Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Progress on the analysis of Pn -values relevant for the formation ofthe r-process rare-earth peak
M. Pallàs,∗1 A. Tarifeño-Saldivia,∗2,∗1 G. G. Kiss,∗3 J. L. Tain,∗2 A. Tolosa-Delgado,∗4,∗2 A. Vitéz-Sveiczer,∗3,∗5
F. Calviño,∗1 J. Agramunt,∗2 A. Algora,∗2 N. T. Brewer,∗8,∗6 R. Caballero-Folch,∗9 T. Davinson,∗10I. Dillmann,∗9,∗11 A. Estrade,∗12 N. Fukuda,∗7 R. K. Grzywacz,∗8,∗6 O. Hall,∗10 N. Mont-Geli,∗1 A. I. Morales,∗2A. Navarro,∗1 N. Nepal,∗7 S. Nishimura,∗7 B. C. Rasco,∗8,∗6 K. P. Rykaczewski,∗6 T. N. Szegedi,∗3 V. Phong,∗7
R. Yokoyama,∗13 M. Wolińska-Cichocka,∗14 and P. J. Woods∗10 for the BRIKEN Collaboration∗15
Rapid neutron capture (the r-process) producesnearly half of the nuclei heavier than iron in explosive
stellar scenarios. Above the mass number A = 100,
there are two main peaks in the r-process solar-systemabundances, are located at A ∼ 130 and A ∼ 195.
Located between them, the Rare-Earth Peak (REP)
is a tiny but deﬁnite peak at mass number A ∼ 160
that results from the freeze-out during the last stagesof neutron exposure. According to theoretical models
and sensitivity studies, half-lives (T1/2 ) and β-delayed
neutron emission probabilities (Pxn ) of neutron-richnucleus, in the mass region A ∼ 160 for 55 ≤ Z ≤ 64
are critical for the formation of the REP.1,2) As a partof the BRIKEN collaboration, the NP1612-RIBF148
experiment measured half-lives and β-delayed from Bato Gd (Z = 56–64). In 2018, an experimental run centered on 165 Pm was conducted using a total of 5 daysof beamtime. The results for Pm to Gd (Z = 61–64)
species are already published.3) The data analysis for
Ba to Nd (Z = 56–60) species using the method proposed in4) is presented in this report.
The NP1612-RIBF148 experimental setup consisted of the Advanced Implantation Detector Array(AIDA)5) and the BRIKEN neutron counter.6) The
neutron counter was placed surrounding AIDA to detect the β-delayed neutrons oﬀering a nominal valuefor the eﬃciency of 68.6% up to 1 MeV.
In Fig. 1, the preliminary results for the P1n values are compared with evaluated nuclear data fromthe ENSDF and some theoretical predictions.7–9) Preliminary reports include 14 new P1n values (151–152 Ba,Fig. 1. Preliminary P1n values derived in this work (reddot) compared with previous measurements (blue triangle) and theoretical calculations.7–9)

151–153

La, 154–156 Ce, 155–158 Pr, and 159–160 Nd). Twoother P1n values (149–150 La) were also remeasured, obtaining consistent results with previous measurements.
Our data supports the overall trend for all P1n predictions when compared to theoretical models. Thepn-RQRPA + HFM model9) best replicates the experimental data and provides good agreement for themajority of the isotopes.
References
1) A. Arcones et al., Phys. Rev. C 83, 045809 (2011).
2) M. R. Mumpower et al., Phys. Rev. C 85, 045801(2012).
3) G. G. Kiss et al., Astrophys. J. 936, 107 (2022).
4) C. J. Griﬃn et al., Jap. Phys. Soc. Conf. Proc. 14,020622 (2017).
5) A. Tarifeño-Saldivia et al., J. Instrum. 12, P04006(2017).
6) A. Tolosa-Delgado et al., Nucl. Instrum. Methods Phys.
Res. A 925, 133 (2019).
7) P. Möller et al., At. Data Nucl. Data Tables 125, 1(2019).
8) T. Marketin et al., Phys. Rev. C 93, 025805 (2016).
9) F. Minato et al., Phys. Rev. C 104, 044321 (2021).

∗1

Institut de Tècniques Energètiques (INTE), Universitat
Politècnica de Catalunya (UPC)∗2 Instituto de Fı́sica Corpuscular (IFIC), CSIC-UV∗3 Institute for Nuclear Research (ATOMKI)∗4 Department of Physics, University of Jyväskylä
∗5 Doctoral School of Physics, University of Debrecen∗6 Physics Division, Oak Ridge National Laboratory∗7 RIKEN Nishina Center∗8 Department of Physics and Astronomy, University of Tennessee∗9 TRIUMF, Vancouver∗10 School of Physics and Astronomy, University of Edinburgh∗11 Department of Physics and Astronomy, University of Victoria∗12 Department of Physics and Science of Advanced Materials
Program, Central Michigan University∗13 Center for Nuclear Study, University of Tokyo∗14 Heavy Ion Laboratory, University of Warsaw∗15 www.wiki.ed.ac.uk/display/BRIKEN/Home- 22 -