A Pair Spectrometer Using a Large Coaxial Lithium-Drifted Germanium Detector

A gamma-ray spectrometer, using a 30 cc coaxial Ge(Li) detector, which can be operated as a 3 crystal pair spectrometer at high energies and in the Compton suppression mode at low energies, provides an effective means for studying complex gamma spectra. Pair spectrometer operation enhances peak to background ratios by reducing background and eliminating single escape and full energy peaks. The peak to background ratio for the 2.614 MeV gamma of ThC" is improved by about a factor of 70 with only a factor of 7 loss of efficiency. The energy resolution (fwhm) of the spectrometer is approximately 0.5% at 1 MeV and 0.1% at 7 MeV allowing capture gamma energies to be determined to an accuracy of about 1 keV. A comparison is given of the performance of the pair spectrometer using two smaller Ge(Li) detectors (3 cc and 5 cc) and the large 30 cc detector. Capture gamma spectra of Ti and Zr are given to illustrate the performance of the spectrometer.