Activity measurements and determination of nuclear decay data of 166Ho in the MRTDosimetry project.

Holmium-166 is a high-energy ß--emitter radionuclide (~ 1.8 MeV) with a short half-life (~26.8h) that offers great potential as an alternative to 90Y for the treatment of liver cancer based on radioembolization. The possibility of quantitative Single Photon Emission Computed Tomography (SPECT) imaging of the main γ-ray emission at 80.6 keV, in addition to strong paramagnetic properties suitable for Magnetic Resonance Imaging (MRI), complement this therapeutic potential. The present paper describes the measurements carried out in three European radionuclide metrology laboratories for primary standardization of 166Ho and new determinations of X- and γ-ray photon-emission intensities in the framework of the European EMPIR project MRTDosimetry. New half-life measurements were also performed.

Application of "wet" extrapolation method for activity standardisation of electron capture radionuclides.

The activity of electron capture radionuclides is usually determined by 4pi(proportional counter, PC)-gamma coincidence counting. The corrections necessary for the final activity value calculation are obtained by an extrapolation method. Variation of the PC detection efficiency can be achieved through different methods, e.g. by changing the self-absorption of the source using absorbing foils or by adding carriers. Another possibility is a "wet" extrapolation method, which utilises an absorption change during the drying of a water droplet added onto the source surface. In this paper, slopes of extrapolation curves and resulting activity values obtained by different methods are compared for several radionuclides ((54)Mn, (139)Ce, (88)Y, (57)Co). In some cases a digital coincidence system was used for the analysis of measured data. The "wet" extrapolation, due to its very simple procedure, seems to be convenient for routine measurement and its accuracy is similar to the other methods.

International exercise on 124Sb activity measurements.

An international exercise, registered as EUROMET project no. 907, was launched to measure both the activity of a solution of (124)Sb and the photon emission intensities of its decay. The same solution was sent by LNE-LNHB to eight participating laboratories. In order to identify possible biases, the participants were asked to use all possible activity measurement methods available in their laboratory and then to determine their reference value for comparison. Thus, measurement results from 4pibeta-gamma coincidence/anti-coincidence counting, CIEMAT/NIST liquid-scintillation counting, 4pigamma counting with well-type ionization chambers and well-type crystal detectors were given. The results are compared and show a maximum discrepancy of about 1.6%: possible explanations are proposed.

International exercise on 124Sb photon emission intensities determination.

An international exercise, registered as EUROMET project no. 907, was launched to measure both the activity of a solution of (124)Sb and the photon emission intensities of its decay. The same solution was sent by LNE-LNHB to eight participating laboratories, six of which sent results for photon emission intensities both in absolute and in relative terms. From these results and including previous published values, a consistent decay scheme was worked out, proving that problems in activity measurements have not been due to decay scheme data.