The epithermal neutron spectrum shape parameter in nuclear reactors is explained from a theoretical point of view in terms of the neutron slowing down density function. The latter is approximated by Fermi's age theory. Values for are calculated for a simple approximation of a nuclear reactor: a disk shaped fission neutron source in an infinite graphite moderator. The model produces -values with the correct sign and magnitude, compared to experimental values from the literature, determined in a real reactor. It is shown that varies strongly with distance to the neutron source and less strongly with neutron energy. The inappropriateness of average -values, obtained from the slope of quasi-straight lines produced by log-log plots of E– versus E, for the correction of non-ideal epithermal neutron activation is discussed. Conclusions are formulated concerning the impact of an energy dependent on comparator type NAA.
Authors:Lin Xilei, F. De Corte, L. Moens, A. Simonits, and J. Hoste
USGS BCR-1 and G-2, NBS 1633a Coal Fly-Ash and a 7-element synthetic standard for biological material have been analysed in this work by reactor NAA, using the k0-standardization method. The analyses were performed independently in the analytical laboratories of the Institute for Nuclear Sciences (INW), Gent, and the Central Research Institute for Physics (KFKI), Budapest. This procedure allowed not only a comparison with the specified data or with other published values, but enabled a check of the consistency of our own results obtained in largely different experimental circumstances. As concluded the k0-standardization method combines general versatility (with respect to irradiation and counting conditions) with good accuracy, while keeping the experimental work as simple as possible. Since the k0 method is a computer-oriented technique, a FORTRAN IV program was designed and applied on a VAX 11/780 machine.
is dominated by the first lowest resonance energies for a given nuclide, making its vulnerability to literature updates of resonance parameters almost equal to those of individual resonances. The effect, on the epithermal and total activation of specific nuclides, of large systematic and statistical errors on
is calculated for final NAA results in terms of concentrations, botained by a comparator technique based on the197Au reference nuclide. Conclusions are drawn concerning the impact of the foregoing on the usefulness of comparator type reactor NAA as an alternative to classical NAA using multi-element standards.
Passive air samplers (polyurethane foam disks) were deployed at 25 urban sites and 66 rural sites over the period of July
to October 2005, partly between October 2005 and January 2006 for about 120 days across China, and analyzed for extractable
organo-chlorine /-bromine /-iodine (EOCl/EOBr/EOI) and polychlorinated biphenyls (PCBs) using hybrid neutron activation analysis
(NAA) combined with gas chromatographymass spectrometry (GC-MS). The average concentration of EOCl, EOBr, EOI and ΣPCBs among
all the sites were 173.7, 3.5, 1.0 and 0.74 ng/d, respectively. Higher values of EOCl/Br/I and PCBs were detected in the areas
of high usage and high emission, which were linked to relatively high-income areas in China, while lower in the west ill-developed
region of China, which indicated that these pollutants mainly came from industrial pollution. Higher EOCl contents in traffic
areas stated that the exhaust emission from vehicle was another main source of organochlorines in the air. The relative proportions
of the known organochlorines (84 PCB congeners) to total EOCl were 0.02–3.0%, which implied that most of EOCl measured in
air were unknown.
The neutron spectra of one outer (#10) and two inner (#2 and #3) sites of the Dalhousie University SLOWPOKE-2 reactor (DUSR) have been calibrated for the k0-based neutron activation analysis (k0-NAA). The parameters determined include the cadmium ratio (RCd), epithermal neutron flux shape factor (), subcadmium-to-epithermal neutron flux ratio (f), thermal-to-fast neutron flux ratio (fF), modified spectral index r()(Tn/T0)1/2, Westcott gLu(Tn)-factor, and absolute neutron temperature (Tn). The a-values of -0.0098±0.0045 and -0.0425±0.0047 and -0.0422±0.0053 and f-values of 57.1±2.2 and 18.8±0.4 and 18.9±0.4 were obtained for the sites #10, #2 and #3, respectively. The modified spectral index (MSI), gLu(Tn)-factor, and Tn have been determined for the handling of non 1/v (n,) reactions. The accuracy of the method was evaluated by analyzing reference materials.
Authors:Tatyana Baptista, Marcelo Redígolo, Cibele Zamboni, Ivone Sato, and Jose Marcelino
The World Health Organization states that envenomation is responsible for a high number of deaths per year, especially in
equatorial areas. The only effective specific treatment is the use of hyperimmune serum (antivenom). In Brazil, Crioula breed
horses are used for antivenom production, with great importance in the maintenance of public health programs. A strict biochemical
and metabolic control is required to attain specificity in antiserum. Inorganic elements represent only a small fraction of
whole blood. Nonetheless, they play important roles in mammalian metabolism, being responsible for controlling enzymatic reactions,
respiratory and cardiac functions and ageing. In this work, whole blood samples from Crioula breed horses were analyzed by
EDXRF technique. The reference interval values were determined for the elements Na (1955–2013 μg g−1), Mg (51–75 μg g−1), P (523–555 μg g−1), S (1628–1730 μg g−1), Cl (2388–2574 μg g−1), K (1649–1852 μg g−1), Ca (202–213 μg g−1), Cu (4.1–4.5 μg g−1) and Zn (2.4–2.8 μg g−1) and a comparative study with NAA results was outlined. The samples were obtained from Instituto Butantan. Both techniques
showed to be appropriate for whole blood sample analyses and offer a new perspective in Veterinary Medicine.
Authors:D. Tenorio, M. G. Almazán-Torres, F. Monroy-Guzmán, N. L. Rodrígiez-García, and Luis C. Longoria
Ceramic samples found in San Miguel Ixtapan, Mexico State, Mexico, were analyzed by means of NAA, PIXE, SEM and XRD. Statistical
treatments such as bivariate cluster and principal-components analysis were applied to the data set. The origins of these
ceramic samples were classified as local, regional and foreign.
The use of a Zr-Au-Lu alloy allows the simultaneous determination of all neutron spectrum parameters relevant to the k-0standardization of NAA, in terms of both the Høgdahl and the Westcott convention. The present paper reports on the fundamental aspects (theoretical considerations, desired composition; gamma-spectrometry protocol) of this “all-in-one” alloy and on the experimental results (radiation stability; homogeneity tests) obtained for a variety of prototypes that were produced by some firms specialized in alloying technology. It is concluded that for the most recently produced material all criteria are fulfilled to pass on to the development of a certified Zr-Au-Lu alloy, which would be quite useful not only in the practice of k-0NAA, but for neutron spectrum monitoring in general.
After 36 years of operation, reactor Thetis at the Institute for Nuclear Sciences (Ghent University) was decommissioned in
December 2003. On this occasion, a survey is presented of the characteristics and features of Thetis, which were opening the
way to its significant contribution to NAA and its leading role in the development of the k0-standardization. A summary is given, including a few specific examples, of fundamental analytical developments and practical
applications based on irradiations in the reactor Thetis.