SOME OF THE PROBLEMS INVOLVED IN THE THEORY OF THE LABORATORY PHOTONEUTRON METHOD USED FOR THE DETERMINATION OF BERYLLIUM

The method based on the ( gamma ,n) reaction is widely used for determining Be in ores, concentrates, and metallurgical products. Under laboratory conditions, linear sources with coaxially arranged samples were found desirable for photoneutron analysis. In further improvement of method, an analytical expression was derived, allowing the number of neutrons produced in the ( gamma ,n) reaction to be calculated as a function of the dimensions of the radiation source, taking into account their relative positions under conditions of coaxial geometry. In order to simplify the expression, it was assumed that the centers of the source and of the specimen are at the same level and that a point source is used. The equation was then numerically integrated by means of a computer and the reaction yield data, obtained with and without considering the absorption of gamma rays in the specimen, were compared. The divergence of these 2 sets of data, ranging from 3 to 5%, was found to depend on the dimensions of the powder sample. Increasing the ratio of the height of the specimen to the lengih of the source resulted in a decrease of the divergence of the neutron yields from linear and point sources; atmore » a ratio of 2: 1, these results coincided. This indicated that use of the simplified formula is justified. (TTT)« less