Determination of Pu Amount in a Waste Carton by Gamma-Ray Measurements

The amount of Pu-239 in a waste carton is determined by gamma-ray measurements. The measuring deviations caused by non-uniform distirubtion in the carton and by the large volume are minimized by rotating and scanning the object. Attenuation corrections by two methods were studied and compared: (1) the use of an external gamma-ray source to measure the attenuation as a function of position in a carton , and (2) the estimation of attenuation factor on the basis of weight of the carton and the density of the matrix. Calibration standards were made with 4 different types of matrix material and locations for well measured sources containing from 3 to 80 mg of Pu. Using a Nal(Tl) scintillation detector, and accumulating the activity in the 360-470 KeV region for 400 to 1,000 seconds, Pu content can be determined to within about 50% at 7 mg and about 10% at 80 mg level in a 17 liter cardboard carton.