Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

Beta-decay half-lives of 78 Kr fragments from Cu to Ge

Counts / ms

The most commonly observed decay process for
proton-rich nuclei is β + decay. Further away fromstability, the Q value of this process increases andthe proton separation energy decreases, allowing βdelayed proton (βp) emission. The half-lives and proton branching ratios of nuclei near the proton drip line,
especially around Z = 30 − 40, are of particular interest for astrophysical rp-process (rapid-proton capture)
calculations in X-ray bursts on the surface of accreting neutron stars. The beta and beta-delayed proton
decays compete with the rapid-proton capture process.
Nuclei in this mass region were produced and identiﬁed with unprecedented statistics at RIBF in 2015
within the RIBF4R1 experiment.1) The fragments
were produced by fragmentation of a 78 Kr beam(350 MeV/A and 150 pnA) on a Be target. Afterthe selection and identiﬁcation by the BigRIPS fragment separator, the nuclei were implanted in the silicondetectors of the WAS3ABi setup2) surrounded by theEURICA γ-detector array.3)
The position and time correlations between the implantation and subsequent decay events provide thetime distribution used to determine the half-lives of
the nuclei of interest. The ﬁt function is composedof the contribution of the parent nucleus, the daughter nuclei for the diﬀerent decay branches (β and βpdecays) and a constant background. The backgroundcomponent of the function is extracted from a ﬁt ofnegative times between implantation and decay.
More accurate half-lives and proton branching ra-55Cu

T1/2 = 55.4(18) ms

10Counts / ms

T. Goigoux,∗1 P. Ascher,∗1 B. Blank,∗1 M. Gerbaux,∗1 J. Giovinazzo,∗1 S. Grévy,∗1 T. Kurtukian Nieto,∗1C. Magron,∗1 J. Agramunt,∗2 A. Algora,∗2,∗3 V. Guadilla,∗2 A. Montaner-Piza,∗2 A. I. Morales,∗2S. E. A. Orrigo,∗2 B. Rubio,∗2 D. S. Ahn,∗4 P. Doornenbal,∗4 N. Fukuda,∗4 N. Inabe,∗4 G. G. Kiss,∗4 T. Kubo,∗4S. Kubono,∗4 S. Nishimura,∗4 H. Sakurai,∗4,∗5 Y. Shimizu,∗4 C. Sidong,∗4 P.-A. Söderström,∗4 T. Sumikama,∗4H. Suzuki,∗4 H. Takeda,∗4 P. Vi,∗4 J. Wu,∗4 Y. Fujita,∗6,∗7 M. Tanaka,∗6 W. Gelletly,∗2,∗8 P. Aguilera,∗9F. Molina,∗9 F. Diel,∗10 D. Lubos,∗11 G. de Angelis,∗12 D. R. Napoli,∗12 C. Borcea,∗13 A. Boso,∗14R. B. Cakirli,∗15 E. Ganioglu,∗15 J. Chiba,∗16 D. Nishimura,∗16 H. Oikawa,∗16 Y. Takei,∗16 S. Yagi,∗16
K. Wimmer,∗3 G. de France,∗17 and S. Go∗18Cu

10

1400600

800 1000 1200 1400

60Ga200400600

800 1000 1200 1400

Time (ms)63Ge102

T1/2 = 70.8(20) ms1020Time (ms)Counts / ms

200

Counts / ms

056

T1/2 = 80.2(7) ms

102

T1/2 = 153.6(11) ms

1010200

400600800 1000 1200 1400

Time (ms)Counts / ms

00500

1000

1500

Time (ms)

65

As

103

T1/2 = 130.3(6) ms

0500

1000

1500

Time (ms)55

Fig. 1. Time distributions of Cu, 56 Cu, 60 Ga, 65 As and63
Ge with their respective β-decay half-lives determinedin this work. The dotted red lines are the contributionsof the isotopes of interest, whereas the full red lines
represent the sums of the decay of interest and a constant background. In the case of 55 Cu, the additional
light blue line is the contribution of the daughter decay(55 Ni), also included in sum line.

tios were obtained from the analysis of the experiment.
The values for the βp emitters 57 Zn, 61 Ge, 65 Se, 68 Kr
and 69 Kr were previously reported in Ref. 4). Furthermore, new half-life values of the β emitters 55 Cu, 56 Cu,60Ga, 65 As and 63 Ge were determined. Their ﬁt andtime distributions are shown in Fig. 1. Half-life values
with a better precision than literature were obtained,providing new inputs to future rp-process calculations.

∗1CEN Bordeaux GradignanIFIC, CSIC-Universidad de Valencia∗3 MTA ATOMKI, Debrecen∗4 RIKEN Nishina Center∗5 Department of Physics, University of Tokyo∗6 Department of Physics, Osaka University∗7 Research Center for Nuclear Physics, Osaka University∗8 Department of Physics, University of Surrey∗9 Comisı́on Chilena de Energia Nuclear∗10 Institute of Nuclear Physics, University of Cologne∗11 Physik Department E12, Technische Universität München∗12 Laboratori Nazionali di Legnaro dell’ INFN
∗13 IFIN-HH∗14 INFN Sezione di Padova and Dipartimento di Fisica∗15 Department of Physics, Istanbul University∗16 Department of Physics, Tokyo University of Science∗17 Grand Accélérateur National d’Ions Lourds∗18 Dept. of Physics and Astronomy, University of Tennessee∗2References
1) B. Blank et al., Phys. Rev. C 93, 061301(R) (2016).
2) S. Nishimura et al., RIKEN Accel. Prog. Rep. 46, 182(2013).
3) P. A. Söderström et al., Nucl. Instrum. Methods B 317,649 (2013).
4) T. Goigoux et al., RIKEN Accel. Prog. Rep. 50, 35(2017).

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