Search

This paper reports on absolute measurements made at the NMISA by the 4π[LS]β-γ coincidence extrapolation technique, which formed part of a key comparison of activity measurements of the radionuclide lutetium-177, a beta-gamma emitter. A detection efficiency analysis based on the decay scheme indicated that the coincidence extrapolation method is feasible for extracting the source disintegration rate of (177)Lu. A simulation was undertaken utilizing the efficiency equations to give an indication of the expected variation of the source count rate with efficiency for different gamma-ray windows. Both the simulation and experiment indicated that the window giving the highest counting efficiency was centered about the 208.4 keV photopeak, with the data showing linear variation in the upper efficiency range. The extracted activity concentration of the (177)Lu solution proved to be highly accurate, being higher than the proposed comparison reference value by 0.15%, well within one standard uncertainty (σ=0.26%) as specified by the NMISA., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

An international Key Comparison of (177)Lu has recently been carried out. Twelve laboratories performed assays for radioactivity content on aliquots of a common master solution of (177)Lu, leading to eleven results submitted for entry into the Key Comparison Database of the Mutual Recognition Arrangement. A proposed Comparison Reference Value (CRV) was calculated to be 3.288(4)MBq/g using all eleven results. Degrees of equivalence and their uncertainties were calculated for each laboratory based on the CRV. Most of the values reported by the participating laboratories were within 0.6% of the CRV., (Copyright © 2012. Published by Elsevier Ltd.)

At the National Metrology Institute of South Africa (NMISA) absolute activity measurements of γ-emitting radionuclides are maintained for longevity on a secondary standard ionization chamber. Because the ionization chamber has lower gas pressure than that normally produced by the manufacturer, this paper focuses attention on explaining a normalization scheme devised to allow NMISA to make use of the manufacturer's supplied radionuclide calibration factors when necessary. The applicability of the procedure is justified through analysis of some results from a comprehensive simulation of the chamber undertaken in an independent study. Comparisons of the derived normalized calibration factors against those obtained through measurement at NMISA are made for a variety of radionuclides. • The NMISA secondary standard ionization chamber calibration process is described. • An explanation of a normalization scheme applied to manufacturer's radionuclide calibration factors is provided. • The effect of reduced current output due to depleted gas within the chamber is analyzed using simulated data. • Comparisons of the derived normalized calibration factors against those obtained through measurement for a variety of radionuclides. • Most secondary standards produced are of radionuclides for dissemination to the nuclear medicine community. [ABSTRACT FROM AUTHOR]

The radionuclides 99m Tc and 57 Co were standardized via absolute liquid scintillation counting techniques. We provide the first technical report on the absolute standardization of 99m Tc using 4 π (LS) e - γ coincidence counting. The low detection efficiency of low-energy conversion electrons translates into a large efficiency extrapolation range. A simulation indicated that the γ -ray interacting with the liquid scintillator introduces curvature to the count rate vs. efficiency relationship, the approximation of the functional form used for extrapolation providing the main measurement uncertainty for 99m Tc. A detection efficiency analysis for both radionuclides is presented. Results from the standardizations, and SIRTI and SIR comparison exercises are reported. [ABSTRACT FROM AUTHOR]

The hypothesis that proximity to the Sun causes variation of decay constants at permille level has been tested and disproved. Repeated activity measurements of mono-radionuclide sources were performed over periods from 200 days up to four decades at 14 laboratories across the globe. Residuals from the exponential nuclear decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ from one data set to another and are attributable to instabilities in the instrumentation and measurement conditions. The most stable activity measurements of alpha, beta-minus, electron capture, and beta-plus decaying sources set an upper limit of 0.0006% to 0.008% to the amplitude of annual oscillations in the decay rate. Oscillations in phase with Earth's orbital distance to the Sun could not be observed within a 10 − 6 to 10 − 5 range of precision. There are also no apparent modulations over periods of weeks or months. Consequently, there is no indication of a natural impediment against sub-permille accuracy in half-life determinations, renormalisation of activity to a distant reference date, application of nuclear dating for archaeology, geo- and cosmochronology, nor in establishing the SI unit becquerel and seeking international equivalence of activity standards. [ABSTRACT FROM AUTHOR]