Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

β-NMR measurement in coincidence with β-delayed γ rays of 39 S
L. C. Tao,∗1,∗2 Y. Ichikawa,∗1 H. Ueno,∗1 Y. Ishibashi,∗1,∗3 A. Takamine,∗1 A. Gladkov,∗1,∗4 T. Fujita,∗1,∗6K. Asahi,∗7 T. Egami,∗8 C. Funayama,∗7 K. Imamura,∗1,∗5 T. Kawaguchi,∗8 S. Kojima,∗7 T. Nishizaka,∗8T. Sato,∗7 D. Tominaga,∗8 and H. Yamazaki∗1We aim to measure the ground-state magnetic moment of neutron-rich S isotopes. The β-NMR measurement of 39 S was carried out before 41 S and 43 S,
in order to check the AP value that was produced
through fragmentation reaction and was kept in a CaSstopper1) . The β-decay of 39 S was reported but spinparities of the produced 39 Cl excited states have notbeen fixed other than the two excited states whose energies respectively are 396 keV and 1697 keV2) . β-γ
spectroscopy with polarized beams was carried out toestablish a complete decay scheme including fixed spinparities, which is required for an accurate evaluationof AP value.
This experiment was carried out at the RIPS ofRIBF in December 2015. A beam of 39 S was obtained from the fragmentation of 48 Ca projectiles atE = 63 MeV/nucleon on a 9 Be target with a thicknessof 0.5 mm. The intensity of 48 Ca beam on the Be target was typically 200 pnA. The isotope separation of39
S was performed with RIPS where an emission angleof θF > 2.0◦ and a momentum window of p F = p 0× (1.02 ± 0.02) were selected in order to produce spinpolarization in 39 S. Here, p 0 represents the central momentum of fragment 39 S.
The 39 S beam was then transported to the final focal
plane and implanted into a 0.5-mm-thick CaS stopperin the β-NMR apparatus. The β-NMR apparatus consists of a collimator, a CaS crystal stopper, a dipolemagnet, a radio frequency Helmholtz coil and scintillator telescopes located above and below the stopper.
The CaS stopper was mounted between the poles ofthe dipole magnet. The experimental setup for NMR
measurement was same as described in Ref1) . The βdelayed gamma rays of 39 S that stopped in the CaS
crystal were detected using two high purity Ge detectors that were diagonally placed at a distance of 30 cm
from the stopper. Fig. 1 shows the photograph of theexperimental setup around the stopper. The data acquisition system was triggered by a gamma-hit event
defined by a logical OR of signals from the Ge detectors.
In this experiment, we also observed six gamma-ray
peaks with energies of 396 keV, 485 keV, 874 keV,
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8Fig. 1. Photograph of experimental setup. The top partof one Ge detector is seen on the right side of the figure, and the other detector is located behind the dipolemagnet. Two sets of plastic scintillators are inserted
between the poles of the magnet.

Fig. 2. γ ray spectrum with the energy of 396 keV.

904 keV, 1300 keV and 1697 keV, which had been observed in the previous experiment2) . As an example,
the energy spectrum of 396 keV is shown in Fig. 2.
The further analysis to obtain the polarization effectin coincidence with the β rays is in progress.

RIKEN Nishina Center
School of Physics and State Key Laboratory of NuclearPhysics 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

References
1) Y. Ishibashi et al., RIKEN Accel. Prog. Rep. 49 (in thisreport).
2) J. C. Hill, R. F. Petry, K. H. Wang: Phys. Rev. C 21,
384 (1980).

- 59 -