Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Low-pressure MWDC system for ESPRI experiment (II)10050100 (a)Efficiency [%]500100 (c)50 i-C4H10Total
M1C1200300
400500600700
High voltage (cathode foils and potential wires) [-V]

Next, the dependence of these quantities on thebeam intensity and energy was investigated. The data
corresponding to 300 ×103 particles per pulse are plotted with closed markers in Fig. 1 and 2. The data indicate negligibe intensity dependence. This is becauseof a small cell size of 5 mm. The results for the 200MeV/nucleon Xe beam were the same as above.
Finally, the detection eﬃciency for a cocktail beam
∗2∗3∗4(b) C2H650 Torr100 Torr200 Torr(c) i-C4H10400
450500550600650700
High voltage (cathode foils and potential wires) [-V]

0100
50
0100
500(a) CH4Z=25Z=35Z=45300 MeV/nucleon(b) C2H6200 MeV/nucleon(c) i-C4H10200 MeV/nucleon

200300400500600700
High voltage (cathode foils and potential wires) [-V]

Fig. 3. Total detection eﬃciency at 50 Torr for secondarybeams. (a) CH4 , (b) C2 H6 , and (c) i-C4 H10 .

Fig. 1. Detection eﬃciency at 50 Torr for Xe beam. (a)CH4 , (b) C2 H6 , and (c) i-C4 H10 .

∗1(a) CH4CH40100 (b)50 C2H60150
100500100
500100500Fig. 2. Position resolution at 50-200 Torr for Xe beam. (a)CH4 , (b) C2 H6 , and (c) i-C4 H10 .

Efficiency [%]Elastic scattering of protons with RI beams (ESPRI)
has been used to study the ground-state properties of
unstable nuclei1) . In ESPRI experiments, the trajectories of the RI beams, the energy and intensity of which
are respectively 200-300 MeV/nucleon and 105–6 particles per second, should be measured. Recently, in orderto improve the detection eﬃciency and tracking resolution, a low-pressure multi wire drift chamber (MWDC)
system was constructed2) . This report describes thecharacteristics evaluated with various beams ( 132 Xeand its secondary beams) and detector gases (CH4 ,C2 H6 , and i-C4 H10 ).
The experiment was performed at NIRS-HIMAC.
Figure 1 shows the detection eﬃciency for the 300
MeV/nucleon Xe beam when the pressure of each gas
was controlled at 50 Torr. The beam intensity was
5×103 particles per pulse (pulse width of 1 s). The
threshold voltage of the ASDs was −20 mV. The definition of symbols in Fig. 1 is the same as in Sec.
2.3 of Ref. 3. For all the gases, the eﬃciency reaches
100%. While the voltage increased with an increase in
the pressure, the voltage at ≤ 50 Torr was almost unchanged. Figure 2 shows the position resolution for an
X plane. For all gases at 50–200 Torr, the resolution
reaches about 50 µm (rms).

Position resolution [μm]Y. Matsuda,∗1,∗2 J. Zenihiro,∗2 S. Terashima,∗2,∗3 and H. Sakaguchi∗2,∗4

Department of Physics, Konan University
RIKEN Nishina Center
School of Physics and Nuclear Energy Technology, Beihang
UniversityRCNP, Osaka University- 170 -was investigated. Figure 3 shows the total detection
eﬃciency for the Z =25, 35, and 40 particles when thepressure of each gas is 50 Torr. Except for the absolutevoltage, a speciﬁc diﬀerence of the tendency does notexist among the gases.
In summary, we evaluated the characteristics of alow-pressure MWDC system with heavy-ion beams.
The detection eﬃciency and position resolution reach
100% and about 50 µm, respectively, with all thetested gases (CH4 , C2 H6 , and i-C4 H10 ). These results
demonstrate that the constructed system is suitable asa beam tracker for ESPRI experiments, and the systemshows potential for experiments using various heavyion beams.
References
1) Y. Matsuda et al.,: Phys. Rev. C 87, 034614 (2013);
S. Terashima et al.,: RIKEN Accel. Prog. Rep. 47, xviii(2014).
2) Y. Matsuda et al.,: RIKEN Accel. Prog. Rep. 48, 211(2015).
3) Y. Matsuda et al.,: Nucl. Instr. Meth. A 670, 25 (2012).