of magnitude, offering unique access to the structure of exotic nuclei.

Speaker: Dr Juergen Gerl (GSI Darmstadt)

Slides GerlJuergen.pdf

6 Medium-mass nuclei from chiral effective field theory interactions

As ab-initio calculations of atomic nuclei enter the A=20-100 mass range, one of the biggest challenges is to provide accurate predictions for the vast majority of open-shell (degenerate) isotopes. I discuss recent developments of ab-initio nuclear structure theory for medium-mass nuclei, with focus on extensions to open-shell systems and inclusion of three-body forces. I then present the latest results of Gorkov-Green's function method, including the first applications with two- and three-body forces from chiral effective field theory in several isotopic chains around oxygen and calcium.

Speaker: Dr Vittorio Soma (EMMI/TU Darmstadt)

Slides SomaVittorio.pdf

7 The AGATA Campaign at GANIL

The GANIL facility, Caen (France), will host the European AGATA germanium array from 2014 to 2015. AGATA will be coupled to the VAMOS spectrometer and/or other available ancillary detectors using the high intense stable heavy ions beam delivered by the GANIL cyclotron and the radioactive beam delivered by the SPIRAL1 facility. At GANIL, the AGATA spectrometer can be couple with a large number of detector making the setup very versatile. In this presentation a review of the future campaign will be presented.

Speaker: Dr Emmanuel Clement (GANIL, Caen)

Slides ClementEmanuel.pdf

8 The Strange Case of 210Hg: an Unexpected Structure

The neutron-rich lead and mercury region has been so far scarcely explored due to its high mass and neutron excess, which force the use of fragmentation reactions with relativistic beams. Neut on rich nuclei beyond 208Pb were populated by using a 1 GeV/A 238U beam at GSI. The resulting fragments were separated and analyzed with the FRS-RISING setup. Many neutron-rich isotopes were identified for the first time and a significant number of new isomers were hence discovered, enabling us to study the structure of these isotopes. The new exotic isotopes bserved 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. New isomers were observed in 212-216Pb, in 217Bi, in 211,213Tl and in 210Hg. The isomers in 212-216Pb correspond to the expected seniority scheme, with an 8+ isomer from neutrons coupling in the g9/2 shell. Considering that the same isomers was observed in 208Hg, one would expect the two-proton hole Hg isotopes to follow the same scheme. On the contrary, the observed isomeric states in 210Hg correspond to the expected seniority scheme and to an unexpectedly low-lying state, indicating a sudden change in nuclear structure with respect to 208Hg. A similar situation happens in 211,213Tl isotopes with respect to the standard seniority isomer observed in 209Tl. Therefore, the experimental data seem to suggest a modification of the expected nuclear structure in this scarcely-explored region of the nuclide chart. Several possibilities will be discussed, considering the systematics of electromagnetic transition rates and the predictions of shell model with realistic interactions.

Speaker: Andrea Gottardo (INFN Legnaro)

Slides GottardoAndrea.pdf

12:35 Lunch Break

Session 3

Convener: Dr Piotr Bednarczyk (IFJ-PAN)

9 GRETINA: status and future plans

The gamma ray tracking array GRETINA started operation at MSU in spring 2012. It was installed at the target position of the S800 spectrometer at NSCL. Currently it has 7 modules each with four 36-fold segmented Ge detector, covering 1-p solid angle in the angular range of 60 to 90 degrees. The tracking detectors have the unique ability of resolving the energy and position of the individual interaction points and establishing the gamma-ray scattering sequence. GRETINA with S800 is a powerful combination for fast radioactive beam experiments at NSCL; their high position resolution is crucial for Doppler correction to achieve good energy resolution; their higher efficiency overcomes the low intensity of exotic beams and extends the range of study to more neutron-rich and proton-rich nuclei; and gamma ray tracking reduces background and improves spectral quality. More than 20 experiments have been approved by the PAC and will be completed by July of 2013. We will report on selected results from the campaign of GRETINA at the MSU and discuss the future plans.

Speaker: Dr I-Yang Lee (Lawrence Berkeley National Laboratory)

Slides LeeIYang.pdf

10 Exotic structure and decay of medium mass nuclei near the drip lines within beyond-mean-field approach

The interest for the investigation of medium mass nuclei near the drip lines goes beyond the frontier of nuclear structure and dynamics. Detailed knowledge of the properties and decay rates of nuclei near the drip lines are required by the simulation of many astrophysical objects. The structure and dynamics of proton-rich A~70 nuclei and neutron-rich A~100 nuclei are influenced by shape coexistence effects. A realistic description of shape coexistence phenomena requires beyond-mean-field approaches. A self-consistent description of exotic structure and beta-decay of proton-rich A~70 nuclei as well as neutron-rich A~100 nuclei within the complex Excited Vampir variational approach using realistic effective interactions in large model spaces will be presented.

Speaker: Prof. Alexandrina Petrovici (HH IFIN, Bucharest)

Slides PetroviciAlexandrina.pdf

11 On the Elusive Links Between High-K and Low-K States in 176Lu and 180Ta

Nature's heaviest naturally occurring odd-odd isotopes, 176Lu and 180Ta have a pair of high and low-K levels at low energies formed by parallel or anti-parallel coupling of the unpaired proton and neutron to give a total projection, K = | Omega p ± Omega n |. One consequence of this is the formation of a long-lived 9- state in 180Ta, the only naturally occurring nuclear isomer, with a lifetime of tm > 1 x 10^16 years, 77 keV above the Kpi = 1+ short-lived ground state. The opposite situation occurs in 176Lu: it exhibits a long-lived Kpi = 7- ground state and a 1- short-lived isomer at 123 keV. Both nuclei present issues for nucleosynthesis; 180mTa in terms of its abundance, creation, and survival in stellar environments; 176Lu because, while definitely s-process (a possible s-process chronometer or thermometer), it could be destroyed through neutron capture to the short-lived beta-decaying state. Furthermore, photon excitation via intermediate-K states, passing from the 1- isomeric level to the ground state, or the equivalent transition in the opposite direction, could either increase or decrease its abundance, and that of 176Hf. (See Refs. [1,2], for example.) The presentation will cover some recent results [3,4] from gamma-ray spectroscopy that bear on these issues, partly in the context of the relationship between the strong resonances observed in laboratory photo-activation (see, for example, Ref. [5]) and the nuclear structure problem of associating these resonances and their properties with specific excited states. 1. P. Mohr, F. Kappeler, R. Gallino, Phys. Rev. C 75, 012802(R) (2007). 2. P. Mohr et al., Phys. Rev. C 79, 045804 (2009) 3. G. D. Dracoulis et al. Phys. Rev. C, 81, 011301(R) (2010) 4. G. D. Dracoulis and G.J. Lane, to be published 5. D. Belic et al. Phys. Rev. C 65, 035801 (2002).

Speaker: Prof. George Dracoulis (Australian National University)

Slides DracoulisGeorge.pdf

12 Evolution of Collectivity in the Vicinity of Pb-208

A systematic experimental programme has been started to derive the evolution of quadrupole collectivity near the heaviest stable doubly-magic nucleus Pb-208. Here, B(E2;0+ -> 2+)-values are being measured via relativistic Coulomb excitation. Despite the fact that the energy, E(2+), and strengths, B(E2;0+ -> 2+), of the first 2+ state in even-even nuclei is one of the key quantities in nuclear structure physics, surprisingly little is known about the latter in the direct neighbourhood of the heaviest stable doubly-magic nucleus Pb-208. In October 2012 an experiment was conducted within the PRESPEC-AGATA campaign at the UNILAC-SIS accelerator complex at the GSI Helmholtzcentre for Heavy-Ion Research in Darmstadt, Germany. Following the fragmentation of a 1 AGeV Pb-208 primary beam, heavy Pb, Hg, and Pt secondary beams were prepared by the GSI Fragment Separator and focused onto a gold target foil. Gamma-rays were measured by AGATA and HECTOR, and the outgoing ions were discriminated by the LYCCA detector system. Results from the ongoing data analysis will be presented and compared to contemporary nuclear structure model calculations.

