Speaker
Alvaro Tolosa Delgado
(IFIC (Instituto de Fisica Corpuscular))
Description
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{\small \it Nuclear Physics in Astrophysics 8, NPA8: 18-23 June 2017, Catania, Italy}
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\TITLE{Commissioning of the BRIKEN $\beta$-delayed neutron detector for the study of exotic
neutron-rich nuclei}\\[3mm]
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\AUTHORS{A. Tolosa-Delgado$^{1}$ on behalf of the BRIKEN collaboration }
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\AFFILIATION{1}{Instituto de Fisica Corpuscular, CSIC and Univ. Valencia, E-46980 Paterna, Spain}
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\centerline{Contact email: {\it alvaro.tolosa@ific.uv.es}}
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Beta-delayed neutron emission $\beta n$ is the dominant decay mode of exotic nuclei produced
along the path of the rapid neutron capture process. The final abundance distribution
of the elements synthesized is affected by this decay mode in a complex way,
since it primarily shifts the distribution to lower
masses, while the additional neutrons injected in the system after freeze-out induce late neutron
captures that shift the distribution to higher masses [1].
Thus a correct description of the observed elemental abundances requires a good knowledge
of delayed neutron emission probabilities $P_{n}$ of these very exotic nuclei.
Moreover for these nuclei with very large neutron excess more than one neutron can be emitted
in the decay. Our current understanding of the beta-delayed multiple neutron emission
process $\beta x n$, in particular of the competition between the different decay modes, is incomplete
because of the scarcity of experimental data [2]. Finally the $P_{xn}$ values are sensitive to the
nuclear wave function allowing nuclear structure studies through the test of theoretical
beta-strength distributions [3].
With these ideas in mind the BRIKEN Collaboration has set up a powerful detection system consisting of:
1) a large neutron counter with 148 $^{3}$He tubes that has high and constant neutron detection
efficiency [4], 2) the high granularity implantation-decay detection array AIDA [5],
and 3) two CLOVER type HPGe detectors. The setup will exploit the very high
intensity of secondary radioactive beams available
at the focal plane of the BigRIPS separator [6] in the RIKEN Nishina Center to measure implant-beta,
implant-beta-neutron and implant-beta-neutron-gamma correlations for nuclei very far
from the $\beta$-stability valley.
The setup received the first radioactive beam of isotopes close to the
doubly-magic $^{78}$Ni in Autumn 2016.
In this presentation we will report on the first results of this commissioning run, including an evaluation
of the performance of the setup. We will also present preliminary results of $P_{n}$ values
obtained for nuclei in this region including some for which previous values are uncertain or correspond
to a single measurement.
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{\small
\noindent
[1] A. Arcones and G. Martinez-Pinedo, Phys. Rev. C 83,045809 (2011) ;
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[2] R. M. Mumpower et al., Phys. Rev C 94, 064317 (2016);
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[3] M. Madurga et al., Phys. Rev. Lett. 117, 092502 (2016);
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[4] A. Tarifeno-Saldivia et al., https://arxiv.org/abs/1606.05544, submitted to J. of Instr. (2016);
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[5] T. Davinson et al., http://www2.ph.ed.ac.uk/$\sim$td/AIDA/;
\noindent
[6] T. Kubo et al., AIP Conference Proceedings 1224, 492 (2010).
}
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Primary author
Alvaro Tolosa Delgado
(IFIC (Instituto de Fisica Corpuscular))
