Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 52 (2019)

Feasibility study of 199 Pt Q-moment measurement
using in-gas-jet laser ionization spectroscopy at KISS
H. Choi,∗1 Y. Hirayama,∗2 Y. X. Watanabe,∗2 P. Schury,∗2 M. Mukai,∗2 M. Ahmed,∗2,∗3 M. Oyaizu,∗2M. Wada,∗2 and H. Miyatake∗2
KEK Isotope Separation System (KISS)1) has beendeveloped to study nuclei in the region of neutron magic
number N = 126. We investigated the nuclear structureof 199 Pt and Ir isotopes by measuring their hyperﬁnestructures (HFSs) through the in-gas-cell laser ionization technique.2) In the measurement, we obtained precise values of magnetic dipole moments µ = +0.75(8) µN
and µ = −0.57(5) µN for 199g Pt and 199m Pt, respectively.
However the errors of electric quadrupole moments werequite large, Qg = +1.7(17) b and Qm = +3.5(21) b. To
improve the spectral resolution, we developed an in-gasjet laser ionization spectroscopy technique at KISS. In
the laser system, a diode laser (TOPTICA, DLC DL ProHP, 450 nm) is used for the seed laser of a pulsed dyeampliﬁer (Sirah), which creates UV light (λ1 = 225 nm)
for the excitation to the state 5d8 6s6p 5 F2 . A Nd:YAGlaser (EdgeWave) is used to pump the dye ampliﬁer andfor ionization as the second step (λ2 = 355 nm). Compared to in-gas-cell ionization, we improved the resolution from 12.5(5) GHz to 0.6(1) GHz in the full width of
the half maximum owing to the low density and temperature conditions of the gas jet.3) From this result, we areexpecting to obtain a much more precise value of electromagnetic moments and isotope shift for 199 Pt throughthe in-gas-jet laser ionization spectroscopy technique.
The feasibility of 199 Pt HFS measurement throughthe in-gas-jet laser ionization spectroscopy was investigated by the Monte Carlo simulation. Based on the HFS
spread and present resolution of 0.6 GHz by the in-gasjet method, we determined the measurement step ∆ν 1= 0.27 GHz. From the yield of 199g+m Pt, we determined
the measurement time of 10 min for each data point,
which corresponds to a measurement of 20 h. A Voigt
function with Gaussian width ΓG = 316(27) MHz andLorentzian width ΓL = 110(76) MHz, which were determined from the oﬀ-line measurement of 196 Pt (Iπ =0+ ), was used in a response function of the resonancepeak. Relative intensities between each resonance peakwere computed via the Racah coeﬃcient. We assumed
the unknown electric quadrupole hyperﬁne coupling constant of the atomic excited state of 199g Pt to be 1 GHz.
Figure 1 shows the simulated hyperﬁne splitting spectrum of 199g+m Pt. The vertical axis indicates the expected β-ray events detected by MSPGC4) during the10 min beam accumulation. The total β-ray events wereevaluated to be 4915 counts. Figure 2 shows the simulated HFS spectrum of 199m Pt nuclei obtained by gat∗1∗2∗3Seoul National University
Wako Nuclear Science Center (WNSC), Institute of Particle
and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK)
Department of Physics, University of Tsukuba

Fig. 1. Simulated HFS spectrum of 199g+m Pt. Red line indicates the simultaneous fitting function.

Fig. 2. Simulated HFS spectrum of 199m Pt obtained by gating on 392-keV γ-ray.

ing on a 392 keV γ-ray. Total γ-ray events detected by
the four super clover Ge detectors were evaluated to be3941 counts. In the analysis, the spectra in Figs. 1 and 2
were simultaneously ﬁtted using the common parameters(electromagnetic hyperﬁne coupling constants) for 199i Pt(i = g, m). The reduced chi-square of ﬁtting was 1.13.
In the simulation, we assumed µg = +0.75 µN and Qg =+1.7 b, and µm = −0.57 µN and Qm = +3.5 b for 199g Pt
and 199m Pt respectively. The evaluated electromagneticmoments from the ﬁtting were µg = +0.7434(58) µN ,Qg = +1.75(10) b, µm = −0.5740(49) µN , and Qm =+3.42(10) b. From the simulation, we conﬁrmed thatthe 20 h measurement is enough to achieve precise values of electromagnetic moments for 199 Pt.
References

1) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
353, 4 (2015).
2) Y. Hirayama et al., Phys. Rev. C 96, 014307 (2017).
3) Y. Hirayama et al., in this progress report.
4) M. Mukai et al., Nucl. Instrum. Methods Phys. Res. A
884, 1 (2018).

- 55 -