Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 52 (2019)

Profile measurement of a large target cell of liquid hydrogen
M. Miwa,∗1,∗2 M. Sasano,∗2 X. Sun,∗3,∗2 L. Stuhl,∗4 J. Gao,∗3,∗2 and M. Kurata-Nishimura∗2The (p, n) reaction in inverse kinematics is a powerful probe for studying nuclear isovector responses inunstable nuclei. In May 2018, the SAMURAI 30 experiment was performed using PANDORA1) and SAMURAI2) setup with a liquid hydrogen target3) to study
the GT transitions ,including their resonances, in the11
Li and 14 Be neutron drip line nuclei.4,5)
In general, the target thickness along the beam direction is required to obtain the cross sections. However, inthe case of a liquid hydrogen target that contains withthin membranes, the target thickness strongly depends
on the inﬂation of the membranes due to the diﬀerential
pressure between liquid hydrogen and the vacuum in thetarget chamber.
In the SAMURAI 30 experiment, the target cell wastilted at 45◦ with respect to the beam direction, sothat the recoil neutrons of interest, which were emitted
around 90◦ , did not penetrate the target frame structures. Because the inﬂated target cell was tilted withrespect to the beam line, the evaluation of the target
thickness required three-dimensional analysis of the target shape. In this work, we measured the proﬁle of alarge target cell of liquid hydrogen by using a laser displacement meter and obtained the eﬀective target thickness along the beam direction by analyzing the proﬁledata.
Figure 1 schematically shows the setup for the target
proﬁle measurement. The target cell was ﬁlled with N2gas, instead of liquid H2 , at 1719 Pa, which corresponds

Fig. 1. Schematic of the setup for the two-dimensional profile measurement of the target thickness. The membranesof both sides are irradiated with a laser in the beam direction.
∗1
∗2
∗3
∗4

Department of Physics, Saitama University
RIKEN Nishina Center
School of Physics, Peking University
Center for Nuclear Study, University of TokyoFig. 2. Profile result of the target shape. The vertical axis
indicates the spatial coordinate along the beam direction.
The blue and red plots are the original data after thecalibration and the data at an angle of 45◦ respectively.

to the diﬀerential pressure of 0.72 kPa. A laser displacement meter (KEYENCE LJ-G5000) was used to measure the target proﬁle. The laser vertically irradiatedthe target cell surface. The conﬁguration of the laser intensity was automatic, and the sampling time was 2 ms.
The measurement can decide the absolute value only inthe beam direction, while the position information in thehorizontal direction can be just obtained as relative values. The scale of the horizontal position was calibrated
by adjusting the inner diameter of the target frame to be
the designed value, 50 mm. Here, we note that a typicalbeam spot of an RI beam at the SAMURAI F13 focal
plane has a width of ±10 mm and a height of ±20 mm.
As a result of the proﬁle measurement, we obtained
the target shape data shown in Fig. 2. The blue plots
represent original data while the red plots are tilted at
an angle of 45◦ . The proﬁle analysis provided the target thickness after 45-degree rotation as 15.8 mm at thecenter, 14.3 mm at x = ±10 mm, and 7.40 mm at y =±20 mm.
In summary, we evaluated the target proﬁle in theSAMURAI 30 experiment, taking into account the target tilting with respect to the beam direction throughthe three-dimensional analysis of the target cell.
References

1) L. Stuhl et al., Nucl. Instrum. Methods Phys. Res. A 866,164 (2017).
2) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 304 (2013).
3) H. Ryuto et al., Nucl. Instrum. Methods Phys. Res. A
555, 1 (2005).
4) L. Stuhl et al., in this report.
5) J. Gao et al., in this report.

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