Use of single planar Ge(Li) detectors as gamma-ray polarimeters

Abstract

The polarization sensitivity of a single rectangular Ge(Li) detector 40 × 25 × 3.5 mm has been studied as a function of energy using gamma rays of known linear polarization produced in (p,p′γ) reactions. The counting rates in the total absorption peaks were measured with the 40 × 25 mm face perpendicular [Formula: see text] and parallel [Formula: see text] to the plane defined by the ion beam and gamma-ray direction. The asymmetry ratio [Formula: see text] was measured using E2 gamma rays with known polarization. From these results the following values of Q for complete polarization were deduced for a series of energies: 0.847 MeV (16.4 ± 1.0)%, 1.368 MeV (13.1 ± 1.0)%, 1.779 MeV (12.4 ± 1.5)%, and 4.43 MeV (6.4 ± 1.0)%. These results were in quantitative agreement with calculations made using the Klein–Nishina formula. A large volume detector 60 × 35 × 6.5 mm was studied in a similar manner. The corresponding results for complete polarization are: 0.847 MeV (16.4 ± 1.0)%, 1.368 MeV (14.3 ± 2.0)%, 1.779 MeV (11.6 ± 1.2)%, and 4.43 MeV (5.8 ± 1.5)%. These values are slightly higher than those obtained in calculations. Tests were also made with a lead collimator 6.25 cm long with an aperture of 1 cm in front of the larger polarimeter. The results for complete polarization are: 1.779 MeV (14.0 ± 1.5)% and 4.43 MeV (9.0 ± 1.0)%. Some recent applications of high-resolution Ge(Li) linear polarimeters are briefly discussed.