Protactinium-231 is one of the lesser known actinides, yet the measurement of this radionuclide is central to dating studies in both paleoclimate and nuclear forensics measurements; furthermore, it is important as the immediate parent nuclide of the 227Ac decay chain. In this paper, we present the preparatory work for an upcoming CCRI(II) supplementary comparison of this radionuclide. The material used in this work was of poorly known provenance, and it was necessary to carry out a chemical purification of this material prior to use. A new extraction chromatography resin, TK 400, which has been developed for the separation of 231Pa, was tested at NPL. The aims of the work were achieved; the recovery of 231Pa was ~85%, the decay products were recovered in good yield (~95%) and stable element impurities were removed.

The EMRP project MetroDECOM was concerned with research addressing all aspects of nuclear decommissioning in order to deliver integrity and cost-effectiveness in support of clearance and disposal processes as well as improving safety and accuracy. One of the work packages was focused on the characterisation of materials present on decommissioning. Within this work package, work on scaling factors was aimed at applying the principles set out in ISO 21238:2007 to the measurement of contaminated areas in decommissioning sites. In this paper, we report the progress made under MetroDECOM in identifying decommissioning matrices of specific relevance to nuclear decommissioning within the EU and selecting priority hard-to-measure radionuclides for further study.

Thorium-227 is a potential therapeutic radionuclide for applications in targeted alpha-radioimmunotherapy for the treatment of various types of cancer. To provide nuclear medicine departments involved in Phase I clinical trials traceability to the SI unit of radioactivity (Bq), a standardisation of a radiochemically pure Th-227 aqueous solution has been performed at the National Physical Laboratory. This was achieved via two primary liquid scintillation (LS) techniques -4 pi(LS)-gamma digital coincidence counting (DCC) and 4 pi LS counting. These absolute techniques were supported by the indirect determination of the Th-227 activity via the measurement of the ingrowth and decay rate of the decay progeny by both ionisations chambers and high purity germanium (HPGe) gamma-ray spectrometry. The results of the primary techniques were found to be consistent, both with each other (zeta score = 1.1) and to the decay progeny ingrowth measurements. An activity per unit mass of 20.726 (51) kBq g(-1) was determined for the solution. A procedure has been developed that provided an effective separation of the Th-227 from its decay progeny, which was shown by the effective time zero of the Th-227-Ra-223 nuclear chronometer measured by HPGe gamma-ray spectrometry.

Reliable measurement of Naturally Occurring Radioactive Materials is of significance in order to comply with environmental regulations and for radiological protection purposes. This paper discusses the standardisation of three reference materials, namely sand, tuff and TiO2 to serve as quality control materials for traceability, method validation and instrument calibration. The sample preparation, material characterization via γ, α and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and the assignment of values for both the 4n (Thorium) and 4n+2 (Uranium) decay series are described.

This paper addresses the measurement facilities for pre-selection of waste materials prior to measurement for repository acceptance or possible free release (segregation measurement system); and free release (free release measurement system), based on a single standardized concept characterized by unique, patented lead-free shielding. The key objective is to improve the throughput, accuracy, reliability, modularity and mobility of segregation and free-release measurement. This will result in a more reliable decision-making with regard to the safe release and disposal of radioactive wastes into the environment and, resulting in positive economic outcomes. The research was carried out within "Metrology for Decommissioning Nuclear Facilities" (MetroDecom) project.

The determination of characteristic limits in the measurement of radioactive materials is an important aspect of low-level measurements and the underlying principles are well understood by scientists working on such measurements. ISO 11929:2010 provides a rigorous basis for the systematic calculation of detection limits, but may be difficult to interpret for the routine user. This paper attempts to simplify some of the more arcane aspects of this standard.

The aim of the current work is to develop and validate a radiochemical separation scheme capable of separating both 236gNp and 236Pu from a uranium target of natural isotopic composition (~1g uranium) and ~200 MBq of fission decay products. A target containing 1.2g of UO2 was irradiated with a beam of 25MeV protons with a typical beam current of 30 μA for 19h in December 2013 at the University of Birmingham Cyclotron facility. Using literature values for the production cross-section for fusion of protons with uranium targets, we estimate that an upper limit of approximately 250Bq of activity from the 236Np ground state was produced in this experiment. Using a radiochemical separation scheme, Np and Pu fractions were separated from the produced fission decay products, with analyses of the target-based final reaction products made using Inductively Couple Plasma Mass Spectrometry (ICP-MS) and high-resolution α particle and γ-ray spectrometry.