Speaker: Dr Luis Sarmiento (Lund University)

Slides SarmientoLuis.pdf

13 Study of highly-excited states in 140Ce via inelastic scattering of 17O

Giant Resonances are collective modes of excitation of atomic nuclei, providing useful information on nuclear structure and on the effective nucleon-nucleon interaction. It is possible to excite such resonances with different probes as for example: photons, charged particles or heavy ions, followed by subsequent decays by emission of particles and γ’s. Below particle threshold, a large fraction of highly excited states has been found to be of a dipole nature and it has been associated to the Pygmy Dipole Resonance, caused by the oscillation of the neutron skin against the inert proton-neutron core. Main aim of this study is a deeper understanding of the nuclear structure properties of the Pygmy Dipole structures in 140Ce, excited via inelastic scattering of an 17O ion beam. Comparison with previous results for this nucleus, investigated in (γ,γ') and (α,α') experiments, will be helpful for drawing final conclusions. The experiment was performed at Laboratori Nazionali di Legnaro, Italy. Inelastic scattering of 17O projectiles at 20 MeV/A was used to excite the resonance modes in the 140Ce target (2.5 mg/cm2 thick). Gamma rays were registered by 5 AGATA triple clusters and 8 large volume scintillators (LaBr3), useful for high γ-energy. The detectors were mounted at a distance of about 20 cm from the target position, resulting in a full absorption efficiency of about 0.8% at 10 MeV. The scattered 17O ions were identified by two ΔE-E Si telescopes of the TRACE array mounted inside the scattering chamber at 9° (which is the grazing angle for the reaction) with respect to the beam axis. The telescopes consisted of 2 segmented Si-pad detectors, each made of 60 pixels (with a pixel size of 4x4 mm2) covering an active area of 20x50 mm2. The resulting solid angle for the Si telescope was about 100 msr. During the talk, issues concerning complex data analysis will be discussed and preliminary results of the experiment will be presented.

Speaker: Mr Mateusz Krzysiek (IFJ PAN Kraków)

Slides KrzysiekMateusz.pdf

14 Neutron rich Ni isotopes studied by intermediate energy knock-out reactions

Neutron-rich isotopes represent a steady source of new information on the behavior of the nucleus. Sometimes, unexpected phenomena occur such as halo-nuclei or the disappearance of the well-established magic numbers. Spin-isospin parts in the nucleon-nucleon interaction, e.g., the proton-neutron tensor force (in particular, the strongly attractive monopole parts) are expected to modify shell structure in exotic nuclei. These potential changes in the intrinsic shell structure are of fundamental interest. Since the properties of 78Ni are much debated, neutron-rich Ni, Co and Cu isotopes have been the object of much experimental effort. The study of the single-particle character of the first excited states of odd-A, n-rich Ni isotopes allows to document the effective single-particle energies (ESPE) of neutron orbitals around the Fermi surface, and represents a step forward in the understanding of the region and the nature of the NN interaction at large N/Z ratios. Detailed knowledge of neutron and proton ESPE in the vicinity of the 78Ni doubly-magic shell closure will serve as a fundamental benchmark for the modelling of nuclear structure in regions with even larger N/Z ratios. At the National Superconducting Cyclotron Laboratory we studied the distribution in single-particle strength in the neutron-rich 67,69,71Ni isotopes via one-neutron knockout reactions, a well-established technique to address this specific issue. The secondary 68,70,72Ni beams were produced by fragmentation reactions of a primary 82Se beam impinging on a Be target, and further purification and separation of the beam was achieved with the A1900 fragment separator. The secondary beams were transported to the S800 large-acceptance spectrometer, tuned to accept the one-neutron knock-out fragments. The de-excitation rays were measured by means of the GRETINA tracking array. This work was supported by the National Science Foundation under Grant No. PHY-0606007 and by the Department of Energy, Office of Nuclear Physics, under contract No. DE-AC02-06CH11357.

Speaker: Francesco Recchia (Dipartimento di Fisica e Astronomia - Universita' di Padova)

Slides RecchiaFrancesco.pdf

16:10 Coffee Break

Session 4

Convener: Giovanna Benzoni (MI)

15 Decay spectroscopy of exotic nuclei at RIBF

Decay spectroscopy is expected to provide a great chance to look inside the structure information of nuclei far from the stability. A new project EURICA (EUROBALL RIKEN Cluster Array) has been launched to perform experimental campaign of decay spectroscopy, utilizing gamma-rays detectors (EUROBALL Germanium Cluster detectors) and new generation radioactive beam facility (RIBF) at RIKEN[1,2]. A first EURICA campaign with U-beam was conducted in 2012 December to study isomeric and beta-delayed gamma-spectroscopy of very neutron-rich nuclei around doubly-magic nuclei 78Ni and 128Pd region. Highly segmented double-sided silicon-strip detectors (WAS3ABi)[3], located in the center of EURICA, was employed as an active stopper of produced isotopes transfered from the BigRIPS and ZeroDegree spectrometer. In this paper, we will report our preliminary results obtained by the EURICA spectrometer and future perspective of decay spectroscopy at RIBF. [1] H.J.Wollersheim et al., Nucl. Instrum. Meth. A 537, 637 (2005). [2] S.Nishimura, Nucl. Phys. News Vol. 22, 39 (2012); P-A. Soderstorm et al., submitted to Nucl. Instrum. Meth. B (EMIS Conference). [3] S.Nishimura, submitted to RIKEN Accel. Prog. Report.

Speaker: Dr Shunji Nishimura (RIKEN Nishina Center (RNC))

Slides NishimuraShunji.pdf

16 In beam gamma-ray spectroscopy at the RIBF

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 in-beam gamma-ray spectroscopy experiments these radioactive beams are incident on a secondary target for Coulomb excitation, inelastic scattering, or knockout reaction measurements. While ejectiles are measured with the ZeroDegree spectrometer, gamma-rays are detected by the NaI(Tl) scintillator based DALI2 array. The first in-beam gamma-ray experiments performed at the RIBF 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. Recent experiments include the first spectroscopy of 54Ca, the regions around the doubly-magic 78Ni and 100,132Sn nuclei, as well as investigations on the N=28 shell closure erosion around 42Si. Besides showing (preliminary) selected results from these first experiments and a description of the gamma-ray spectroscopy setup, an outlook on future gamma-ray spectroscopy campaigns at the RIBF including the active liquid hydrogen target MINOS will be given.

Speaker: Dr Pieter Doornenbal (RIKEN)

Slides DoornenbalPieter.pdf

17 High-spin yrast isomers in 204Hg

This work reports the observation of high-spin states in 204Hg using time-correlated γ-ray spectroscopy to identify isomers populated in deep-inelastic collisions of a ̴1.4 GeV 208Pb beam on a thick 238U target. A high-spin isomer with τ > 1 µs has been found and the observed γ-ray decay has established the yrast states below it, including another isomer with τ = 33(3) ns. Spin and parity assignments were based on conversion coefficients deduced from intensity balance and on the observed γ-decay patterns. The experimental results are compared with shell model calculations that include four holes in the entire configuration space between 132Sn and 208Pb. Observed agreement with the calculation gave the supplementary arguments to the spin-parity assignments and clarified configurations of experimental states. The τ > 1 µs isomer is suggested to be the πh-211/2ν-213/2, 22+ states that results from the coupling to maximum spin available for the four valence holes. Few prompt transitions feeding the isomer were also observed.

