This work shows that nuclear data and neutron flux parameters can be applied to calculate directly the elemental concentrations. Techniques for extracting neutron flux parameters pertaining to the irradiation positions and nuclear data pertaining to the isotopes concerned from measured reaction rates have been previously developed. This method is compared to the comparator and relative methods of activation analysis. The principles, advantages and disadvantages of each method and sources of errors are discussed. It also briefly discusses other factors such as accuracy and precision, sensitivity, detection limits and limit of quantitative determination. The three methods are applied to the analysis of five environmental reference materials. The concentrations of more than 20 elements are determined. The results show a good agreement with the certified and/or literature values.

The Cooperative Research Centre for Catchment Hydrology (CRCCH) has embarked on a research project under the Climate Variability Program to build a tool kit that will include stochastic models to generate climate data. Stochastic models for generating climate data are usually evaluated subjectively by comparing a number of parameters estimated from the historical and the generated data. Models generally use a set of parameters to generate data and these are referred to as the basic parameters. However, there are other parameters or characteristics of the data that also need to be preserved if the generated data is considered to acceptably represent the historical data. A good generated data series should preserve both the basic and other characteristics. In addition to preserving the parameters at the time scale at which the data are generated, parameters at the longer time scales also should be preserved. To assess the generated data automatically, a set of decision rules covering the number of parameters to be preserved and the tolerance of each parameter are defined. These are then applied to generated annual, monthly and daily rainfall data at a number of sites in Australia and found to give satisfactory results. Following further refinement, these rules will be incorporated in the tool kit to enable users to automatically evaluate the generated data.

The half-life of 233Pa has been determined by following the emission rates of eight gamma rays from the decay of 233Pa produced by neutron irradiation of 232Th. Several data evaluation procedures were used in the analysis of the half-life data. The measured half-life resulting from these measurements is 27.02(3) days. An evaluation in conjunction with 4 literature values leads to 26.975(13) days as the current best estimate of the half-life of 233Pa.

Relative gamma-ray emission probabilities in the decay of 226Ra and its decay products have been measured using a HPGe detector. The resulting data have been evaluated together with five previously published sets of 226Ra gamma-ray emission probabilities.

The depth to which contamination has migrated is information that is potentially useful in the process of decontamination of nuclear facilities. Conventionally this information can be obtained by analysing core samples. There are, however, advantages in using a non-destructive, in situ technique to measure migration depths.Such an in situ technique has been developed at Imperial College for the determination of uranium contamination of concrete floors or walls. It uses the energy-dependent attenuation of photon radiation to determine the coefficients of an exponential depth profile of uranium. The in situ results have been compared with those obtained from destructive analysis of core samples using delayed neutron counting (DNC) following neutron activation. DNC is a very rapid and sensitive technique for the measurement of fissile materials such as U-235 and (239)pU.

Techniques for extracting neutron flux parameters pertaining to the irradiation positions and nuclear data pertaining to the isotopes concemed from measured reaction rates have been developed. An adjustment procedure based on the generalized least squares method with incorporates the, evaluated literature nuclear data, estimates of flux parameters and the experimentally measured reaction rates using high resolution γ-ray spectrometry is applied. More precise values of the nuclear data, i.e., thermal neutron cross sections, resonance integrals and γ-ray emission probabilities are thus generated. The irradiation of a multi-element standard (MES) containing 24 elements is carried out in six diffieret positions in two diverse types of reactor in the UK and Russia. It is shown that the improvement in nuclear data is revelaed in moire than 90% of the cases.

Electron conversion spectra from the Rh-103(n,e(-))reaction have been measured with a magnetic beta-particle spectrometer (BILL) at the High Flux Reactor in Grenoble. These spectra were analysed to determine some of the decay characteristics of the excited stares of Rh-104. Energy and emission probability uncertainties of 0.5 eV and 2%, respectively were directly determined for the most intense electron lines. A standard averaging procedure was used to calculate better defined gamma-ray energy and emission probability uncertainties of 0.2 eV and 1%, respectively for the most intense transitions of the excited states of Rh-104. The M3-multipolarity transition of 31.86 keV was determined to have a gamma-ray emission probability of 26.8(15) x 10(-8) per neutron capture. The detailed listing of the evaluated data is accessible on request via the e-mail address kond@lnpi.spb.su.

