Apparatus for the measurement of total body nitrogen using prompt neutron activation analysis with Californium-252

Abstract

Details of clinical apparatus designed for the measurement of total body nitrogen (as an indicator of body protein), suitable for the critically ill, intensive-care patient are presented. Californium-252 radio-isotopic neutron sources are used, enabling a nitrogen measurement by prompt neutron activation analysis to be made in 40 min with a precision of ±-3.2% for a whole body dose equivalent of 0.145 m Sv. The advantages of Californium–252 over alternative neutron sources are discussed. A comparison between two irradiation/detection geometries is made, leading to an explanation of the geometry adopted & the apparatus. The choice of construction and shielding materials to reduce the count rate at the detectors and consequently to reduce the pile-up contribution to the nitrogen background is discussed. Salient features of the gamma ray spectroxopy system to reduce spectral distortion from pulse pile-up are presented.