Design shielding assessment for a nuclear medicine service / Evaluación del diseño de blindaje de un servicio de medicina nuclear

Abstract It is recognized worldwide that the security of radioactive substances is very important and that the design of facilities where these sources are used and stored must cater for the implementation of good security measures, including the shielding of some treatment and diagnostic rooms. The radiation protection assessment of a nuclear medicine facility consists of the evaluation of the annual effective dose both to workers occupationally exposed and to members of the public. This assessment take into account the radionuclides involved, the facility features, the working procedures, the expected number of patients per year, the administered activity, the distribution of rooms, the thickness and physical materials of walls, floors and ceilings and so on. The assessment results were compared to the design requirements established by the Cuban regulatory body in order to determine whether or not, the nuclear medicine facility complies with those requirements, both for workers and for members of the public. The work presented is useful for facility designer that uses unsealed radionuclides and for the regulatory body.

Resumen A nivel mundial se reconoce que la seguridad de las sustancias radiactivas es muy importante y que el diseño de las instalaciones, donde se utilizan y almacenan las mismas, tienen que implementar medidas de seguridad adecuadas, incluyendo el blindaje de algunos locales de tratamiento y diagnóstico. La evaluación de la protección radiológica de una instalación de medicina nuclear consiste en la determinación de la dosis efectiva anual, tanto para los trabajadores ocupacionalmente expuestos a las radiaciones como para los miembros del público. Esta evaluación tuvo en consideración los radionúclidos involucrados, las características de la instalación, los procedimientos de trabajo, la cantidad de pacientes que se espera tratar o diagnosticar por año, la actividad administrada, la distribución de los locales y el espesor de los materiales empleados en las paredes, pisos y techo, entre otros. Los resultados obtenidos de la evaluación fueron comparados con los requerimientos de diseño establecidos por el órgano regulador cubano para determinar si cumplen o no con tales requerimientos para los trabajadores expuestos y miembros del público. El trabajo presentado resulta útil para diseñadores de instalaciones que utilizan sustancias abiertas y para el órgano regulador.

Natural radionuclide content in building materials and gamma dose rate in dwellings in Cuba.

An extensive research project to investigate the radioactive properties of Cuban building materials was carried out because there is a lack of information on the radioactivity of such materials in Cuba. In the framework of this project 44 samples of commonly used raw materials and building products were collected in five Cuban provinces. The activity concentrations of natural radionuclides were determined by gamma ray spectrometry using a p-type coaxial high purity germanium detector and their mean values were in the ranges: 9-857Bqkg(-1) for (40)K; 6-57Bqkg(-1) for (226)Ra; and 1.2-22Bqkg(-1) for (232)Th. The radium equivalent activity in the 44 samples varied from 4Bqkg(-1) (wood) to 272Bqkg(-1) (brick). A high pressure ionisation chamber was used to measure the indoor absorbed dose rate in 543 dwellings and workplaces in five Cuban provinces. The average absorbed dose rates in air ranged from 43nGyh(-1) (Holguín) to 73nGyh(-1) (Camagüey) and the corresponding population-weighted annual effective dose due to external gamma radiation was estimated to be 145+/-40microSv. This value is 51% lower than the effective dose due to internal exposure from inhalation of decay products of (222)Rn and (220)Rn and it is 16% higher than the calculated value for the typical room geometry of a Cuban house.

Studies on internal exposure doses received by the cuban population due to the intake of radionuclides from the environmental sources.

Studies for the determination of radionuclide concentrations in foodstuffs, water and air were carried out in Cuba for the estimation of annual committed effective doses to members of the public as a result of environmental radionuclides via ingestion and inhalation. As a result of these studies, it was possible to determine the concentrations of 226Ra, 210Pb, 210Po, 232Th, 90Sr and 137Cs in different food groups that constitute the diet of the Cuban population, as well as the 222Rn concentrations in air. Based on these results and using previously obtained results for doses due to the 40K body content, the annual committed effective doses due to the intake of studied radionuclides were estimated. An average value of 120+/-4 microSv y-1 was obtained for doses due to ingestion of food and water and the obtained value for 222Rn inhalation was 240+/-1 microSv y-1. Using the representative value obtained previously for 40K (150+/-40 microSv y-1) and assuming a dose of 50+/-50 microSv y-1 for the probable contribution of 220Rn by inhalation, a representative value of 560+/-20 microSv was estimated for the average annual committed effective doses due to ingestion and inhalation of radionuclides for the Cuban population. Obtained values are consistent with the expected results, taking into account the characteristics of Cuban exposure scenarios, with low-activity concentration levels in environmental objects and high air exchange rates in dwellings: These results are in the same order of magnitude as results obtained by other authors and the reference values established by the USNCEAR.