RESUMO
During the last two years, a triple-to-double coincidence ratio (TDCR) system was assembled and adjusted at the CNEA-LMR, Argentina. The new counting system will add complementary capabilities to the absolute measurements section of the CNEA-LMR. This work describes its implementation and validation. Several checks and a set of beta-emitting standard solutions were used in order to perform the validation experiments. In preliminary measurements, a 3H LNHB solution with reference activity concentration of (119.7+/-0.9) kBq/g on 11 November 2003 was used. The CNEA-LMR TDCR counter gave, at the same reference date, an activity concentration of (120+/-1) kBq/g. Results and improvements are presented in detail. Concerning the asymmetry of the system, the quantum efficiency of the three photomultiplier tubes was studied for different operating conditions of the focusing voltage. The counter also includes an automatic system to change the efficiency by defocusing the photomultipliers and on the other hand, it was coupled to a HPGe detector to also measure beta-gamma coincidences.
Assuntos
Algoritmos , Modelos Químicos , Radioisótopos/análise , Radioisótopos/normas , Contagem de Cintilação/instrumentação , Contagem de Cintilação/métodos , Argentina , Simulação por Computador , Doses de Radiação , Radioisótopos/química , Padrões de Referência , Valores de Referência , Contagem de Cintilação/normasRESUMO
The activity of 72Ga sources produced by irradiation at the IEA-R1 reactor have been performed in a 4pibeta-gamma coincidence system by using the extrapolation technique. The measurements were undertaken selecting two windows in the gamma-channel, in order to check the consistency of the results. A Monte Carlo calculation was performed in order to predict the behavior of the observed activity as a function of the 4pibeta detector efficiency and the results were compared to experimental values.
Assuntos
Algoritmos , Radioisótopos de Gálio/análise , Radioisótopos de Gálio/normas , Contagem de Cintilação/normas , Espectrometria gama/normas , Brasil , Guias como Assunto , Doses de Radiação , Padrões de Referência , Valores de Referência , Reprodutibilidade dos Testes , Contagem de Cintilação/métodos , Sensibilidade e Especificidade , Espectrometria gama/métodosRESUMO
32P and 204Tl solutions were standardized within the frame of the international key comparisons organized by bureau international des poids et mesures, in 2002. The activity concentration of 32P was measured by counting solid sources in a 4pibeta proportional gas flow counter and by liquid scintillation counting. The self-absorption in solid sources for 4pibeta counting and the presence of 33P as an impurity were evaluated. The combined standard uncertainty for 32P was 0.59% in the 4pibeta counting and 0.38% in the liquid scintillation counting. Liquid scintillation counting was used to measure the activity concentration of 204Tl with combined standard uncertainty of 0.35%.