Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 48 (2015)

Current status of RI beam production at electron-beam-driven RIseparator for SCRIT (ERIS)
T. Ohnishi,∗1 S. Ichikawa,∗1 M. Togasaki,∗1,∗2 K. Kurita,∗1,∗2 and M. Wakasugi∗1ERIS (electron-beam-driven RI separator for SCRIT) consists of an RI generator, a FEBIAD-type ion
source, and an RI separator. The photoﬁssion of uranium driven by an electron beam is used for RI production in ERIS. Details of ERIS were reported in Ref .
2. During the present year, we improved the releaseeﬃciency including the eﬃciency of release from theproduction target and that of transport from the target to the ionization chamber. In this paper, we report
improvements and the present status of ERIS.
One of the improvements is the stable supply of a
1-mm uranium carbide target disk. Using a 1-mm target disk, the eﬃciency of release from the production
target is expected to increase, because the total surface area of target disks becomes larger than in thecase of 2-mm target disks used in the previous test3) .
Uranium carbide is obtained by the carbothermal reduction of uranium oxide in presence of carbon. Details of constructing the target were presented in Ref .
3. In order to construct a thin disk, the careful selection of the graphite grain size is required for theprocess of constructing a disk from graphite powder.
Furthermore, the uranium-oxide-coated graphite powder is also needed to construct a disk without a binder.
These requirements are aimed at reducing the vacancy
inside the disk and the crack at the edge of the disk.
The obtained disk was approximately 1 mm in a thickness and 18 mm in a diameter. In total, 23 disks wereprepared. The total amount of uranium was about 15g, and the average mass concentration of uranium inthe disk was estimated as 3.4 g/cm3 .
Another improvement involved strengthening theheat shield. In particluar, the heat shield of the transfer tube located between the target and the ionizationchamber was increased in order to ensure no cold spots
were present.
After these improvements, the uranium-carbide
disks were irradiated with an electron beam accelerated to 150 MeV. The electron beam power was nearly
10 W. Tantalum disks with a thickness of 5 mm and adiameter of 20 mm were inserted in front of the production target to increase the production of γ rays. The
temperature of the target and the transfer tube wasapproximately 2000 ◦ C. The produced RIs were accelerated to 20 kV and mass-separated by the analyzing
magnet. They were identiﬁed by the measurement ofγ rays corresponding to the decay of the RIs using aGe detector.
Figure 1 shows the rate of Sn and Xe isotopes at1)

∗1
∗2

RIKEN Nishina Center
Department of Physics, Rikkyo University

the Ge detector. These rates are estimated from theobserved γ-ray yield using the eﬃciency of the Ge detector and the half-life of each isotope. The overall eﬃciency is the ratio of the observed rate to the expected
production rate inside the target. This eﬃciency includes the eﬃciency of release from the target, ionization in the ion source, and eﬃciency of transport fromthe ion source to the detector. The overall eﬃciency ofstable xenon with a calibrated gas ﬂow was also measured during the experiment. Because stable xenon
was introduced into the ionization chamber througha gas inlet, the measured overall eﬃciency of stablexenon includes only ionization and transport eﬃciencies. In the case of tin isotopes, the same ionizationand transport eﬃciency as those of xenon can be used,which is supported by the results at ALTO4) . As aresult, the release eﬃciency of xenon and tin isotopes
can be estimated. Table 1 shows the summary of rateand eﬃciency in the case of 137 Xe and 132 Sn. Compared with the previous results3) , the release eﬃciencies of 137 Xe and 132 Sn become almost nine and six
times larger, respectively. Furthermore, the overall efﬁciency of 132 Sn at ERIS is achieved at same level asALTO4) . Further studies are in progress in order torealize the electron elastic scattering experiment with
RI.

Fig. 1. Rate of Sn and Xe isotopes at the particle identiﬁcation detector at ERIS. The electron beam power wasalmost 10 W. Total amount of uranium is 15g.
Table 1. Summary of rate and eﬃciency with 10-W beam
137
132XeSn
6Observed rate (atoms/s)
6.4×10
2.6×105
Expected rate (atoms/s)
7.5×107 1.3×107
Overall eﬃciency
8.4%
2.1%
Overall eﬃciency of stable xenon
14%
15%
Release eﬃciency
61%
14%

References
1) M. Wakasugi et. al: Nucl. Instr. Meth. B317, 668(2013).
2) T. Ohnishi et. al: Nucl. Instr. Meth. B317, 357(2013).
3) T. Ohnishi et. al: RIKEN Accel. Prog. Rep. 47, ?(2014).
4) M. Cheikh Mhamed et. al: Nucl. Instr. Meth. B266,4092(2008).

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