M.J. Woods

The calibration of the 1383 A ionisation chamber for 67Ga

Abstract The standardisation of 67Ga has been carried out giving a calibration figure of 9·93 pA/mCi for the type 1383 A ionisation chamber used without liner. The random uncertainty is ±0·4 per cent for a 99 per cent confidence level, and the systematic uncertainty is estimated at ±1·0 per cent. The half-life was measured as 78·26 ± 0·07 h and that of the 93 keV level is 67Zn as 9·15 ± 0·15 μs. Both uncertainties are for 99 per cent confidence levels.

Standardization of 192Ir

Abstract Two 192 Ir solutions were standardized by NPL and CBNM within the framework of EUROMET project no. 219. The 4 πβ - γ -coincidence method was used for these measurements, a 4 π CsI(Tl) detector for gamma-ray spectrometry, and NaI(Tl) well counter for 4 π -gamma integral counting. The uncertainty of the result was 0.3% corresponding to one standard deviation. Traceability was established to BIPM for the 192 Ir activity measurements.

The calibration of the 1383A ionisation chamber for Sr87m

Abstract The standardisation of Sr87m has been carried out giving a calibration figure of 9·75 ± 0·15pA/mCi for the N.P.L. standard 1383A ionisation chamber used without liner and a value of 0·212 ± 0·002 for the total internal conversion coefficient of the 388 keV gamma ray. The half-life of Sr87m was measured as 2·805 ± 0·003 hr.

Calibration of the NPL secondary standard radionuclide calibrator for 32P, 89Sr and 90Y

Abstract Pure beta particle emitting radionuclides have many therapeutic applications in nuclear medicine. The response of the NPL secondary standard radionuclide calibrator to 32 P, 89 Sr and 90 Y has been measured using accurately calibrated solutions. For this purpose, high efficiency solid sources were prepared gravimetrically from dilute solutions of each radionuclide and assayed in a 4π proportional counter; the source activities were determined using known detection efficiency factors. Measurements were made of the current response (pA/MBq) of the NPL secondary standard radionuclide calibrator using the original concentrated solutions. Calibration figures have been derived for 2 and 5 ml British Standard glass ampoules and Amersham International plc P6 vials. Volume correction factors have also been determined. Gamma-ray emitting contaminants can have a disproportionate effect on the calibrator response and particular attention has been paid to this.

Homogeneity testing of spiked reference materials

As part of a EUROMET project to produce a range of γ-ray emitting radioactive spiked reference materials, a technique, based on analysis of variance, was developed to evaluate the uncertainties in characterising such materials. A particular concern was to ensure that users of these materials are properly informed regarding the consequences of any remaining inhomogeneities in them. A minimum of five random samples of each reference material were counted six times on a suitable γ-ray spectrometer. Once all of the data were collected and normalised, between-sample (MS BS ) and within-sample (MS WS ) variances were calculated. The quantity MS WS includes factors associated with sample measurement such as counting statistics, background stability, detector response stability, source-to-detector geometry and electronic stability. The quantity MS BS includes not only all of the terms in MS WS , but also includes terms for sample inhomogeneity, mass determination and density determination. These quantities enable the following calculation to be performed ; σ mat 2 = σ tot 2 - σ meas 2 where σ tot is the overall uncertainty, σ meas is the measurement uncertainty and σ mat is the uncertainty arising from sample inhomogeneity ; it is assumed here that the effects arising from mass and density determinations are negligible. The value of σ mat is only valid at the sample weight at which it was measured, and data are presented to show the variation of the uncertainty arising from sample inhomogeneity with changing sample weight.

192Ir brachytherapy sources: Calibration of the NPL secondary standard radionuclide calibrator

Abstract The increasing use of brachytherapy sources has highlighted the need to confirm the traceability to national standards of air kerma rate measurements made by suppliers and to provide a simple means for the user to check the activity of such sources. A programme of work has been initiated under the auspices of EUROMET to confirm the traceability to NPL of air kerma rate measurements made by Amersham International plc for wire sources of 192 Ir. Intercomparison exercises are also under way between a number of national laboratories. The wires used in this work have been used to calibrate the NPL secondary standard radionuclide calibrator both in terms of the air kerma rate and the activity, and thus provide the hospital user with the basis of a simple and accurate quality control system for these particular types of source.

The standardization and measurement of decay scheme data of 124I

Abstract The increasing use of Positron Emission Tomography (PET) has highlighted the need to standardize and improve the quality of decay scheme data for some positron emitters. This paper presents the results of such work for 124 I.

Standardisation and measurement of the decay scheme data of 243Am and 239Np

Abstract 243 Am is of great importance as a chemical yield tracer for the radiochemical determination of 241 Am in environmental and other samples. 239 Np can also be used in a similar fashion for 237 Np, although there are significant limitations because of the short half-life. The use of both of these radionuclides has been inhibited by the absence of accurately standardised solutions and the poor quality of the associated decay data, particularly the γ-ray emission probabilities for 239 Np. Standardised solutions of 239 Np alone and of an equilibrium mixture of 243 Am and 239 Np have been prepared, and these solutions have been used in conjunction with an intrinsic Ge spectrometer to measure the relevant γ-ray emission probabilities.

The half-lives of 152Eu and 154Eu

The half-lives of 152Eu and 154Eu have been measured. The values obtained were (4943 ± 4) days and (3138 ± 2) days respectively.

The half-life of 68Ge

Abstract The half-life of 68Ge has been remeasured using a high-pressure ionisation chamber resulting in a value of 270.82 ± 0.27 days.