Abstract :
When a bulky environmental sample with radioactive hot particles, as e.g. soil, is repeatedly mixed in the counting bottle and its gamma-ray emission rate counted each time subsequently, the resulting frequency distribution of the counts is no longer symmetric but strongly skewed to the right. For this reason, it is possible to detect the presence of one or more hot particles in such samples simply by testing at a given level of significance whether the total number of counts observed after each mixing belong to the same Poisson distribution. It is shown by Monte Carlo calculations that if (i) the height of the counting bottle is about 5 cm, (ii) the total number of counts collected each time is around 1000, and (iii) the background activity of the sample matrix is not exceeding that of all hot particles in the sample, about 4 mixings will be sufficient to detect in this way the presence of up to 4 hot particles with a probability >95%. This probability is even higher if more than 1000 counts are collected, the hot particles have different activities, the height of the counting bottle is increased, or self attenuation of the gamma radiation in the sample is present. An efficiency calibration for the counting geometry used is not required. An experimental example is given.