Speaker: Dr Jacek Wrzesinski (IFJ PAN Krakow)

Slides WrzesinskiJacek.pdf

18 Study of shape transitions in the neutron-rich Os isotopes

The nuclei with A~190 between Hf and Pt exhibit a great variety of nuclear phenomena, including K-isomerism, triaxiality and shape transition across the isotopic chain. This region has been in fact a crucial testing ground for the nuclear models aspiring at the description of such complex nuclear phenomena. Of particular interest is the transition from axially symmetric deformed, prolate (gamma = 0 deg.) to oblate (gamma = 60 deg.) shapes in the neutron-rich Os isotopic chain. While a study by Wheldon et al. [1] of the neutron-rich 194Os nucleus populated via deep-inelastic reactions suggests a prolate shape for its yrast states, Podolyak et al. [2] proposed an oblate shape for the ground state of 198Os by comparing the excitation energies of the first and second 2+ states. The ground state of $196Os, the even-even isotope lying between the two previously mention ones, is predicted to be prolate, oblate or gamma-soft by different state-of-the-art nuclear models. This region of the Segrè chart is very difficult to study experimentally, only fragmentation and multi-nucleon-transfer reactions can be used to populate neutron-rich nuclei in this region, hence the knowledge for this nucleus is limited to two excited states without any known gamma transition [3]. To further elucidate this shape transition, the key nucleus 196Os was investigated in-beam using the AGATA demonstrator and the large acceptance heavy ion spectrometer PRISMA at LNL, Italy. A two nucleon transfer from a 198Pt target to a stable 82Se beam was utilised to populate medium-high spin states of 196Os. The ongoing data analysis for AGATA and PRISMA spectrometer will be discussed together with the latest results for 196Os. [1] C. Wheldon et al., Phys. Rev. C63, (2000) 011304(R). [2] Zs. Podolyak et al., Phys. Rev. C79, (2009) 031305. [3] P.D. Bond et al., Phys. Lett. B130, (1983) 167.

Speaker: Mr Philipp Rudolf John (University and INFN Padova)

Slides JohnPhilipp.pdf

19 Configurations and decay hindrances of high-K states in 180Hf

Nuclei in the A=180 region are characterized by quite favorable conditions for the realization of K isomers. These include rigid, axially symmetric deformed shapes, and the presence of both proton and neutron orbitals near the Fermi surface with large projections of the intrinsic angular momentum along the symmetry axis. K isomers constitute a very effective spectroscopic means of investigating both intrinsic and collective excitation modes. While K-isomeric decays offer insight into the degree of conservation of the K quantum number, high-K rotational bands yield information about the properties of the underlying core. Multi-quasiparticle high-K states are observed in 180Hf through excitation with a 1.4 GeV 207Pb beam obtained from the ATLAS accelerator at Argonne National Laboratory, incident on an enriched, 250 mg/cm2 180Hf target. Both prompt and delayed gamma rays were detected using the Gammasphere array, and several new high-K structures identified, in addition to the K isomers already established from previous work [1]. Lifetimes of isomeric states in the nanosecond-microsecond range are measured using centroid-shift and decay measurements within the microsecond coincidence time window. Configurations for the high-K states involve two, four and six quasiparticles, with states up to K=22 established. High-K states are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest observed spins as evidenced by large values of reduced hindrance for isomeric decays. Rotational bands built on several high-K states are identified, and the measured branching ratios in these structures have allowed assignment of underlying configurations. Multi-quasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well. References [1] R. D'Alarcao et al., Phys. Rev. C 59, R1227 (1999).

Speaker: Prof. S.K. Tandel (University of Massachusetts Lowell and UM-DAE Centre for Excellence in Basic Sciences)

Slides TandelSujit.pdf

Tuesday, 11 June

Session 5

Convener: Adriana Nannini (FI)

20 Investigation of exotic nuclei with absolute transition probabilities

Nuclei far from the valley of stability are of current interest in nuclear structure physics. Especially, big effort has been devoted to investigate the evolution of collectivity of nuclei with large isospin. In order to gain experimental data related to this topic reactions with radioactive beams or deep inelastic reactions have been successfully used. With both types of reactions absolute transition probabilities can be determined using the plunger technique. Dedicated plunger devices have been designed to accommodate the specific issues imposed by these reaction types. In this presentation the following examples will be presented: 1. Reaction with radioactive beams at intermediate energies (≈ 100 MeV/u). The experiments were performed at the NSCL/MSU. Low lying yrast states in 58,60,62Cr isotopes were populated in 1p-knockout reactions using high purity 59,61,63Mn-beams at 𝐸 ∼ 95 MeV/u which were produced by fragmentation of a 82Se beam at 140 MeV/u on a Be target. The 59,61,63Mn-beams were separated from other fragments by the A1900 separator. The reaction products of of the secondary knockout reaction were identified by the S800 spectrograph and the gamma-spectra were measured by the Segmented Germanium Array (SeGA). The measured transition probabilities will be compared to shell model calculations as well as to neighboring Fe nuclei close to the sub-shell closure at N=40. 2. As an example of a lifetime measurement using deep inelastic reactions at grazing angles an experiment on 84,86Se will be presented. The experiment was performed at the LN Legnaro using the PRISMA-AGATA setup with a plunger device especially constructed for such experiments. First preliminary results will be discussed.

Speaker: Alfred Dewald (IKP Universität zu Köln)

21 Nuclear structure studies of heavy nuclei

The investigation of the structure and stability of the heaviest elements has been a constant theme in nuclear physics research since the 1940’s. In the last decade or so, a wealth of new data has been produced, both in terms of new elements (up to Z=118) and in detailed spectroscopic studies of nuclei with masses above 240. Such studies provide data concerning nuclear parameters such as masses, decay modes, half-lives, moments of inertia, single-particle properties, etc., in systems with the highest possible number of protons. The main focus of current experiments is the search for the next closed proton- and neutron- shells beyond the doubly magic 208Pb. This search can be made directly, by producing nuclei in the region of interest (Z>112 and N>176), or indirectly through the study of lighter deformed nuclei where the orbitals of interest at sphericity are active at the Fermi surface. Nuclei in the region of 254No are produced with cross-sections large enough to allow in-beam studies using recoil-decay tagging techniques. Advances in digital electronics and data acquisition have led to the observational limit in this region being pushed down to the level of ten nanobarns, as demonstrated by recent studies of 246Fm and 256Rf. In addition, the capabilities of focal plane spectrometer devices have been greatly improved, which has recently allowed the structure of a number of high-K isomeric states to be determined in a systematic manner. New instruments such as the recently commissioned SAGE combined conversion-electron and gamma-ray spectrometer provide additional information such as conversion coefficients to aid determination of transition multipolarities. Examples of recent highlights in in-beam studies of heavy elements will be presented.

Speaker: Prof. Paul Greenlees (University of Jyväskylä)

Slides GreenleesPaul.pdf

22 Differential Plunger Lifetime measurements of Proton-Unbound Nuclear States (DPUNS).

A new differential-plunger device, DPUNS, has been commissioned to measure the lifetimes of excited states beyond the proton drip line. DPUNS has been coupled to the Jurogam II and RITU spectrometers at the University of Jyvaskyla using proton tagging and to isolate the weakly populated nuclei of interest. Recoil-Distance-Doppler-Shift measurements have been employed to measure the lifetimes of exited nuclear states in these exotic nuclei. So far, our new experiments have measuring the lifetimes and extracting deformations for states in the near-spherical proton emitters, 109I and 151Lu. However, even for these somewhat easier to understand near-spherical proton emitters, the theoretical situation is somewhat complex. Current calculations based on the CD-Bonn potential tend to underestimate the spectroscopic factors and overestimate the B(E2) reduced transition probabilities for the unbound states in 109I, whereas, the opposite situation is found in 151Lu. As part of this work, our collaboration is developing a non-adiabatic model which has the ability to self-consistently calculate energy levels, electromagnetic transition rates and proton decay tunnelling rates within a common theoretical framework. Prior to this work, theoretical tunnelling calculations have relied on deformations which were inferred from the alignment properties of the states built upon the proton decaying state. With these new lifetime measurements, the extracted deformations should be more reliable. In summary, this talk will review the new experimental and theoretical knowledge obtained from our measurements in this region of exotic nuclear states and will close with a discussion of potential future experiments and additional knowledge that can be gained from a study of deformed proton emitters.

