Advantages of large-volume HPGe detectors throughput-limited applications

The demand for high-resolution gamma spectroscopy performed at high count rates is increasing in areas such as neutron activation, primary coolant monitoring, and cleanup work. With increasing count rate, a condition is reached in which the counts into the data memory are limited by a component of the system and not the activity of the sample or the efficiency of the detector itself. Once this condition is reached, further increases of the count rate at the detector will not increase the rate at which data are stored and may reduce it. In most cases, throughput is limited by the amplifier or the analog-to-digital converter of the multichannel analyzer (MCA). When this is the case, often the initial reaction is to reduce the count rate by using a small-volume (low-efficiency) high-purity germanium (HPGe) detector. This reasoning does not consider the quality (the relative number of peak counts to background counts) of the spectrum being processed and counted. Improving the quality of the spectrum improves the detection limit, the counting time, or the measurement uncertainty. These results clearly demonstrate that large HPGe detectors (collimated if necessary) provide better results for high and ultrahigh count-rate gamma spectroscopy just as they do for low-level measurements. Large detectors may be expected to provide better results from the standpoint of MDA, counting time, and measurement uncertainty