Title: Xray Polarimetry with gas proportional counters through risetime
1X-ray Polarimetry with gas proportional counters
through rise-time
- K. Hayashida, T. Horikawa, Y. Nakashima, H.
Tsunemi - (Osaka University, Japan)
- Acknowledge to
- Y. Namito (KEK, Japan)
- N.Tokanai (Yamagata Univ, Japan)
- B.Paul (TIFR, India)
2X-ray Polarimeters in Astronomy
- Bragg Crystal Reflection
- OSO8,ArielV satellites (1970s)
- Compton Scattering
- Planned for Spectrum X-Gamma mission (1990s)
- Tracking Photo-electron Emission Direction
- X-ray CCD (Tsunemi et al., 1992)
- Micro electrodes Gas Chambers (Costa et al.,
2001 Tanimori et al., 1999 Sakurai et al., 1996)
Observations have been almost stagnant since
1970s for more than 20 years.
3Rise Time Polarimeterusing Gas Proportional
Counter
- Proposed by Riegler et al., Sanford et al., in
1970. - We re-examined the method. (Hayashida et al.,
1999, NIMA, 421,p.241)
Working principle
4Experiment at Synchrotron Facility (1992-1993)
- Ex10-40keV (Pbeam0.8 measured)
- Xe proportional counter Ginga ASM backup
- Xe736mmHg CO225mmHg
- Multi cell type 5cm depth, 5cmx30cm for each
cell - Anode 50mm Be HV1950V
Irradiate position 12 mm from anode 2mmf
(Hayashida et al., 1999, NIMA, 421,p.241)
5Rise Time Measurement
- Sampling the output pulse from CSPA with
Digitized Oscilloscope. - RT and PH are determined from the waveform data
transferred to the computer
6Results (Ex34keV)
ltRTgt vs Q
RT distribution
(Hayashida et al., 1999, NIMA, 421,p.241)
7X-ray Energy dependence
- Large modulation longer RT at higher energy
- Note Xe-K edge 34.6keV
- Events were selected using PH.
- RT cutoff of 1ms is employed.
- Most of the events with K-fluorescent were likely
to be excluded.
(Hayashida et al., 1999, NIMA, 421,p.241)
8Modulation Factor M
Figure of merit for polarimter, larger the better.
M
(Hayashida et al., 1999, NIMA, 421,p.241)
9Extra Experiment for Verification
- Thin Sn filter was placed at the beam exit,
which produced Sn Ka,Kb fluorescent X-rays in
addition to polarized 36 keV X-rays.
(Hayashida et al., 1999, NIMA, 421,p.241)
10Feasibility Study PC polarimeter
- Merit of the PC rise time polarimeter
- Only need to add RT processing unit to
conventional PCc - Large effective area is easily realized without
mirrors.
T20ks Balloon Observation A pair of 300cm2 PCs
will provide Polarization degrees (if Pgt5) for
each 5keV band.
11Polarized X-ray Beam Line at Osaka
Monochromatic beam with linear polarization
degree of 40-50 is obtained. (Koike et al.,
2000, SPIE4012, p.414)
Electron Impact type X-ray Generator
Measurement Chamber
Double Crystal Monochrometer
Bremstrahlung X-rays are partially polarized.
Pickup X-rays whose energy (Ex keV) is close to
applied High Voltage (HV kV)
12Experiment at Osaka Beam Line (2001-2002)
angle
E
X-ray
90,270
- Two kinds of Gas PCs
- Ar gas flow type PC
- Wire 50mm
- Quenching gas (CH4) of various contents were
examined. - Xe gas shield type PC (the same one used in
Synchrotron Facility) - Data taking system was upgraded.
X-ray
0,180
13However, Results are
Incident position 12mm from anode for Xe PC 10mm
from anode for Ar PC
- Contents of Quenching Gas is very sensitive to
RT. - Ar 99.3 CH4 0.7 provided M of 0.05-0.1. Small!
- More seriously, the same Xe counter used in
1992-1993 yielded M of less than 0.05.
Discrepancy!
14Preliminary Simulation using EGS4
- EGS4 (Electron Gamma Shower Simulator ver4) KEK
low energy extensions - Energy deposit and path of photoelectrons are
simulated. - Large effect of multiple scattering is observed.
Ar-Gas P1atm Ex20keV
Ar-Gas P1atm Ex50keV
15M expected from EGS4 Simulation
) If multiple scattering does not exist, M would
be 0.78.
Dispersion of the distance to anode (s ) cm
M
Size s (cm)
M
- Small energy dependence
- M0.03-0.06 for Ar, lt0.03 for Xe
- NOTE gas processes (diffusion, avalanche etc) is
not considered.
16Capillary Plate Gas Chamber
Pulse width is measured
Saito et al, 2001
0 case
Xrays(90)
Electron Cloud
Electric Vector
Xray Detection Layer
Xrays(0)
PMT Out
time
Gas Amplification
90 case
Capillary Plate
CPGC with Ar gas provided M21_at_20keV in an
experiment at Osaka Beam Line ?EGS4 simulation
predicts M5 How valid the EGS4 simulation
(multiple scattering) is in the low energy end ?
Quartz
PMT Out
PMT
time
17What causes the discrepancy ?
- Strong dependence of X-ray incident position on
RT was observed. - Misalignment of rotation axis could have made an
artifact modulation. - But, the modulation should have 1 peak / 360,
not like observed 2 peaks / 360. - Sn-filter result was not explained by the
misalignment, either.
Anode
Experiment at Synchrotron Facility is planed in
this Nov.
12mm
18Summary
- Gas proportional counter polarimeter with rise
time measurement is introduced. - Previous experiment at Synchrotron facility
provided M of 0.1-0.3 with Xe PC, while recent
experiment (Xe PC, Ar PC) provides much smaller
M. - Preliminary simulation also suggests M lt0.1 It
also contradicts the CPGC result of M0.2. - No firm solution has not yet been obtained for
the discrepancy. Sorry for inconclusive,
confusing results.
19Xe 1atm
Xe-Gas P1atm Ex20keV
Xe-Gas P1atm Ex50keV
1mm
1mm
20Ne 1 atm
Ne-Gas P1atm Ex20keV
Ne-Gas P1atm Ex50keV
10mm
10mm
21(No Transcript)
22XrayCCD(12µm,6.8µm pixel)simulation and Experiment
M(NV-NH)/(NHNV)
Experimental data Tsunemi et al., 1992 Hayashid
et al., 1999 Schmidt et al., 1995
23Feasibility Study PC polarimter
Pmin (99 confidence)
T100ks
- Merit of PC polarimter
- Large effective area is easily realized without
mirrors. - Suitable for balloon experiment