A Method for Simultaneously Determining the Depth and Radioactivity of an Embedded Source in a Medium

This study therefore focuses on the development of a simple and advanced algorithm to simultaneously estimate the depth of an embedded source and its radioactivity in the medium. A simple program equipped with an algorithm for the simultaneous determination of two variables was developed by establishing a database for the results from a Monte Carlo simulation for unscattered photon fluences at several geometries and detector response according to the photon energy. The method was then designed to determine the source depth and its radioactivity in the medium using theoretically calculated photon fluence and measured count rate from the in situ measurement. The existing method to determine the source depth demands the information on the effective center of a detector so that this method depends on the type of a detector. In addition, the expensive in-situ program should be prepared to evaluate the radioactivity of the embedded source. This makes severe time and cost constrain. A simple program equipped with an algorithm regarding the simultaneous determination of the embedded source depth and its radioactivity was developed based on the Excel VBA. The program was then applied to the results on the in situ gamma-ray spectrometry using a HPGe detector to find the depth and activity of ¹³⁴Cs and ¹³⁷Cs. Good agreements at the source depth as well as the radioactivity between the estimated and calculated values were achieved less than 10 % and 15 % differences compared with the real values using the developed program. In the feasibility on the application of the developed program to the general situation regarding the source distribution, this program still had an effect on the estimation of the depth and activity in the maximum strength of diffused sources into a layer.