II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Results on the β decay of 60 Ge and 62 Ge measured at RIBF

Counts / 2 ms

The investigation of the structure of nuclei close tothe limits of stability is a topic of paramount importancein modern nuclear physics. The Tz = −2, 60 Ge nucleus
is a semi-magic, N = 28 isotone whose decay is almost
unknown. An exotic feature seen in other Tz = −2 nuclei1,2) is the competition between the γ de-excitationand the (isospin-forbidden) proton emission from theT = 2 isobaric analog state populated by β decay in thedaughter nucleus. Little was known about the decay of
the Tz = −1, 62 Ge nucleus. In other Tz = −1 nuclei asuppression of isoscalar γ transitions between J π = 1+ ,T = 0 states (Warburton and Weneser quasi-rule3,4) )has been observed.5)
Heavy proton-rich nuclei can be produced with un-60

Ge2

10T1/2 = 25.0(3) ms

101−200 −1000100

200

300
400 500
600Correlation time [ms]Fig. 1. Time correlations between 60 Ge implants inWAS3ABi and subsequent β-delayed protons (Ep >1 MeV) detected in the same pixel of WAS3ABi.
∗1IFIC, CSIC-Univ. Valencia
Department of Physics, Surrey University∗3 Chilean Nuclear Energy Commision∗4 MTA ATOMKI∗5 RIKEN Nishina Center∗6 CEN Bordeaux Gradignan∗7 National Institute for Physics and Nuclear Engineering, IFINHH∗8 INFN Sezione di Padova∗9 Department of Physics, Istanbul University∗10 Department of Physics, Tokyo University of Science∗11 INFN Laboratori Nazionali di Legnaro∗12 GANIL∗13 Institute of Nuclear Physics, University of Cologne∗14 Department of Physics, Osaka University∗15 Dept. of Physics and Astronomy, University of Tennessee∗16 Physik Department E12, Technische Universität München∗17 Department of Natural Sciences, Tokyo City University∗18 Faculty of Physics, VNU University of Science∗19 Department of Physics, University of Tokyo∗2Counts / 2 ms

S. E. A. Orrigo,∗1 B. Rubio,∗1 W. Gelletly,∗1,∗2 P. Aguilera,∗1,∗3 A. Algora,∗1,∗4 A. I. Morales,∗1 J. Agramunt,∗1D. S. Ahn,∗5 P. Ascher,∗6 B. Blank,∗6 C. Borcea,∗7 A. Boso,∗8 R. B. Cakirli,∗9 J. Chiba,∗10 G. de Angelis,∗11G. de France,∗12 F. Diel,∗13 P. Doornenbal,∗5 Y. Fujita,∗14 N. Fukuda,∗5 E. Ganioğlu,∗9 M. Gerbaux,∗6J. Giovinazzo,∗6 S. Go,∗15 T. Goigoux,∗6 S. Grévy,∗6 V. Guadilla,∗1 N. Inabe,∗5 G. G. Kiss,∗4,∗5 T. Kubo,∗5S. Kubono,∗5 T. Kurtukian-Nieto,∗6 D. Lubos,∗16 C. Magron,∗6 F. Molina,∗3 A. Montaner-Pizá,∗1 D. Napoli,∗11D. Nishimura,∗17 S. Nishimura,∗5 H. Oikawa,∗10 V. H. Phong,∗5,∗18 H. Sakurai,∗5,∗19 Y. Shimizu,∗5 C. Sidong,∗5P. -A. Söderström,∗5 T. Sumikama,∗5 H. Suzuki,∗5 H. Takeda,∗5 Y. Takei,∗10 M. Tanaka,∗14 J. Wu,∗5 S. Yagi∗1062Ge

T1/2 = 73.5(1) ms

104

0200

400

600
800Correlation time [ms]Fig. 2. Time correlations between implanted 62 Ge ions andβ decays in the same or adjacent pixel of WAS3ABi.

precedented statistics at the Radioactive Isotope Beam
Factory (RIBF) of the RIKEN Nishina Center. In theNP1112-RIBF82 experiment, 1.5×104 60 Ge and 2.1×106
62
Ge ions were recorded. They were produced by fragmenting a 78 Kr primary beam (345 MeV/nucleon andintensity up to 250 particle nA) on a Be target. Thefragments were selected and identiﬁed by the BigRIPS
separator by means of the Bρ-∆E-ToF method. They
were then implanted in the WAS3ABi setup, consistingof three 1-mm-thick double-sided Si strip detectors of
a 6 × 4 cm2 area. The EURICA array, arranged in 12clusters containing 7 high-purity Ge crystals each, wasused for γ detection.
For 60 Ge, the ﬁrst experimental information on boththe β-delayed proton and γ emissions has been extracted. By gating on the β-delayed proton emission,a half-life value of 25.0(3) ms has been obtained for60Ge (Fig. 1). For 62 Ge, new information on the βdelayed γ emission has been obtained, indicating thepersistence of the quasi-rule.3,4) A half-life value of73.5(1) ms has been extracted for 62 Ge (Fig. 2). The
precision on both 60 Ge and 62 Ge half-lives has been improved in comparison with values in the literature.
References

1) S. E. A. Orrigo et al., Phys. Rev. Lett. 112, 222501 (2014).
2) S. E. A. Orrigo et al., Phys. Rev. C 93, 044336 (2016).
3) G. Morpurgo, Phys. Rev. 110, 721 (1958).
4) D. H. Wilkinson, Isospin in Nuclear Physics, (ElsevierScience Publishing Co Inc.,U.S., 1969).
5) F. Molina et al., Phys. Rev. C 91, 014301 (2015).

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