Statistical Analysis of Radioactivity: Lamprecht Uranium Mine in Texas.

ABSTRACT: The former Lamprecht uranium mine facility in Texas ceased operations well before the new millennium. However, decommissioning activities were never completed by the licensee. Consequently, a legal proceeding was authorized between state and licensee representatives. Meanwhile, state funds were used to hire an independent contractor to perform radiological surveys and assess the magnitude of residual radioactivity across the terrain at the site. The purpose of this study was to apply advanced spatial statistical methods to the survey data measured by contractors at the Lamprecht site to precisely predict remaining radioactive hotspot locations post soil remediation activities. To accomplish this, descriptive statistics such as Google maps and boxplots along with inferential spatial statistical techniques, e.g., kriging and semivariograms, were employed. R coding was also used throughout. Specifically, the descriptive statistical methods included geographical mapping of targeted areas at the site coupled with summary statistics. Inferentially, spatial analytical techniques were employed to pinpoint the locations of elevated radiation levels above regulatory limits. Our results suggest that fewer hotspots were identified after remediation activities were completed at the site. This study provides an additional analytical resource for the State of Texas regarding the release of this former in situ leach uranium mine site to landowners for unrestricted use.

A Cyclotron Decommissioning Radiological Assessment Exercise Performed by Student Mentees Underrepresented in the Radiation Safety Profession.

Cyclotrons used in nuclear medicine imaging accelerate protons, deuterons, and helium ions to bombard a target, which produces nuclear reactions that generate positron-emitting radionuclides. Secondary neutrons are nonuniformly emitted in these reactions and induce heterogeneous activation of the cyclotron components and concrete vault enclosure. This poses radioactive waste management complications when decommissioning a cyclotron facility, since the objective is to ensure that exposures are within regulatory limits and as low as reasonably achievable (ALARA). The McGovern Medical School in The University of Texas Health Science Center in Houston housed a Scanditronix MC40 cyclotron that produced short-lived radioisotopes for Positron Emission Tomography (PET) imaging from 1984 to 2001 until Tropical Storm Allison rendered it inoperable. The purpose of this study was to provide underrepresented Science, Technology, Engineering and Mathematics (STEM) students an ALARA experience with a practical problem encountered in the radiation safety profession. Gamma dose rate measurements were performed with both a Mirion InSpector 1000 spectrometer and Fluke 451P survey meter in the vault at locations identified as hotspots based on preliminary scoping surveys with the Ludlum model 44-9 detector. However, gamma spectra were measured with the spectrometer exclusively at hotspots along the west wall. Results indicated the maximum gamma dose rate of 129 ± 31 nSv h was about 2 times background near the central beam transport line of the now inoperable cyclotron. Furthermore, gamma emission peaks were identified in the spectra from trace amounts of Co and Eu in the vault's concrete walls.

Measurement of the Background Gamma Dose Rates in Houston, Texas: A Descriptive Summary of an Undergraduate Research Mentored Project Performed by Students Underrepresented in the Health Physics Profession.

Natural background radiations include cosmic, terrestrial, and medical sources. Cosmic radiation is mostly shielded by the magnetic field of the Earth; however, those that penetrate can produce nuclear interactions within the Earth's atmosphere yielding cosmic ray showers. Terrestrial and medical sources of radioactivity are typically identified through radionuclide-specific decay signatures. Medical sources of radiation mainly result from diagnostic x rays, which attenuate into the environment. These x rays also contribute slightly to background radiation. The purpose of this study was to have students involved with the Texas Southern University (TSU) health physics program measure and report background gamma dose rates in Houston, Texas, using the Canberra InSpector 1000 Digital Hand-Held Multichannel Analyzer. The results were compared with the average gamma dose rate on Earth. Of note, TSU is one of the largest historically black colleges and universities (HBCUs) in the nation and currently boasts the only undergraduate health physics program in Houston. Targeted locations were selected within the I-610 loop of Houston covering an area of approximately 100 km. Measurements were performed at nine locations and verified by GPS latitude and longitude coordinates. The dose rate was measured over a 100 m area at each location, while spectral analysis was simultaneously performed for natural gamma-emitters. Our results suggest the dose rate averaged over all geographical locations in this study was 0.114 ± 0.001 µSv h and thus, consistent with most literature. The only radionuclide identified in the spectra in all measurements was K due to the limited energy resolution of the InSpector 1000.

Feasibility studies of a passive scatter proton therapy nozzle without a range modulator wheel.

