Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 51 (2018)

Performance test of low-pressure MWDC
for missing mass spectroscopy at BigRIPS
T. Nishi,∗1 S.Y. Matsumoto,∗2 H. Fujioka,∗2,∗1 K. Itahashi,∗1 T. Kawabata,∗2,∗1 Y. Matsuda,∗3,∗1 K. Miki,∗4
M. Miwa,5,∗1 M. Takaki,∗6 Y.K Tanaka,∗7,∗1 T. Uesaka,∗1 Y.N. Watanabe,∗8,∗1 K. Yako∗6 and J. Zenihiro∗1

∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8eﬀect. Under this severe condition, we conﬁrmed thatthe detection eﬃciency does not change by more thana few percent.
From the above results, we found that the MWDC
shows satisfactory performance for the experiments atBigRIPS. The precise analysis is ongoing.

Beam

Plastic
Scintillator

Fig. 1. New constructed MWDCs and plastic scintillatorsplaced on the beam line at CYRIC.

1

Detection Efficiency [%]In December 2017, we conducted a performance
test for a new low-pressure multi-wire drift chamber(MWDC) using proton beams to evaluate tracking resolution and eﬃciency, as well as their stability undera high-rate beam condition. In this paper, we report
the online results of the test experiment.
The MWDC is developed as a tracking detector at
the F5 focal plane in BigRIPS, mainly for two experiments of missing mass spectroscopy: a precise measurement of deeply bound pionic atoms via the (d, 3 He)
reaction1) (piAF) and a search for double GamowTeller giant resonance (DGTGR) via the (12 C, 12 Be)
reaction.2) In these experiments, the tracking detector
is required for (1) the detection of light ions under ahigh-rate background condition (an order of MHz triton in the DGTGR experiment and proton in the piAFexperiment) and (2) operation in vacuum to avoid multiple scattering from a vacuum window. For these experiments, we designed and constructed the new lowpressure MWDCs.3)
The test experiment was conducted in 1.5 days at
CYRIC, Tohoku University, by using primary proton beams of 30 MeV/u. The beam energy was selected to simulate the energy loss of the signal 3 Heof 120 MeV/u in the pionic atom experiment. Thebeam was detected and identiﬁed by two plastic scintillators at the upstream and downstream of the MWDCsas shown in Fig. 1. MWDC consists of 9 planes(XX’X”(0◦ ), UU’U”(+30◦ ), VV’V”(−30◦ )), and is operated with pure isobutane gas at 13.3 kPa. Figure 2shows the evaluated detection eﬃciency as a functionof the voltage applied to cathode planes and potential
wires. As shown in the ﬁgure, the single-plane eﬃciency is greater than 98% with a voltage of higher than−1300 V. The plane resolution and stability under
the high-rate condition are also evaluated with voltage of −1350 V. Though the precise evaluation is stillin progress, the position resolution is apparently better than 0.5 mm (FWHM), which satisﬁes the experimental requirement. The stability test of the MWDC
was performed with ≃ 100 kHz proton beams. Thecondition is comparable with the expected high-rate
background in BigRIPS in terms of the space charge

0.8

0.6

0.4

0.2

01150

12001250

1300- Voltage [V]

1350

1400

1450

Fig. 2. Evaluated detection eﬃciency of the single plane asa function of voltage for cathode planes and potentialwires. The red, blue, and magenta colors correspondto the multiplicity (≡ number of ﬁred wires par plane)
is one, two, and more than three in one event, and theblack shows the overall eﬃciency of the plane.

References

RIKEN, Nishina Center
Department of Physics, Kyoto University
CYRIC, Tohoku University
Department of Physics, Tohoku University
Department of Physics, Toho University
Center for Nuclear Study, University of Tokyo
GSI Helmholtzzentrum für Schwerionenforschung GmbH
Department of Physics, University of Tokyo

1) K. Itahashi et al., RIBF Proposal 135, (2015).
2) T. Uesaka et al., RIBF Proposal 141, (2015).
3) S. Y. Matsumoto et al., RIKEN Accel. Prog. Rep. 50,
205 (2017).

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