Energy calibration: The use of [sup 192]Ir as a reference standard source with HPGe detectors

To improve precise measurement of photon energy with germanium detectors, a new method for energy calibration has been developed after consideration of a photo-peak shape function. The function is the convolved function of an [open quotes]instrument function[close quotes] and incident signal function around a peak profile i.e., a line photon of interest, a half-continuum of small angle scattering photons, and a half-continuum possibly caused by random summing of the line photon and an accompanying bremsstrahlung photon continuum laid on a background continuum. According to the model, the photon energy should be adjusted onto the mean, namely, the centroid of normal distribution, which is one of the key components of instrument function, instead of the [open quotes]conventional[close quotes] position of a peak maximum (the peak position). The model predicts use of the peak position as the adjusting position of energy, if one uses a reference standard source (e. g., [sup 192]Ir-the photon energy of which is known in wave-length scale) as an internal standard (i.e., standard and radio-nuclide measured together). It is necessary to use the centroid as a calibrating point to complete the model of the peak shape because the reference standards for higher energies based on the wavelength scalemore » are unavailable today. Therefore, it is indispensable to elucidate any contribution of the random summing on the photo-peak shape function. This paper has two aims (a) to confirm the new calibration method with the internal reference standard method and (b) to clear any parameter of the random summing events that affect the shift of peak position.« less