Photon Factory Activity Report 2004 #22 Part B (2005)
Instrumentation and Technique

14A/2004G030

Basic Performance for hard X-ray Polarimeter Using MAPMTShuichi Gunji1, Toshiji Suzuki1, Ryo Nakajima1, Yuichiro Yamashita1, Kazufumi Suzuki1,Fuyuki Tokanai1, Hirohisa Sakurai1, and Shunji Kishimoto2
1
Yamagata Univ., Kojirakawa, Yamagata, 990-8560, Japan2
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan
Introduction
In X-ray astronomy, various information on stellarobjects has been obtained through the energy spectrum,
the time variability, and the image. Though theobservation for the polarization is also very important, theobservation has been rarely carried out. So we have beendeveloping a hard X-ray polarimeters, applying newtechnology[1] and had several basic experiments in KEKPF BL14A to investigate the basic performance of theprototype polarimeter.
Design of Hard X-ray Polarimeter
We have applied Compton scattering as the principle ofthe polarimeter. Since the direction of the scattered hard
X-ray depends on the polarization vector of incident hard
X-ray, the information on the polarization can be obtainedby measuring the direction of the scattered hard X-ray.
Figure.1 shows the schematic view of the Compton
scattering type polarimeter developed by us[1].

Figure 1: The design of the polarimeter.
This polarimeter consists of 36 plastic scintillators and 28
CsI(Tl) scintillators surrounding them. They are read out
by one multianode photomultiplier (MAPMT) H8500,
which is manufactured by Hamamatsu Photonics Inc. As
the incident hard X ray is coming to any plastic
scintillator, the hard X ray is scattered and the scattered
hard X ray is absorbed by any CsI(Tl) scintillator. By
detecting the scattering and absorption positions, the 2dimensional scattering direction can be determined andhence the information on the polarization for incident
hard X rays can be obtained.
Results
Figure. 2 shows the experimental setup and the results.
The polarized hard X rays of 80 keV were injected to thecenter of the detector as shown in left figure. Fromacquired events, the events which satisfy the following
two criteria were extracted and used for analysis.
1) The deposited energy in the plastic scintillator due tothe Compton scattering of 80 keV hard X rays is around11 keV. So we selected the events with the energy
deposit which corresponds to ~11 keV in the plasticscintillator.
2) The energy deposit in the CsI(Tl) scintillator due to theCompton scattering corresponds to ~70 keV. So weselected the events with energy deposit around 70 keV
in only one CsI(Tl) scintillator.
With the extracted events, we investigated the hit pattern
for the CsI(Tl) scintillators. The x axis and y axis in theright figure correspond to the channel number for theCsI(Tl) scintillators and the number of events,respectively. The bars and the crosses are the results ofthe experiment and computer simulation, respectively. As
shown in the right figure, the modulation can be clearlyobserved. We recognized that our polarimeter can obtain
the good modulation factor of ~60% for 80 keV.
Moreover, the detection efficiency was ~20%.

Figure.2; The left figure shows the notation for CsI(Tl)scintillators. The right figure shows the modulation of thecounts for CsI(Tl) scintillators. The x axis and the y axis
corresponds to the channel number for the CsI(Tl)scintillators and the number of events, respectively.
Conclusions
We have developed Compton scattering type polarimeter
sensitive to hard X-ray band, using MAPMT (H8500). To
investigate the performance, we have carried out basic
experiments utilizing polarized X-ray beam of 80 keV in
BL14A of KEK PF. From the results, we confirmed that it
can obtain the modulation factor and the detection
efficiency of ~60% and ~20% at 80 keV, respectively.
References[1] S. Gunji etal. Adv. Space Res. Vol.33 (2004)
pp1771-1776* gunji@sci.kj.yamagata-u.ac.jp

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