Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Extraction of multi-nucleon transfer reaction products in the 136 Xeand 198 Pt system
Y. Hirayama,∗1 Y.X. Watanabe,∗1 H. Miyatake,∗1 M. Wada,∗1,∗2 H.S. Jung,∗1 M. Oyaizu,∗1 Y. Kakiguchi,∗1M. Mukai,∗2,∗3 S. Kimura,∗2 H. Ishiyama,∗4 S.C. Jeong,∗4 N. Imai,∗5 and T. Sonoda∗3
We have developed the KEK Isotope Separation System (KISS)1) to study the β-decay properties of theneutron-rich isotopes with neutron numbers aroundN = 126 for astrophysics research.2–4) We extracted
elastic events of 198 Pt and unstable nuclei of 199 Pt and196,197,198
Ir produced in the 136 Xe beam and 198 Pt target system. We successfully dissociated the molecularions by using a new multi-pole ion-guide (MPIG) system and measured the lifetime of the unstable nucleiof 199 Pt3) and 196 Ir.
We performed on-line tests using the 136 Xe beamwith an energy of 10.75 MeV/nucleon and a maximum
intensity of 20 pnA. The 136 Xe beam was directed onto
the 198 Pt target placed in the gas cell, and was stopped
at a tungsten beam dump after passing through the gascell. The thermalized and neutralized reaction products were re-ionized in the gas cell, and the ions wereextracted and detected after mass separation using aChanneltron detector for ion counting. The lifetimes
were measured by using newly developed β-ray telescopes5) whose background rate was reduced to 0.09
cps.
In our previous experiment, the extracted 198 Pt+
ions formed molecular ions such as 198 PtH+
2,198
PtH2 O+ , and 198 PtAr+
withtheintensity
ratioof2
1, 1, and 6, respectively, relative to the intensity of198
Pt+ ions. The extraction eﬃciency of the mostintense 198 PtAr+
2 ion was 0.2 %. In order to reduce
the amount of the molecular ions and increase the extraction yields, we developed three MPIGs which wereinstalled at the exit of the gas cell to dissociate themolecular ions by applying a DC voltage of 15 V between the ﬁrst and the second MPIGs as well as totransport the ions from the high pressure region to thelow pressure region and, then, accelerate them by applying a high voltage of 20 kV. Figure 1 shows themeasured mass distribution of 198 Pt+ ions extracted
from KISS through the MPIGs. In the present measurement, we can successfully dissociate the molecularions. Considering the molecular ion formation probability in the previous experiment, the extraction eﬃciency of 198 Pt+ ion with the most intensity was recovered to be 0.3%, which was a factor of about 1.5
higher than of 0.2% for 198 PtAr+2 ion. This indicates
∗1

∗2
∗3
∗4
∗5

Wako Nuclear Science Center (WNSC), Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator
Research Organization (KEK)
Department of Physics, University of Tsukuba
RIKEN Nishina Center
Institute for Basic Science, Rare Isotope Science ProjectCenter for Nuclear Study, University of Tokyo- 184 -that almost all molecular ions dissociated to 198 Pt+ion.
We extracted the laser-ionized iridium isotopes
196,197,198
Ir atoms. Figure 2 shows the measured lifetime of the 196 Ir (t1/2 = 52(1) s) isotope. The measured lifetime t1/2 = 67(13) s was in good agreementwith the reported value.

Fig. 1. Measured mass distribution of the platinum ions.
Red and blue lines indicate the spectra measured withand without the irradiation of ionization lasers, respectively.

Fig. 2. Lifetime measurement of 196 Ir.

To extend this study to more neutron-rich nuclei,
we have been developing a doughnut-shaped gas cellto increase the available primary beam intensity and a
low-background beta-ray telescope.
References
1) Y. Hirayama et al., Nucl. Instr. and Meth. B353, 4(2015).
2) S.C. Jeong et al.: KEK Report 2010-2.
3) Y. Hirayama et al.: RIKEN Accel. Prog. Rep. 48, 233(2015).
4) H. Ishiyama et al.: RIKEN Accel. Prog. Rep. 45, 151(2012).
5) S. Kimura et al.: RIKEN Accel. Prog. Rep. 48, 234(2015).