M. Blaauw

The holistic analysis of gamma-ray spectra in instrumental neutron activation analysis

Abstract A method for the interpretation of γ-ray spectra as obtained in INAA using linear least squares techniques is described. Results obtained using this technique and the traditional method previously in use at IRI are compared. It is concluded that the method presented performs better with respect to the number of detected elements, the resolution of interferences and the estimation of the accuracies of the reported element concentrations. It is also concluded that the technique is robust enough to obviate the deconvolution of multiplets.

The use of sources emitting coincident γ-rays for determination of absolute efficiency curves of highly efficient Ge detectors

Abstract The effects of coincidence summing in γ-ray spectrometry were used in a novel method to obtain absolute photopeak and total efficiency curves of effi

The 2000 IAEA intercomparison of PIXE spectrum analysis software

Seven programs for analysis of PIXE spectra were compared using the 2000 IAEA test spectra, i.e. Geopixe, Gupix, Pixan, Pixeklm, Sapix, Winaxil and Witshex. A systematic statistical study of the analysis results was performed based on z-scores. The results indicate that most of the programs perform reasonably well with respect to peak areas. Except for a very rare exception, the statistical analysis shows that the participants generally reported smaller uncertainties than would have been expected from the reference uncertainty values. The results show that all the participants reported a number of statistically significant “false hits” and “misses” in their reports. All this indicates that programs in general still leave room for further improvements.

Neutron-Resonance Capture Analysis of Materials.

In this paper neutron resonance capture analysis (NRCA) is explored as a new method to analyse the elemental composition of materials and objects using a pulsed beam of epithermal neutrons and a time-of-flight system to recognize resonances of isotopes in the energy range from about 1 to 10 keV. Some test experiments have been carried out with bronze artefacts. Advantages, as compared to instrumental neutron activation analysis (INAA), are the low activation of the objects and the direct availability of results after the measurement.

Cascade summing in gamma-ray spectrometry in marinelli-beaker geometries: the third efficiency curve

Radionuclides emitting multiple gamma-rays in cascade give rise to summing effects that may be a source of error in the efficiency-curve based interpretation of gamma-ray spectra obtained in highly efficient counting geometries. Correction methods for sources that are small enough for the detector efficiency to be constant over the source volume are well-known. However, in geometries where the detector efficiency is not constant throughout the sample volume, such as Marinelli-beaker geometries, appreciable underestimation of the source activity may still occur if the variation of the efficiencies over the source volume is not accounted for. By introducing a third efficiency curve that accounts for the variation of the detector efficiency over the source volume, we have developed a practical, easy-to-use method that allows for determination of all three efficiency curves from a single, high-resolution gamma-ray spectrum, as well as for accurate correction for cascade summing effects.

The 1995 IAEA intercomparison of γ-ray spectrum analysis software

Abstract In an intercomparison organized by the IAEA, 12 PC-based programs for γ-ray spectrum analysis were tested using seven reference spectra and a sum of squared differences method. It was found that all programs yield peak areas without bias, relative to each other. Most of the programs could analyze a spectrum containing only singlets in reasonable statistical control with respect to peak areas. Peak positions generally are reported with too small or absent uncertainties. Statistical control was found to be lacking in the analysis of doublet peak areas.

Variation of neutron flux and related parameters in an irradiation container, in use with k0-based neutron activation analysis

Profiles of thermal flux, epithermal flux, f and α have been determined for a multisample irradiation container in use with k0-based NAA. It could be concluded that for accurate NAA with the IRI-reactor, samples should be surrounded by at least two thermal flux monitors. Since f and α values were found to vary considerably between irradiations as compared to the variations within one container, the possibility of determining f and α just once for the irradiation facility used, and monitoring only the thermal flux in future irradiations, was ruled out. The use of average values for f and α within a container was shown to yield unacceptable inaccuracies mainly for Zr and U determinations.

IAEA γ-ray spectra for testing of spectrum analysis software

Abstract Test spectra for γ-ray spectrum analysis software intercomparison purposes were created. The spectrum of 226 Ra with progeny was used for this purpose. Peak areas and positions in the test spectra were determined from a spectrum measured under the same conditions but with a much longer counting time. Doublets with varying but known separation and peak area ratios were generated by adding spectra with selected counting times after shifting one of them by a small integer number of channels. A set of seven test spectra and a calibration spectrum are now available for intercomparison purposes.

The confusing issue of the neutron capture cross-section to use in thermal neutron self-shielding computations

In the absence of scattering, the thermal neutron self-shielding as occurs in neutron activation experiments can be corrected for if the macroscopic thermal absorption cross-section of the material is known. It is generally accepted that the average cross-section 〈 Σ 〉 to be used for this purpose differs from the cross-section Σ0 for neutrons with a velocity of 2200 m/s by a factor of φ2. In this paper, it is shown that the correct factor to use in the case of thin samples is not φ2, but 2φ. An empirical formula for the computation of self-shielding factors for samples of intermediate thickness is also presented.

THE 1997 IAEA INTERCOMPARISON OF COMMERCIALLY AVAILABLE PC-BASED SOFTWARE FOR ALPHA-PARTICLE SPECTROMETRY

Abstract Four commercially available, PC-based analysis programs for alpha-particle spectrometry were compared using the 1997 IAEA test spectra, i.e. AlphaVision 1.20 (EG&G Ortec, USA), Alps 4.21 (Westmeier GmbH, Germany), Winner Alpha 4.0f5 (Eurisys Mesures, France) and Genie-2000 (Canberra Industries Inc., USA). A systematic statistical study of the analysis results was performed based on z -scores. The results indicate that the four programs leave room for substantial improvement.