Neutron-induced fission and photon-induced fission are techniques that can be used to determine fissionable isotopes of uranium, thorium, plutonium, and other actinides in a number of matrices. The purpose of this work is to compare the advantages and disadvantages of those techniques based on theoretical and experimental considerations.
Photofission and electrofission cross sections for fissionable isotopes of uranium, thorium, plutonium and other actinides have been known for several decades. Published data on electrofission and photofission reactions for energies lower than 60 MeV indicate that the238U cross sections range from a fraction of one mbarn up to about 2.0 mbam for the first of these reactions, and for the second is about 150 nbarn. However, the use of photofission and electrofission as analytical tools to measure uranium, thorium, plutonium and other fissionable actinides is still quite recent. This work examines the potential use of photofission and electrofission to measure thorium, uranium, neptunium, plutonium, americium and curium in environmental and biological samples.
Authors:J. Justo, H. Evangelista, and A. S. Paschoa
The main shortcoming with the procedure to determine 226Ra in a gamma spectrum of an environmental sample by means of the 214Bi and 214Pb photopeaks is the likelihood of 222Rn leakage from the sample counting vial. An option to make such determination is to disregard the 226Ra gamma-contributions to the spectrum, other than 186.2 keV (3.5%), subtracting the 235U contribution to the 226Ra+235U peak at 186 keV. The use of this option to determine directly 226Ra activity concentrations in environmental samples and in NORM/TENORM matrices will be presented and discussed.
Authors:A. Paschoa, E. Eisenberg, N. Parker, and M. Wreen
The theoretical aspects of fission track production in polycarbonate foils are briefly discussed. An automatic couning system for fissio tracks based on a spark gap chamber is described. A linear response for a low fission track density, typical of environmental and biological samples, was obtained with a252Cf source using an electrode of 33.2 mm2 The system also functions with electrodes of larger and smaller areas without any major changese in the instrument.
Authors:A. Paschoa, M. Cholewa, K. Jones, N. Singh, and M. Wrenn
A combination of two techniques, PIXE (particle induced x-ray emission) and RBS (Rutherford backscattering), is proposed as an analytical tool to measure uranium and thorium in environmental and biological samples and in the study of the micro-distribution of uranium is low Z matrices such as biological tissue.
Authors:G. Baptista, E. Montenegro, C. Barros Leite, and A. Paschoa
The accuracy of the quantitative analysis of thick targets by XRF is impaired by effects due to the absorption of X-rays in
the matrix associated with the non-uniformity of the X-ray beam and the lack of knowledge of the actual distribution of trace
elements in the target. The uncertainty in the elemental mass associated to a definite number X-rays detected is discussed
in the paper. A correction factor is derived to account specifically for the effect of the absorption of X-rays and the non-uniformity
of the X-ray beam.
Authors:C. Barros Leite, G. Baptista, E. Montenegro, and A. Paschoa
A graphical method was developed to relate data from Rutherford backscattering spectrometry to sample characteristics, such as thickness and concentration profiles. The method was then applied to analyze these characteristics of a gold film.