Virginia Peyres

An intercomparison of Monte Carlo codes used in gamma-ray spectrometry

In an intercomparison exercise, the Monte Carlo codes most commonly used in gamma-ray spectrometry today were compared with each other in order to gauge the differences between them in terms of typical applications. No reference was made to experimental data; instead, the aim was to confront the codes with each other, as they were applied to the calculation of full-energy-peak and total efficiencies. Surprising differences between the results of different codes were revealed.

Standardisation and precise determination of the half-life of (44)Sc.

The half-life of the positron-emitter (44)Sc has been determined by following the decay rate with two measurement systems; an Ionisation Chamber and a HPGe detector. The combination of seven results gives a value of T1/2=4.042 (25)h, about 2% higher than the recommended value of T1/2=3.97 (4)h (Browne, 2011) and with a lower uncertainty. This radionuclide has also been standardised by coincidence counting, and liquid scintillation counting techniques. A (44)Ti/(44)Sc generator developed at CIEMAT was used to obtain the (44)Sc solutions used in all measurements.

A novel radionuclide-specific detector system for the measurement of radioactivity at steelworks

A new instrument to detect radioactive contamination in cast steel, slag and fume dust from steelworks is proposed. It is based on an electrically cooled HPGe detector. Experimental data presented show that it matches the requirements of the European Metrology Research Project “MetroMetal” and can replace, with significant advantages, existing equipment. The advantages (energy resolution, better nuclide identification) over common systems (scintillators) as well as drawbacks (lower efficiency) are discussed and typical MDAs values are presented together with the results from measurements of reference sources.

Assessment of the uncertainty budget associated with 4πγ counting

The 4πγ-counting technique is recognized as a powerful primary method for the standardization of radionuclides decaying with abundant gamma emissions. Based on the use of a gamma detector in quasi 4π-geometry, a detection efficiency close to 100% and a low uncertainty can be achieved thanks to the summing effect of subsequent gamma transitions. Uncertainties have to be assigned to the realistic modelling of the source–detector geometry with respect to dimensions, density and material composition, the calculation of the total counting efficiency of the detector for the various emitted radiation, and the effect of possible flaws in the decay scheme of a radionuclide on the calculated total efficiency. Other uncertainty factors pertain to typical metrological sources of uncertainty, such as weighing, nuclear counting with pulse pile-up and system dead-time effects, impurity corrections, decay corrections, timing and frequency, etc. In order to ensure good metrological practices at NMIs, the uncertainties particular to the method are discussed.

Preparation and characterisation of a (226)Ra spiked slag as reference material for radioactive control of steelworks.

One of the issues of the European Research Project MetroMetal is to develop reference materials in order to provide SI-traceable radioactivity monitoring in foundries. For this purpose, a protocol for preparing a set of identical standard slag samples, containing known activity concentrations of (226)Ra, has been developed. This paper describes the preparation of the raw material, the characterisation in terms of its mineralogical, chemical and radiological features, the spiking procedure and the homogeneity testing of the spiked samples.

Radioactive waste management: Review on clearance levels and acceptance criteria legislation, requirements and standards

In 2011 the joint research project Metrology for Radioactive Waste Management (MetroRWM)(1) of the European Metrology Research Programme (EMRP) started with a total duration of three years. Within this project, new metrological resources for the assessment of radioactive waste, including their calibration with new reference materials traceable to national standards will be developed. This paper gives a review on national, European and international strategies as basis for science-based metrological requirements in clearance and acceptance of radioactive waste.

Standardization of Ga-68 by coincidence measurements, liquid scintillation counting and 4πγ counting.

The radionuclide (68)Ga is one of the few positron emitters that can be prepared in-house without the use of a cyclotron. It disintegrates to the ground state of (68)Zn partially by positron emission (89.1%) with a maximum energy of 1899.1 keV, and partially by electron capture (10.9%). This nuclide has been standardized in the frame of a cooperation project between the Radionuclide Metrology laboratories from CIEMAT (Spain) and CNEA (Argentina). Measurements involved several techniques: 4πβ-γ coincidences, integral gamma counting and Liquid Scintillation Counting using the triple to double coincidence ratio and the CIEMAT/NIST methods. Given the short half-life of the radionuclide assayed, a direct comparison between results from both laboratories was excluded and a comparison of experimental efficiencies of similar NaI detectors was used instead.

Standardization of Sn-113.

The radionuclide (113)Sn is a quasi-monoenergetic gamma emitter often used in the efficiency calibration of gamma spectrometers in the energy region around 390keV. This paper presents the results of the standardization of this radionuclide by three methods: integral (4π-γ) counting with a well-type NaI(Tl) detector, liquid scintillation counting applying the CIEMAT-NIST method and 4π coincidence counting (conversion electron-X) with a digital coincidence system.

Measurement of NORM samples with CeBr3 detectors

This paper discusses the use of CeBr3 detectors for the analysis of NORM samples. These detectors have a number of characteristics that make them suitable to field measurements: they can work at ambient temperatures, have better energy resolution than NaI(Tl) detectors for energies over 100keV and do not present the radioactive contamination typical of the lanthanum halides detectors. Results of the measurements made at the laboratory for three reference materials are compared to those made using a conventional HPGe gamma-ray spectrometer system. Spectra from both measurement systems are presented and discussed.

The half-life of 129I

The radionuclide 129I is a long-lived fission product that decays to 129Xe by beta-particle emission. It is an important tracer in geological and biological processes and is considered one of the most important radionuclides to be assessed in studies of global circulation. It is also one of the major contributors to radiation dose from nuclear waste in a deep geological repository. Its half-life has been obtained by a combination of activity and mass concentration measurements in the frame of a cooperation of 6 European metrology institutes. The value obtained for the half-life of 129I is 16.14 (12) × 106 a, in good agreement with recommended data but with a significant improvement in the uncertainty.