RESUMO
The effect of different X ray radiation qualities on the calibration of mammographic dosemeters was investigated within the framework of a EUROMET (European Collaboration in Measurement Standards) project. The calibration coefficients for two ionization chambers and two semiconductor detectors were established in 13 dosimetry calibration laboratories for radiation qualities used in mammography. They were compared with coefficients for other radiation qualities, including those defined in ISO 4037-1, with first half value layers in the mammographic range. The results indicate that the choice of the radiation quality is not crucial for instruments with a small energy dependence of the response. However, the radiation quality has to be chosen carefully if instruments with a marked dependence of their response to the radiation energy are calibrated.
Assuntos
Mamografia/instrumentação , Radiometria/instrumentação , Calibragem/normas , Feminino , Humanos , Mamografia/normas , Doses de Radiação , Radiografia , Radiometria/normas , Padrões de Referência , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
Thick walled cavity ionization chambers are used by primary standard laboratories as primary air kerma standards in 137Cs and 60Co gamma-rays. Application of the cavity theory requires correction for the effects of photon attenuation and scattering in the chamber walls. For more than a decade there have been intensive discussions about the validity of wall correction factors determined by more traditional extrapolation methods versus those calculated by Monte Carlo methods. For existing primary standards the alternative methods lead to results that differ by up to 50% of the correction itself. This report presents both experimental and theoretical results which strongly support the validity of calculated wall correction factors. Moreover, it is demonstrated that, in selected cases, the application of a linear extrapolation method leads to errors in the determination of the air kerma reaching up to 13%.
Assuntos
Algoritmos , Análise de Falha de Equipamento/métodos , Modelos Lineares , Modelos Estatísticos , Garantia da Qualidade dos Cuidados de Saúde/métodos , Radiometria/instrumentação , Radiometria/métodos , Calibragem/normas , Simulação por Computador , Análise de Falha de Equipamento/normas , Garantia da Qualidade dos Cuidados de Saúde/normas , Radiometria/normas , Reprodutibilidade dos Testes , Espalhamento de Radiação , Sensibilidade e EspecificidadeRESUMO
Strontium-89 is an important radiotherapy nuclide in bone palliation. The standardization of 59Sr has been performed at the National Office of Measures (OMH) within the frame of the BIPM CCRI(II)-K2.Sr-89 key comparison. The activity concentration of the 89Sr solution was measured by two different methods. The conventional 4pi beta counting technique was used with two proportional counting measurement systems. The 4pi beta-gamma-coincidence efficiency tracing method was used with a 4pi beta-gamma-coincidence measurement system using 24Na as the tracer radionuclide. The beta efficiencies of each of these counting techniques were nearly 100%. The combined uncertainties of the activity concentration determined by these absolute methods are 0.3%. The general agreement of results between the two methods was 0.5%. The measurement equipment, evaluation methods and results of activity concentration measurements with their uncertainty budgets are reported.
