I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Development of the gaseous Xe scintillation detector for heavy RI beams

Fig. 1. Photograph of the new version of the gaseous Xe
scintillation detector. Four 2-inch-ϕ PMTs (Hamamatsu,R6041-406) were attached to the corners.
∗1Department of Physics, Kyoto University
RIKEN Nishina Center∗3 CNS, University of Tokyo∗4 Department of Physics, Toho University∗5 CYRIC, Tohoku University∗6 Department of Natural Sciences, Tokyo City University∗7 RCNP, Osaka University∗8 Department of Physics, Rikkyo University∗9 School of Physics, Beihang University∗10 Department of Physics, University of Tokyo∗237Z

In this contribution, we brieﬂy report on the performance test of the gaseous Xe scintillation detector installed in the F7 vacuum chamber of BigRIPS. In thistest, we use the detector for the particle identiﬁcationof heavy RI beams up to the atomic number Z ∼ 90
for the ﬁrst time. At present, RIBF is the best facility
for the generation of high-intensity and high-energy RI
beams in the world. However, the use of high-intensityRI beams is now limited because of radiation damage
and/or the slow responses of the standard detectors ofBigRIPS.1) As machine time is also limited because of
the hogh cost of electric power, failure to use the highintensity RI beams would be a signiﬁcant loss.
Therefore, we proposed a new detector using scintillation photons from Xe gas. Because the average energy
expended per scintillation photon is very small (<20 eV)
and its lifetime is relatively short (5 ns and 100 ns),2)
the detector is expected to have a good energy resolutionand a fast response time. The Xe detector is promising
for the ∆E measurements of high-intensity RI beams(>100 kcps), where the ion chamber (IC) cannot work
because of the slow response. To replace the IC with theXe detector, we must ﬁrst compare its energy resolution

ZY. Hijikata,∗1 J. Zenihiro,∗1 H. Baba,∗2 M. Dozono,∗3 S. Enyo,∗1 N. Fukuda,∗2 T. Harada,∗2,∗4 Y. Matsuda,∗5S. Michimasa,∗3 D. Nishimura,∗6 S. Nishimura,∗2 S. Ota,∗3 H. Sakaguchi,∗7 H. Sato,∗2 Y. Shimizu,∗2S. Sugawara,∗6 H. Suzuki,∗2 H. Takahashi,∗6 H. Takeda,∗2 S. Takeshige,∗8 J. Tanaka,∗2 S. Terashima,∗9 R. Tsuji,∗1T. Uesaka,∗2 S. Yamamura,∗10 and K. Yoshida∗236

1035

3736

1035
134

134

33

33

−1

10−1

1032

2.44

2.48

2.52

2.56

2.60

32

A/Q

2.44

2.48

2.52

2.56

2.60

A/Q

Fig. 2. Z obtained using the IC (left) and the Xe detector(right) vs. A/Q spectra with the Ge setting.

to that of the IC. A prototype of the detector was tested
using a cocktail secondary beam at 300 MeV/nucleon upto Z = 55 at HIMAC, QST in Chiba. An rms resolutionof ∆Z = 0.2 around Z = 55 in sigma was achieved.3)
However, it is diﬃcult to install the prototype in thevacuum chambers at the focal planes in the BigRIPS
beamline owing to the thick detector material, which
consists of 4-atm and 12-cm-thick Xe gas and 2-mmthick Al windows. We recently built a new version ofthe Xe detector with 2-atm and 9-cm-thick Xe gas and125-µm-thick Kapton windows, as shown in Fig. 1. The
material thickness is approximately 100 mg/cm2 , whichis comparable to that of the IC.
In November 2020, we installed the new detector inthe F7 vacuum chamber for the ﬁrst time and performed
a test experiment by using several heavy RI and primary beam settings such as Ge, Sb, Er, Th, and U.
We successfully acquired data of particles of diﬀerent Z
and diﬀerent beam intensities. For the readout circuits,ﬂash ADC (CAEN V1730) have been used in addition tothe conventional QDC and TDC modules to check thehigh-rate torelance. Figure 2 shows the obtained twodimensional PI spectra with the Ge setting. To deduce
Z and A/Q values, the energy loss ∆E of the IC and theXe detector as well as time of ﬂight between the F3 andF7 plastic scintillators are used. The rms resolution of∆Z ∼ 0.22 determined from the ∆E in the Xe detector
is very close to that of the IC. Although the analysis
is ongoing, the preliminary spectra show that the Xe
detector will be helpful under high-intensity beam conditions.
References

1) T. Kubo et al., Nucl. Instrm. Methods Phys. Res. B 204,97 (2003).
2) M. Mimura et al., Jpn. J. Appl. Phys. 48, 076501 (2009).
3) J. Zenihiro et al., RIKEN Accel. Prog. Rep. 51, 156 (2018).
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