Speaker: Dr David Cullen (University of Manchester)

Slides CullenDave.pdf

23 Gamma spectroscopy in the fermium region at SHIP

Besides the synthesis of new superheavy elements detailed nuclear structure investigations are an important tool helping to reveal information on the location and strength of the next spherical proton and neutron shells above the 208Pb (Z=82, N=126). Of specific interest are well prolate deformed nuclei beyond the deformed neutron shell N=152 and Z=100 (fermium) where levels relevant for an expected shell gap at Z = 114 come close to the Fermi level. Recent developments of alpha, gamma and conversion electron (CE) spectroscopy techniques opened the door to investigate the structure of heaviest nuclei (A>250). The results of those experiments provide crucial information on the structure of these nuclei and are stringent tests for nuclear models. At the velocity filter SHIP at GSI Darmstadt we performed an extensive program aimed at nuclear structure studies of trans-fermium isotopes using CE-gamma and alpha-gamma spectroscopy. Besides single particle isomers we observed or investigated in details several K isomers having high spins and excitation energies [1-4]. In this contribution the main results from these measurements will be presented and discussed, in particular those from the gamma-spectroscopy measurements of 253No and 253Md [4]. The contribution will aim also at possibilities and limits of the used detector setup. An example is the gamma-decay spectroscopy of heavier nuclei at the focal plane of the separator, for example K isomers in rutherfordium isotopes, which would require the use of larger germanium arrays.

Speaker: Dr Stanislav Antalic (Comenius University in Bratislava)

Slides AntalicStanislav.pdf

10:25 Coffee Break

Session 6

Convener: Prof. George Dracoulis (Australian National University)

24 Gamma-ray Spectroscopy with GRETINA at NSCL

In early summer 2012, the Gamma-Ray Energy TRAcking In-beam Nuclear Array GRETINA was installed in front of the S800 Magnetic Spectrograph for in-flight gamma-ray spectroscopy campaign with fast beams of rare isotopes. In this type of experiments rare-isotopes beams provided by the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory (NSLC) are delivered onto a reaction target placed at the center of GRETINA. Reaction residues are detected in the spectrograph in coincidence with gamma rays in GRETINA. The high spatial resolution of GRETINA allows to perform accurate Doppler-shift reconstruction of the gamma-ray energies emitted by the reaction residues moving at velocities typically exceeding 30% of the speed of light. GRETINA's tracking capability enables to acquire gamma-ray data of high spectral quality. More than 20 experiments have been performed covering topics in nuclear structure and nuclear astrophysics. This presentation will summarize the performance of GRETINA in this powerful configuration for fast beam spectroscopy and give an overview on the physics program accomplished in this campaign.

Speaker: Dr Dirk Weisshaar (NSCL/MSU Michigan)

Slides WeisshaaDirk.pdf

25 Study of nucleon transfer and knockout reactions with high-resolution gamma-ray spectroscopy

Nucleon-transfer reactions like (d,p) or (t,p) have been a well-established tool to investigate the single-particle properties of nuclei for many decades. Applied to exotic nuclei they have to be performed in inverse kinematics and, in many cases, combined with gamma-ray spectroscopy. The region around the ``island of inversion'' where the traditional shell closure at N=20 disappears has been studied at REX-ISOLDE (CERN)[1,2] with the MINIBALL array consisting of 24 six-fold segmented HPGe detectors [3] and the particle detector T-REX [4]. Similar investigations have been performed around 68Ni evaluating a local shell closure at N=40 [5]. For more energetic beams nucleon-knockout reactions are a similar tool. A possible new magic number at N=32 or 34 beyond 48Ca has been addressed at GSI by studying neutron-rich Ti and Sc isotopes [6,7]. The combination of the FRS with MINIBALL allowed for the measurement of exclusive momentum distributions. Nucleon-knockout reactions are also a sensitive method to populate different configurations in the final nucleus by varying the primary beam. This has been exploited recently to study neutron-rich Mg and Na isotopes at NSCL employing the GRETINA array for gamma-ray detection [8]. We will present the status of the research programmes as well as discuss the perspectives for future experiments at HIE-ISOLDE (CERN) and with R3B at FAIR. This work is supported by the German BMBF (grants No. 06DA9036I, 05P12RDCIA, and 05P12RDFN8), HIC for FAIR, EU through EURONS (No. 506065) and ENSAR (No. 262010) and the MINIBALL and REX-ISOLDE collaborations. References [1] K. Wimmer et al., Phys. Rev. Lett. 105, 252501 (2010). [2] V. Bildstein et al., to be published. [3] N. Warr et al., Eur. Phys. J. A 49, 40 (2013). [4] V. Bildstein et al., Eur. Phys. J A 48, 85 (2012). [5] J. Diriken et al., to be published. [6] P. Maierbeck et al., Phys. Lett. B 675, 22 (2009). [7] S. Schwertel et al., Eur. Phys. J. A 48, 191 (2012). [8] K. Wimmer et al., to be published.

Speaker: Prof. Thorsten Kroell (TU Darmstadt)

Slides KroellThorsten.pdf

26 Collectivity in N=Z mass 70 nuclei

There has been intense physics interest in the structure of self-conjugate medium mass nuclei in recent years [1-3]. Specific effort has been undertaken to map out the development of collectivity above mass 60, with emphasis on the influence of the deformation-driving g9/2 orbital. A number of even-even nuclei in this area have been studied, with B(E2) values deduced for 64Ge, 68Se, 72Kr and 76Sr (see ref. [4] and references therein). However no published measurements exist for the intervening odd-odd N=Z nuclei. An experiment was thus conducted to continue the mapping of deformation in the A=70 region by measuring the lifetime of the first excited 2+ state in the odd-odd N=Z nucleus 70Br. Excited states in 70Br were populated via one-nucleon-knockout at the NSCL facility at Michigan State University. De-excitation gamma rays were detected using the SeGA array, recorded in coincidence with recoils identified in the S800 spectrograph. The lifetime was deduced using the recoil distance Doppler shift technique, made possible through the use of a new differential plunger apparatus (TRIPLEX). The lifetime of the 2+ state in neighbouring 70Se was also measured for comparison, due to recent controversy over the shapes of the two nuclei. Lifetimes of low-lying states in 70Br, 70Se and other neighbouring nuclei will be presented and discussed. [1] A. Petrovici, J. Phys. G Nucl. Part. Phys., 37 064036 (2010) [2] K. Kanecko et al., Phys. Rev. Lett., 109 092504 (2012) [3] M. Hasegawa et al., Phys. Lett. B, 656 51-55 (2007) [4] A. Lemasson et al., Phys. Rev. C, 85 041303(R) (2012)

Speaker: Mr Adam Nichols (University of York)

Slides NicholsAdam.pdf

27 Coulomb excitation of re-accelerated 208,210Rn and 206Po at MINIBALL

In regions near magic nuclei, seniority can be regarded as a good quantum number. In the trans-Pb nuclei near the Z=82 and N=126 shell closures, relative high-j single-particle proton orbitals dominate the structure and thus levels up to I=2j−1 could, in principle, be understood within the seniority scheme. In N=122, N=124 and especially in the closed shell N=126 isotones with Z≥82, behaviour of the B(E2) values resembling the seniority scheme predictions has been observed. These nuclei lie in, or at the boundary of the region where seniority scheme could persist. However, contributions from collective excitations can not be ignored when moving away from the N=126 closed shell. To date, surprisingly little is know of the transition probabilities between the low-spin states in this region. In the present study, B(E2;0+→2+) values have been measured in 208,210Rn and 206Po nuclei through Coulomb excitation of re-accelerated radioactive beams in inverse kinematics. The radioactive beams were produced at ISOLDE by bombarding a UCx primary target with 1.4 GeV protons. The mass separated radioactive beams were re-accelerated with the REX-ISOLDE linear accelerator to 2.8 MeV/u and delivered to the target position of the MINIBALL γ-ray spectrometer, which recorded γ-rays following Coulomb excitation. The resulting B(E2;0+→2+) values in 208,210Rn and 206Po are presented and discussed in terms of systematics and relevant nuclear models. The present study provides new insight into the interplay between collective excitations and single-particle regime near N=126.

