II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Half-lives and β-delayed neutron emission for the most exotic
neutron-rich Se and Br isotopes
R. Caballero-Folch,∗1 I. Dillmann,∗1 S. Devinyak,∗1 C. J. Griﬃn,∗1 L. Sexton,∗1,∗2 J. Agramunt,∗3
R. K. Grzywacz,∗4 M. Pallas,∗5 K. P. Rykaczewski,∗6 J. L. Taı́n,∗3 A. Tarifeño-Saldivia,∗5 A. Tolosa-Delgado,∗3S. Nishimura,∗7 and the BRIKEN Collaboration.
The BRIKEN collaboration performed measurements on several neutron-rich nuclei regions across thenuclear chart during the period 2017–2021. Focused on
the double magic 78 Ni region, the experiment RIBF127
aimed to determine experimental β-decay half-lives,
neutron emission probabilities, and γ spectroscopy ofisotopes beyond the N = 50 neutron shell, which are
all important parameters to provide reliable data formodels of the astrophysical rapid-neutron capture process. The most neutron-rich isotopes of elements fromFe (Z = 26) to Kr (Z = 36) were identiﬁed using theBigRIPS spectrometer on an event-by-event basis with
the Bρ–ΔE–ToF method.1) At the end of the beamline, the detection setup consisted of the Advanced Impantation and Detector Array (AIDA)2) surrounded by
the BRIKEN detector.3) The AIDA consists of an array of six highly segmented layers of double-sided Sidetectors (DSSSD), enabling the detection of the implants of the ions and their β-decays. The BRIKEN
array is a high eﬃciency neutron detector based on 1403
He counters embedded in a polyethylene matrix tomoderate the emitted neutrons, and two HPGe clover
γ detectors. It enabled the detection of the neutrons
and the γ-rays emitted after the β-decays.
The isotopic species of interest in this study are
91–94
Se and 94–96 Br. They have been implanted in
AIDA (see Table 1), and for most of them, the decay properties were determined for the ﬁrst time. The
data analysis is based on the time correlation of theimplants and β-decays registered in AIDA, and theneutrons and γ-rays detected with the BRIKEN detector. In addition to the time correlation, spatial correlations between implants and β-decays are studied
owing to the DSSSD’s segmentation. This allowed us
to adjust the best signal-to-noise rate in the correlations.4) Using the Bateman equations and corrections
due to the physical limitations of the detection systems,5,6) the half-life and the β-delayed neutron emission probability, P1n -value, were determined. Figure 1
shows the analysis of 91 Se, in which multiple simultaneous ﬁts of implant-β and implant-β-neutron correlation histograms were performed to determine its
∗1
∗2
∗3
∗4
∗5
∗6
∗7

Table 1. Number of implants of the isotopes of interest andavailable data in the literature.
Nucleus Number of ions Previous literature values
implanted
half-life (s) P1n value (%)
91

Se
Se
93
Se
94
Se
94
Br
95
Br
96
Br

59728
340337
16631
525
2627
2289
159

92

21(10)7)30(10)7)-0.27(5)0.070(20)-91

Se decay chain implant-βcorrelations

91

Se β decays
Br β decays
Br β decays

91
90

10291

CountsSe implant-βncorrelations

101− 1000

−500

0500

1000
1500
Correltaion time (ms)

2000

2500

3000

Fig. 1. Implant-β (blue) and implant-β-neutron (red) correlation histograms for 91 Se. Fitted curves obtainedby simultaneously sharing common parameters, fromwhich the half-life and the P1n -value were determined.

properties. Preliminary results show slightly shorter
half-life and higher P1n -value compared with the literature for 91 Se. An upcoming publication will report
new half-lives and P1n values in the region, some ofthem for the ﬁrst time.
References
1) N. Fukuda et al., Nucl. Instrum. Methods Phys. Res. B
317, 323 (2013).
2) C. Griﬃn et al., POS (NIC-XIII), 097 (2014).
3) A. Tarifeño-Saldivia et al., J. Instrum. 12, (2017).
4) R. Caballero-Folch et al., Phys. Rev. C 95, 064322(2017).
5) A. Tolosa-Delgado et al., Nucl. Instrum. Methods Phys.
Res. A 925, 133 (2019).
6) J. Agramunt et al., Nucl. Instrum. Methods Phys. Res.
A 807, 69 (2016).
7) J. Liang et al., Nucl. Data Sheets 168, 1 (2020).

Physical Science Division, TRIUMF
Department of Physics, University of Surrey
Institut the Fı́sica Corpuscular de València
Department of Physics and Astronomy, University of TennesseeUniversitat Politècnica de Catalunya
Oak Ridge National Laboratory
RIKEN Nishina Center- 16 -1