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Xray Polarimetry with gas proportional counters through risetime

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Title: Xray Polarimetry with gas proportional counters through risetime


1
X-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)

2
X-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.
3
Rise 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
4
Experiment 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)
5
Rise Time Measurement
  • Sampling the output pulse from CSPA with
    Digitized Oscilloscope.
  • RT and PH are determined from the waveform data
    transferred to the computer

6
Results (Ex34keV)
ltRTgt vs Q
RT distribution
(Hayashida et al., 1999, NIMA, 421,p.241)
7
X-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)
8
Modulation Factor M
Figure of merit for polarimter, larger the better.
M
(Hayashida et al., 1999, NIMA, 421,p.241)
9
Extra 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)
10
Feasibility 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.
11
Polarized 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)
12
Experiment 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
13
However, 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!

14
Preliminary 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
15
M 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.

16
Capillary 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
17
What 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
18
Summary
  • 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.

19
Xe 1atm
Xe-Gas P1atm Ex20keV
Xe-Gas P1atm Ex50keV
1mm
1mm
20
Ne 1 atm
Ne-Gas P1atm Ex20keV
Ne-Gas P1atm Ex50keV
10mm
10mm
21
(No Transcript)
22
XrayCCD(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
23
Feasibility Study PC polarimter
Pmin (99 confidence)
T100ks
  • Merit of PC polarimter
  • Large effective area is easily realized without
    mirrors.
  • Suitable for balloon experiment
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