Speaker: Dr Tuomas Grahn (University of Jyväskylä)

Slides GrahnTuomas.pdf

12:35 Lunch Break

Session 7

Convener: Dr Juergen Gerl (GSI)

28 From GASP to ROSPHERE: Gamma-ray spectroscopy at NIPNE – Bucharest

First, a brief overview of some outstanding results obtained with GASP within the Italian-Romanian collaboration will be given. Then, recent developments for gamma-ray spectroscopy at the Tandem Laboratory in Bucharest are presented. The ROSPHERE (ROmanian array for SPectroscopy in Heavy ion REactions) array, now in use at this laboratory, is a 'sphere' with 25 detector positions. HPGe of ~50% relative efficiency, with anti-Compton shields, can be used in these positions, for 'classical' gamma-ray spectroscopy experiments, like gamma-gamma coincidences and DSAM and plunger lifetime determinations. Until now, however, the most successful use of this setup was that as a mixed array, with both HPGe detectors and LaBr3:Ce scintillator detectors. The fast timing properties and relatively good energy resolution of the lanthanum bromide detectors allowed the extension of the fast timing method for nuclear lifetime determinations to in-beam experiments with fusion-evaporation, incomplete fusion and fragmentation reactions with alpha particle and various heavy ion beams. Lifetimes of nuclear excited states can be measured in the domain from several tens of ps to ns, a range that only partially overlaps with that of other methods and usually highlights interesting nuclear structure effects. Some physics cases will illustrate the performances of this array.

Speaker: Dr Dorel Bucurescu (HH IFIN Bucharest)

Slides BucurescuDorel.pdf

29 Gamma Spectroscopy as a Tool to Search for Particle-Phonon Coupled States: Status and Perspectives

The coupling between a particle and a phonon is a very important issue in nuclear structure studies, being a key process at the origin of the anharmonicities of vibrational spectra, quenching of spectroscopic factors and damping mechanism of giant resonances. The experimental and theoretical investigation of this problem is presented in connection with gamma spectroscopy works on neutron-rich nuclei around 48Ca and 64Ni. Results are reported from experiments performed at Legnaro National Laboratory, NIPNE (Bucharest) and ILL (Grenoble), using complex detection systems such as PRISMA-CLARA, ROSPHERE and EXOGAM. It is shown the feasibility of complete in-beam gamma spectroscopy, in terms of angular distributions, polarization and lifetime analysis, allowing to firmly establish spin and parity of excited states and their nature. The focus is, in particular, on 47Ca, 49Ca and 65Cu nuclei, which provide evidence for particle-phonon coupled states based on the 3- octupole phonons of the 48Ca and 64Ni cores, respectively. They are among the few fully established examples of particle-vibration coupling in nuclei with mass A<100, showing the robustness of nuclear collectivity in rather light systems. Perspectives will also be given in connection with similar type of studies around the 132Sn core, of great interest for future experiments with radioactive beams.

Speaker: Silvia Leoni (University and INFN Milano)

Slides LeoniSilvia.pdf

30 The 49/2+ Isomer in 147Gd – Study of the most complex isomeric decay

The LINAC-ALPI accelerator at LNL and the GASP array were used to perform gamma spectroscopy experiment aimed at two separate goals. The first one was to test the possibility to observe the Coulomb excitation of 147Gd states located above the 49/2 isomer in a secondary scattering of reaction products in the 208Pb catcher. The second goal was to clarify the gamma branching in the earlier studied isomeric decay. The 76Ge+ 290 MeV 76Ge fusion evaporation reaction produced abundantly the 147Gd high-spin isomeric state and the collected gamma coincidence data were analysed taking into account both aims of the experiment. A brief summary of the analysis concerning the Coulomb excitation test will be followed by an extended presentation of results obtained in the study of the 147Gd isomer decay. The gamma coincidence analysis revealed in this decay more than 300 gamma transitions with intensities down to about 10-4 per decay level. All of them were safely placed in the level scheme, which in some parts had to be substantially modified compared to previous results [1,2]. A nearly perfect intensity balance observed at all populated levels indicated the completeness of the presently established decay scheme and fully confirmed the earlier anticipated complexity of the gamma branching. The intensity balance allowed to extract total electron conversion coefficients for many low energy transitions which uniquely characterized their multipolarity. Together with the earlier measured angular distribution coefficients [1,2] and electron conversion results [2], spin and parity values could be unambiguously assigned to nearly all of the populated levels. The 49/2+ assignment [2] of the isomer was confirmed and assignments of all populated levels revealed the decay paths through yrast and many non-yrast states. The studied decay presents the most complex isomeric decay known today in the whole chart of nuclides. 1. R. Broda et al. Z.Phys.A305, 281 (1982) 2. O. Bakander et al. Nucl.Phys.A389, 93 (1982)

Speaker: Prof. Rafal Broda (Institute of Nuclear Physics PAN, Krakow, Poland)

Slides BrodaRafal.pdf

31 Lifetime measurements by Doppler methods with the RoSphere array

The Doppler techniques ( DSAM- Doppler Shift Attenuation Method and RDDS Recoil Distance Doppler Shift) are widely used gamma-ray spectroscopy techniques aimed at measuring the lifetime of excited nuclear states by using the Doppler shift of the de-exciting gamma-ray transition as a stopwatch. The RoSphere setup installed at the Bucharest TANDEM was used for lifetime measurements by the DSAM method in heavy ions and alpha induced reactions and by the RDDS method, in connection with a plunger device build following the Cologne design. Combined with in-beam fast timing technique, the lifetime experiments yielded a quasi-complete study of 120Te, part of a wider experimental campaign aimed at studying the collective behaviour in light Tellurium isotopes. The specific details of the methods and reaction mechanisms will be discussed and results will be presented.

Speaker: Constantin Mihai (HH IFIN Bucharest)

Slides MihaiConstantin.pdf

32 The continuous-angle Doppler-shift attenuation method – sub-picosecond lifetime measurements with position-sensitive HPGe detector arrays

The Doppler-shift attenuation method (DSAM) is a well-established technique for the determination of sub-picosecond nuclear level lifetimes. It is based on analyzing the characteristic shape of Doppler-broadened photo-peaks from nuclear transitions observed at specific observation angles in in-flight γ-ray spectroscopy experiments, when the de-excitation of a nuclear level occurs while the emitting nucleus is being decelerated in a thick target. We have extended the method in order to exploit the possibilities arising from state-of-the-art position sensitive HPGe detector arrays by analyzing the Doppler-broadened peaks not only as a function of the Doppler-shifted γ-ray energy, but also as a continuous function of the polar angle of γ-ray detection with respect to the incident beam direction. This approach significantly boosts the sensitivity and applicability of the method. The corresponding two-dimensional fit algorithm in the energy – polar detection angle (Eγ, θγ) space is also applicable to conventional HPGe detector arrays without intrinsic position-sensitivity. We have furthermore extended this new technique to experiments with relativistic ion beams, where we analyze Doppler-corrected, two-dimensional γ-ray spectra in the (Eγ, θγ) space without stopping the beam ions in the target. This is especially useful for experiments with radioactive and/or cocktail beams, because it avoids the accumulation of radioactivity at the target position and makes ion identification behind the reaction target possible. With this “differential” DSAM technique, a second sensitivity region for level lifetimes in the range of 100ns arises from geometric effects.

