Speaker
Mr
Kaori Hattori
(Cosmic Ray Group, Dept. of Physics, Kyoto Univ.)
Description
We are developing a micro-Time Projection Chamber (micro-TPC) based
on a micro-pixel chamber (μ-PIC). A Micro-TPC is employed for an
electron-tracking Compton camera [1,2].
A μ-PIC is a fine pixel-type two-dimensional imaging detector with a
pixel pitch of 400μm and it has a detector area of 10×10cm2. We
achieved a maximum gas gain of 15,000 and stable operation over
1,000 hours at a gas gain of 5,000. However, the stable gas gain of
5,000 is not high enough for detecting Compton-recoil electrons,
dE/dx of which are the same as that of minimum ionizing particles
(MIPs). A required gas gain for MIP detection is 2 – 4 times as large
as the achieved one.
Therefore, a hybrid detector consisting of a μ-PIC and a gas
electron multiplier (GEM) is employed for realizing the required
gain. A GEM is installed just above a μ-PIC and operated at a low
gas gain (less than 50). We plan to use a GEM temporarily until a
gas gain of a μ-PIC reaches the aimed gas gain alone by improvements
of the electrode structure and manufacturing process. We used a GEM
developed by Center for Nuclear Study, the University of Tokyo. The
GEM consist of 50μm a thick kapton foil, and copper clad on each
side, 70μm holes arranged with 140μm between centers, with detection
area of 10×10cm2.
Operating a μ-PIC at a gas gain of 2.5×103, we achieved a maximum
total gas gain of more than 105, and energy resolution of 1.2keV
(21%) FWHM at 5.9keV (at a gas gain of 3.3×104). Long-term stability
over 170 hours was also confirmed at a total gas gain of 2.0×104
(the μ-PIC was operated at a gas gain of 2.0×103, the GEM at 10). We
achieved enough stable gain to detect MIPs and detected cosmic ray
muons by micro-TPC. The ion feedback was suppressed to less than
10%, when GEM was operated at a gas gain of 10, which enables us to
detect tracks of particles at higher rates.
Now we are developing a larger μ-PIC with a detection area of
30×30cm2 and GEM with that of 28×25cm2. The larger hybrid detector
will increase detection efficiency of detecting charged particles,
and enable us to measure longer tracks.
Primary author
Mr
Kaori Hattori
(Cosmic Ray Group, Dept. of Physics, Kyoto Univ.)
