Two Compton polarimeter constructions for modern standard γ-spectroscopy

Two types of Compton polarimeters for γ-linear polarization measurements are presented. The first one consists of standard Ge-detectors and unites an easy handling and high grade of universality with high polarization sensitivity in the γ-ray energy range 180–2500 keV. In this device, a low efficiency Ge-crystal scatterer is used with a special diameter-to-length ratio which optimizes the probability for Compton scattering. In addition, the background in the summed energy spectra is significantly reduced by requiring coincident γ-ray energies to obey the Compton scattering formula. The second device fits the need of accessory units which can be used with the new generation of multi-detector arrays. It is based on a segmented planar Ge-crystal surrounded by an anti-Compton shield and possesses a high coincidence efficiency in the 50–1000 keV range. For both spectrometers we performed calibration measurements to obtain the sensitivity Q and the coincidence efficiency εc. From these values we deduced the “figure of merit” F = Q2εc which gives a kind of quality description for polarimeters.