Thorium-227 is currently undergoing evaluation as a potential radionuclide for targeted cancer therapy, and as such a high chemical purity of the material is required. To establish a reliable procedure for radiochemical isolation of 227Th from the parent 227Ac and decay progeny, which includes the radiotherapeutic 223Ra, the performance of three different separation schemes based on ion-exchange and extraction chromatography have been evaluated. The results suggest that both ion exchange and extraction chromatographic techniques can be successfully used for the separation of 227Th from its decay progeny, however extraction chromatographic resins demonstrate favourable performance in terms of Th recovery and purification from radionuclide impurities.

•This paper reviews the current state of the art for neptunium reference materials.•Options for the production of Neptunium-236 at three institutes are detailed.•Role of reference materials in age dating and forensics measurements is described.•User requirements for the provision of neptunium reference materials are summarised.

Basic equations for age dating through activity ratio measurements are presented and applied to nuclear chronometers based on parent-daughter decay. Uncertainty propagation formulae are derived which relate the relative uncertainty on the half-lives and measured activity ratios with the relative uncertainty on the calculated time of a nuclear event. Particular attention is paid to the case of relatively short-lived radionuclides for which the change in decay rate during the measurement is non-negligible. Mathematical solutions are presented to correct the perceived activity ratio and adapt the uncertainty propagation formulae to complete the uncertainty budget. The formulae have been applied to 140Ba-140La chronometry, which is particularly useful for dating a nuclear explosion through measurement of the produced activity ratio of 140La and 140Ba in a finite time interval. They were also applied to the 227Th-223Ra parent-daughter pair produced for therapeutic use. The impact of inaccuracies in the nuclear decay data on the performance of these nuclear chronometers is shown and discussed.

A multi-detector modular coincidence gamma-ray spectrometer is being designed and constructed for use at the UK's National Physical Laboratory (NPL) for use in direct measurement and metrological standardisation of nuclear decay activities. In its first generation, the NPL National Nuclear Array (NANA) will consist of twelve individual halide scintillation detectors placed in a high-efficiency geometry around a well-defined central point source position. This brief conference paper provides details of the measured detector module and coincidence energy and timing responses for the LaBr3(Ce) detectors which will be used in the NANA array. Preliminary GEANT4 simulations of the array's full energy peak efficiency and expected gamma-ray coincidence response are also presented.

Utilising a chemically purified solution the radioactive half-life of (227)Th has been determined indirectly by observation of the ingrowth of (223)Ra using an ionisation chamber (IC) and for the first time by direct observation of the change in activity with time using a high-purity germanium (HPGe) γ-ray spectrometer. The radioactive decay was observed for ~104 days (~5.6 half-lives) by γ-ray spectrometry and approximately 63 days and 72 days (~3.4 and ~3.9 half-lives) using an ionisation chamber (IC). The resulting half-life values - 18.695 (4) days (IC) and 18.683 (20) days (HPGe) - are consistent and detailed uncertainty budgets are presented for the two measurement techniques. A weighted mean of our results of 18.695 (4) days is inconsistent with the most precise published half-life value of 18.7176 (52) days (Jordan and Blanke, 1967). A critical evaluation of literature data has been performed, indicating a paucity of reliable and independent measurements. Selected independent published values have been used to determine a recommended half-life of 18.697 (7) days. A method has been introduced in the course of this work so that the recommended half-life of (227)Th as determined by ingrowth can be modified if a different (223)Ra half-life has been determined, evaluated and adopted.

We present a brief report on the progress towards the construction of the National Nuclear Array (NANA), a gamma-ray coincidence spectrometer for discrete-line nuclear structure and decay measurements. The proposed spectrometer will combine a gamma-ray energy resolution of approximately 3% at 1MeV with sub-nanosecond timing discrimination between successive gamma rays in mutually coincident decay cascades. We also review a number of recent measurements using coincidence fast-timing gamma-ray spectroscopy for nuclear structure studies, which have helped to inform the design criteria for the NANA spectrometer.

The threat to global security from terrorist attack does not solely arise from illicit use of firearms, explosives or weapons of mass destruction. Terrorist threats will inevitably become more subtle as information and expertise is acquired by terrorist groups, and one vulnerable area is food and the food supply chain. Many laboratories, especially in countries with nuclear programmes, are involved in the routine monitoring of foodstuffs, and will be required to respond with increased food monitoring necessary for ensuring food safety and protecting public health after real (or perceived) contamination of food by either accidental or illicit means. This paper examines the needs for reference and performance testing materials that were identified at an international workshop to discuss this matter held at NIST in 2008, and further refined at a follow-up workshop in 2009.

