The impact of high-energy tailing in high-purity germanium gamma-ray spectrometry on the activity determination of 224Ra using the 241.0 keV emission

Calculation of the detection limits with the least-squares method in gamma-ray spectrometry: A simple procedure

A metrologically consistent procedure for assessing the detection limits of activity measurements for gamma-ray emitters with high-resolution spectrometers using the LSQ method is described and tested. As the input to the assessment, besides the measured contents of the spectral channels, the results of the peak analysis, i.e., the indication and its uncertainty, are used. The unfolding of the spectral region of interest into its components corresponding to the peak representing the indication and its background allows us to take into account the uncertainty budget, describing the uncertainty of the indication and the shape of the corresponding peak, making possible to include these sources of uncertainty in the calculation of the decision threshold. To assess the detection limit, the variance of the indication is calculated as a function of the indication itself, while considering the relative uncertainty of the conversion factor. The variance of the indication observed is approximated by a polynomial of the second order of the indication, thus making it possible to calculate the detection limit analytically. The method was tested on measured spectra using the empirically determined spectral shape of the peak representing the indication. It was shown how the empirically determined shape of an isolated and expressive peak close to the peak representing the indication can be used in the calculation of the decision threshold and how the presence of a peak overlapping with the peak representing the indication affects the decision threshold and the detection limit. It is explained that besides the counting statistics, the sources of uncertainty due to the shape of the peak representing indication also contribute to the decision threshold. However, to the increase of the detection limit over the decision threshold, besides the counting statistic, only the uncertainty of the conversion factor contributes. It is shown that in the presence of the indication, the decision threshold and the detection limit can be used to quantify the comparison between the observed value and the true value of the measurand with a predetermined quantity value in terms of the probabilities of making errors of the first and second kind. The application of the decision thresholds and detection limits to a conformity assessment is proposed.

Absolute emission intensities of the gamma rays from the decay of 224Ra and 212Pb progenies and the half-life of the 212 Pb decay

Absolute gamma-ray emission intensities for 36 characteristic gamma rays from the decay of 224Ra, 212Pb, and their progeny were determined by measuring sources calibrated for activity by means of primary methods based on well-defined high-purity germanium (HPGe) detectors at both NIST and NPL. Results from the two laboratories agree with recent data evaluations, except for gamma rays with low emission intensities. The decay schemes have been re-balanced based on the new results. In addition, the half-life for 212Pb was measured using several HPGe detectors, ionization chambers, and a well-type NaI(Tl) detector.

A new determination of the 68Ga half-life and evaluation of literature data

Inconsistencies within the 68Ga half-life dataset have been repeatedly identified in nuclear decay data evaluations performed over the past decade. In this paper, a half-life has been determined using ionisation chambers measurements and HPGe gamma-ray spectrometry (T1/2 = 67.783(27) min). The current literature has been reviewed and possible causes of discrepancy have been identified, such as neglected contaminant effects, robustness of analysis, and underestimation of systematic effects. This could lead to a significant improvement of the half-life in future evaluations.

Determination of the Terbium-152 half-life from mass-separated samples from CERN-ISOLDE and assessment of the radionuclide purity

Terbium-152 is one of four terbium radioisotopes that together form a potential theranostic toolbox for the personalised treatment of tumours. As 152 Tb decay by positron emission it can be utilised for diagnostics by positron emission tomography. For use in radiopharmaceuticals and for activity measurements by an activity calibrator a high radionuclide purity of the material and an accurate and precise knowledge of the half-life is required. Mass-separation and radiochemical purification provide a production route of high purity 152Tb. In the current work, two mass-separated samples from the CERN-ISOLDE facility have been assayed at the National Physical Laboratory to investigate the radionuclide purity. These samples have been used to perform four measurements of the half-life by three independent techniques: high-purity germanium gamma-ray spectrometry, ionisation chamber measurements and liquid scintillation counting. From the four measurement campaigns a half-life of 17.8784(95) h has been determined. The reported half-life shows a significant difference to the currently evaluated half-life (ζ-score = 3.77), with a relative difference of 2.2 % and an order of magnitude improvement in the precision. This work also shows that under controlled conditions the combination of mass-separation and radiochemical separation can provide high-purity 152Tb.

Ra-224 activity, half-life, and 241 keV gamma ray absolute emission intensity: A NIST-NPL bilateral comparison

The national metrology institutes for the United Kingdom (UK) and the United States of America (USA) have compared activity standards for 224Ra, an α-particle emitter of interest as the basis for therapeutic radiopharmaceuticals. Solutions of 224RaCl2 were assayed by absolute methods, including digital coincidence counting and triple-to-double coincidence ratio liquid scintillation counting. Ionization chamber and high-purity germanium (HPGe) γ-ray spectrometry calibrations were compared; further, a solution was shipped between laboratories for a direct comparison by HPGe spectrometry. New determinations of the absolute emission intensity for the 241 keV γ ray (Iγ = 4.011(16) per 100 disintegrations of 224Ra) and of the 224Ra half-life (T1/2 = 3.6313(14) d) are presented and discussed in the context of previous measurements and evaluations.