The purpose of this work was to determine the feasibility of producing a spread out Bragg peak (SOBP) without a range modulation wheel (RMW) using the passive scattering beam delivery technique. For this study, a comprehensive Monte Carlo model of a passive scattering treatment nozzle was used. The RMW was removed from the model leaving only the initial fixed scatterer (RMW-free configuration). Range modulation was achieved by directly changing the energy of the proton beam entering the nozzle. To produce a uniform SOBP, the number of protons injected into the nozzle at each beam energy was "dose weighted." To do so, the effective number of protons was calculated for the individual initial energies using an analytical dose-weighting function, and the resulting weighted Bragg curves were summed together to produce an SOBP of the desired width. We found that SOBPs calculated using the RMW-free nozzle configuration were in very good agreement to those calculated with the standard nozzle configuration containing the RMW for the 250, 180, and 100 MeV maximum beam energies. The depth of the distal 90% dose and the 80%-20% distal dose falloff of SOBPs calculated with the two different nozzle configurations agreed to within a millimeter for the three beam energy options considered in this study. In addition, the 80%-20% lateral penumbra for the cross-field dose profiles calculated with the RMW-free delivery method agreed with results calculated using the standard RMW technique to less than one millimeter. For an equal number of protons injected into the nozzle, an increase of up to 10% in the delivered dose and a significant reduction in both the in-air secondary neutron fluence and dose equivalent (H/D) were observed at the isocenter by removing the RMW from the treatment nozzle and modulating the initial proton beam energy. However, increases in delivery time of up to 70% were also estimated with this method. Our results suggest that it is feasible to deliver a passively scattered dose distribution with an RMW-free nozzle configuration with clinical characteristics comparable to those using standard methods.

Initial beam size study for passive scatter proton therapy. I. Monte Carlo verification.

The purpose of this work was to provide an initial validation of a Monte Carlo (MC) model of the passive scattering treatment nozzle at the University of Texas M. D. Anderson Cancer Center Proton Therapy Center. The MC model included a detailed definition of each beam-modifying element in the nozzle, and calculations accounted for interactions of the beam with the rotating modulator wheel used to create the spread out Bragg peak. In this work we show comparisons of calculated dose and fluence profiles with measured data from the nozzle for the 250 and 180 MeV beam energies used for patient treatments. Agreement to within 1.5 mm of measured data was observed for all MC calculations. The high level of agreement between the measurements and the MC model for the two beam energies studied provides validation for use of the model in a study of the dosimetric effects of the proton beam size and shape at the nozzle entrance.

Initial beam size study for passive scatter proton therapy. II. Changes in delivered depth dose profiles.

In passively scattered proton radiotherapy, a clinically useful treatment beam is produced by spreading a small proton "pencil beam" extracted from the accelerator to create both a uniform dose profile laterally and a uniform spread-out Bragg peak (SOBP) in depth. Lateral spreading and range modulation of the beam are accomplished using specially designed components within the treatment delivery nozzle. The purpose of this study was to determine how changes in the size of the initial proton pencil beam affect the delivery of dose with a passive scatter treatment nozzle. Monte Carlo calculations were used to study changes of the beam's in-air energy distribution at the exit of the nozzle and the central axis depth dose profiles in water resulting from changes in the incident beam size. Our results indicate that the width of the delivered SOBP decreases as the size of the initial beam increases.

Nitrogen oxides elicit antipredator responses in juvenile channel catfish, but not in convict cichlids or rainbow trout: conservation of the ostariophysan alarm pheromone.

Recent studies with cyprinid and characin (superorder Ostariophysi) fishes suggest that purine-N-oxides function as chemical alarm cues (alarm pheromones) and that the nitrogen oxide functional group acts as the chief molecular trigger. To further test the hypothesis that the nitrogen-oxide functional group is evolutionarily conserved as an active component of the Ostariophysan alarm pheromone system, we exposed juvenile channel catfish (Ictalurus punctatus, Siluriformes) to conspecific skin extract, hypoxanthine-3-N-oxide (the putative alarm pheromone) and a suite of structurally and functionally similar compounds. Conspecific skin extract and hypoxanthine-3-N-oxide elicited significant increases in species typical antipredator behaviors. A structurally dissimilar compound possessing a nitrogen oxide functional group (pyridine-N-oxide) elicited a significant, but less intense alarm response. Compounds lacking a nitrogen oxide functional group were not significantly different from control stimuli. In addition, two non-Ostariophysan species known to possess chemical alarm cues (convict cichlids, Acrchocentrus nigrofasciatus, Cichlidae, Acanthopterygii and rainbow trout, Oncorhynchus mykiss, Salmonidae, Protacanthopterygii) did not show any increase in antipredator behavior in response to hypoxanthine-3-N-oxide. These data demonstrate the conservation of chemical alarm cues within at least three orders of the superorder Ostariophysi.