Speaker: Mr Christian Stahl (IKP, TU Darmstadt)

Slides StahlChristian.pdf

33 Collectivity in neutron-rich Co and Mn isotopes going towards N = 40

In the last decade, a large experimental an theoretical effort has been devoted to the study of the sub-shell closure N = 40 and the evolution of the magic number N = 50 for the Ni isotopic chain. Meanwhile the N = 50 78Ni excited states represent still nowadays an experimental challenge, the evolution of the sub-shell closure at N = 40, when taking away protons from the Ni core, has been thoroughly studied. In fact, it has been measured that, by removing protons from the f7/2 shell below 68Ni, the N = 40 subshell gap vanishes and a new region with large quadrupole deformation appears, as is the case of 66Fe and 64Cr [1,2]. A large theoretical effort within the shell-model framework has been done to describe this development of deformation and it has been shown that only by the inclusion of the d5/2 neutron orbital beyond N = 50 the deformation can be reproduced in this so called new island of inversion [3,4]. In this work we employed the AGATA demostrator coupled to the PRISMA spectrometer to study the low-lying excited states in the neutron-rich Co. With one proton hole respect to Ni, Co isotopes present both collective and single-particle states [5,6]. We have also studied the excited states in neutron-rich Mn isotopes (three proton holes respect to Ni). The lifetimes of the excited states in 63,65Co as well as 59,61Mn have been measured employing the Recoil-Distance-Doppler-Shift method. The experimental B(E2) values have been compared with LSSM calculations, which lead us to draw some conclusions on the role of the d5/2 and g9/2 neutron orbitals in driving collectivity below 68Ni. [1] W. Rother et al. Phys. Rev. Lett. 106, 22502 (2011) [2] A. Gade et al. Phys .Rev. C81, 051304 (2010) [3] E. Caurier et al. Eur. Phys. Jour. A. 15, 145 (2002) [4] S. Lenzi et al. Phys. Rev. C82, 54301 (2010) [5] A. Dijon et al. Phys. Rev. C83, 64321 (2011) [6] D. Pauwels et al. Phys. Rev. C79, 44309 (2009)

Speaker: Dr Victor Modamio Hoybjor (LNL)

Slides ModamioVictor.pdf

16:10 Transfer to Legnaro National Laboratory

Departure at 16:30

Session 8

Convener: Dr Nicolae Marius Marginean (IFIN-HH Bucharest)

34 Welcome

Speaker: Giovanni Fiorentini (FE)

35 Mirror displacement energies and neutron skins

Mirror displacement energies and neutron skins A gross estimate of the neutron skin [0.80(5) (N-Z)/A fm] is extracted from experimental proton radii, represented by a four parameter fit, and observed mirror displacement energies (CDE). The calculation of the latter relies on an accurately derived Coulomb energy and smooth averages of the charge symmetry breaking potentials constrained to state of the art values. The only free parameter is the neutron skin itself. The Nolen Schiffer anomaly is reduced to small deviations (rms=127 keV) that exhibit a secular trend. It is argued that with state of the art shell model calculations the anomaly should disappear. Highly accurate fits to proton radii emerge as a fringe benefit.

Speaker: Prof. Andres P. Zuker (IPHC Strasbourg)

36 Mirror energy differences and the J=2 anomaly

Mirror energy differences and the J=2 anomalyThe study of differences in excitation energy between analogue states in isobaric multiplets allows to verify the validity of isospin symmetry and independence as a function of the angular momentum. These differences are of the order of tens of keV and can be well reproduced by state-of-the-art shell model calculations. Several nuclear structure properties can be deduced from these data, such as the alignment of nucleons along rotational bands, the evolution of the nuclear radius and the identification of pure single particle excitations across two main shells. In addition, the isospin breaking of the nuclear interaction is suggested by the systematic comparison with data. The different ingredients that enter the calculation of the Coulomb energy differences between mirror nuclei are discussed in comparison with the experimental data of nuclei in the f7/2 and in the sd shell.

Speaker: Prof. Silvia Monica Lenzi (University and INFN Padova)

Slides LenziSilvia.pdf

37 The SPES RIB Facility

Speaker: Gianfranco Prete (LNL)

Slides PreteGianfranco.pdf

38 The GALILEO Gamma-Ray Array

Speaker: Calin Alexandru Ur (PD)

Slides CalinAUr.pdf

19:05 Visit to LNL

20:00 Social Dinner

Wednesday, 12 June

Session 9

Convener: Dr Gilles de FRANCE (GANIL)

39 Gamma Ray Spectroscopy at an external neutron beam of the Institut Laue-Langevin

Gamma ray spectroscopy at external neutron beams offers unique possibilities for nuclear structure studies. The present talk summarises the recent efforts within the EXILL campaign, in which a highly efficient HPGe detector cluster was put around the intense cold neutron beam Pf1b at the Institut Laue Langevin (ILL). The setup consisted of clover detectors from the EXOGAM array, coaxial detectors from the GASP array and clover detectors from the ILL. All detectors were mounted with AntiCompton shields at a close distance to a sample to allow prompt spectroscopy studies. Data were taken with a trigger free digital acquisition system. The campaign included several detailed (n,gamma) studies and spectroscopy of fission products populated in neutron induced fission of 235U and 241Pu. Lifetime measurements with the fast timing technique using 16 LaBr3:Ce scintillators in combination with 8 clover detectors were also done. A comparison of first results to experimental data obtained from in-pile (n,gamma) experiments and from measurements with spontaneous fission sources will be presented. Finally an outlook of further developments for multi detector setups at neutron beams will be given. Here the concept of the ILL project FIPPS will be introduced, a combination of a fission fragment mass spectrometer with HPGe-detector clusters.

Speaker: Dr Michael Jentschel (Institut Laue-Langevin, Grenoble)

Slides JentschelMichael.pdf

40 Structure of exotic nuclei through nuclear moment and transition probability studies.

The studies of exotic nuclei have revealed some new phenomena including modifications of the shell structure or appearance of regions of rapid onset of deformation. The nuclear moments and transition probabilities are among the observables that could shed light both on the single-particle and collective nuclear properties. Therefore they could prove of key importance in regions where interplay between spherical and deformed features is considered. The neutron-rich A~100 region has attracted important experimental and theoretical interest for several decades. One of the most sudden onset of deformation throughout the nuclear chart is observed at N=60 for a number of isotopic chains lighter than Molybdenum. The south border of this region has been roughly established few decades ago but more detailed studies for the microscopic origin of the deformation have become possible only recently with the advances of radioactive ion beams techniques. Coulomb excitation studies of the odd-mass Rubidium isotopes, 93-99Rb, have been performed at REX-ISOLDE using the Miniball setup. The low-energy structure in those isotopes, and their transition probabilities obtained, show distinctively different feature for the quasi spherical nuclei (93,95Rb) below and the well-deformed ones (97,99Rb) above N=60. These results establish 97Rb as the corner stone of the region of deformation allowing for a clear identification of the orbitals on which it is built. Obtaining high precision g-factor information on short-lived picosecond states is a non-trivial task. The experimental techniques usually applied, as e.g. TF or RIV, require calibration measurements on known states. This can be overcome performing time-dependent studies using charge states for which the hyperfine field can be calculated from first principles. The g(2+) of 24Mg has been measured at ALTO, Orsay using the Orsay Universal Plunger System (OUPS) in combination with the ORGAM array. Time Dependent Recoil In Vacuum technique on H-like charge states has been applied for the first time in “radioactive beam geometry”. The preliminary results, showing the power of this method and demonstrating its applicability for precise moment studies of picosecond states, will be presented.

