Assessment of the volume activity of α-radioactive wastes on surface and specific contamination by portable γ-spectrometry method

The aim of the study is to evaluate the volume activity of radioactive waste (RW) by surface and specific alpha contamination using portable gamma-spectrometry.

Materials and methods. Methods of rapid assessment of the content of α-emitting radionuclides in solid waste of various morphologies using gamma-spectrometers based on germanium detectors are considered. Computational methods for determining the effectiveness of radionuclide registration are presented.

Results. The possibility of using portable gamma-ray spectrometry to assess the surface and specific activity of various materials contaminated with α-emitters (²³²Th, ²³⁵U, ²³⁸U, ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu and ²⁴¹Am) is shown. The calculated values of the registration efficiency of low-energy gamma-emitters obtained by modeling the spatial-energy parameters of the detector are given.
To simplify the solution of this problem, the calculation program used 20 standard templates of various geometries (rectangular, cylindrical, conical, spherical, etc.). The main sources of error in the survey of contaminated surfaces, largesized equipment and building structures were investigated.

Conclusions. The possibilities of portable γ-spectrometry for estimating the volume of RW based on the surface density of contamination of materials with radionuclides of uranium and transuranic elements are investigated. When using γ-spectrometer with a high-purity germanium detector with a range of γ-quanta extended in the low-energy region, radionuclides such as ²³²Th, ²³⁵U,²³⁸U, ²³⁷Np, ²⁴¹Am were determined by their own radiation or by the radiation of their daughter products.
The “problem” element is plutonium, for rapid evaluation of which it is proposed, in accordance with the radionuclide vector methodology, to use ²⁴¹Am, which accumulates during the β-decay of ²⁴¹Pu.
According to calculations, the most likely value of the activity ratio ²³⁹Pu/²⁴¹Am for the object where the work was performed (scaling factor) varies in the range from 5.0 to 9.0.
Based on the results of calculations and experimental studies, the parameters of the efficiency of registration of various α-emitting radionuclides by portable γ-spectrometers. It has been found that for germanium detectors with an absolute efficiency of registering a point source of 7÷15%, it is n×10^–5÷n×10^–4%.

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