Gamma Ray Transmission Imaging Detectors Using Double Gap
Resistive Plate Chambers
K. S . Lee, Korea Detector Laboratory,
Korea University,
Seoul, Korea
Authors
S. H. Ahn, B. Hong, S. J. Hong, T. J. Kim, T. I. Kang, K. S. Lee,
J. G. Lim, D. H. Moon, J. K. Oh, S. Park, M. S. Ryu, K. S. Sim.
VII Workshop on Resistive Plate Chambers and Related Detectors
Clermont-Ferrand FRANCE
October 20-22, 2003
Contents
1. Motivation of the RPC study for gamma ray detections
2. Basic Idea
3. Detector structure of two dim. signal read-out
4. GEANT simulations for Q. E. of gamma rays
5. Basic comic ray tests of single gap RPCs in the streamer mode operations
6. Transmission images using 10 mCi Cs137
7. Conclusions
1. Motivation of the RPC study for gamma 2. Basic idea
ray detections
Gamma rays are detected by Compton scattering
1) High resolution properties of gaseous chambers at surfaces of the resistive plates.
2) RPCs : Relatively high Q.E. for gamma rays,
comparing to wire chambers
Multi-gap solution
e- Resistive
plate
3) Gas electron amplification volume is simple. In gas gaps
Various modification of the detector structure.
For two dim. Detection,
* Disadvantages
1) Q.E. for gamma ray drops rapidly as energy Y–axis strips
less than 1 MeV GEANT simulations Bakelite
++ ++
-- --
Gap #1
Bakelite
2) Limitation of rate capability : X-axis strips
~ 1 kHz/cm2/single-gap Bakelite
++ Gap#2
--
Bakelite
Y–axis strips
3. Detector structure of two dim. signal read-out
1) Choice of melamined bakelite : 4) Strip pitches : 10 mm to get ~ 5 mm resolution
Resistivity ~ 1011 cm
Adequate for low noise streamer mode 5) Negative charge from anode side
instead of avalanche mode to start x-strips on the GND side of gaps
a feasibility study using a 10 mCi Cs137 source Positive image charge from cathode side
y-strips on the H.V. side of gaps
2) Double gap RPCs with 2 mm gap
3) Active area : 96 cm 96 cm
5) Starting R&D with small sources ~ 10 mCi 6) Front-End electronics for the streamer mode
Have to minimize detector noise level 96 for x-strips and 96 for y-strips
Avalanche mode Streamer mode OP amp(no gain, only for pulse shaping)
for the feasibility study + comparator(for discrimination)
Noise rate > line scanning type
do not need a very high Q.E.
Due to the limitation of the two dim. read-out,
# of layer of gas gaps limited 1 ~ 8
2) Line scanning type detector
One dimensional detectors with signal pads,
moving the detector in the vertical direction.
Q.E. > 20 % can be obtained for
E > 2 MeV with more than 32-gaps
Possibility of the line scanning using
an high energy X-ray generator