RESUMEN
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%.
Asunto(s)
Radioisótopos de Fósforo/análisis , Radioisótopos de Fósforo/normas , Estándares de Referencia , Conteo por Cintilación/métodos , Conteo por Cintilación/normas , Radioisótopos de Talio/análisis , Radioisótopos de Talio/normas , Brasil , Agencias Gubernamentales , Semivida , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , SolucionesRESUMEN
The activity of the pure beta-emitter phosphorus-33 (33P) has been directly determined by the triple-to-double coincidence ratio (TDCR) efficiency calculation technique, thus extending the number of radionuclides that have been standardized by this simple, non-extrapolation liquid scintillation (LS) method. The major advantage of inherently accounting for chemical quenching without the need for additional external measurements is demonstrated. The 33P solution activity concentration was verified by tracing with cobalt-60, utilizing 4pi(LS)beta-gamma coincidence counting. Agreement to within 1.2% confirmed the reliability of the TDCR measurements.
Asunto(s)
Algoritmos , Transferencia Lineal de Energía , Modelos Químicos , Modelos Estadísticos , Radioisótopos de Fósforo/análisis , Radioisótopos de Fósforo/normas , Conteo por Cintilación/métodos , Conteo por Cintilación/normas , Radiometría/métodos , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , SolucionesRESUMEN
An improved triple-to-double coincidence ratio system has been developed to obtain efficiency variation by means of geometrical displacement, that is, three photomultiplier (PM) tubes move back and forth direction from a vial source. The detection unit of the system is located in a cylindrical chamber for light shielding, and a stepping motor connected to the three PM tubes controls the source-to-detector distance up to 50 mm with 1 mm resolution. In activity measurements of 14C and 204Tl using this measurement technique, the efficiencies varied from 0.60 to 0.90 for 14C and from 0.87 to 0.96 for 204Tl. In this study, the characteristics of the system are described as well as data acquisition and analysis methods.
Asunto(s)
Algoritmos , Radioisótopos de Carbono/análisis , Análisis de Falla de Equipo/métodos , Modelos Químicos , Modelos Estadísticos , Radioisótopos de Fósforo/análisis , Conteo por Cintilación/métodos , Radioisótopos de Talio/análisis , Diseño de Equipo , Estudios de Factibilidad , Transferencia Lineal de Energía , Radioisótopos de Fósforo/normas , Reproducibilidad de los Resultados , Conteo por Cintilación/normas , Sensibilidad y Especificidad , Soluciones/análisis , TransductoresRESUMEN
The simultaneous analysis of three radionuclides present in a sample is demonstrated. The approach requires fitting a series of counting data acquired over a period of time to a triple exponential mathematical expression. The use and advantages of the method are illustrated for the case of the standardisation of 32P in the presence of 33P and 35S by 4pi-beta liquid scintillation spectrometry. The effects of sample preparation, chemical quenching and different activity ratios were studied.
Asunto(s)
Algoritmos , Mezclas Complejas/análisis , Modelos Químicos , Modelos Estadísticos , Radioisótopos de Fósforo/análisis , Conteo por Cintilación/métodos , Radioisótopos de Azufre/análisis , Mezclas Complejas/normas , Transferencia Lineal de Energía , Radioisótopos de Fósforo/normas , Radiometría/métodos , Reproducibilidad de los Resultados , Conteo por Cintilación/normas , Sensibilidad y Especificidad , Soluciones , Radioisótopos de Azufre/normasRESUMEN
The liquid scintillation counting standardization of pure-beta solutions containing pure-beta emitter impurities is a difficult task because, unlike that which can be achieved by using gamma-ray spectrometry, the continuous characteristics of beta spectra and the poor intrinsic resolution of LSC spectrometers do not allow an easy identification and precise determination of the activity concentration of these impurities. This problem was recently encountered in the standardization of a 32P solution in the framework of an international comparison, where the activity contribution of the impurities was over 10% of the main nuclide activity at the reference date. This paper describes the method used to identify the impurities in this 32P solution and the calculation of the detection efficiencies using the triple to double coincidence ratio model. Details on the calculation of the uncertainties of each activity and the covariances between these activities are given.
Asunto(s)
Algoritmos , Partículas beta , Modelos Químicos , Modelos Estadísticos , Radioisótopos de Fósforo/análisis , Radioisótopos de Fósforo/normas , Conteo por Cintilación/métodos , Conteo por Cintilación/normas , Control de Calidad , Estándares de Referencia , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , SolucionesRESUMEN
Two solutions, one of 32P with a significant contribution of 33P, and another one of 204Tl were standardized by liquid scintillation counting in the frame of two intercomparison exercises organized by the BIPM in 2002. For the 32P solution, the counting efficiencies for 32P and 33P were obtained by the CIEMAT/NIST method. The individual contributions of 32P and 33P were determined by fitting a set of measurements to a function of the half-lives and counting efficiencies of both component nuclides. 204Tl was also standardized by the CIEMAT/NIST method using two counters, three scintillators, HiSafe 3, Insta-Gel Plus and Ultima-Gold, and two different kinds of samples. A total of 480 samples were measured over 45 days with results in full agreement within the uncertainties considered. The efficiency values are also compared to those used in the previous 204Tl intercomparison (1997).
Asunto(s)
Algoritmos , Radioisótopos de Fósforo/análisis , Radioisótopos de Fósforo/normas , Conteo por Cintilación/métodos , Conteo por Cintilación/normas , Radioisótopos de Talio/análisis , Radioisótopos de Talio/normas , Calibración/normas , Estándares de Referencia , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , SolucionesRESUMEN
The uses of beta-particle emitting radionuclides in therapeutic medicine are rapidly expanding. To ensure the accurate assays of these nuclides prior to administration, radioactivity standards are needed. The National Institute of Standards and Technology (NIST), the national metrological standards laboratory for the United States, uses high-efficiency liquid scintillation counting to standardize solutions of such beta emitters, including 32P, 90Sr/90Y, and 188Re. Additional measurements are made on radionuclidic impurities, half lives, and other decay-scheme parameters (such as branching decay ratios or gamma-ray abundances) using HPGe detectors and reentrant ionization chambers. Following such measurements at NIST, standards are disseminated in three ways: Standard Reference Materials (SRMs), calibrations for source manufacturers, and calibration factors for commercial instruments. Uncertainties in the activity calibrations for these nuclides are of the order of +/-0.5% (at approximately 1-standard deviation confidence intervals).