S.E.M. Lucas

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.

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.

Half-life of 90Sr — measurement and critical review

Abstract Recent evaluations of the half-life of 90Sr have demonstrated the variable quality of the available experimental data which has prevented the estimation and adoption of a value that commands confidence. In an attempt to reduce the uncertainty in the half-life to an acceptable level, the decay of a 90Sr source has been followed for over six years at NPL. The equipment comprised matching, re-entrant, high-pressure ionization chambers and a long-lived reference source to reduce non-random effects. The experimental technique is described together with the statistical procedure used to analyse the measured data. A half-life value was determined together with an estimate of the associated uncertainties. A new evaluation of the 90Sr half-life has been made, taking account of the new NPL data and other recent measurements. Particular attention has been paid to the experimental techniques used to produce the data and the uncertainties attributed to them. An objective evaluation has been conducted to produce a new recommended half-life value of 10 516 ± 21 days.

131I diagnosis and therapy capsules and low dose rate 125I and 137Cs brachytherapy sources. Calibration of the NPL secondary standard radionuclide calibrator

The radionuclide 131I has important thyroid-related diagnostic and therapeutic applications. The response of the NPL secondary standard radionuclide calibrator has been measured for commercially available 131I capsules used in these applications. The capsules were assayed in the secondary standard ionization chamber using an appropriate jig. They were then dissolved to enable the activity to be accurately measured. A calibration figure relating ionization chamber current to capsule activity was thus derived. As a result of this work, the user has a simple yet accurate method of measuring source activity immediately prior to administration. The saturation characteristics of the ionization chamber have been considered. Treatment of disease by the use of brachytherapy sources is a well established technique. Recent incidents together with an increased awareness of the importance of quality assurance has led to the requirement for a simple but accurate procedure for the measurement of dose rates from such sources. Using a simple holder, the responses of the NPL secondary standard radionuclide calibrator to a range of commercially available brachytherapy sources of 125I and 137Cs have been determined, providing the user with a convenient, traceable in-house calibration facility that meets the necessary accuracy requirements.

The half-life of 192Ir

Abstract The current interest in the use of 192 Ir for brachytherapy prompted a re-evaluation of existing half-life values. Using the evaluation criteria adopted in a recent IAEA-Coordinated Research Programme, it was determined that the uncertainty in the half-life obtained by evaluating published data spanning the last 20 years is too large. Further measurements of the half-life have been carried out using high-pressure re-entrant ionization chambers. The results of these latest measurements are presented together with a re-evaluation of the half-life using the IAEA-CRP criteria. The recommended half-life of 192 Ir is 73.830 ± 0.018 d.

The half-life of 82Rb

Abstract The half-life of 82 Rb was determined by two independent methods. The result obtained was 75.45±0.03 s.

Standardization of 123I

Abstract A solution of 123 I was assayed by five laboratories. The uncertainty of the result was 0.3%, corresponding to one standard deviation of the mean.

The decay of 47Sc

Abstract The decay data of 47 Sc have been remeasured using various methods. The following results were obtained: the half life, t 1 2 = (3.3492 ± 0.0006) d , the γ-ray emission probability, P γ = 0.683 ± 0.004, the transition probabilities for the two β − branches, P β 1 = 0.316 ± 0.006 and P β 2 = 0.684 ± 0.006, the endpoint energies of the two β − spectra, E β 1 = (600.5 ± 1.9) keV and E β 2 = (439.0 ± 1.6) keV, and the internal conversion coefficients, α = 0.0045 ± 0.0003, α K = 0.00406 ± 0.00021, and α L+ = 0.00041 ± 0.00010. These data have been compared with the results obtained from previous measurements.