Methods for the determination of total carbon (TC), total nitrogen (TN), and total phosphorus (TP) in cattail (Typha domingensis) using cold and thermal neutron prompt gamma activation analysis (CNPGAA and TNPGAA) have been developed in the CNPGAA and
TNPGAA facilities at the National Institute of Standards and Technology (NIST), and evaluated through the analysis of Standard
Reference Materials (SRMs) in previous studies. There are major issues that impact the sensitivities of C, N and P using CNPGAA
and TNPGAA including the effects of hydrogen content in samples, sample thickness and Compton scattering. However, interference
from chlorine (Cl) in cattails has a major impact on the detection of P. This paper compares the effects of hydrogen content,
sample thickness and Compton scattering on the sensitivities of C, N, and P between CNPGAA and TNPGAA and provides a resolution
to the Cl interference on P in cattail.
Previous studies including the development of methods for the determination of carbon, nitrogen, and phosphorus in cattail
using cold neutron prompt gamma activation (CNPGAA) and thermal neutron prompt gamma activation analysis (TNPGAA); evaluation
of the precision and accuracy of these methods through the analysis of Standard Reference Materials (SRMs); and comparison
of the sensitivity of CNPGAA to TNPGAA have been done in the CNPGAA and TNPGAA facilities at the National Institute of Standards
and Technology (NIST). This paper integrates the findings from all of these prior studies and presents recommendations for
the application of CNPGAA and TNPGAA in environmental studies of plants based on synergistic considerations of the effects
of neutron energy, matrix factors such as chlorine content, Compton scattering, hydrogen content, sample thickness, and spectral
interferences from Cl on the determination of C, N, and P. This paper also provides a new approach that simulates a sensitivity
curve for an element of interest (S), which is a function of hydrogen content (X) and sample thickness (Y) as follows: S = aX + bY + c (where a, b, and c are constants). This approach has provided more accurate results from the analysis of SRMs than traditional methods and an
opportunity to use models to optimize experimental conditions.
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.
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.
This report presents results from the application of the Monte Carlo N-Particle (MCNP) computer code to the252Cf neutron activation analysis (NAA) Device in the Technical Physics Institute of the Heilongjiang Science Academy of the
People's Republic of China. The thermal and epithermal neutron flux at the sample positions and the neutron and photon fluxes
on the surfaces of the device were calculated. A comparison between the calculated and experimental thermal and epithermal
neutron fluxes at sample positions yield relative errors of less than 10% for the thermal neutron flux.
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 HFIR's 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 Alzheimer's disease (AD) and for NIST SRM 1577b, Bovine Liver.
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.
Plutonium in nanogram quantities was isolated from uranium targets irradiated with charged particles. High decontamination was achieved using a method that combines anion exchange with extraction chromatography in tributyl phosphate/hydrochlorid acid solution system.
The flux of cold neutrons that is obtainable from various high energy netron sources is studied for a particular model of
a cold neutron source when the cold moderation region of the apparatus is at 20, 70, and 298K. The maximum flux obtained with
a californium-252 source was 2.7·10−3 cold neutron per (cm2·second (source neutron)). This flux was obtained when the cold moderation region of the apparatus was at 20K and when the
thermal moderator is either polyethylene or trimethylbenzene and the cold moderator is polyethylene. This flux should allow
sensitive prompt and delayed neutron activation analysis measurements.
A new chemical method based in two separation steps was developed to isolate235Np from uranium targets irradiated with charged particles. Neptunium and plutonium are separated from uranium and most of the fission products by ion exchange. Then, neptunium is isolated from plutonium and remaining contaminants by extraction chromatography with tributyl phosphate in hydrochloric acid solution. High decontamination was achieved.