A. Simonits

Calculation of the absolute peak efficiency of gamma-ray detectors for different counting geometries

Abstract A new technique is outlined for the calculation of the full-energy peak efficiency of cylindrical gamma-detectors, including coaxial Ge(Li) detectors. Different source geometries are considered, i.e. point, disk and cylindrically shaped sources. Full account is taken of gamma attenuation in the source and in any interjacent absorbing layer. No simplifying mathematical model is adopted and no Monte Carlo calculations are required. Although this method is to be qualified as semi-empirical, the experimental work involved in it is simple and of common practice in most nuclear laboratories. For the calculations a FORTRAN IV + computer program is presented on a VAX 11/780 machine.

Recommended nuclear data for use in the k0 standardization of neutron activation analysis

Abstract k0 factors (composite nuclear constants) for use in the k0 standardization of reactor neutron activation analysis were experimentally measured with great care in several laboratories. The recommended values thus obtained for the relevant gamma rays of 144 analytically interesting radionuclides are tabulated, together with evaluated values for their associated parameters such as resonance integral to thermal cross-section ratios and effective resonance energies. A classification is also given of the various activation-decay types, to which the data are strictly correlated.

Single-comparator methods in reactor neutron activation analysis

A critical evaluation of different comparator methods is given. The method based on experimentally-determined and convertible comparison factors (k) is considered to be the most suitable for general use. An alternative method is proposed, introducing generalized k0 factors which are independent of irradiation and measuring conditions. This approach combines the simplicity of the absolute methods with nearly the same accuracy attained by the relative ones. It is suggested that k0 factors be compiled in all cases when using single-comparator methods, to allow a continuous re-evaluation.

k0-Measurements and related nuclear data compilation for (n, γ) reactor neutron activation analysis

Recommended k0-factors and related nuclear data for use in (n, γ) activation analysis are given for 72 isotopes. In addition the basic nuclear constants and experimental parameters needed in the k0 standardization method are reviewed. For convenient data reduction, computer programs were developed.

Accuracy and applicability of the k0-standardization method

The present paper deals with the accuracy and applicability of the k0-standardization technique in NAA. Topics included are: user-oriented outline of the method, relevant nuclear data (k0, Q0, ětc.), the non-1/E epithermal flux distribution, small detector separations and/or extended source geometries, (n, γ) reactions with a Westcott-g≠1, primary interferences, subsequent (interrupted) irradiations, the non-constancy of the neutron flux during irradiation, and a final account of the accuracy. Although the paper is written in terms of the k0-methodology, a good deal of the considerations can be transferred to most types of single-comparator standardization.

k0-Measurements and related nuclear data compilation for (n, γ) reactor neutron activation analysis - IIIb: Tabulation

Abstractk0-Factors and related nuclear data are tabulated for 112 radionuclides of interest in (n, γ) reactor neutron activation analysis. Whenever relevant, critical comments are made with respect to the accuracy of literature data for e. g. isotopic abundances, half-lives, absolute gamma-intensities and 2200 m · s−1 (n, γ) cross-sections. As to the latter, a comparison is made with the values calculated from the experimentally determined k0-factors, by introduction of selected literature data for the input parameters.

The accuracy and precision of the experimental α-determination in the 1/E1+α epithermal reactor-neutron spectrum

Some methods for the experimental α-determination in the 1/E1+α epithermal reactorneutron spetrum are critically compared with respect to their accuracy and precision. The analysis is based on the error propagation theory. Besides the general formulae numerical examples are elaborated for specific conditions in the Thetis reactor (Gent) and the WWR-M reactor (Budapest).

Recent advances in the k0-standardization of neutron activation analysis: Extensions, applications, prospects

This paper reports on the contribution made by some cooperating laboratories to the further development of the k0-method. As to the extensions and improvements, emphasis is put on the availability of an Al−0.1% Au reference material for the k0-standardization of NAA, on the counting of large-diameter samples, on the use of a low-energy photon detector, and on the introduction of the Westcott formalism for the handling of “non-1/v” (n, γ) reactions. A survey is given of a large variety of scientific and industrial applications, including the analysis of biological, geological and geochronological samples, various kinds of reference materials, high-purity products and ceramics, and a number of environmental pollution indicators. As shown, the advantage of the k0-standardization will be fully exploited with an increasing level of automation in NAA laboratories. Eventually, new measurements and evaluations of k0-factors and related nuclear data are given in an Appendix.

Modification and generalization of some methods to improve the accuracy of α-determination in the 1/E1+α epithermal neutron spectrum

Some methods described in the literature for the determination of α in the 1/E1+α epithermal neutron spectrum are critically reviewed with respect to their accuracy. The multi resonance—detector method with Cd-covered irradiations, as used by SCHUMANN and ALBERT, is generalized by subtracting the epithermal 1/v-tail and by introducing the effective resonance energy, as defined by RYVES. The two-detector method of RYVES is modified by using Cd-ratio measurements, thus eliminating the introduction of systematic errors due to the inaccuracy of absolute nuclear data. The adapted methods are applied in channel 15 of the Thetis reactor (Gent).

Comparative study of measured and critically evaluated resonance integral to thermal cross section ratios, III

In the present paper, a tabulation is given of recommended Q0-values [the ratio of the resonance integral (I0) to the 2200 m·s−1 cross-section (δ0)] for 107 (n, γ) reactions of interest in NAA, including a revision and updating of formerly published results for 57 isotopes. The values were either critically evaluated from literature, or-in the majority of cases — experimentally determined according to the Cd-ratio method, with a correction for a non-ideal epithermal neutron flux distribution. These Q0-measurements were performed at INW, Gent, at KFKI, Budapest, and occasionally at Risø. A comparison is made with results obtained by other workers or with values derived from δ0s and I0s quoted in recent compilations.