Title:
Gamma and neutron dose profiles near a Cf-252 brachytherapy source

dc.contributor.advisor Wang, C.-K. Chris
dc.contributor.advisor Gauld, Ian C.
dc.contributor.author Fortune, Eugene C., IV en_US
dc.contributor.committeeMember Sang Cho
dc.contributor.department Nuclear and Radiological Engineering en_US
dc.date.accessioned 2010-09-15T19:05:18Z
dc.date.available 2010-09-15T19:05:18Z
dc.date.issued 2010-07-07 en_US
dc.description.abstract A new generation of medical grade Cf-252 sources was developed in 2002 at the Oak Ridge National Laboratory (ORNL). The combination of small size and large activity of these Cf-252 sources makes them suitable to be used with the conventional high-dose-rate (HDR) remote afterloading systems for interstitial brachytherapy. A recent in-water calibration experiment showed that the measured gamma dose rates near the new source are slightly greater than the neutron dose rates; contradicting the well established neutron-to-gamma dose ratio of approximately 2:1 at locations near a Cf-252 brachytherapy source. Specifically, the MCNP-predicted gamma dose rate is a factor of two higher than the measured gamma dose rate at the distance of 1 cm, and the differences between the two results gradually diminish at distances farther away from the source. To resolve this discrepancy, we updated the source gamma spectrum by including in the ORIGEN-S data library the experimentally measured Cf-252 prompt gamma spectrum as well as the true Cf-252 spontaneous fission yield data to explicitly model delayed gamma emissions from fission products. We also investigated the bremsstrahlung x-rays produced by the beta particles emitted from fission-product decays. The results show that the discrepancy of gamma dose rates is mainly caused by the omission of the bremsstrahlung x-rays in the MCNP runs. By including the bremsstrahlung x-rays, the MCNP results show that the gamma dose rates near a new Cf-252 source agree well with the measured results and that the gamma dose rates are indeed greater than the neutron dose rates. The calibration experiment also showed discrepancies between the experimental and computational neutron dose profiles obtained. Specifically the MCNP-predicted neutron dose rates were ~25% higher than the measured neutron dose rates at all distances. In attempting to resolve this discrepancy the neutron emission rate was verified by the National Institute of Standards and Technology (NIST) and an experiment was performed to explore the effects of bias voltage on ion chamber charge collection. So far the discrepancies between the computational and experimental neutron dose profiles have not been resolved. Further study is needed to completely resolve this issue and some suggestions on how to move forward are given. en_US
dc.description.degree M.S. en_US
dc.identifier.uri http://hdl.handle.net/1853/34781
dc.publisher Georgia Institute of Technology en_US
dc.subject EBFNT en_US
dc.subject ORNL en_US
dc.subject CPE en_US
dc.subject Dual-ion chamber en_US
dc.subject.lcsh Radioisotope brachytherapy
dc.subject.lcsh Californium
dc.subject.lcsh Gamma rays Measurement
dc.subject.lcsh Neutrons Measurement
dc.title Gamma and neutron dose profiles near a Cf-252 brachytherapy source en_US
dc.type Text
dc.type.genre Thesis
dspace.entity.type Publication
local.contributor.advisor Wang, C.-K. Chris
local.contributor.corporatename George W. Woodruff School of Mechanical Engineering
local.contributor.corporatename College of Engineering
relation.isAdvisorOfPublication 71d23899-d6d4-4d7f-b9bc-d30323a6f442
relation.isOrgUnitOfPublication c01ff908-c25f-439b-bf10-a074ed886bb7
relation.isOrgUnitOfPublication 7c022d60-21d5-497c-b552-95e489a06569
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