RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-1. Nuclear Physics

Study on the β decay of 39 S
L. C. Tao,∗1,∗2 Y. Ichikawa,∗1 Y. Ishibashi,∗1,∗3 A. Takamine,∗1 A. Gladkov,∗1,∗4 T. Fujita,∗1,∗6 K. Asahi,∗1,∗7T. Egami,∗1,∗8 C. Funayama,∗1,∗7 K. Imamura,∗1,∗5 T. Kawaguchi,∗1,∗8 S. Kojima,∗1,∗7 T. Nishizaka,∗8T. Sato,∗1,∗7 D. Tominaga,∗8 H. Yamazaki,∗1 and H. Ueno∗1
We performed β-decay spectroscopy on the neutronrich nucleus 39 S. The neutron-odd S isotopes withneutron numbers larger than 20 have negative-parity
ground states, which decay into highly excited stateswith negative-parity in the Cl isotopes via allowedtransitions. The investigations on the level structureof 39 Cl including both spin parities are necessary forunderstanding the nuclear structure in this mass region.
The experiment was carried out with the fragment
separator RIPS in December 2015 together with theβ-NMR measurement of 39 S2) . A secondary beam of39
S was obtained from the projectile fragmentation reaction of a 48 Ca projectile at an energy of 63 A MeV
on a 9 Be target with a thickness of 0.5 mm. The beam
was pulsed with the duration of the beam-on and oﬀ
periods, 16 s and 16 s, respectively. The 39 S beam
was implanted into a 0.5-mm-thick CaS stopper which
was tilted at an angle of 45 degrees with respect tothe beam axis. Two plastic scintillators with thicknesses of 0.5 mm and 1 mm were placed upstream anddownstream of the stopper, respectively, in order tocount the beam particles implanted into the stopper.
The β-delayed γ rays of 39 S were detected using twohigh-purity Ge detectors that were diagonally placedat distances of 30 cm from the stopper.
In this measurement, three γ rays with energies of1210.3(2) keV, 2571.9(4) keV and 3377.4(5) keV were
newly identiﬁed to originate from 39 S, because theirhalf-lives, 11.6(5) s, 11.5(5) s and 11.2(6) s, respectively, are in a good agreement with the known half-lifeof 39 S, 11.5(5) s1) . As a result of the γ-γ coincidence
analysis, the 1210-keV γ ray was found to have significant coincidence with the 485-keV one, as shown inFig. 1. This γ ray was assigned to be a de-excitationfrom a new level at 2995 keV, as shown in Fig. 2. The
2572-keV γ ray was assigned to decay to the groundstate directly because its energy is consistent with theknown level energy1) . On the other hand, the 3377keV γ ray has not been assigned to the decay scheme,
although its source is conﬁrmed to be 39 S. The deduction of the branching ratio and the log f t values
reﬂecting the new assignments are in progress.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8Fig. 1. γ-γ coincidence between the 1210-keV γ ray andthe 485-keV γ ray.

Fig. 2. β decay scheme of 39 S. Two γ rays of 1210 keV and2571 keV newly identiﬁed in this work are assigned.
Spin-parity values are taken from the compilation3) .

RIKEN Nishina Center
School of Physics and State Key Laboratory of Nuclear
Physics and Technology, Peking University
Department of Physics, University of Tsukuba
Department of Physics, Kyungpook National University
Department of Physics, Meiji University
Department of Physics, Osaka University
Department of Physics, Tokyo Institute of Technology
Department of Physics, Hosei University

References1) J. C. Hill, R. F. Petry, K. H. Wang: Phys. Rev. C 21,384 (1980).
2) Y. Ishibashi et al.: RIKEN Accel. Prog. Rep. 49, 57(2015).
3) B. Singh and J. Cameron, Nuclear Data Sheets 107,225 (2006).

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