RESUMO
The present work describes the methodology for predicting the behavior of extrapolation curves obtained in radionuclide standardization by 4pibeta-gamma coincidence measurements, applied to (22)Na, developed at the Laboratório de Metrologia Nuclear of IPEN-CNEN/SP (LMN-Nuclear Metrology Laboratory). The LMN system consists of a proportional counter (PC) in 4pi geometry coupled to a single or a pair of NaI(Tl) scintillation crystals. Two standardization techniques were used: the Sum-Peak and the Nuclear-Peak methods. The theoretical response functions of each detector have been calculated using the MCNPX Monte Carlo code. The code ESQUEMA, developed at LMN, has been used for calculating the extrapolation curve in the 4pibeta-gamma coincidence experiment. Modifications were performed in order to include response tables for positrons and coincidences with annihilation photons. From the calibration results it was possible to extract both the activity value and the positron emission probability per decay. The latter was compared with results from the literature.
RESUMO
A technique for simulating all detection processes in a 4pi(beta,e,X)-gamma coincidence system by means of the Monte Carlo technique is described. This procedure yields a more realistic behaviour of the extrapolation curve as compared to the usual polynomial fit. The present paper describes its application to the standardisation of a typical pure beta emitter, namely 35S, by the efficiency tracing technique, and an EC-gamma radionuclide, namely 133Ba. The calculated extrapolations were compared to experimental values obtained at the IPEN.
Assuntos
Algoritmos , Raios gama , Método de Monte Carlo , Monitoramento de Radiação/métodos , Software , Simulação por Computador , Modelos Químicos , Modelos Estatísticos , Análise Numérica Assistida por Computador , Doses de Radiação , Monitoramento de Radiação/normas , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
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
Cascade summing corrections for application in HPGe gamma ray spectrometry have been calculated numerically by the Monte Carlo method. An algorithm has been developed which follows the path in the decay scheme from the starting state at the precursor radionuclide decay level, down to the ground state of the daughter radionuclide. With this procedure, it was possible to calculate the cascade summing correction for all gamma ray transitions present in the decay scheme. Since the cascade correction requires the values of peak and total detection efficiencies, another code has been developed in order to estimate these parameters for point and cylindrical sources. The radionuclides 60Co, 133Ba and 131I were used for testing the procedure. The results were in good agreement with values in the literature.