Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 53

Stopping examination for high-energy RI beams in the parasitic gas cell†T. Sonoda,∗1 I. Katayama,∗1 M. Wada,∗2 H. Iimura,∗3 V. Sonnenschein,∗4 S. Iimura,∗1 A. Takamine,∗1M. Rosenbusch,∗2 T. M. Kojima,∗1 D. S. Ahn,∗1 N. Fukuda,∗1 T. Kubo,∗1 S. Nishimura,∗1 Y. Shimizu,∗1H. Suzuki,∗1 H. Takeda,∗1 M. Tanigaki,∗5 H. Tomita,∗4 K. Yoshida,∗1 and H. Ishiyama∗1Fig. 1. Experimental setup.
†∗1∗2
∗3
∗4
∗5Condensed from the article in Prog. Theor. Exp. Phys. 2019,
113D02 (2019)
RIKEN Nishina Center
IPNS, High Energy Accelerator Research Organization
Applied Nuclear Physics Laboratory, Japan Atomic Energy
AgencyFaculty of Engineering, Nagoya University, Nagoya
Institute for Integrated Radiation and Nuclear Sciencedegrader thickness (mm)
12.77
13.14

12.48

1
transmitted/stopped fraction

We are developing a scheme of parasitic low-energy
RI-beam production (PALIS)1) to establish the eﬀective
utilization of rare isotopes and to perform comprehensive measurements of physical properties of exotic nuclei.
So far, we spent totally about two days of on-line commissioning beam time from 2015,2,3) thanks to the RIBF
MT committee. However, as the beam time is insuﬃcient to optimize the new device, we requested the PAC
committee for authentic beam time in 2017, and 3 daysof beam time was approved. Our plan in this formallyprovided beam time consists of 3 stages: 1) stopping examination for high-energy RI beams in the parasitic gas
cell, 2) an extraction test for stopped RIs and eﬃciency
evaluation, and 3) the demonstration of physical spectroscopy using a low-energy RI beam. Here we report
the results of the 12 h of on-line experiment in the ﬁrststage.
A schematic of the experimental setup is shown inFig. 1.
Two silicon surface barrier Detectors (SSDs) were installed inside the BigRIPS F2-chamber and used for examining the ∆E-E relation. The ﬁrst detector (∆E-SSD)
was mounted immediately after the (glass) energy degrader, and the second (E-SSD) was mounted inside thegas cell. A radioactive 67 Se beam was introduced to thissetup as the main secondary beam, which was produced
by projectile fragmentation via 78 Kr (340 MeV/nucleon)
and a beryllium target. We conﬁrmed that each isotonebeam with the same neutron number (N ) = 31, 32, and33 was well separated energetically after the energy degrader. Here, the N = 33 isotone-beam, consisting of
67
Se, 66 As, 65 Ge, and 64 Ga, was adjusted to maximize

13.59

transmitted fraction
at 440 mbar
(calculation)

0.8
exp. data (440mbar)
exp. data (no-gas)

0.6
0.4

stopped fraction
at 440mbar(exp.data)

stopped fraction
at 440mbar(calculation)

0.2
016182022242628degrader angle (degrees)

30Fig. 2. Normalized transmitted and estimated stopped fractions as functions of the degrader angle.

the stopping eﬃciency in the gas. The eﬀective thicknessof the energy degrader was varied by adjusting its rotation using a stepping motor. Energy-loss spectra wereobtained with ∆E-SSD and E-SSD as the angle of theglass degrader was varied from 18 to 28 degrees.
The normalized transmitted fraction at E-SSD andexpected stopped fractions in the gas cell are plotted inFig. 2 as functions of the degrader angle for the casesof no-gas (green rhombuses) and 440 mbar argon (redcircles) in the gas cell. The experimental data at 440
mbar were well reproduced by LISE++ calculations. In
addition, the expected stopped fraction in the gas wasestimated by comparing the transmitted fractions withand without gas. In this experiment, we conﬁrmed thatapproximately 30% of the ensemble of N = 33 isotonebeams were stopped in 440 mbar argon at the optimum
degrader angle.
As a next step, we will establish the extraction technique of stopped RIs for low-energy RI-beams.
References

1) T. Sonoda et al., Prog. Theor. Exp. Phys. 2019, 113D02(2019).
2) T. Sonoda et al., RIKEN Accel. Prog. Rep. 49, 16 (2015).
3) T. Sonoda et al., RIKEN Accel. Prog. Rep. 51, 169 (2017).

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