II-9. Instrumentation

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Improvements in the working environment for target handling at ERIS
T. Ohnishi,∗1 Y. Abe,∗1 S. Ichikawa,∗1 and M. Wakasugi∗1,∗2
The electron-beam-driven radioactive isotope separator for SCRIT (ERIS)1) at the SCRIT electron scatteringfacility2) is an online isotope-separator system used toproduce low-energy radioactive isotope (RI) beams using
the photoﬁssion of uranium. In this year, we transported
a 137 Cs beam to the SCRIT system installed inside theelectron storage ring3) and performed the RI trap. Under these circumstances, ERIS has become a full-scale
operation, around 4-month RI beam operation in a year.
Therefore, it is important to maintain the working environment of target handling. In this paper, we introduce
the working environment of the RI production target, as
one of the recent developments of ERIS.
Uranium carbide is used as a RI production target
using the ﬁssion reaction of uranium. It is more suitablefor RI production target than uranium oxide because itsvapor pressure and density are lower and higher thanthose of uranium oxide, respectively. Further, damages
to materials of the ion source can be reduced using asmall amount of oxygen.
The recent study shows that the porous structure with
the nano material is important for fast diﬀusion inside
the target and high-extraction eﬃciency of RI.4) However, this porous structure causes high susceptibility tooxidation. Figure 1 shows the oxidation reaction of uranium carbide in the air. The uranium carbide disks
shown in Fig. 1 are made with graphene. Oxidation
started 1 min after the removal from the vacuum container, and it ended after almost 10 min. The temperature of uranium carbide disks reaches around 800◦ C, as
shown in Fig. 1. After oxidation, these disks cannot holdtheir shape and turn into powder. The uranium oxide
powder is planned to be cemented solid after suﬃcientcooling.
A glove box was installed in the draft chamber at
the working area to handle uranium carbide targets
safely. Figure 2(a) shows the setup with the glove box.
Since this glove box has the capacity of vacuum gas replacement, the oxygen concentration becomes less than
0.001% vacuum gas replacement with nitrogen gas (lessFig. 2. (a) Photograph of the setup with the glove box inside the draft chamber. (b) Photograph of handling theuranium carbide disks inside the glove box.

than 2% per one replacement is performed three times).
In this situation, target handling can be performed without worrying about oxidation. One such example isshown in Fig. 2(b).
The present size of the glove box is smaller than thetarget chamber, and therefore, we need to work in the air
to install the target in the target chamber. A graphitetarget container with keyway, as shown in Fig. 3, is used
to reduce the installation time, and the target insertion
practice is performed beforehand. It took almost 5 sec toremove the graphite-target container with the uranium
target disks from the container ﬁlled with nitrogen gas,
insert it into the target holder inside the target chamber,and start the vacuum pump. This short time was suﬃcient, as evidenced by the small amount of gas released
during heating.
In the near future, the safety treatment of the production target will become an important issue because of
the high radiation (a few mSv/h), which is two orders ofmagnitude higher than the present value (∼10 μSv/h),and active operation. Therefore, we plan to introduce
a large glove box adapted to the target chamber andestablish a remote handling system.

Fig. 3. (a) Photograph of the graphite-target container withkeyway (left) and the target holder (right). (b) Photograph of keyway of the graphite-target container.

References
Fig. 1. Photograph of the oxidation reaction of uranium carbide disks in the graphite container. Diameter and thickness of a disk are 18 mm and 0.8 mm, respectively. The
amount of uranium in a disk is about 0.7 g.
∗1∗2

RIKEN Nishina Center
Institute for Chemical Research, Kyoto University

1) T. Ohnishi et al., Nucl. Instrum. Methods Phys. Res. B
317, 357 (2013).
2) M. Wakasugi et al., Nucl. Instrum. Methods Phys. Res. B
317, 668 (2013).
3) Y. Abe et al., in this report.
4) A. Gottberg, Nucl. Instrum. Methods Phys. Res. B 376,8 (2016).

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