The isobaric distribution of fission residues produced following the bombardment of a natural uranium target with a beam of 25MeV protons has been evaluated. Decay analysis of thirteen isobarically distinct fission residues were carried out using high-resolution γ-spectrometry at the UK National Physical Laboratory. Stoichiometric abundances were calculated via the determination of absolute activity concentrations associated with the longest-lived members of each isobaric chain. This technique was validated by computational modelling of likely sequential decay processes through an isobaric decay chain. The results were largely in agreement with previously published values for neutron bombardments on 238U at energies of 14MeV. Higher yields of products with mass numbers A~110–130 were found, consistent with the increasing yield of these radionuclides as the bombarding energy is increased.

Organically-bound tritium (OBT) present in the environment represents a proportionately higher hazard than tritiated water due to the increased latency time in the body when ingested. Reference materials are required in order to demonstrate the validity of analysis techniques used to determine the levels of OBT in environmental monitoring programmes. This work describes the production and certification of a new environmental radioactivity standard of OBT which may be used as a reference material in validating such monitoring programmes. Rather than 3H-thymidine, 3H-d-glucose is proposed as an alternative starting material with demonstrated improvements in the medium-term stability when stored at room temperature. At the time of first measurement, no tritiated water could be detected in the standard material, and these tests were repeated twice over a 4-month period with the same result. In addition, the process for standardising the material has been improved via the application of the triple- to double- coincidence ratio (TDCR) technique.

The radionuclides (88)Zr and (89)Zr have been produced by cyclotron irradiation of (nat)SrO with 35 MeV α-particles at a beam current of 15 μA. The thick source production yield of (89)Zr is ~3.1 MBq μA(-1) h(-1). A two-step radiochemical purification utilising anion-exchange chromatography in hydrochloric and hydrofluoric acids has been developed to separate (88,89)Zr from the target material, natural strontium, the target substrate, aluminium, and long-lived (88)Y.

Uncertainty propagation formulae are presented for age dating in support of nuclear forensics. The age of radioactive material in this context refers to the time elapsed since a particular radionuclide was chemically separated from its decay product(s). The decay of the parent radionuclide and ingrowth of the daughter nuclide are governed by statistical decay laws. Mathematical equations allow calculation of the age of specific nuclear material through the atom ratio between parent and daughter nuclides, or through the activity ratio provided that the daughter nuclide is also unstable. The derivation of the uncertainty formulae of the age may present some difficulty to the user community and so the exact solutions, some approximations, a graphical representation and their interpretation are presented in this work. Typical nuclides of interest are actinides in the context of non-proliferation commitments. The uncertainty analysis is applied to a set of important parent-daughter pairs and the need for more precise half-life data is examined.

Radiochemical analysis of 237Np is important in a number of fields, such as nuclear forensics, environmental analysis and measurements throughout the nuclear fuel cycle. However analysis is complicated by the lack of a stable isotope of neptunium. Although various tracers have been used, including 235Np, 239Np and even 236Pu, none are entirely satisfactory. However, 236gNp would be a better candidate for a neptunium yield tracer, as its long half-life means that it is useable as both a radiometric and mass spectrometric measurements. This radionuclide is notoriously difficult to prepare, and limited in scope. In this paper, we examine the options for the production of 236gNp, based on work carried out at NPL since 2011. However, this work was primarily aimed at the production of 236Pu, and not 236gNp and therefore the rate of production are based on the levels of 236Pu generated in the irradiation of (i) 238U with protons, (ii) 235U with deuterons, (iii) 236U with protons and (iv) 236U with deuterons. The derivation of a well-defined cross section is complicated by the relevant paucity of information on the variation of the 236mNp:236gNp production ratio with incident particle energy. Furthermore, information on the purity of 236gNp so produced is similarly sparse. Accordingly, the existing data is assessed and a plan for future work is presented.

We apply a PARADISE-style evaluation to a human-human dialogue corpus that was collected to support the design of a spoken dialogue system for library transactions. The book request dialogue task we investigate is informational in nature: a book request is considered successful if the librarian is able to identify a specific book for the patron. PARADISE assumes that user satisfaction can be modeled as a regression over task success and dialogue costs. The PARADISE model we derive includes features that characterize two types of qualitative features. The first has to do with the specificity of the communicative goals, given a request for an item. The second has to do with the number and location of overlapping turns, which can sometimes signal rapport between the speakers.