Neutron activation analysis has for many years been considered to be a method that relatively is free from matrix interference. While this may be true for the majority of samples such as liquid, biological, air filters and geological aluminum-silicate specimens, there are many other types of samples that contains high Z materials in relatively high abundance that do attenuate low and medium energy gamma-rays. Samples such as heavy metal contaminated soils, ore concentrates and meteorites are prime examples. One can minimize the gamma-ray attenuation phenomena by using small masses of sample. This is not possible when using field environmental samples that are more than often not homogenous, and more sample mass is needed. Using a program called SELFABS, we have developed a very careful evaluation of the self-attenuation factors for a several of low and high Z reference materials. Special attention was given to the effect of the sample mass. Our conclusions indicate that while a great effort is given to various QA/QC procedures little literature information is ever published on the need or use for the calculation of these self-attenuation factors.
A fast pneumatic transfer facility was installed in Nuclear Engineering Teaching Laboratory (NETL) of the University of Texas
at Austin for the purpose of cyclic thermal and epithermal neutron activation analysis. In this study efforts were focused
on the evaluation of cyclic epithermal neutron activation analysis (CENAA). Various NIST and CANMET certified materials were
analyzed by the system. Experiment results showed 110Ag with its 25 s half-life as one of the isotopes favored by the system. Thus, the system was put into practical application
in identifying silver in metallic ores. Comparison of sliver concentrations as determined by CENAA in CANMET certified reference
materials gave very good results.
In virtually all neutron activation analysis laboratories, researchers are given film badges known as thermoluminescence dosimeters
(TLD's) that are monitored on a monthly basis. Sometimes additional pocket dosimeters are worn to get a daily reading of exposure,
while in other instances ring badges are worn to assess beta doses. However, more than often little consideration is given
to beta-exposure rates that arise from the plethora of radionuclides produced in the many types of samples irradiated. A common
mistake is to assess gamma-exposures of activated samples that rely on the use of a beta-shield on the survey meter. Our experimental
results have shown that there are many high energy beta-particles from neutron activated samples that can easily penetrate
the beta-shield and thus give an underestimation of the total beta-exposure.
Authors:S. Landsberger, M. S. Basunia, and S. Schroit
We have determined nineteen trace elements in 685 aerosol filter samples collected during 1964-1978 in northern Finland by the Finnish Meteorological Institute. In this paper we present some procedures and results for very short (~25 s), short (~3-54 min), and medium (12-35 h) lived isotopes as determined by epithermal NAA in conjunction with and without Compton suppression. Elements with a Iγ/σthratio are favorable to be determined by epithermal NAA. Silver was determined by a one minute epithermal irradiation because of a very short 110Ag half-life. Antimony, arsenic, cobalt, bromine, indium, iodine, potassium, silicon, tin, tungsten, and zinc were determined by a ten minute epithermal irradiation. For silver determination, samples were counted without transferring the filter from the irradiated vial, however, for ten minute irradiation all samples were transferred to a non-irradiated vial and counted both in the normal and Compton mode by the HPGe gamma-spectrometry system with a decay time of about 10 minutes and counting time of 15 minutes. Each day a maximum of 16 samples were irradiated and immediately following the short counting, these samples were loaded into an automatic sample changer in sequence of irradiation and counted for an hour in both normal and Compton modes. This has proven to be an extremely cost effective measure thus reducing the need to employ long-lived NAA to analyze other elements such as Ag, Co, Sn and Zn and Ag for air pollution source receptor modeling.
Cigarette smoking is a major source of particles released in indoor environments. A comprehensive study of the elemental distribution in cigarettes and cigarette smoke has been completed. Specifically, concentrations of thirty elements have been determined for the components of 15 types of cigarettes. Components include tobacco, ash, butts, filters, and cigarette paper. In addition, particulate matter from mainstream smoke (MS) and sidestream smoke (SS) were analyzed. The technique of elemental determination used in the study is instrumental neutron activation analysis. The results show that certain heavy metals, such as As, Cd, K, Sb and Zn, are released into the MS and SS. These metals may then be part of the health risk of exposure to smoke. Other elements are retained, for the most part, in cigarette ash and butts. The elemental distribution among the cigarette components and smoke changes for different smoking conditions.
Over 50 million tons of coal ash are produced annually in North America. Technological improvements in air pollution control have decreased stack emissions but have also increased contaminant concentrations in the ash of coal-fired boiler applications. The leaching of heavy metals and other elements during regulatory tests may cause coal ash ro be classified as hazardous waste, complicating land disposal. The hazardous nature of coal ash remains unclear because current toxicity tests fail to effectively characterize the elemental distribution and chemical solubility of trace metals in the landfill environment. Leaching characteristics of ash samples can be investigated with various laboratory extraction procedures in association with multi-elemental analytical techniques (e.g., neutron activation analysis and inductively coupled plasma-atomic emission spectroscopy). Such methods provide more thorough analyses of coal ash leaching dynamics than the regulatory assessments can demonstrate. Regulatory elements including Ag, As, Ba, Cd, Cr, Hg, Pb, and Se were shown to remain in largely insoluble forms while elements such as B and S leached at higher levels. Experimental results may assist operators of coal-fired boiler industries in selecting coal types and disposal options to curtail the leaching of potentially toxic inorganic contaminants.
Authors:A. Michenaud-Rague, S. Robinson, and S. Landsberger
While there is a lot of information on the elemental content of food for nutritional and pollution studies, the analysis of
fruits has received little attention. We have investigated 11 commonly eaten fruits for their trace and minor element constituents
by neutron activations including thermal and epithermal neutron activation analysis. Our results revealed that both blueberries
and strawberries had the most of top two highest elemental concentrations followed by raspberries, oranges and mango. Bananas,
grapes, plums, apples, pears, and cherries had the fewest or none of the most elevated elemental concentrations.
Neutron activation analysis has been used to analyze sediment cores from the Rock River and two branches of Kent Creek, one of its tributaries, to determine the concentrations of thirteen heavy metals (Ti, Cu, V, Mn, As, Sb, Se, Cr, Ni, Sc, Fe, Zn, and Co) and two rare earths (Sm and La). The downstream sites of both the Rock River and the two branches of Kent Creek have elevated concentrations of several heavy metals including arsenic, antimony, and zinc. In addition, hundreds of parts per million of copper have been found in samples from the downstream site of the North Fork of Kent Creek. Toxicity tests of the sediment also indicate that the downstream sites are detrimental to lifeforms. Analysis of the data from the two branches of Kent Creek clearly indicate that heavy metal concentrations increase as the distance from the center of industrial activity (Rockford) decreases.
The AL-R8 stainless steel sealed insert that is currently used for interim storage of plutonium pits at the Pantex facility in Amarillo, Texas, is designed to provide an inert storage environment for the plutonium pits for a 50-year service life. There is concern that the high chlorine content and absorbed moisture present in the packaging material, Celotex, may lead to corrosion of the container over time. The main objective of this study was to determine chlorine in the Celotex as well as in the various leaching procedures using neutron activation analysis.
The separation of99Mo from low-enriched uranium (LEU, 19.5%235U) targets was evaluated using natural uranium (NU) and non-radioactive tracers. Neutron activation analysis was used to determine (1) the efficiency of molybdenum recovery and (2) the decontamination factor of numerous fission product elements from the molybdenum product. Using NU and non-radioactive elements simplified procedures and allowed tests to be completed in a fume hood instead of a shielded cell. During activation of the non-radioactive tracers, uranium fission occurs, which can interfere with subsequent gamma-ray analysis. A comparison was made of the interferences caused by these fission products from both NU and LEU.