Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Pressure dependence of eﬀective gas gain of THGEM in deuteriumgas
C.S. Lee,∗1,∗2 S. Ota,∗2 H. Tokieda,∗2 Y.N. Watanabe,∗3 R. Saiseau,∗4 and T. Uesaka∗1equation:Geﬀ =Qpads
qe · ∆E/Wi(1)

where Geﬀ is the eﬀective gas gain of GEM, ∆E isthe energy loss of particle, Wi is mean energy for ionelectron pair creation of certain gas (36.4 eV for D2 ),qe , the elementary charge, and Qpads is the collectedcharges on the readout pad. Figure 2 shows the obtained gain curves including the achievable gain froma triple THGEM conﬁguration for 0.18-0.5 atm D2 asa function of the voltage between the upper and thelower electrodes of THGEM, ∆ VTHGEM . A triple
THGEM conﬁguration provides the eﬀective gas gainof more than 104 for every pressure, and even morethan 105 for under 0.35-atm.
0.18-atm
0.20-atm

105

0.25-atm
0.30-atm

Effective Gas Gain

A low-pressure gaseous active target called CNS active target (CAT) has been developed for a deuteroninelastic scattering oﬀ unstable nuclei1) . The CAT
consists of a combination of gas electron multipliers(GEMs) and time projection chamber (TPC) as a vertex tracker, and Si detectors as a total kinetic energy
detector for high momentum recoil particles. Three
400 µm-thick thick gas electron multipliers (THGEMs)
are employed for the ampliﬁcation inside the TPC inorder to achieve an eﬀective gas gain of 104 at 0.4 atm
deuterium gas. This gas gain of 104 fulﬁls the detection of the minimum energy deposition of our interest,
5 keV/cm, which is the energy loss per centimeter ofa recoiling deuteron to 9◦ in the centre-of-mass framefrom 132 Sn(d, d’) reaction at 100 MeV/nucleon. The
properties of a double THGEM conﬁguration in 0.2-,
0.3- and 0.4-atm deuterium were investigated for theﬁrst time by corresponding authors2) . In addition to
the previous work, the pressure dependence and thelong-term stability of the eﬀective gas gain were investigated by using a triple THGEM conﬁguration.
A schematic view of the experimental setup is shownin Fig. 1. The collected electrons on the readout padwere integrated with a charge-sensitive preampliﬁer,
which has a conversion gain of 200 mV/pC and a timeconstant of 80 ns. The output signal from the preampliﬁer was treated by a shaping ampliﬁer (ORTEC571), and the pulse height of the shaped signal wasrecorded by a multi-channel analyser (MCA) (Kromek102). The eﬀective gas gain Geﬀ is derived from the0.35-atm

104

0.40-atm
0.45-atm
0.50-atm

103

102
300

400

500

600

700

800900∆ VTHGEM[V]Fig. 2. Gain curves of a triple THGEM configuration at0.18-0.5 atm D2 as a function of ∆ VTHGEM .

Fig. 1. Experimental setup of this work. Voltages tothe THGEMs are supplied from a single channel ofa HV module, by using a register chain, where each
∆VTHGEM is equally provided.
∗1∗2∗3∗4RIKEN Nishina Center
Center for Nuclear Study, Graduate School of Science, TheUniversity of Tokyo
Department of Physics, The University of Tokyo
University Paris-Sud- 175 -Every set of measurements for each pressure wassuspended when a normal spectrum can hardly betaken due to the discharge problem. In this measurement, the ratio of the voltages on each electrode of
the THGEMs was retained in constant by using a resistance chain. The strength of the transfer ﬁeld was
2.25 to 4.16 kV/cm/atm where the transfer eﬃciency isalmost maximum and reached a plateau. The strengthof the induction ﬁeld was 3.0 to 5.56 kV/cm/atm.
References
1) S. Ota et al., CNS Annual Report 2011 CNS-REP90(2013) 70-71.
2) C.S. Lee et al., JINST 9 (2014) C05014.
3) M. Tokuda et al., JINST 7 (2012) C04006.