Consistency test of coincidence-summing calculation methods for extended sources.

An internal consistency test of the calculation of coincidence-summing correction factors FC for volume sources is presented. The test is based on exact equations relating the values of FC calculated for three ideal measurement configurations. The test is applied to a number of 33 sets of FC values sent by 21 teams. Most sets passed the test, but not the results obtained using the quasi-point source approximation; in the latter case the test qualitatively indicated the magnitude of the bias of FC.

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.

Measurement of absolute γ-ray emission probabilities in the decay of 227Ac in equilibrium with its progeny.

The emission probabilities of γ rays produced in the 227Ac decay series were determined by high-resolution γ-ray spectrometry of sources with standardised activity. The sources were prepared quantitatively on glass discs by drop deposition of a solution with 227Ac in radioactive equilibrium with its daughter nuclides. Their activity was measured by a primary standardisation technique based on alpha-particle counting at a defined low solid angle. Four laboratories performed γ-ray spectrometry and derived absolute γ-ray intensities. Mean values were calculated and compared with literature data and the currently recommended evaluated data. New values on certain γ-ray emission probabilities are proposed.

Measurement of absolute γ-ray emission probabilities in the decay of 235U.

Accurate measurements were performed of the photon emission probabilities following the α decay of 235U to 231Th. Sources of highly enriched 235U were characterised in terms of isotopic composition by mass spectrometry and their activities were standardised by means of alpha-particle counting at a low defined solid angle. The standardised sources were subsequently measured by high-resolution γ-ray spectrometry with calibrated high-purity germanium detectors to determine the photon emission probabilities. Four laboratories participated in this work and reported emission probabilities for 33 γ-ray lines. Most of them agree with previously published evaluated data. In addition, new values are proposed for γ-lines which have been measured only once in the past.

Use of a Si(Li) detector as ß spectrometer.

The aim of this work is to demonstrate the capability of a Si(Li) detector for the measurement of ß spectra, despite the energy absorption in air and in the Be window. A simple source holder fixes the source on the symmetry axis at 3mm from the detector window. The ß-sources are produced by evaporation on a plastic backing plate. Absorbing materials between the source and the sensitive volume of the detector are 3 mm of air, a Be window, 0.1 µm Si and 20 nm of gold. A model of the detector was created for ß spectra simulation using the MCNP 4A code. Experimental spectra of (14)C, (147)Pm, (204)Tl, (90)Sr/(90)Y were compared with simulated spectra.

Activity measurement of gamma-ray emitters in aerosol filters exposed in Lithuania, in March-April 2011.

Two aerosol sampling stations in Lithuania were simultaneously used for assessing consequences of the accident at the Fukushima Dai-ichi nuclear power plant. The maximum activity concentrations of (129 m)Te, (131)I, (134)Cs and (137)Cs were 0.59 ± 0.06, 3.5 ± 0.3, 0.90 ± 0.08, 0.90 ± 0.07 mBq m(-3) at station #1 in Vilnius, and 0.29 ± 0.03, 1.0 ± 0.1, 0.41 ± 0.04, 0.41 ± 0.0 4 mBq m(-3) at station #2 in northeastern part of Lithuania, respectively.

Correction of the TRUE summations in volume sources.

The correction factors for volume sources may be approximated using average efficiencies determined by experiment or by Monte Carlo methods in the same way as for point sources. This simple technique does not take into account properly the absorption of photons in the source, nor the change of the effective solid angle. A more precise method must take into account for the spatial distribution of products of efficiencies η(peak)*η(total) (for summing-out) or η(peak)*η(peak) (for summing-in) over the volume of the source. The differences between the approximate and the more precise method are discussed.

Standardization, decay data measurements and evaluation of 64Cu.

The purposes of this study were to create national activity standards of (64)Cu, to make possible the definition of an international key comparison reference value and to determine the decay data in order to improve the decay scheme. Four laboratories measured the activity of a (64)Cu solution; these results were compared through the International Reference System. Moreover, the laboratories carried out new measurements of the photon emission intensities and of the half-life. A new decay scheme was derived from these new values and the previously published ones.

Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry--part II (volume sources).

The second part of an intercomparison of the coincidence summing correction methods is presented. This exercise concerned three volume sources, filled with liquid radioactive solution. The same experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing corrective factors for several energies of (152)Eu and (134)Cs, and different source-to-detector distances. They are presented and discussed.

Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry.

A comparison of the coincidence summing correction methods is presented. Since there are several ways for computing these corrections, each method has advantages and drawbacks that could be compared. This part of the comparison was restricted to point sources. The same experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing correction factors for several energies of (152)Eu and (134)Cs, and three source-to-detector distances. They are presented and discussed.

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.

The new IAEA-372 grass-certified reference material for (40)K and (137)Cs.

A new grass-certified reference material characterized for (137)Cs and (40)K has been issued by the International Atomic Energy Agency. Characterization of this material was conducted by a group of national metrological institutes and expert laboratories. The paper describes the process for assigning the certified reference value to the material.

Determination of emission probabilities of gamma photons in the decay of (56)Co.

The emission probabilities of gamma photons in the decay of (56)Co were determined at Czech Metrology Institute (CMI) by means of an HPGe detector. This detector was calibrated experimentally and by MCNP-computation in the energy range from 40 to 2754keV for a point source geometry and source-to-detector distance of 25cm. Experimental and computed peak and total efficiencies were compared and calibration curves were determined. Full-peak efficiencies were calculated for all (56)Co gamma-ray energies, and were used to calculate the emission probabilities. A set of point sources was prepared from a (56)Co solution. The solution was standardized using the 4pibeta-gamma coincidence method, and an ampoule was sent to international reference system for activity measurement of gamma-ray emitting radionuclides (SIR). Each point source was measured with the HPGe detector at a source-to-detector distance of 25cm. Coincidence emission probabilities of all the gamma photons were calculated and used to determine the summing correction factors.

Experience with checking potentially contaminated materials released to the environment and testing of the measuring instruments used

Several systems with large area plastic scintillators were tested, which are used to avoid the undesirable and illegal transport of radioactive materials especially at border crossings, in metallurgical works and in plants processing metal scrap, were tested. Measuring equipment with germanium detectors, which is used for check of material released from the Dukovany Nuclear Power Plant, was also tested. The detection possibilities of a chamber with plastic scintillators, for the use during checking of materials released to the environment, were investigated.