When determining the recommended value for a physical quantity, the evaluator is sometimes faced with the problem of how best to derive such a value. A literature search often yields discrepant values from different experiments or laboratories. In the present work a number of data evaluation procedures proposed in the last two decades have been tested on randomly generated data sets with different types of outliers. A modified Bayesian procedure is shown to be the most reliable, and this method has been applied to half-life data to give the following values: 137Cs = 10985±12 d, 90Sr = 10544±20 d, 154Eu = 3138.5±0.3 d and 252Cf = 968.0±0.8 d.

A comparison of maximum likelihood (or chi-square) and Bayesian peak fitting techniques shows that the latter can reduce peak intensity uncertainties by a factor of up to ten in the case of closely separated doublets, leading to greatly improved doublet resolution. The need for laboratories to demonstrate the reliability of their chosen peak fitting techniques and measures of peak intensity is also demonstrated.

New measurements of relative gamma-ray emission probabilities in the decay of 101Mo and 101Tc are reported. Previously published conversion-electron data have been used along with the gamma-ray data to formulate self-consistent decay schemes.

A class of fitting functions which provides an adequate representation of a wide variety of Ge detector spectral peaks is proposed. Members of this class are composed of a summation of five functions, containing a total of ten parameters. A new fitting technique, based on Bayesian statistics, is also proposed. By adding a penalty function to the normal chi-square term, this technique improves the speed of convergence and the reliability of the minimization algorithms used during peak fitting. The Bayesian approach offers a satisfactory statistical treatment of peak-area uncertainties, avoiding the often unreliable approximations inherent in most other approaches to uncertainty estimation.

An evaluation has been carried out of previously published gamma-ray emission probabilities in the radioactive decay of 125Sb. Beta branching ratios and internal conversion coefficients have been taken into account in testing the consistency of the total decay scheme. Measurements have also been made of the absolute gamma-ray emission probabilities in 65Ni and 125Sb using a combination of high resolution gamma-ray spectroscopy and 4πβ-γ coincidence techniques

Objective data evaluation procedures involve the use of a formal set of rules rather than subjective judgements to detect, adjust and eliminate rogue measurements during the course of an evaluation. It is necessary to specify explicitly the error probability density function (a function specifying the extent to which experimentalists misestimate the uncertainties in their measurements) in order to establish the reliability of a data evaluation procedure, or to compare the effectiveness of different data evaluation procedures.

Thirty four elements (Al, As, Ba, Br, Ca, Ce, Co, Cr, Cs, Dy, Eu, Fe, Gd, Hf, Ho, K, La, Lu, Mg, Mn, Na, Nd, Rb, Sb, Sc, Sm, Ta, Tb, Th, Ti, U, V, W, Yb) were determined by instrumental neutron activation analysis in the second set of Chinese geochemical standard reference materials (sediments from GSD-9 to GSD-12, soils from GSS-1 to GSS-8, rocks from GSR-1 to GSR-6) using both thermal and epithermal irradiations. Irradiation schemes designed to utilise short, medium and long-lived nuclides were employed in order to analyse major, minor and trace elements with different half-lives. The gamma-ray spectra were measured by Ge(Li) and HP(Ge) detectors. Relevant nuclear data and possible interferences are listed, and analytical results are presented and discussed.

To carry out neutron activation analysis without using multielement standards requires knowledge of (i) the absolute photopeak efficiency as a function of energy of the gamma-ray detector, (ii) nuclear data for each reaction used, and (iii) neutron flux parameters for the irradiation position. The present paper discusses each of these topics and shows an example of the determination of flux parameters and improved nuclear data.