Basic performance of unitized Compton scattering type polarimeter

We have been developing a Compton scattering type polarimeter which consists of nine unit counters to detect the polarization of hard X-rays from stellar objects such as the Crab Nebula. We constructed one unit counter which consists of one plastic scintillator (7/spl times/7/spl times/5 cm/sup 3/) and four phoswich scintillators (6.7/spl times/1.1/spl times/32.2 cm/sup 3/) made of NaI(Tl)+CsI(Na). The characteristics of the unit counter were measured in detail to determine the detection efficiency (20.3%) and the modulation factor (27.5%) at 53.4 keV. The background spectrum of the unit counter in the laboratory is also measured. Based on the results, the background from the outside of the active collimator is reduced by 50.5% when used with the PSD. On the basis of these results, the performance of the planned polarimeter was estimated by computer simulations. The results showed that the polarimeter can detect the polarization of hard X-rays from the Crab Nebula at a MDP (minimum detectable polarization) of 14.0% with a 3-hour balloon observation.

[1]  Hirohisa Sakurai,et al.  Development of a new hard x-ray polarimeter , 1994, Optics & Photonics.

[2]  Shaul Hanany,et al.  Status of the stellar x-ray polarimeter for the Spectrum-X-Gamma mission , 1991, Optics & Photonics.

[3]  Robert Novick.  Stellar and solar X-ray polarimetry , 1975 .

[4]  B. Ramsey,et al.  Optical imaging chamber for X-ray astronomy , 1993 .

[5]  Takamasa Yamagami,et al.  Newly developed low background hard X-ray/gamma-ray telescope with the well-type phoswich counters , 1992, IEEE Conference on Nuclear Science Symposium and Medical Imaging.

[6]  Enrico Costa,et al.  Scattering polarimetry for x-ray astronomy by means of scintillating fibers , 1994, Optics & Photonics.

[7]  Hirohisa Sakurai,et al.  Hard x-ray polarimeter utilizing Compton scattering , 1991, Optics & Photonics.

[8]  K. Long,et al.  A precision measurement of the X-ray polarization of the Crab Nebula without pulsar contamination. , 1978 .

[9]  Shaul Hanany,et al.  Status of the stellar x-ray polarimeter for the Spectrum-X-Gamma mission , 1994, Optics & Photonics.

[10]  W. Heitler,et al.  The quantum theory of radiation , 1936 .

[11]  H. Murakami,et al.  A simple pulse shape discrimination method for the phoswich counter , 1991, Conference Record of the 1991 IEEE Nuclear Science Symposium and Medical Imaging Conference.

[12]  Tsvi Piran,et al.  Polarization features of x-ray radiation emitted near black holes , 1980 .

[13]  Masaharu Nomachi,et al.  Well-type phoswich counter for low-flux X-ray/ gamma -ray detection , 1991 .

[14]  D. Rogers,et al.  EGS4 code system , 1985 .

[15]  M. Noma,et al.  A new design of hard X-ray polarimeter , 1994 .