Authors:Rachel Popelka-Filcoff, Claire Lenehan, Michael Glascock, John Bennett, Attila Stopic, Jamie Quinton, Allan Pring, and Keryn Walshe
Ochre is a significant material in Aboriginal Australian cultural expression from ceremonial uses to its application on many
types of artifacts. However, ochre is a complex material, with associated surrounding minerals potentially challenging the
overall analysis. In recent literature several studies have attempted to characterize ochre by a variety of techniques to
understand procurement and trade. However, ochre is difficult to differentiate on major elemental or mineralogical composition
and requires a detailed analysis of its geochemical “fingerprint”. Neutron activation analysis (NAA) provides the high sensitivity
(sub-ppm), precision and accuracy in multi-elemental analysis required for ochre. The elements of interest for ochre generally
include rare earth elements (REEs) and certain transition metal elements as well as arsenic and antimony. Data from relative
comparator NAA (MURR, University of Missouri, USA) is compared with data from k0-NAA OPAL (ANSTO, Lucas Heights, Australia). A discussion of the two methods will be examined for their utility in “fingerprinting”
the provenance of ochre. The continuing importance of NAA to archaeometry will also be discussed.
Since 1996, two new cases were detected in our laboratory for which the elemental concentrations derived from k0 neutron activation analysis seem questionable. These cases concern the inconsistencies observed (1) in the concentration of Ca obtained via 47Ca and 47Sc, and (2) in the concentration of Yb obtained via the 228.5 and 396.3 keV lines of 175Yb. A recommendation is made to re-evaluate the corresponding k0-values or true-coincidence correction factors.
A novel method is presented for the calculation of uncertainties of neutron flux parameters and element mass fractions and
their uncertainties in k0-neutron activation analysis (k0-NAA) using the Kragten universally applicable spreadsheet technique. The results obtained are compared with other approaches
for evaluation of uncertainties of the neutron flux parameters and element mass fractions, namely with the Kayzero for Windows,
k0-IAEA and ERON programs. The differences observed are discussed in terms of how the above programs take into account various
uncertainty sources and their correlations.
The GammaLab is a collection of computer codes, written in MATLAB, for performing calculations involved in k0 neutron activation analysis. The main features of the program include calibrations including energy-channel, energy-FWHM
and energy-efficiency for different geometries, background subtraction, nuclide identification, spectral interference correction,
elemental concentration and limit of detection determination. The data input is taken from two files one is the spectrum file
stored in IAEA ASCII format and other is report file containing peak energy and peak area data. The information about sample,
irradiation and counting conditions, background spectra are retrieved from QAQCData database. GammaLab takes nuclear data
such as gamma lines, emission probabilities, half-lives, and k0 factors from NucData database. The sample results which contain elemental concentrations with uncertainties are stored in
the QAQCData database. The program has been evaluated by analyzing several hundred spectra and results were found satisfactory.
The Algerian research reactor (Es-Salam) is a 15 MW heavy water reactor type, operating since 1992. It became essential to
characterize the neutron field in the most useful irradiation positions, in order to guarantee the accuracy in the application
of k0-neutron activation analysis (k0-NAA). Experimental value of the thermal to epithermal neutron flux ratio (f) and of the deviation of the epithermal neutron spectrum from 1/E shape (α) were determined using different methods. This work focuses the verification of Monte Carlo neutron flux calculation
in typical irradiation channel. Comparison of the results for parameter f obtained experimentally and by Monte Carlo simulations
shows good agreement in the irradiation channel studied. The difference between both results is about 2.08%.
The Portuguese Research Reactor (RPI) is a 1 MW swimming pool type reactor, operating since the early 1960s. The fuel is MTR type, with flat plates of U-Al alloy enriched to 93% in 235U. As the core configuration changed in April 2000, it became essential to characterise the neutron field in the most useful irradiation positions of RPI, in order to guarantee the accuracy in the application of k0-neutron activation analysis (k0-NAA). Experimental values of the thermal to epithermal neutron flux ratio (f) and of the deviation of the epithermal neutron spectrum from the 1/E shape (a) were determined using the Cd-ratio for multi-monitor method. The neutron temperature (Tn) was obtained from co-irradiation of Lu with 1/v
monitors. The results for several irradiation positions are presented and discussed in this work. Some element concentrations are determined based on the parameters obtained in this work, and compared with the certified reference material concentrations.
Authors:F. Farina Arboccò, K. Strijckmans, P. Vermaercke, L. Verheyen, and L. Sneyers
Reactor channel characterization is commonly performed by irradiating bare and cadmium-covered “fluence rate monitors”, avoiding
as much as possible the use of irradiation vials and spacers to position the monitors inside the channel. However, in routine
k0-Neutron Activation Analysis often samples are packed in small polyethylene vials prior to irradiation. This work aims at
studying the impact of typical NAA polyethylene vials (~1 mm wall thickness) on the determination of the f and α channel-specific parameters through the “Bare”, “Cadmium-Covered” and “Cadmium-Ratio” methods. The impact of these vials
on each method was studied for 3 irradiation channels of the Belgian Reactor 1 at SCK·CEN (Mol, Belgium) with low to high f and α-values. The net impact was 1% on each parameter. Inconsistencies between the different methods were found when the impact
of the polyethylene was neglected, implying that all determination methods must be pooled and thin monitors should be used
for an accurate channel characterization.