In order to determine the physical location of contaminants in soil, two solidified soil
"thin" sections, which preserve the undisturbed structural characteristics of the original
soil, containing weapons-grade plutonium from the Rocky Flats Environmental Test Site
were prepared. Two autoradiographic methods were used in radionuclide mapping:
contact autoradiography using CR-39�� plastic alpha track detectors and neutron-induced
autoradiography that produced fission fragment tracks in Lexan�� plastic detectors. The
combination of the two autoradiographic methods distinguished alpha-emitting particles
of natural U, from ������������������Pu and non-fissile alpha-emitters. The locations of 990 alpha
"stars" caused by plutonium "hot particles" in two soil sections were recorded, particles
were sized, their size-frequency and depth distributions were analyzed. Several large
colloidal conglomerates of "hot particles" were found in soil profiles. One such
conglomerate with a geometric size of about 500 ��m contained over 94% of the total
recorded contaminant alpha activity in the sample. It was found that the upper 6.5 cm of
soil contained 20% of all recorded particles (mean equivalent size 0.35 ��m). The deeper
portion of the surface 6.5 cm soil layer contained 80% of the particles (with mean
equivalent size 0.25 ��m). The average specific activity (SA) for 989 hot particles (with
the conglomerate of the particles excluded) with equivalent diameters over 80 nm was
found to be greater than 23.9 Bq g����� (about 90% of the overall average SA). For dissolved
and defragmented (below 80 nm of equivalent diameter) actinide particles, SA was found
smaller than 2.9 Bq g�����. Over 99% of the total actinide contaminant activity in the
analyzed soil sample (with the conglomerate of the particles included) was found in
particles with equivalent diameters over 0.08 ��m. it suggests that larger particles of
plutonium oxide moved down more slowly than smaller ones and no significant breakup
of plutonium oxide particles occurred since the original plutonium soil deposition. Both
profiles of the depth contaminant activity and number of actinide particles have
distinctive peaks at the same depth, about 10 cm. Independent from nuclear track
analysis, this pattern of the actinides depth distribution was observed in the measured
gamma activity depth profile of �������Am (daughter product of �������Pu beta decay) in
solidified soil blocks. / Graduation date: 2001
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32672 |
| Date | 19 December 2000 |
| Creators | Povetko, Oleg G. |
| Contributors | Higley, Kathryn A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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