Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 52 (2019)

New implant-decay correlation method for β-delayed neutron
emission measurements with the BRIKEN setup
O. Hall,∗1 A. Estrade,∗2,∗3 J. Liu,∗4 G. Lorusso,∗3,∗5 K. Matsui,∗3 F. Montes,∗6 N. Nepal,∗2 S. Nishimura,∗3V. H. Phong,∗3,∗7 J. Agramunt,∗8 D. S. Ahn,∗3 A. Algora,∗8 H. Baba,∗3 S. Bae,∗9 N. T. Brewer,∗10C. G. Bruno,∗1 R. Cabellero-Folch,∗11 F. Calvino,∗12 T. Davinson,∗1 I. Dillmann,∗11 C. Domingo-Pardo,∗8S. Go,∗13 C. J. Griﬃn,∗1 R. Grzywacz,∗10,∗13 T. Isobe,∗3 D. Kahl,∗1 G. Kiss,∗3 S. Kubono,∗3 M. Labiche,∗14A. I. Morales,∗8 B. C. Rasco,∗10 K. P. Rykaczewski,∗10 H. Sakurai,∗3 Y. Shimizu,∗3 T. Sumikama,∗3 H. Suzuki,∗3H. Takeda,∗3 J. L. Tain,∗8 A. Tarifeno-Saldivia,∗12 A. Tolosa-Delgado,∗8 P. J. Woods,∗1 R. Yokoyama,∗11 for theBRIKEN collaboration
With the observation of a binary neutron-starmerger accompanied by the spectroscopic identiﬁcation of r -process nucleosynthesis1) taking place in2017, there have been major developments in identifying a site of the r -process. These new observations
will increase the demand for precise nuclear data thatis necessary to reach a clearer understanding of the r process mechanisms thought to be occurring in theseenvironments.
In June 2017, an experiment was performed to study
the decay properties of the β-delayed neutron emittersin the mass region A = 130 near the doubly magic
nucleus 132 Sn. The active-stopper array AIDA2) was
placed at F11 with the nuclei of interest being implanted and detected alongside their subsequent decays in the silicon detector stack. Neutrons emitted
from the β-decay of the implanted ions were detectedby the BRIKEN neutron counter array3,4) surrounding AIDA. The neutron counter array consisted of 140
gas-ﬁlled 3 He counters, which were held inside a large
moderation block made of high-density polyethylene.
In carrying out analysis on the data, a new methodof correlating beta events with implanted ions was developed. As the detectors that comprise the AIDA
detector stack are double-sided silicon strip detectors(DSSDs), positional information of both high energy
implant and low energy decay events is obtained. Withβ-decay energies of 100 s of keV and a narrow strip
pitch of 560 µm, decay events will be spread acrossmultiple strips. This results in a trade-oﬀ between
detection eﬃciency and a background from electronic

Fig. 1. Comparison between the old correlation method (a)and the new method (b). In both images the red circle
indicates an implant particle, the orange circle a beta
particle and the blue circles as noise events.

noise for low energy signals, which is sensitive to thedetection threshold and the correlation method.
In previous experiments single points have been assigned to the location of the implants and betas withcorrelation performed based upon the beta points thatfall within an area around the implant signal, typicallya 7×7 pixel square shown in Fig. 1 a). The new method
instead takes into account all of the strips that ﬁre during an event and assigns an area for both implant anddecay signals. Correlations can then be performed bysearching for an overlap between the areas of the beta
and implant events as shown in Fig. 1 b). This new
method has been shown to reduce the amount of noisecorrelated with implants whilst maintaining the betadetection eﬃciency of the previous method, as noise
events that would otherwise fall within the 7 × 7 area
will now be rejected.
The data analysis for the experiment is ongoing.
The data shows the potential of the BRIKEN setup toextend the systematics of β-delayed neutron emission
probabilities along the N = 82 and Z = 50 shell closures south and east of 132 Sn. The results will improve
the reliability of nuclear data for r -process models.

∗1School of Physics and Astronomy, University of Edinburgh
College of Science and Engineering, Central Michigan Univeristy∗3 RIKEN Nishina Center∗4 Department of Physics, The University of Hong Kong
∗5 National Physics Laboratory∗6 NSCL and Department of Physics and Astronomy, Michigan
State University∗7 Faculty of Physics,VNU Hanoi University of Science∗8 Instituto de Fı́sica Corpuscular∗9 Department of Physics, Seoul National University∗10 Oak Ridge National Laboratory∗11 TRIUMF∗12 Universitat Politècnica de Catalunya∗13 Department of Physics and Astronomy, University of Tennessee∗14 STFC Daresbury Laboratory∗2References
1) E. Pian et al., Nature 551, 67–70 (2017).
2) C. J. Griﬃn et al., Proc. XIII Nuclei in the Cosmos 1,97 (2014).
3) A. Tarifeño-Saldivia et al., J. Instrum. 12, 04006 (2017).
4) B. C. Rasco et al., Nucl. Instrum. Methods Phys. Res.
911, 78–86 (2018).

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