Julian Dean

Radiocarbon dioxide detection based on cavity ring-down spectroscopy and a quantum cascade laser

Monitoring of radiocarbon (C14) in carbon dioxide is demonstrated using mid-infrared spectroscopy and a quantum cascade laser. The measurement is based on cavity ring-down spectroscopy, and a high sensitivity is achieved with a simple setup. The instrument was tested using a standardized sample containing elevated levels of radiocarbon. Radiocarbon dioxide could be detected from samples with an isotopic ratio C14/C as low as 50 parts-per-trillion, corresponding to an activity of 5  kBq/m(3) in pure CO(2), or 2  Bq/m(3) in air after extraction of the CO(2) from an air sample. The instrument is simple, compact, and robust, making it the ideal tool for on-site measurements. It is aimed for monitoring radioactive gaseous emissions in a nuclear power environment, during the operation and decommissioning of nuclear power plants. Its high sensitivity also makes it the ideal tool for the detection of leaks in radioactive waste repositories.

An intercomparison of 222Rn measurement systems in European laboratories

Abstract Recent years have seen an increase in awareness of the health hazards posed by environmental 222 Rn. This has led to a large increase in the number of studies pertaining to this nuclide, which in turn has led to a requirement for standards and calibration facilities. A recent meeting of European national standards laboratories (under the EUROMET scheme) revealed that many laboratories had developed (or were developing) measurement systems for 222 Rn. It was decided that an intercomparison of these systems would serve to demonstrate the consistency of measurements being made within EUROMET laboratories and increase confidence among participants. A subsequent survey conducted by the National Physical Laboratory led to the establishment of an intercomparison involving thirteen laboratories (including NPL itself). NPL conducted the intercomparison exercise by generating and standardizing a set of 222 Rn samples, and dispatching a unique subset of samples to each participating laboratory. The laboratories measured their samples and reported the results to NPL. The results of the exercise are presented and discussed.

A review of NPL Environmental radioactivity measurement intercomparison exercises: 1989–1995

Abstract Since 1989 the National Physical Laboratory (NPL) has conducted a series of five intercomparison exercises directed initially at the environmental radioactivity measurement community in the UK, but now open to overseas participants. The complexity of the intercomparison samples has increased with time. In general the results have been encouraging, but some problems have been highlighted, such as cascade summing and the sources of nuclear data. The intercomparisons are reviewed and the changes and improvement observed over time are discussed. The implications for quality assurance are also addressed.

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.

56Co standardization and half-life

Abstract A recent study of radionuclides used for the calibration of gamma-ray detection systems highlighted 56 Co as one for which a better half-life value and improved standards are required. A EUROMET project was established between three national standards laboratories to standardize a solution of 56 Co and to conduct new measurements of the half-life. The standardization results agreed within the uncertainties. For the half-life, values of 77.210±0.028 and 77.290±0.040 d were obtained. After a re-evaluation of published half-life data, a value of 77.233±0.027 d is recommended.

Standardisation of positron-emitters in gas with the NPL primary gas counting system

A primary standard for positron-emitters in gas has been developed. The method involves internal gas proportional counting and the use of the PENELOPE Monte Carlo code to determine corrections for counting losses. The development work was carried out using (11)C, although the method can be applied to other positron emitters. The results were compared with measurements of (11)C (in solution) carried out using a secondary standard re-entrant ionisation chamber previously calibrated with reference to absolute counting techniques.

A review of data obtained in a series of radioactivity measurement intercomparison exercises in the UK: γ-ray emitters 1989–1994

During the past 5 years, the National Physical Laboratory (NPL) has conducted a series of four intercomparison exercises directed at the environmental radioactivity measurement community in the UK. In general, the results have been encouraging but some problems have been highlighted, such as cascade summing and the sources of nuclear data. The intercomparisons are reviewed and the changes and improvements observed over time are discussed. The implications for the UK National Measurement Accreditation Service (NAMAS) are also addressed.

A second intercomparison of 222Rn measurement systems in European laboratories

Abstract A recent intercomparison exercise (established under the auspices of EUROMET) involving seventeen laboratories was conducted by NPL, who generated and standardised a set of glass-encapsulated 222Rn samples and then dispatched a unique subset of the samples to each participant. The reported measured activities of the samples were normalised to the NPL values. The spread of results, for the laboratories who had participated in an earlier exercise, was of the order of ± 5%; the results of 12 of the participants agreed at the 1 σ level.

Evaluation of the response of tritium-in-air instrumentation to HT in dry and humid conditions and to HTO vapor

Abstract Nuclear plant operators (power generation, decommissioning and reprocessing operations) are required to monitor releases of tritium species for regulatory compliance and radiation protection purposes. Tritium monitoring is performed using tritium-in-air gas monitoring instrumentation based either on flow-through ion chambers or proportional counting systems. Tritium-in-air monitors are typically calibrated in dry conditions but in service may operate at elevated levels of relative humidity. The NPL radioactive gas-in-air calibration system has been used to study the effect of humidity on the response to tritium of two tritium-in-air ion chamber based monitors and one proportional counting system which uses a P10/air gas mixture. The response of these instruments to HTO vapour has also been evaluated. In each case, instrument responses were obtained for HT in dry conditions (RH ~2%), HT in 45% Relative Humidity (RH), and finally HTO at 45% RH. Instrumentation response to HT in humid conditions has been found to slightly exceed that in dry conditions.

Development and Testing of a Prototype Modular Tritium and Carbon-14 Gas Environmental Monitoring System

Abstract Increasing quantities of radioactive waste are being placed into storage facilities. Many of the waste products contain organic materials which may undergo degradation leading to the release of tritium and carbon-14 species into waste containers and potentially into the environment. Monitoring for radioactive gas releases are required for environmental regulatory compliance and for radiation protection of facility workers. Research is currently being undertaken at the National Physical Laboratory (NPL) as part of a European Metrology Research Programme (EMRP) project MetroRWM to adapt and automate existing environmental sampling techniques for tritium and carbon-14 species. An innovative modular system is being developed which will lead to the introduction of an on-site small scale system capable of gas collection, liquid scintillation sample preparation and measurement. This paper outlines the evaluation of a liquid scintillation system that has been performed to date using active solutions of spiked trapping medium of similar activity concentrations to those anticipated in a waste repository. This system will operate using pre-set conditions for quench and luminescence derived from these and subsequent trials, unlike most other counters for which corrections for these phenomena are applied post measurement.