Radiological contamination penetration depth in Fernald transite panels Page: 4 of 8
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intensities, image analysis could likely produce quantitative results. However, such a quantitative analysis
would require extremely consistent image processing. Because UV light interacts with just the surface of
the sample, this method provides information about contamination on the surface, and is very quick,
simple, and inexpensive [4,5]. For the UV photography in this study, the transite samples were placed in a
light box equipped with ultraviolet fluorescent bulbs which emitted light at a 254 nm wavelength. A 35
mm camera was attached to the viewport with 200 speed film and an exposure duration of 4 seconds. For
comparative purposes, consistent settings and development were crucial. Different levels of contamination
resulted in varied intensities and hues of green. Optically scanning the image into a digital format allowed
some image enhancement to emphasize the actual contamination. However, an accurate interpretation of the
UV photography images often required comparison to the equivalent autoradiograph.
Autoradiography differs from typical radiography only in that the source of radiation is provided by the
sample itself and a separate radioactive source is not required. Classical radiography involves capturing the
image of the sample on a photographic plate based on the attenuation of radiation from an external source
by the intervening sample, while autoradiography captures the actual pattern and intensity of radiation from
a sample. Consequently, the only requirements for autoradiography are radiosensitive film and a means of
handling the light sensitive media for exposure purposes. Since autoradiography also provided a spatial
representation of contamination across the surface of the sample, it was used for comparison to the UV
photography results for verifying which regions contain uranium contamination. Autoradiography provides
surface or near surface information. Therefore, autoradiography requires destructive analysis to provide
information about the contamination distribution through the thickness of the transite panels. The
autoradiographs were produced using standard X-ray imaging film with a central polymeric base coated on
both sides with a thin emulsion covered with an anti-scratch layer. The film was placed in direct contact
with a sample and stored in a light-tight box for an appropriate exposure time. Consistent developing was
provided by a standard automated developer.
Non-Destructive Analysis
The contamination distribution results from the destructive analysis were used to both characterize the
transite and to provide verification of a novel non-destructive technique using gamma-ray spectrometry
proposed by Chung, et al.[6]. This non-destructive method was based on measuring the gamma-ray spectra
from both sides of the sample. Fig. 1 illustrates the implementation of this technique. Note the different
photopeak areas recorded by the two detectors in the two gamma-ray spectra. In conjunction with
knowledge of the gamma-ray linear attenuation coefficient for the material and proper diffusion or leaching
models representative of how the material was contaminated, the ratio of photopeak areas at several energies
from these spectra can be used to infer the most-probable contamination distribution. Use of a high-purity
germanium (HPGe) detector provides sufficient energy resolution to discern all of the photopeaks of
interest. Comparing the measured ratio of the respective photopeak areas from both sides of the panel (Fig.
1-b) over a range of energies to computer-generated ratios for possible contamination distributions provides
a prediction of the most-probable distribution (Fig. 1-c). The computer generated ratios were based on
distributions predicted by diffusion theory for given types of exposures, or initial conditions. In particular,
for a single instantaneous exposure, the distribution was based on a gaussian function, and for a constant
exposure, the distribution was based on a complementary error function [7]. For this study, the condition
of constant exposure existed and the complementary error function proved to be applicable.
RESULTS
Destructive analysis was conducted on both sides of one A sample and eleven C samples using the G-M
detector to obtain quantitative contamination distributions. Approximately six layer removals were required
per side to reach background level. As representative G-M detector data, sample C5a produced the results
shown in Table 1 and Figure 2. Figure 2 also illustrates the correlation with the contamination distribution
predicted by the non-destructive technique. To determine how the contamination distributions vary from
sample to sample, the depth at which count rates from the G-M detector approached background were
recorded. Table 2 lists the sample sides analyzed and their corresponding depth to background level.
To further verify the penetration of uranium concentration into the thickness of the transite panels, both UV
photographic and autoradiographic analyses were performed on several samples. The autoradiography
required an exposure time of either 24 or 48 hours, depending on the contamination level. It was
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Russ, W. R.; Valentine, J. D. & Chung, Wei. Radiological contamination penetration depth in Fernald transite panels, report, December 6, 1995; Cincinnati, Ohio. (https://digital.library.unt.edu/ark:/67531/metadc667349/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.