RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-1. Nuclear Physics

Search for β-delayed two and three-neutron emitters in the vicinity
of N=28 using the BRIKEN array
V. H. Phong,∗1,∗2 S. Nishimura,∗1 J. Agramunt,∗3 D. S. Ahn,∗1 A. Algora,∗3 H. Baba,∗1 S. Bae,∗4
N. T. Bewer,∗5 R. Caballero-Folch,∗6 T. Davinson,∗7 I. Dillmann,∗6 A. Estrade,∗1,∗8 S. Go,∗9 C. J. Griﬃn,∗7
R. Grzywacz,∗5,∗9 J. Ha,∗1,∗4 O. Hall,∗7 D. Kahl,∗7 G. Kiss,∗1 M. Labiche,∗10 J. Liu,∗11 K. Matsui,∗1B. Moon,∗12 N. Nepal,∗8 H. Sakurai,∗1 Y. Shimizu,∗1 P.-A. Söderström,∗1 H. Suzuki,∗1 B.C. Rasco,∗5K. P. Rykaczewski,∗5 H. Takeda,∗1 J. L. Tain,∗3 A. Tarifeño-Saldivia,∗13 and A. Tolosa∗3The measurement of β-delayed multi-neutron emission probability (P2n , P3n , and so on) is an experimental challenge. Most of the existing P2n values are forisotopes with masses below A=100, while only four P3nvalues were reported so far1) : 11 Li, 17 B and the upperlimits for 19 B and 23 N. The BRIKEN project (betadelayed neutron emission measurement at RIKEN) offers a unique opportunity to measure this rare decaymode. The BRIKEN setup, illustrated in Fig. 1, consists of an array of 3 He detectors embedded in a highdensity polyethylene matrix as moderator,3) surrounding a stack of silicon detectors called AIDA (AdvancedImplantation Detector Array).2) The 3 He array serves
as an eﬃcient neutron counter, which detects the delayed neutrons following the β decay of neutron-richnuclei implanted in AIDA. In addition, two clover-typeHPGe detectors placed close to the implantation point
are employed to identify the daughter nuclei by thedetection of delayed γ rays.
For the purpose of commissioning of the BRIKEN
detection system for the β-delayed multi-neutron emission measurement and evaluation of the statistical errors, neutron background conditions and β-delayed γidentiﬁcation, an experiment has been performed in
the parasitic mode with the in-beam gamma ray experiment,4) targeting the neutron-rich nuclei around
N=28.
The secondary beam, produced by the reaction of a345-MeV/nucleon 48 Ca beam on a rotating Be target,
was impinged on a ﬁxed target at the F8 focal planesurrounded by the DALI2 gamma ray detector. The reaction products and unreacted beam were transported
through the ZeroDegree spectrometer and eventuallyreached the BRIKEN setup at the F11 focal plane.

Figure 2 shows a preliminary particle identiﬁcation
plot of RI in the ZeroDegree spectrometer, which isassumed to be implanted into the AIDA detector. In
this region, the β-delayed multi-neutron emission of41−43Si, 38−42 Al and 35−40 Mg predicted by Ref.5) are
expected to be measured for the ﬁrst time. Moreover,the eﬀect of the degrader setting on the neutron background can be clariﬁed, providing useful information
to optimize the background condition for the main
BRIKEN experiments.
The data are currently being analyzed.

∗1Fig. 2. A preliminary particle identiﬁcation spectrum of
the RI identiﬁed by the ZeroDegree spectrometer. The
RI with known half lives are on the left side of the blacksolid line. The N=28 isotopes are tagged by red circles.

RIKEN Nishina Center
Faculty of Physics, VNU Hanoi University of Science∗3 IFIC (CSIC-University of Valencia)∗4 Department of Physics, Seoul National University∗5 Oak Ridge National Laboratory∗6 TRIUMF∗7 School of Physics and Astronomy, University of Edinburgh∗8 College of Science and Engineering, Central Michigan University∗9 Department of Physics and Astronomy, University of Tennessee∗10 STFC Daresbury Laboratory∗11 Department of Physics, University of Hong Kong
∗12 Department of Physics, Korea University∗13 Secció d’Enginyeria Nuclear,Universitat Politecnica deCatalunya (UPC)∗2Fig. 1. A schematic view of the experimental setup.

References
1) M. Birch et al., Nucl. Data Sheet 128, 131 (2015).
2) C. J. Griﬃn et al.; Proc. XIII Nuclei in the Cosmos,Vol.1 (2014), p. 97.
3) A. Tarifeño-Saldivia et al., arXiv:1606.05544.
4) NP1312-RIBF03R1
5) P. Moller et al., Phys. Rev. C 67.5, 055802 (2013).

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