The special features of the Advanced Neutron Source research reactor with planned beginning of construction in 1994 are listed. Pneumatic and beam irradiation facilities will be included and are described in the text of this paper.
Studies were made on the uptake of zirconium, hafnium and niobium isotopes onto zeolites and amorphous zirconium phosphate. Ion exchange capacities and distribution coefficients were determined and the influence of pH examined. Kinetic experiments were made to determine the rates of uptake of the radioisotopes on the exchangers and to measure the leaching of isotopes from preloaded exchangers by synthetic sea water, simulated pond water and distilled water.
Iodine-129 was determined by neutron activation analysis (NAA) in mixed-bed ion exchange resins from four light water reactors (LWR), including two pressurized water reactors (PWR) and two boiling water reactors (BWR). Published procedures for NAA of129I in LWR resins were modified and adapted to the particular requirements of the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR) irradiation system. Observed129I concentrations, ranging from 1E-09 to 4E-07 Ci/g, were about 1000 times lower than the beta-gamma detection limits currently reported.
A method was developed to determine thorium and uranium in semiconductor potting plastics. The method is based on neutron activation and subsequent radiochemical separation to isolate and permit measurement of the daughter products233Pa and239Np of the induced233Th and239U. These plastics typically contain macro amounts of silicon, bromine and antimony and nanogram per gram amounts of thorium and uranium. The radiochemical method provides the necessary sensitivity and makes it possible to easily attain adequate decontamination of the tiny amounts of233Pa and239Np from the high levels of radioactive bromine and antimony.
One of the more difficult problems associated with comparative neutron activation analysis (CNAA) is the preparation of standards which are tailor-made to the desired irradiation and counting conditions. Frequently, there simply is not a suitable standard available commercially, or the resulting gamma spectrum is convoluted with interferences. In a recent soil analysis project, the need arose for standards which contained about 35 elements. In response, a computer spreadsheet was developed to calculate the appropriate amount of each element so that the resulting gamma spectrum is relatively free of interferences. Incorporated in the program are options for calculating all of the irradiation and counting parameters including activity produced, necessary flux/bombardment time, counting time, and appropriate source-to-detector distance. The result is multi-element standards for CNAA which have optimal concentrations. The program retains ease of use without sacrificing capability. In addition to optimized standard production, a novel soil homogenization technique was developed which is a low cost, highly efficient alternative to commercially available homogenization systems. Comparative neutron activation analysis for large scale projects has been made easier through these advancements. This paper contains details of the design and function of the NAA spreadsheet and innovative sample handling techniques.
On a récemment installé un nouveau dispositif pour l'analyse par activation neutronique avec un flux thermique de 5X1014 cm−2 sec−1 au réacteur à haut flux du ORNL. Ce flux particulièrement élevé combiné avec un petit ordinateur et un programme adapté à
la spectrométrie γ avec un détecteur Ge (Li), rend possible une irradiation plus courte, une analyse d'identification plus
rapide et plus économique que si on utilise des moyens plus conventionnels. On discute des caractéristiques et des expériences
du nouveau laboratoire d'analyse par activation neutronique à haut flux, de même des résultats obtenus sur plusieurs types
de matrices concernent l'environnement pour le mercure, le cadmium, le brome, l'arsenic, le chlore et le sodium.
Authors:F. Dyer, J. Emery, K. Northcutt, and R. Scott
Uranium and thorium were measured by absolute neutron activation analysis in high-purity materials used to manufacture semiconductor
memories. The main thrust of the study concerned aluminium and aluminum alloys used as sources for thin film preparation,
evaporated metal films, and samples from the Czochralski silicon crystal process. Average levels of U and Th were found for
the source alloys to be ≈65 and ≈45 ppb, respectively. Levels of U and Th in silicon samples fell in the range of a few parts
per trillion. Evaporated metal films containted about 1 ppb U and Th, but there is some question about these results due to
the possibility of contamination.
The forensic activation analyst must often evaluate his own results as they relate to certain legal or moral situations, since
investigative officers, and courts of law are not usually competent to make judgements of the validity or meaning of scientific
data. In providing scientific evidence in court, two criteria for criminal identification must be met: (1) suspect's sample
should be similar to sample found at the scene of the crime, (2) samples relared to other people in the same statistical population
should not generally match that found at the crime site. When two or more specimens are submitted for comparison by NAA they
will usually fall into one of three classes: (a) materials about which we have partial or inconclusive data, (c) materials
with an excellent analytical data background. Ideally all cases would fall in category c; in practice, very few. Some examples
of cases and/or situations that fall into these three categories in both individual and corporate investigations are given.
Authors:L. Robinson, R. Hobbs, F. Dyer, L. Pugh, J. Snelgrove, and N. Teasley
This paper describes an automated fuel element scanning system, based upon gamma-ray spectroscopy, that has been developed at the Oak Ridge Research Reactor. The scanning system is located in the reactor pool and allows fuel elements to be scanned nondestructively at various intervals during their core life. Fuel elements are located 430 cm beneath the pool. Gamma-ray measurements (aided by a collimating assembly) are made using a GeLi detector positioned above the pool water. Measurements of137Cs count rates from relatively cold elements indicate that the counting data obtained using this apparatus is reproducible within 5%. Power distribution in the reactor's core (element by element) has been derived from140La counting data. The method of determining power is discussed briefly and some example results are presented.
Authors:L. Robinson, F. Dyer, D. Combs, J. Wade, N. Teasley, J. Carlton, A. Ondracek, and J. Stokely
In the early 1950's, a federal facility in Oak Ridge, Tennessee, used a process that required the use of Hg to produce8Li. It was disclosed to the public in 1983 that about 2.4 millions pounds of Hg had been released into the ecosystem. The primary route of mercury into the environment was a stream, East Fork Poplar Creek, whose head waters are in the vicinity of the plant. As part of a study to determine the distribution of Hg as well as As, Cr, Sb, Se, U, and Zn along the flood plains of the creek, a procedure using neutron activation analysis was developed and is described below. The procedure, typical sample analysis results for Hg, and quality assurance and control data are discussed in this paper.