When an accident involving the possibility of a plutonium contaminated wound
occurs, the contamination is often quantified using sodium iodide (NaI(Tl)) and high
purity germanium (HPGe) detection systems. The NaI(Tl) system is used to quantify the
amount of contamination, while HPGe is used to gauge the depth of contamination in the
wound. Assessment of plutonium contaminated wounds is difficult due to the lowenergy
and yield of the uranium L-shell x rays used for the measurement, which can be
effected by source distance, shape, and tissue attenuation. These effects on wound
counting systems used at Los Alamos National Laboratory (LANL) were characterized
experimentally using common source shapes (disk, point, and line) and acrylic plastic as
a tissue substitute. Experiments were conducted to characterize detector responses as a
function of tissue attenuation, source distance, and source depth in tissue. The computer
code MCNP5 was used to model both systems for wound counting and better examine
angular displacement of a line source in tissue.
The NaI(Tl) detector response was characterized using absolute detector
efficiency for all experimental measurements. Measurements showed that the NaI(Tl) system is significantly effected by the source to detector position and depth in tissue.
Characterization of the HPGe detection system was done utilizing the peak-to-peak ratio
from the two low-energy x rays. HPGe peak-to-peak ratios were not affected by source
to detector distance, but showed an increased response to source depth in tissue. MCNP
results suggested that small incident angles from the plane of the detector face can cause
significant effects on the response of both detectors. In summary, the response of both
systems showed dependence on source geometry and depth of contamination in tissue.
Correction values and uncertainties were determined based on these dependencies.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2524 |
| Date | 15 May 2009 |
| Creators | Dimmerling, Paul James |
| Contributors | Braby, Leslie A. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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