P. Robouch

The preparation and homogeneity study of synthetic multi-element standards (SMELS) for QC/QA of k0-NAA

Three new synthetic multi-element standards (SMELS) were developed for testing the performance of the k0-standardization neutron activation analysis (k0-NAA) method when implemented in a laboratory. SMELS consist of a phenol-formaldehyde polymer matrix spiked with different groups of elements according to the half-lives of the formed radionuclides. They are classified as Type I for short-, Type II for medium- and Type III for long-lived radionuclides. This article presents the preparation of SMELS including different aspects such as choice of the matrix and spiking elements, chemical compounds, target concentrations, purity of the matrix and spiking procedure and the homogeneity study for all the spiked elements in order to demonstrate the quality of the produced materials.

Synthetic multi-element standards for QC/QA of k0-NAA: Study of composition, doping procedure and homogeneity

Abstract With the aim to demonstrate the quality of the implementation of k 0 -NAA in a laboratory, synthetic multi-element standards (SMELS) are being developed consisting of an inert material doped with a variety of analytically interesting elements. In the present paper, an outline is given of the results obtained thus far in the development of the SMELS. These results are related to the choice of the doping elements and their optimum concentrations, the selection of the matrix components, the doping procedure itself and the therefrom resulting homogeneity. Further work envisaged is the refinement and optimisation of the above steps, followed by the final preparation, homogeneity control and characterisation of the SMELS.

A Web tool for calculating k0-NAA uncertainties

The calculation of uncertainty budgets is becoming a standard step in reporting analytical results. This gives rise to the need for simple, easily accessed tools to calculate uncertainty budgets. An example of such a tool is the Excel spreadsheet approach of Robouch et al. Here, we present an internet application which calculates uncertainty budgets for k0-NAA. The Web application has built in ‘Literature’ values for standard isotopes and accepts as inputs fixed information such as the thermal to epithermal neutron flux ratio, as well as experiment specific data such as the mass of the sample. The application calculates and displays intermediate uncertainties as well as the final combined uncertainty of the element concentration in the sample. The interface only requires access to a standard browser and is thus easily accessible to researchers and laboratories. This may facilitate and standardize the calculation of k0-NAA uncertainty budgets.

Radiation stability tests of the SMELS materials in the LVR-15 experimental reactor at Řež

Radiation stability of a set of three synthetic multielement standards (SMELS) designed for validation of k0-standardization in neutron activation analysis was tested by monitoring mass and element content changes following irradiation at a high neutron fluence rate (up to 9.1013 n.cm-2.s-1) for stepwise increased periods of time. No mass changes were detected and for all the 26 elements investigated only a chlorine content loss was observed. Thus, radiation stability of the SMELS materials for the given purpose and their suitability for use also in high-power reactors was demonstrated.

Bronze analysis by k0-NAA and PIXE

Five copper alloys were prepared with modern powder metallurgical processes in the frame of the European project ‘Improvement of Means of Measurement on Archaeological Copper-Alloys for Characterisation and Conservation (IMMACO)’ and certified for As, Pb, Sn and Zn mass fractions. Similar in their composition to archaeological bronze alloys, these Certified Reference Materials (CRMs) are to be used for calibration of XRF instruments for characterization of archaeological samples either in the laboratory or in the field. This paper presents and compares the successful contribution of our non-destructive analytical methods (k0-NAA and PIXE) to the IMMACO project and to the certification of the five reference materials.

Target preparation and neutron activation analysis: a successful story at IRMM

Abstract The main task of a target producer is to make well characterized and homogeneous deposits on specific supports. Alpha and/or gamma spectrometry are traditionally used to monitor the quality of actinide deposits. With the increasing demand for enriched stable isotope targets, other analytical techniques, such as ICP-MS and NAA, are needed. This paper presents the application of neutron activation analysis to quality control of “thin” targets, “thicker” neutron dosimeters and “thick” bronze disks prepared by the Reference Materials Unit at the Institute of Reference Materials and Measurements.

Is It Safe to Use Poisson Statistics in Nuclear Spectrometry

The boundary conditions in which Poisson statistics can be applied in nuclear spectrometry are investigated. Improved formulas for the uncertainty of nuclear counting with deadtime and pulse pileup are presented. A comparison is made between the expected statistical uncertainty for loss-free counting, fixed live-time and fixed real-time measurements.

Determination of Burnup Effects in 197Au(n,γ)198Au Prior to Reactor Neutron Field Characterisation

A simple and accurate method is presented to evaluate the burnup effects involved in the neutron activation of 197Au prior to any neutron flux characterisation, based on the spectrometry of the 198Au and 199Au decay gammas. The obtained burnup factor can be used as input for reactor neutron field characterisation techniques using 197Au(n,γ)198Au as a monitor. This way an iterative procedure is avoided.

BCR certified reference materials for reactor neutron dosimetry

A series of reference materials intended for use as activation or fission monitors for neutron fluence rate measurements has been prepared by the Joint Research Centre of the European Commission. Certification has been carried out by expert European laboratories and distribution of the certified reference materials (CRMs) is through the BCR programme of the Commission. The list (18 CRMs) includes materials to cover the complete energy spectrum, and suitable for different irradiation times. Fission monitors are 238UO2 or 237NpO2 in the form of microspheres. Activation monitors are high purity metals (Ni, Cu, Al, Fe, Nb, Rh, or Ti), certified for interfering trace impurities, or dilute aluminium-based alloys, where aluminium is chosen as a suitable matrix for reducing the neutron self-shielding effect. Newly certified materials are IRMM-530R Al-0.1%Au, replacing the exhausted IRMM-530 material, used as comparator for k0-standardization, and three new Al-Co alloys (0.01-1%Co). Two others, in the process of certification are Al-0.1%Ag and Al-2%Sc for thermal and epithermal fluence rate measurements. Other candidate reference materials currently being certified are two uranium-doped glass intended for dosimetry by the fission-track technique.

Method for the determination of neutron field monitor burnup effects by gamma-spectrometry.

A methodological concept is developed to determine the burnup of certain neutron flux monitors in an unknown, intense reactor neutron field. In particular, it is shown how to evaluate the burnup effects involved in the neutron activation of 197 Au prior to any neutron flux characterisation, based merely on the spectrometry of the 198 Au and 199 Au decay gamma rays. Such independent detection method of the burnup factor allows a principally correct evaluation of the specific count rate of the irradiated monitor, which serves as a basic input for the determination of neutron field parameters.