Speaker: Dr Georgi Georgiev (CSNSM, Orsay)

Slides GeorgievGeorgi.pdf

41 Investigation of high spin states near N=50 shell closure in search for emergence of collectivity using INGA

The excited states of nuclei near closed shell at high angular momentum states have attracted lot of attention in theoretical and experimental research. They provide suitable laboratory for testing the interactions of shell model states, possible presence of high spin isomers and help in understanding the emergence of collectivity as the higher orbitals are occupied. An experimental program has been pursued with INGA coupled with a digital data acquisition system to look for emergence of collectivity at high spin in nuclei near shell closure [1]. The Indian National Gamma Detector Array(INGA) is set up at Pelletron Linac accelerator facility at Mumbai, as a part of a collaboration between BARC,IUAC, SINP, TIFR, UGC-CSR-KC, VECC and different Universities. The array is designed for 24 Compton suppressed clover detectors providing around 5% photopeak efficiency. Recently, a digital data acquisition system with 96 channels (based on Pixie-16 modules developed by XIA LLC) has been implemented for this Compton suppressed clover array. In the present work, we will discuss the initial results from the spectroscopic study of the high spin states of the 89Zr and 90Nb. High spin states in these nuclei were investigated using 13C + 80Se and 28Si + 65Cu reactions. The excited levels have been observed up to 12 MeV excitation energy and spin ~ 49/2hbar in 89Zr [2]. The DCO and polarization measurements were carried out to assign the spin and parity of different states. The measured results will be compared with the shell model calculations. In addition, a regular dipole band has been observed which is extended up to 49/2 hbar. Results of Cranking model and deformed Hartree-Fock model calculations agree well with the measured level energies and transition strengths, indicating the emergence of collectivity at high spin in 89Zr. Future plan to couple a highly segmented charged particle array to INGA for such investigations will be discussed. References: 1. R. Palit et al., Nucl. Instr. and Meth. A 680, 90 (2012). 2. S. Saha et al., Phys. Rev. C 86, 034315 (2012).

Speaker: Prof. Rudrajyoti Palit (TIFR Mumbai)

Slides PalitRudrajyoti.pdf

42 Collectivity of the 4+ state in 70Zn studied via Coulomb excitation

Shell evolution in the vicinity of 68Ni has recently attracted many theoretical and experimental investigations. By now it has been clearly established that the presumed subshell closure at N=40 is not very pronounced. While the intruder character of the 1g9/2 and 2d5/2 neutron orbital induces collectivity by pair excitations from the fp shell into the g9/2 orbital, the parity change hinders quadrupole excitations and therefore mimics the properties of a doubly magic nucleus in 68Ni, i.e., a high 2+1 energy and a low B(E2; 2+ → 0+) value. Adding valence nucleons to the N=40 open shell leads to a rapid increase of collectivity, with an interplay of both collective and single-particle degrees of freedom. Such rapid changes indicate underlying complex effects and make this region ideal for testing theoretical calculations. While measurements of B(E2; 2+-> 0+ ) values are useful to investigate the evolution of collectivity along isotopic chains, even more insight into the collective behavior can be gained by measuring lifetimes of higher-lying states. Almost all stable and neutron-rich Zn isotopes present an anomalously low B(E2; 4+ → 2+)/ B(E2; 2+ → 0+) ratio of 1 or less, which is normally observed only around closed shells. A strong increase of collectivity of the 4+ state was observed for 70Zn [2] and could not be explained in the framework of nuclear structure models. A recent lifetime measurement [2] yielded a considerably longer lifetime of this state, yet its accuracy was not sufficient to draw firm conclusions. Given the complex scheme of low-lying states in 70Zn including many nearly degenerate transitions, Coulomb excitation seemed a more appropriate method to study this nucleus. A dedicated Coulomb excitation measurement has been recently performed at the Heavy Ion Laboratory, University of Warsaw, to measure B(E2; 4+ → 2+) in 70Zn. For this study, the EAGLE array coupled to a compact setup of 48 PIN-diodes was used. The preliminary result will be presented. [1] D. Muecher et al, PRC 79 (2009) 054310 [2] C. Louchart et al, PRC, accepted for publication.

Speaker: Dr Magda Zielinska (CEA Saclay)

Slides ZielinskaMagda.pdf

43 Isospin Symmetry Violation in sd Shell Nuclei

The influence of isospin nonconservation is important for testing the fundamental symmetries underlying the Standard Model, e.g., corrections to superallowed 0+ -> 0+ -decay rates [Towner and Hardy (2010)], and is pivotal for computing theoretical amplitudes for nucleon transfer reaction which violates isospin selection rule [Blank and Borge (2008)]. Recently, we have constructed a realistic isospin-nonconserving (INC) shell-model Hamiltonian in sd shell. The INC Hamiltonian consists of an isospin-conserving Hamiltonian, i.e. either USD [Brown and Wildenthal (1988)], or USDA, or USDB interactions [Richter and Brown (2008)], a Coulomb interaction, and a phenomenological charge-dependent forces of nuclear origin. All charge-dependent strengths were determined by a least-squares fit to reproduce newly compiled experimental coefficients of the isobaric multiplet mass equation (IMME) [Y.H.L. et al. (2013)] with very low root-mean-square deviation values 33 keV [Y.H.L. et al. (2013)]. This INC Hamiltonian provides an accurate theoretical description of the isospin mixing in nuclear states. We present two of the important applications: (a) the microscopic description of staggering behavior of IMME isovector and isotensor coefficients; and (b) the breaking of the quadratic IMME in A = 24 , 28 , 32 quintets. Overall, this new INC Hamiltonian shows its robustness in providing an accurate theoretical description of the isospin mixing in nuclear states of sd shell nuclei.

Speaker: Dr Yi Hua Lam (CEN Bordeaux-Gradignan)

Slides LamYiHua.pdf

44 Nuclear shape evolution through lifetime measurement in neutron rich nuclei

A new interest for exotic nuclei further away from the valley of stability arises due to the possibility to use refined experimental methods. In particular, the neutron rich side of the valley still offers a lot of interesting features to be discovered. Our recent experiments on nuclei around A = 100 aim at discovering part of these features trough lifetime measurements and will help understanding nuclear shape evolution in neutron rich nuclei. In this mass region, shapes are changing rapidly, which is reflected in the theoretical calculations by the prediction of occurrence of prolate, oblate, or triaxial shapes. These predictions vary as a function of the theoretical model used, thus experimental measurements will have important implications. The neutron-rich isotopes were produced trough a fusion-fission reaction performed at GANIL in inverse kinematics with a 238U beam. The aim of this experiment was to extend information on the evolution of the collectivity in this mass region by measuring the lifetimes of excited states in more neutron-rich nuclei and up to higher spins. A and Z identification of the fission fragments was performed with the VAMOS spectrometer, while the EXOGAM spectrometer was used for the γ-ray detection. The RDDS (Recoil Distance Doppler Shift) method has been applied to extract the lifetime of excited states. To our knowledge this is the first experimental attempt to perform a RDDS experiment on fission fragments, which are identified in A and Z on an event-by-event basis. Results on the complex analysis performed to achieve the identification of the fission fragments up to Z=54 and A=150 and on the new lifetime values will be presented. A complementary experiment has been performed recently at ILL to measure lifetimes of excited states in the same range of nuclei but populated with a neutron induced reaction on a Pu target. Lifetimes have been measured via the fast-timing method using LaBr3 detectors and the EXOGAM array, which will extend the range of measurable lifetimes to ns. This will give information either on the deformation or on the role of the triaxiality in these nuclei.

Speaker: Lucie Grente (CEA Saclay)

Slides GrenteLucie.pdf

10:45 Coffee Break

Session 10

Convener: Prof. Rafal Broda (Institute of Nuclear Physics PAN, Krakow, Poland)

45 Gamma-ray spectroscopy with large volume scintillator detectors

In the last 10 years a large number of new high light-yield scintillator crystals have been discovered. The most famous among them are LaBr3:Ce crystals. Even though large volume LaBr3:Ce detectors are available since only 2008-2009 some newly arrays with large volume crystals are already in operation as for example HECTOR+ which consists of ten 9 x 20 cm LaBr3:Ce detectors and eight 14.5 x 17.5 BaF2 detectors. The arrays has been coupled to the AGATA demonstrator in both the LNL campaign with stable beams and in the GSI PRESPEC campaign with radioactive beams. The properties of large volume cylindrical 3.5” x 8” LaBr3:Ce scintillation detectors cannot be easily derived from those of small and medium sized detectors. In fact, self absorption, possible crystal in-homogeneities (both of which are more likely to appear with scaled up dimensions), plus the much longer mean free path of the scintillation light towards the photo-cathode and photo-multiplier tube (PMT) non-idealities, can all variously affect the detector performance. Therefore the properties of these large volume detectors in terms of signal lineshape, linearity, energy and time resolution will be discussed. In addition the very preliminary results concerning the analysis of the data in the GARFIELD-LNL, AGATA-LNL and PRESPEC-GSI campaign, where large volume scintillator detectors, had been used will be presented. In particular the topics of Isospin Mixing, Pygmy Dipole Resonance, Dynamical Dipole and low lying collective states will be discussed

Speaker: Franco Camera (University and INFN Milano)

Slides CameraFranco.pdf

46 Gamma-ray spectroscopy at TRIUMF-ISAC: recent results, perspectives and future opportunities

Versatile Germanium-detector array is essential to exploit the unique scientific opportunities at TRIUMF Isotope Separator and ACcelerator (ISAC). The TIGRESS array and its associated auxiliary detectors has been designed for reaction studies with accelerated ion beams. The 8π spectrometer and its powerful suite of ancillary detectors is optimized for a wide program of research in the fields of nuclear structure, nuclear astrophysics and fundamental symmetries with low-energy radioactive beams. Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei (GRIFFIN) will replace 8π spectrometer and take advantage of its auxiliary detectors. Recent results of experiments with TIGRESS and 8π will be presented.

