Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

Progress on the decay spectroscopy and measurement of half-lives andP n values in exotic nuclei near the N = 50 shell closure
C. J. Griﬃn,∗1 R. Caballero-Folch,∗1 L. Sexton,∗1,∗2 I. Dillmann,∗1 R. K. Grzywacz,∗3 K. P. Rykaczewski,∗4J. L. Tain,∗5 J. Agramunt,∗5 A. Algora,∗5 H. Baba,∗6 S. Bae,∗7 N. T. Brewer,∗4 C. G Bruno,∗8 F. Calvino,∗9T. Davinson,∗8 A. Estrade,∗10 S. Go,∗6 J. Ha,∗7 O. B. Hall,∗8 L. J. Harkness-Brennan,∗11 T. Isobe,∗6 D. Kahl,∗8M. Karny,∗12 L. H. Khiem,∗13 G. G. Kiss,∗6 A. Korgul,∗12 S. Kubono,∗6 J. Liang,∗14 J. Liu,∗15 G. Lorusso,∗2,∗6,∗16
K. Matsui,∗6,∗17 K. Miernik,∗12 F. Montes,∗18 A. I. Morales,∗5 N. Nepal,∗3 S. Nishimura,∗6 V. H. Phong,∗6,∗19
B. C. Rasco,∗4,∗3 Y. Saito,∗1 D. W. Stracener,∗4 T. Sumikama,∗6 A. Tarifeño-Saldivia,∗9 A. Tolosa-Delgado,∗5M. Wolinska-Cichocka,∗20 P. J. Woods,∗8 X. X. Xu,∗15 and R. Yokoyama∗3 for the BRIKEN Collaboration∗21Total Fit
31093

Se (Parent)93

Br ( daughter)
Br (n daughter)
Kr ( granddaughter)

92
9392

Countsβ-delayed single- and multi-neutron emission is foundin neutron-rich nuclei in which β decay populates states
above the neutron separation energy (S n ) in the daughter nucleus. New generations of radioactive ion beamfacilities will be able to produce thousands of currently inaccessible neutron-rich nuclei. Delayed neutron emission is expected to be the dominant decay
process for these nuclei, with recent papers detailingthe importance of β-delayed neutron emission for ther -process.1,2)
In 2016, the BRIKEN collaboration constructed andcommissioned the world’s largest and most eﬃcient βdelayed neutron detector3,4) at RIBF to conduct a wideranging and systematic study into the decay propertiesof hundreds of the most exotic neutron-rich nuclei currently available. The BRIKEN detector consists of 1403
He tubes within a HDPE moderator surrounding thehighly-segmented active stopper AIDA and two HPGeclover detectors in close geometry.
The NP1412-RIBF127R1 experiment implemented
the BRIKEN detector to measure β-delayed neutron
emission probabilities and half-lives, as well as conduct
decay spectroscopy studies, around the N = 50 shellclosure near the doubly-magic 78 Ni. This is a region
highlighted as sensitive to β-decay properties.5) In oneof the ﬁrst papers published from this experiment,6,7)
R. Yokoyama et al. observed two neutron emission in∗1

Physical Sciences Division, TRIUMF
Dept. of Physics, University of Surrey∗3 Dept. of Physics and Astronomy, University of Tennessee∗4 Oak Ridge National Laboratory∗5 Instituto de Física Corpuscular (IFIC)∗6 RIKEN Nishina Center∗7 Dept. of Physics and Astronomy, Seoul National University∗8 School of Physics and Astronomy, University of Edinburgh∗9 Universitat Politècnica de Catalunya (UPC)∗10 Dept. of Physics, Central Michigan University∗11 Dept. of Physics, University of Liverpool∗12 Faculty of Physics, University of Warsaw∗13 Institute of Physics, Vietnam Academy of Science and Technology∗14 Dept. of Physics and Astronomy, McMaster University∗15 Dept. of Physics, University of Hong Kong
∗16 National Physical Laboratory (NPL)∗17 Dept. of Physics, University of Tokyo∗18 National Superconducting Cyclotron Laboratory (NSCL),
Michigan State University∗19 Faculty of Physics, VNU University of Science∗20 Heavy Ion Laboratory, University of Warsaw∗21 www.wiki.ed.ac.uk/display/BRIKEN/Home∗2- 29 -Kr (-n / n- granddaughter)
Kr (n-n granddaughter)

91
93

102

92

Rb (-- great granddaughter)
Rb (--n / -n- / n-- great granddaughter)

10-2000

0

2000

4000

6000

Implant -  correlation time (ms)

8000

10000

Fig. 1. Preliminary half-life analysis of 93 Se, showing thecontributions to the total fit from the parent and daughter isotopes.
84, 85, 87

Ga for the ﬁrst time, and detailed dominating
one-neutron emission from two-neutron unbound statesin 86, 87 Ga.
The analysis eﬀorts based at TRIUMF focus on the91–95
Se and 94–97 Br isotopes. From these isotopes, halflives and P n values are expected to be measured for
92–95
Se and 95–97 Br for the ﬁrst time. An example decay
half-life Bateman ﬁt, considering the contributions to
the total ﬁt from each of the daughter nuclei along thedecay chain, is shown in Fig. 1. Decay spectroscopy
information in the neutron-rich region around A ∼ 90–
100 is sparse and this analysis will allow the extractionof the ﬁrst decay spectroscopy data for multiple nuclei
in this region.
Further analysis of the data is ongoing and expected
to yield multiple new P n values and half-lives. Early
publications highlight the potential of the highly eﬃcient BRIKEN detector to expand the systematics ofβ-decay in exotic neutron-rich nuclei, vital in developing accurate r -process nucleosynthesis models.
References

1) A. Arcones, F. Montes, Astrophys. J. 731, 5 (2011).
2) M. R. Mumpower et al., Phys. Rev. C 85, 045801 (2012).
3) A. Tarifeño-Saldivia et al., J. Instrum. 12, P04006 (2017).
4) A. Tolosa-Delgado et al., Nucl. Instrum. Methods Phys.
Res. A 925, 133 (2019).
5) T. Shafer et al., Phys. Rev. C 94, 055802 (2016).
6) B. C. Rasco et al., Nucl. Instrum. Methods Phys. Res.
A 911, 79 (2018).
7) R. Yokoyama et al., Phys. Rev. C 100, 031302(R) (2019).