A brief chronicle is presented of one radiochemist's meanders through the fields of meteoritics, lunar studies, and geochemistry to current studies of possible relationships of trace element imbalances to diseases affecting the brain and spinal cord. This range of studies is used to underscore the broad applications of radiochemistry and the need to maintain educational programs and research in radiochemistry. Our recent studies of tissues from subjects with Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), have shown that imbalances exist for concentrations of many trace elements, compared to corresponding concentrations in control subjects. Among the elements most frequently found imbalanced are aluminum, bromine, cadmium, copper, iron, mercury, rubidium, and zinc. Several of these elements may be involved in processes leading to free-radical-induced oxidative damage in Alzheimer's disease. Our multi-technique analytical approach to these studies is briefly reviewed.
Students at the University of Kentucky are introduced to radiochemistry through an introductory lecture course offered yearly. The course is designed to assure that juniors and seniors can master the fundamental concepts and are exposed to a variety of applications. Enrollment is typically 25–35 students, about 1/2 of whom are undergraduate chemistry majors. The course prompts several students each year to elect undergraduate research projects in radiochemistry. Research is conducted under a course entitled Independent Work In Chemistry and may be elected for up to 9 credits towards B.A. or B.S. degree requirements. Students are required to present the results of their research as a written report, and also in a seminar or an undergraduate research poster competition sponsored yearly by the department.
Accelerator-based 14-MeV or fast neutron activation analysis (FNAA) is a mature tecnique and few major advances in instrumentation and methodology can be expected. However, applications of the technique are numerous and continue to increase. In this paper, recent technique developments and applications of FNAA are reviewed and speculations concerning future progress in the field are presented.
The technique of neutron activation analysis (NAA) was first demonstrated in papers by Georg Hevesy and Hilde Levi in 1936 and 1938. Applications of NAA to biological tissues did not appear in the literature until approximately a decade later, when analysts obtained access to high flux nuclear fission reactors. NAA studies of trace element imbalances in specific diseases developed rapidly in the 1980s with the availability of affordable high resolution, high efficiency, solid-state gamma-ray detectors. A brief history of NAA as related to trace element analyses of human tissues is presented and recent NAA studies of relationships of elemental imbalances to the etiology or pathogenesis of selected diseases are reviewed.
A 14-MeV FNAA system for oxygen analysis has been developed in which both data collection and processing are controlled by a PC-type computer equipped with an ORTEC ACETM-MCS multichannel scaler card. A single loop pneumatic transfer system automatically moves samples to the irradiation position and returns them to a counting position between two NaI(Tl) detectors operated through a summing amplifier. Software for data processing has been developed. Dead times of the BF3 neutron monitor and gamma-ray counting system have been separately determined. Results are presented for a variety of standard samples.
Fifteen elements at trace levels have been determined by neutron activation analysis in the biological standard kale distributed
byBowen. La, Br, As, Se, Sc, Ag, Zn, Co, Cr, Sb, Eu, Fe, and Zr have been determined by a nondestructive technique using a high-resolution
Ge(Li) detector. Two more elements, Au and Hg, have been determined after radiochemical separation. The nondestructive procedure
is shown to yield data in generally good agreement with those obtained by destructive techniques. Potential sources of error
in the nondestructive technique are discussed.
A sensitive analytical technique has been developed to determine zirconium and hafnium at the 1 ppm and 0.01 ppm levels, respectively,
in natural silicate matrices. The technique is based on the use of a Ge(Li) detector for high-resolution γ-ray spectrometry
following irradiation with thermal neutrons. Simultaneous separation of both elements is achieved by addition of only zirconium
carrier and use of a strongly basic anion-exchange resin. Hafnium was shown to follow zirconium throughout the chemical procedures.
The chemical yield of the separation procedure was determined for each sample by use of an automated fast-neutron activation
analysis system, which obviated the need to convert the separated zirconium to a conventional gravimetric weighing form. The
method has been applied to the analysis of a variety of standard rocks and related natural materials.
Various theoretical and practical aspects of epithermal neutron activation analysis (ENAA) and fast-neutron-induced reaction interferences in conventional instrumental thermal neutron activation analysis (TNAA) have been considered. A new generalized advantage factor which reflects a practical improvement of detection limits in ENAA is proposed. In the determination of practical advantage factors, consideration is also given to the different irradiation channels available for the experiment in a given reactor, or even in several accessible reactors. Fast neutron reaction interference factors are tabulated for both ENAA and TNAA and examples are given of specific interferences in TNAA for some biological and geological matrices.
A simple two step radiochemical separation scheme has been developed which permits the RNAA determination of As, Cd, Cu and Mo in biological matrices. The RNAA separation is applied following the INAA determination of at least 17 other elements in the same samples. Under our experimental conditions which included a four day decay period for handling and shipping from a remote reactor site, detection limits for As, Cd, Cu and Mo are 0.24, 6.6, 45 and 3.4 ng, respectively, in NBS biological standard reference materials SRM 1571 and 1567. Decontamination factors for the major spectral interferences,82Br,42K,24Na32P and122Sb have been determined and found to be sufficiently high for measurement of the elements of interest in most biological matrices. The overall INNA/RNAA procedure takes full advantage of high resolution Ge(Li) gamma-ray spectroscopy and involves minimal chemical processing.
A boron nitride irradiation vessel designed for use with a pneumatic tube transfer system has been used to analyze short-lived radionuclides by NAA. Bare and Cd-shielded irradiations on Co, Zr and Au were made to characterize the neutron fluxes in the irradiation position. Bare and BN-shielded irradiations were performed to determine epithermal advantage factors for 16 short-lived reactions and interference factors for a total of 11 (n, p) and (n, ) reactions induced by reactor fast neutrons. To illustrate application of these data, several biological and geological reference materials were analyzed.