Speaker: Dr Zhimin Wang (TRIUMF and Simon Fraser University)

Slides ZhiminWang.pdf

47 NEDA: NEutron Detector Array for spectroscopy studies

Future studies of exotic nuclei will mainly be performed by using reactions induced by radioactive as well as high-intensity stable heavy ions. The need for efficient neutron detection is not only required in heavy-ion fusion-evaporation reactions close to the proton dripline, but also as ”veto” detectors for suppression of reaction channels with high neutron multiplicity in studies of neutron-rich nuclei. The new NEutron Detector Array (NEDA) is a collaborative European effort to construct a modern neutron detector array for experiments with stable and radioactive ion beams. The project benefits from the long-standing experience developed with the realization and use of the Neutron Wall, a highly efficient medium granularity neutron detector array used in combination with the EUROBALL spectrometer and later with EXOGAM. The new device will be versatile and optimized for the operation with stable beams and second generation radioactive ion-beam facilities (SPES, SPIRAL2, FAIR, etc.). NEDA will be composed of 355 detectors, covering a solid angle of about 2pi and will be used as an ancillary detector of AGATA, GALILEO, EXOGAM2 and PARIS. Digital electronics with pulse-shape discrimination capabilities will be used. NEDA will allow the selection of neutron channels in nuclear reactions, providing multiplicity and energy information. It will be realized in different stages, the first one being an upgraded version of the Neutron Wall. A large effort has been devoted, so far, to the validation of the simulations and test of the future prototypes of NEDA. New detector materials as well as traditional ones have been investigated and characterized, in particular, deuterated liquid scintillators as BC537 and the conventional BC501A. Pulse shape discrimination algorithms have been investigated for both liquid scintillators. A design study of the NEDA array geometry is being performed in order to optimize the granularity, the solid angle coverage in conjunction with the future gamma-ray arrays. In this presentation, the physics domain of NEDA as well as the status of the R&D of the NEDA detector array will be discussed.

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

Slides HuyukTaifun.pdf

48 Agata modules as Compton polarimeters for the measurement of gamma-ray linear polarisation

We have investigated the ability of AGATA modules to measure the linear polarisation of gamma rays, exploiting the dependence of the Compton scattering differential cross section on the azimuthal angle. To this aim, partially polarised gamma rays have been produced by Coulomb excitation of the first excited state of 104Pd and 108Pd which deexcite to the ground state by emission of gamma rays of 555.8 keV and 433.9 keV, respectively. The position of the Agata array was chosen to select gamma rays at angles not far from 90 degrees to the beam direction. The azimuthal distributions, with respect to the reaction plane, of the first Compton scattering for a properly selected sample of these gamma rays have been evaluated and compared with the corresponding distribution for the unpolarised 661 keV gammas from a 137Cs source. The instrumental distortions in the measured distributions appear to cancel almost exactly in the ratio R_phi of the COULEX data to those of the 661 kev gammas, and a clear signal of linear polarisation becomes apparent. The amplitude of the cos(2 phi) modulation has been compared to the theoretical linear polarisation of gamma rays from Coulomb excitation (calculated with the help of the GOSIA code) to deduce the experimental analysing power, which turns out to be about 45% in both cases. A ``theoretical'' value of the average analysing power has been deduced from the values calculated, for each of the selected events, as a function of the Compton scattering angle, taking into account the experimental uncertainty on the coordinates of the interaction points. A satisfactory agreement between theoretical and experimental values has been found.

Speaker: Dr Barbara Melon (University and INFN Firenze)

Slides BizzetiPiergiorgio_web.pdf

49 Simulating the position sensitivity of the segmented iThemba LABS HPGe detector

The iThemba LABS detector is made up of four end-closed coaxial, front tapered, electrically segmented n-type germanium crystals, packed closely together in one cryostat. The dimensions of each crystal are: 60 mm width before shaping and 90 mm long. The cathode of each crystal is electrically segmented into 8 contacts with depth segmentation at 35 mm, implying that the back segments are 55 mm long. This results in a total of 36 electronic channels of which 32 are associated with the outer contacts and 4 with the inner core contacts of the detector. The inner core contacts provide high resolution measurements of gamma-ray energy deposition for each crystal whilst the outer contacts provide information about the locations of the gamma-ray interaction inside the detector. The position sensitivity of this segmented iThemba LABS HPGe detector is investigated through simulation using the Multi-Geometry Simulation code. This code simulates the electric potential, electric field, drift velocity, weighting potential and generate the expected pulse shape from an arbitrary gamma-ray interaction’s position within the germanium detector volume. When the charge sensitive pre-amplifier response for the segmented iThemba LABS HPGe detector is convoluted with the total current produced by the MGS, the resulting charge pulse is effectively slowed and smoothed. Using this code, the pulse shape response at the inner and outer contacts has been generated changing the radius, angle and depth of gamma-ray interaction positions within the germanium detector volume. Changes in the pulse shapes reflecting changes in the position of the interaction point were observed. This confirms that the detector is sensitive to the exact position of the gamma-ray interaction. The details about the simulated position sensitivity of the segmented iThemba LABS HPGe detector will be discussed.

Speakers: Mr Sive Noncolela (1. iThemba LABS), Dr Thifhelimbilu Daphney Bucher (1. iThemba LABS)

Slides NoncolelaSive.pdf

50 In-vivo Range Measurement of Therapeutic Protons from Prompt Gamma Emission

Proton beam therapy is emerging as a major radiation therapy modality for cancer patients due to the improved dose distribution of protons, which allows for increased dose to the tumor while sparing surrounding healthy tissues. This work addresses the problem of range uncertainty through the development of a detector, which will measure proton range in each patient during beam delivery with millimeter accuracy, effectively eliminating proton range uncertainty. During proton interactions with atoms in tissues, gamma rays, including prompt photons from nuclear reactions and delayed photons from the decay of unstable products, are emitted. The rate of secondary radiation used in the measurement is low, making accurate measurement challenging. We have used the MCNPX simulation package to model a detector consisting of 35 Cesium Iodide crystals with dimensions of 9x9.9x0.4 cm and a lead based collimator grid with 0.4cm thick plates. A Gaussian proton pencil beam impinged on a cylindrical water phantom with a diameter of 10 cm. The distance between the cylinder axis and the collimator surface was approximately 20 cm. We simulated the response of the detector to several mono-energetic pencil beams delivering protons in the energy range 80MeV - 160MeV. A sigmoid curve fit to the spatial distribution of the simulated gamma emission data was used in order to locate an edge in gamma emission pattern that is correlated with the position of the Bragg peak. These simulations of a prompt gamma detector for in-vivo range measurement for therapeutic proton beam scanning suggest that range measurement for individual pencil beams (spots) may be feasible. Further work will address the optimization of the detector geometry and placement, as well as advanced detector design.

Speaker: Prof. Ricardo Alarcon (Arizona State University)

Slides AlarconRicardo.pdf

Closing Session

14:30 Visit to Palazzo del Bo'