L. Robinson

Determination of Hg and other trace elements in soil using neutron activation analysis

In the early 1950s, 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.

A novel approach to aluminum determination in biological tissues using a pair of pneumatic tube irradiation facilities

A novel method for the determination of trace aluminum (AI) in the presence of high levels of phosphorus (P) has been developed at the Oak Ridge National Laboratory High Flux Isotope Reactor (HFIR). Using successive irradiations in HFIRs two pneumatic tube facilities (PT-1, PT-2) to measure the difference between the two apparent Al concentrations, the true Al concentration in the sample can be calculated without the need for an independent determination of P. Results are presented for brain samples from various regions, some that are strongly affected by Alzheimers disease (AD) and for NIST SRM 1577b, Bovine Liver.

Methods for preparing comparative standards and field samples for neutron activation analysis of soil

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.

Neutron multiple scattering and absorption factors

Absorption and multiple scattering factors for neutrons are determined using the Monte Carlo integration method. This procedure gives results that are as accurate as that from other methods. It is also simpler and apparently converges more rapidly than other methods.

Validation of NAA data for a background soils characterization project

Background soils from areas around the United States Department of Energy facilities in Oak Ridge, Tennessee were characterized as part of an environmental restoration project. The data obtained in this project were validated using guidelines from the Environmental Protection Agency (EPA) Contract Laboratory Program (CLP), when EPA methods were used. However, there are no final EPA guidelines for validation of data obtained using radiochemical analytical methods, so procedures for validation had to be developed. This paper will describe the validation guidelines that were developed for neutron activation analysis (NAA) data and discuss the regulatory basis for them.

Status of NAA facilities in the advanced neutron source

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.

An automated fuel element scanning system

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 reactors core (element by element) has been derived from140La counting data. The method of determining power is discussed briefly and some example results are presented.

Research and learning opportunities in a reactor-based nuclear analytical laboratory

Although considered by many to be a mature science, neutron activation analysis (NAA) continues to be a valuable tool in trace-element research applications. Examples of the applicability of NAA can be found in a variety of areas including archaeology, environmental science, epidemiology, forensic science, and material science to name a few. Each stage of NAA provides opportunities to share numerous practical and fundamental scientific principles with high school teachers and students. This paper will present an overview of these opportunities and give a specific example from collaboration with a high school teacher whose research involved the automation of a gamma-ray spectroscopy counting system using a laboratory robot.

Proposed neutron activation analysis facilities in the Advanced Neutron Source

Abstract A number of analytical-chemistry experimental facilities are being proposed for the Advanced Neutron Source. Experimental capabilities will include neutron activation analysis, prompt gamma-ray analysis and neutron depth profiling. This paper describes the various systems proposed and some of their important characteristics.