Radioisotope Thermoelectric Generators (RTGs) are devices capable of converting thermal energy from the decay of radioactive material into electrical energy. These devices were especially used as a source in lighthouses and luminescent navigation markers, for example [1]. This particularity allowed their installation in remote and harsh climate areas, since there are no major maintenance needs and the most common energy options are practically impracticable [1]. Between the years 1970 and 1980, in Russia and the former Soviet Union, several different types of RTGs were produced containing one or more Radionuclide Heat Sources (RHSs), each of the pellets having up to PBq of Strontium-90 activity [1]. This type of source is classified as ‘Category 1’ by the International Atomic Energy Agency (IAEA) and, consequently, linked to a high risk [2]. Thus, the device is made from the union between multiple layers of shielding and corrosion-resistant materials. However, as already mentioned, the low control and maintenance, in addition to the lack of physical limitations that prevent approach to it, can contribute to the relative ease of access to the source [1]. Therefore, using Monte Carlo simulation, this study aims to investigate the doses received by a man and a woman considering a possible accident, that is, it estimates the dose values received with the device fully sealed, as well as a situation of violation of the envelope and exposure of the source. The aim of the study is to analyze the dose received in the organs of a man and a woman from the simulation of a situation in which there is a violation of the shielding and exposure of the radioactive source present inside. In addition, isodose curves are estimated at different distances from the device, in order to trace a radial profile. The scenario modeling is done using the Blender software, which includes the Beta-M type radioisotope thermoelectric generator and the anthropomorphic MESH Phantoms of the man and woman [3]. After this, with the help of another software, the scenario is translated into the MCNP language [4]. Thus, with the source and materials properly defined, the situations with the device fully sealed and then with the open envelope and the exposed source are simulated. It is important to note that all parameters for device modeling were based on the specifications published in the article by Pretzsch et al [5]. From the analysis of the dose values received by the Phantom with the RTG device properly closed and, later, violated and with the source exposed, the risk associated with tampering with these devices becomes clear. Thus, the completely intact shielding proves to be adequately suitable, while exposure to the source is particularly aggravating for risk organs, especially considering long exposure times and small distances in relation to it. The organs most affected were those located in the abdominal region, such as the intestine, bladder, and kidney. Besides these, the cornea was one of the organs that showed the highest dose values.

The authors would like to thank the Brazilian agencies CNPq (Grants 312160/2023-2 (L.P.N), 312124/2021-0 (A.P.P), 309675/2021-9 (W.S.S) and 406303/2022-3), and FAPEMIG (Grants APQ-04215-22, APQ-01254-23 and APQ-04348-23).