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J F Harmon

Publications and source records attributed to J F Harmon.

4 recordsLinked to original sources
PubMed2001

Investigation of irradiated soil byproducts.

The high dose irradiation of windblown soil deposited onto the surface of spent nuclear fuel is of concern to long-term fuel storage stability. Such soils could be exposed to radiation fields as great as 1.08 x 10(-3) C/kg-s (15,000 R/hr) during the 40-year anticipated period of interim dry storage prior to placement at the proposed national repository. The total absorbed dose in these cases could be as high as 5 x 10(7) Gy (5 x 10(9) rads). This investigation evaluated the potential generation of explosive or combustible irradiation byproducts during this irradiation. It focuses on the production of radiolytic byproducts generated within the pore water of surrogate clays that are consistent with those found on the Idaho National Engineering and Environmental Laboratory. Synthesized surrogates of localized soils containing combinations of clay, water, and aluminum samples, enclosed within a stainless steel vessel were irradiated and the quantities of the byproducts generated measured. Two types of clays, varying primarily in the presence of iron oxide, were investigated. Two treatment levels of irradiation and a control were investigated. An 18-Mev linear accelerator was used to irradiate samples. The first irradiation level provided an absorbed dose of 3.9 x 10(5)+/-1.4 x 10(5)Gy (3.9 x 10(7)+/-1.4 x 10(7) rads) in a 3-h period. At the second irradiation level, 4.8 x 10(5)+/-2.0 x 10(5)Gy (4.8 x 10(7)+/-2.0 x 10(7) rads) were delivered in a 6-h period. When averaged over all treatment parameters, irradiated clay samples with and without iron (III) oxide (moisture content = 40%) had a production rate of hydrogen gas that was a strong function of radiation-dose. A g-value of 5.61 x 10(-9)+/-1.56 x 10(-9) mol/J (0.054+/-0.015 molecules/100-eV) per mass of pore water was observed in the clay samples without iron (III) oxide for hydrogen gas production. A g-value of 1.07 x 10(-8)+/-2.91 x 10(-9) mol/J (0.103+0.028 molecules/100-eV) per mass of pore water was observed in the iron (III) oxide containing clay samples for hydrogen gas production. This value was noticeably larger when the samples were spiked with both KCl and KNO3 salts. The ratio of oxygen to nitrogen gas was observed to increase as a function of absorbed dose particularly in the presence of both KCl and KNO3 salts. The creation of radiolytic byproducts produced an observable but small increase in headspace pressure. Temperature increases during irradiation were not observed. Additionally, KCl and KNO3 salts added to the clays enhanced nitrite production as a function of radiation-dose and the type of clay considered. The addition of aluminum to these samples had no statistically discernable impact at the alpha = 0.05 level. Generation of the irradiation products, hydrogen peroxide and hydrogen gas also depended upon the type of clay irradiated and the presence of both KCl and KNO3 salts and the total dose received.

Aluminum↗
PubMed1998

Inverse radiosurgery treatment planning through deconvolution and constrained optimization.

An inverse radiosurgery treatment planning approach is presented which calculates conformal dose distributions for small, irregularly shaped targets. Two general approaches have been suggested for solution of the inverse radiotherapy problem: explicit and implicit. Explicit methods are typically fast, but generally require geometric and/or dosimetric simplifications. Implicit methods have also been used, but are computationally expensive because they require iterative manipulation of each beam's individual elements. The method presented here incorporates an integrated approach in order to efficiently solve the inverse problem without requiring simplifications which may affect the accuracy of the final result. A deconvolution algorithm (explicit approach) is utilized to determine the intensity modulation function for multiple user-selected beam's eye views of the desired dose distribution. A simulated annealing algorithm (implicit approach) then optimizes each beam's macroscopic weight. Additionally, this method is fully three-dimensional and accurately models phantom scatter by incorporating Monte Carlo generated energy deposition kernels into the dosimetry process. Several small target structure examples are presented and applicability of this methodology to larger targets for general radiotherapy cases is addressed.

Algorithms↗