An application of a Si/CdTe Compton camera for the polarization measurement of hard x-rays from highly charged heavy ions

Kavli Affiliate: Tadayuki Takahashi

| First 5 Authors: Yutaka Tsuzuki, Shin Watanabe, Shimpei Oishi, Nobuyuki Nakamura, Naoki Numadate

| Summary:

The methods to measure the polarization of the x-rays from highly charged
heavy ions with a significantly higher accuracy than the existing technology is
needed to explore relativistic and quantum electrodynamics (QED) effects
including the Breit interaction. We developed the Electron Beam Ion Trap
Compton Camera (EBIT-CC), a new Compton polarimeter with pixelated multi-layer
silicon and cadmium telluride counters. The EBIT-CC detects the
three-dimensional position of Compton scattering and photoelectric absorption,
and thus the degree of polarization of incoming x-rays can be evaluated. We
attached the EBIT-CC on the Tokyo Electron Beam Ion Trap (Tokyo-EBIT) in the
University of Electro-Communications. An experiment was performed to evaluate
its polarimetric capability through an observation of radiative recombination
x-rays emitted from highly charged krypton ions, which were generated by the
Tokyo-EBIT. The Compton camera of the EBIT-CC was calibrated for the 75 keV
x-rays. We developed event reconstruction and selection procedures and applied
them to every registered event. As a result, we successfully obtained the
polarization degree with an absolute uncertainty of 0.02. This uncertainty is
small enough to probe the difference between the zero-frequency approximation
and full-frequency-dependent calculation for the Breit interaction, which is
expected for dielectronic recombination x-rays of highly charged heavy ions.

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