Gamma-Ray Pair Spectrometry from 20–650 MeV

This is the authors' abstract. We don't add key points for this paper.

Two pair spectrometers have been developed to measure gamma-ray spectra over a range from 20 to 650 MeV with good resolution. One is a conventional 180° spectrometer to measure the lower energies; the other, for high energies, utilizes a circular geometry. An expression for the absolute efficiency is given in terms of the geometry, magnetic field, and pair-production cross section. The effects of geometry, electron scattering, and radiation straggling on the efficiency and resolution function are considered. All these factors are then used to provide the proper normalization for the experimental spectra over the range of energies measured. The counting data are stored in a magnetic-core device, then read out on punched cards. A computer program analyzes the data and makes all the necessary corrections and subtractions. These spectrometers have been used in experiments with neutral pions at cyclotron energies.