Bremsstrahlung-Based Imaging and Assays of
Radioactive, Mixed and Hazardous Waste
John Kwofie
Idaho State University
Graduate Student in Physics
A new nondestructive accelerator based x-ray fluorescence (AXRF) approach
has been developed to identify heavy metals in large-volume samples.
Such samples are an important part of the process and waste streams of U.S
Department of Energy sites, as well as other industries such as mining and
milling. Distributions of heavy metal impurities in these process and
waste samples can range from homogeneous to highly inhomogeneous, and non-destructive
assays and imaging that can address both are urgently needed. Our approach
is based on using high-energy, pulsed bremsstrahlung beams (3-6.5 MeV) from
small electron accelerators to produce K-shell atomic fluorescence x-rays.
In addition we exploit pair-production, Compton scattering and x-ray transmission
measurements from these beams to probe locations of high density and high
atomic number. The excellent penetrability of these beams allows assays and
images for soil-like samples at least 15 g/cm2 thick, with elemental impurities
of atomic number greater than approximately 50. Fluorescence yield
of a variety of targets was measured as a function of impurity atomic number,
impurity homogeneity, and sample thickness. We report on actual and
potential detection limits of heavy metal impurities in a soil matrix for
a variety of samples, and on the potential for imaging, using AXRF and these
related probes.