Nondestructive measurements of-ray and X-ray emissions are often made to characterize special nuclear materials.Various computer codes are available to determine the relative isotopic composition of Pu from analysis of the spectra resulting from such measurements.MGA is one of the major isotopic codes and when possible it makes use of the low-energy region below 208 keV. A good analysis of the low-energy region of a spectrum requires a high-resolution germanium detector.A typical Ge detector used for these measurements would be 200 mm~2 in area by 10 to 16 mm deep.Small detectors of this type can provide an excellent resolution of about 500 eV full width half-maximum(FWHM)at 122 keV.Because of the complexity of the important 100 keV region from Pu,it is quite important that the resolution meet certain standards.Historically the suggested FWHM at 122 keV has been 525 eV or better,however in many cases,for example when using large detectors or when a short amplifier time constants are needed,this specification can not be met.The purpose of this study was to investigate MGA performance versus energy resolution of the counting system.A set of Pu standards with different burn-up was measured with several types of detectors having a wide range of energy resolution at 122 keV.The detector set included examples of–the Low-Energy Germanium Detector(LEGe),the Broad-Energy Germanium Detector(BEGe),the Reverse-Electrode Coaxial Germanium Detector(REGe),and the conventional coaxial germanium detector.The effects of a poor resolution on MGA performance were analyzed and are discussed.
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