Method of Determining the Detection Efficiency of the MKS-AT1117M Radiometer FOR Uranium Deposits

In the production of products containing uranium, a portion of the uranium settles in the form of deposits on the walls of pipelines as a result of technological processes. In accordance with the normative documents, it is necessary to determine the mass and surface density of the deposits according to certified procedures [1, 2]. To secure the metrological characteristics of the procedures used, the conventional approach requires a large number of standard samples taking account of the form of the deposits and the range of variation in the uranium mass and surface density. This is a technically complex and expensive problem because of the equipment diversity (type and size), the need to bring in a large amount of uranium (including special-purpose uranium) for fabricating standard samples, and the technical difficulties in fabricating the samples (work performed in boxes and chambers and methods of uranium deposition with a prescribed distribution on samples) as well as meeting the requirements of physical protection and taking account of and monitoring nuclear materials during operation and storage of the samples. The methods of numerical modeling are an alternative approach making it possible to replace the conventional standard samples or reduce their number. With their help, it is possible to determine and evaluate the effect of different factors on the efficiency of detectors. In this article, we present the results of calculations of the detection efficiency of an MKS-AT1117M radiometer performed with the MCNP 4B code for γ-rays emitted by a deposit of highly enriched uranium in cylindrical and planar pipelines [3, 4]. Description of the Computational Model. A radiometer‐object of measurement physical-mathematical model was constructed to calculate the efficiency of the detector. The calculations were performed with the MCNP code in a contact geometry where the detector is placed up against the wall of a pipeline. The 10 mm thick lateral protection of the radiometer and a 40 mm in diameter and 45 mm deep collimator, both made of lead, were used to attenuate the external γ-radiation. The choice of contact geometry makes it possible to optimize the signal/background ratio on the productive sections. In the calculations of the efficiency of the detector for a source of highly enriched uranium deposits, the 50‐400 keV γ-rays attendant to α-decay of 235 U were taken into account and the contribution of the 50‐2700 keV γ-rays from the daughter products of 238 U was neglected.