Calibration of Compton polarimeters

The formula for the angular distribution of γ-ray linear polarization is written in a more transparent form than in terms of the more usual Legendre and associated Legendre polynomials. This form emphasises the special nature of pure dipole, 1→0 and pure quadrupole 2→0,γ-ray transitions, which produce full linear polarization (|P|=1) over the complete angular range, when the initial states are fully aligned in their m=0 substates. f the reactions used previously to calibrate Compton polarimeters cannot be extended to encompass low-energy γ-ray transitions for the new generation of multi-pixel strip detectors and/or tracking detectors with their potentially high-solid angles. Other possible calibration methods are noted.