II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Investigations of magnetic moments in Coulomb fission
G. Häfner,∗1,∗2 R. Lozeva,∗1 M. Si,∗1 Y. Ichikawa,∗3,∗4 H. Ueno,∗3 D. S. Ahn,∗3 K. Asahi,∗3 T. Asakawa,∗3,∗5H. Baba,∗3 A. Esmaylzadeh,∗2 N. Fukuda,∗3 A. Gladkov,∗3 K. Imamura,∗3 N. Inabe,∗3 K. Kawata,∗3,∗6
L. Knaﬂa,∗2 A. Kusoglu,∗7 M. Niikura,∗8 Y. Sasaki,∗3,∗5 H. Sato,∗3 Y. Shimizu,∗3 H. Suzuki,∗3 M. Tajima,∗3A. Takamine,∗3 H. Takeda,∗3 Y. Takeuchi,∗3,∗5 Y. Yanagisawa,∗3 H. Yamazaki,∗3 and K. Yoshida∗3∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8800

Counts / 2.5 ns

1000

103

PID gate: 125AgCounts / keV

Ge2

125

2

10

Ag, (E = 670 keV)
60
Co (source)

10600
1−20

400

02040

#200

60

80 100Time [ns]670684714728Magnetic moments present an important tool tostudy the single-particle character of excited states.
They are directly related to the g factor and provide acrucial test for the wave functions of particular states
predicted by theoretical models. One experimental requirement for the measurement of g factors is the spinalignment of the nuclear ensemble that is obtained in
the reaction populating a nucleus of interest. In thisexperiment, Coulomb ﬁssion is used to produce the nuclear alignment, and the magnetic moments of isomericstates are investigated.
The region around the doubly magic 132 Sn has beenof prime interest in the past decades owing to its importance from the perspectives of astrophysics andnuclear structure. The investigation of nuclei withfew valence particles is interesting because several isomeric structures emerge in them. For example, thethree-proton-hole Z = 47 isotopes 124, 125 Ag have isomers based on the unique parity orbitals π(0g9/2 ) andν(0h11/2 ).1)
The experiment is performed at the RIBF using theBigRIPS spectrometer. A primary 238 U beam at anenergy of 345 MeV/nucleon impinged on a thin 184 W
production target with an average beam intensity ofapproximately 100 particle nA. The momentum distribution is selected with slits at the F1 focal plane. Thenuclei of interest are separated and identiﬁed using theBigRIPS separator.2) The secondary ions are stopped
in a 3-mm-thick Cu host at the F8 focal point. The detection setup consisted of four high-purity Ge (HPGe)and two LaBr3 (Ce) detectors, arranged with each detector type at 90◦ with respect to each other. To measure the magnetic moments, the TDPAD method isused; it has been applied successfully at the RIBF.3–5)
In the experiment, approximately 5·106 ions of 124 Ag
and approximately 3·106 ions of 125 Ag are identiﬁed ineach of the experimental settings. The particle identiﬁcation (PID) of these secondary ions is achieved after
the identiﬁcation and tracking detectors are fully calibrated oﬄine. The spectroscopy could be performed
after calibration and various corrections of the γ-ray
detectors in energy and time. Figure 1 shows the de-##00100

200300400500600

700800

Energy [keV]
Fig. 1. Delayed HPGe energy spectrum for the 125 Ag ions.
Background transitions are labelled with “#.” The inset
shows the time-resolution spectrum of one detector fora source and in-beam measurement.

layed γ-ray energy spectrum of all Ge detectors witha PID gate for the 125 Ag ions. All transitions below
the known (17/2− ) isomer can be identiﬁed. For theTDPAD analysis, a good in-beam time resolution is essential. The setup is optimized using 60 Co and 152 Eu
sources, with a typical resolution of 8(1) ns (FWHM)
achieved by the detectors in the range of interest. Thiscorresponds to a resolution of 12(1) ns in-beam forthe same detector, e.g., for the 670 keV transition in125Ag. As an example, the inset of Fig. 1 shows thetime-resolution spectrum for one of the HPGe detectors, demonstrating the capabilities of this setup. Theanalysis of the magnetic moment from the oscillation
pattern is currently in progress. Therefore, it is necessary to have spin alignment, which will be shown bymeasuring the magnetic moment of a known calibration case.
References

1) S. Lalkovski et al., Phys. Rev. C 87, 034308 (2013).
2) T. Kubo et al., Nucl. Instrum. Methods Phys. Res. B
204, 97 (2003).
3) Y. Ichikawa et al., Nat. Phys. 8, 918 (2012).
4) Y. Ichikawa et al., Nat. Phys. 15, 321 (2019).
5) F. Boulay et al., Phys. Rev. Lett. 124, 112501 (2020).

Université Paris-Saclay, CNRS/IN2P3, IJCLabIKP, University of Cologne
RIKEN Nishina Center
Department of Physics, Kyushu University
Department of Advanced Sciences, Hosei University
Center for Nuclear Study, University of Tokyo
Department of Physics, Istanbul University
Department of Physics, University of Tokyo- 29 -1