John D. Brockman

Demonstration of a radiation resistant, high efficiency SiC betavoltaic

A SiC p-i-n junction betavoltaic was fabricated, and electrical power output under irradiation from an 8.5GBq P33 source was monitored over a period of four half-lives of the radioisotope. The open-circuit voltage (VOC) of the device was 2.04±0.02V, and the peak power (Pout) was 0.58±0.02μW (2.1±0.2μW∕cm2) at 1.60V. The conversion efficiency (ηconv) was 4.5%±0.3% and the normalized power output indicates no device degradation over more than 3months (four half-lives of the source).

Boron neutron capture therapy demonstrated in mice bearing EMT6 tumors following selective delivery of boron by rationally designed liposomes

The application of boron neutron capture therapy (BNCT) following liposomal delivery of a 10B-enriched polyhedral borane and a carborane against mouse mammary adenocarcinoma solid tumors was investigated. Unilamellar liposomes with a mean diameter of 134 nm or less, composed of an equimolar mixture of cholesterol and 1,2-distearoyl-sn-glycero-3-phosphocholine and incorporating Na3[1-(2′-B10H9)-2-NH3B10H8] in the aqueous interior and K[nido-7-CH3(CH2)15-7,8-C2B9H11] in the bilayer, were injected into the tail veins of female BALB/c mice bearing right flank EMT6 tumors. Biodistribution studies indicated that two identical injections given 24 h apart resulted in tumor boron levels exceeding 67 µg/g tumor at 54 h—with tumor/blood boron ratios being greatest at 96 h (5.68:1; 43 µg boron/g tumor)—following the initial injection. For BNCT experiments, tumor-bearing mice were irradiated 54 h after the initial injection for 30 min with thermal neutrons, resulting in a total fluence of 1.6 × 1012 neutrons per cm2 (±7%). Significant suppression of tumor growth was observed in mice given BNCT vs. control mice (only 424% increase in tumor volume at 14 d post irradiation vs. 1551% in untreated controls). In a separate experiment in which mice were given a second injection/irradiation treatment 7 d after the first, the tumor growth was vastly diminished (186% tumor volume increase at 14 d). A similar response was obtained for mice irradiated for 60 min (169% increase at 14 d), suggesting that neutron fluence was the limiting factor controlling BNCT efficacy in this study.

Association of Seafood Consumption, Brain Mercury Level, and APOE ε4 Status With Brain Neuropathology in Older Adults

IMPORTANCE Seafood consumption is promoted for its many health benefits even though its contamination by mercury, a known neurotoxin, is a growing concern. OBJECTIVE To determine whether seafood consumption is correlated with increased brain mercury levels and also whether seafood consumption or brain mercury levels are correlated with brain neuropathologies. DESIGN, SETTING, AND PARTICIPANTS Cross-sectional analyses of deceased participants in the Memory and Aging Project clinical neuropathological cohort study, 2004-2013. Participants resided in Chicago retirement communities and subsidized housing. The study included 286 autopsied brains of 554 deceased participants (51.6%). The mean (SD) age at death was 89.9 (6.1) years, 67% (193) were women, and the mean (SD) educational attainment was 14.6 (2.7) years. EXPOSURES Seafood intake was first measured by a food frequency questionnaire at a mean of 4.5 years before death. MAIN OUTCOMES AND MEASURES Dementia-related pathologies assessed were Alzheimer disease, Lewy bodies, and the number of macroinfarcts and microinfarcts. Dietary consumption of seafood and n-3 fatty acids was annually assessed by a food frequency questionnaire in the years before death. Tissue concentrations of mercury and selenium were measured using instrumental neutron activation analyses. RESULTS Among the 286 autopsied brains of 544 participants, brain mercury levels were positively correlated with the number of seafood meals consumed per week (ρ = 0.16; P = .02). In models adjusted for age, sex, education, and total energy intake, seafood consumption (≥ 1 meal[s]/week) was significantly correlated with less Alzheimer disease pathology including lower density of neuritic plaques (β = -0.69 score units [95% CI, -1.34 to -0.04]), less severe and widespread neurofibrillary tangles (β = -0.77 score units [95% CI, -1.52 to -0.02]), and lower neuropathologically defined Alzheimer disease (β = -0.53 score units [95% CI, -0.96 to -0.10]) but only among apolipoprotein E (APOE ε4) carriers. Higher intake levels of α-linolenic acid (18:3 n-3) were correlated with lower odds of cerebral macroinfarctions (odds ratio for tertiles 3 vs 1, 0.51 [95% CI, 0.27 to 0.94]). Fish oil supplementation had no statistically significant correlation with any neuropathologic marker. Higher brain concentrations of mercury were not significantly correlated with increased levels of brain neuropathology. CONCLUSIONS AND RELEVANCE In cross-sectional analyses, moderate seafood consumption was correlated with lesser Alzheimer disease neuropathology. Although seafood consumption was also correlated with higher brain levels of mercury, these levels were not correlated with brain neuropathology.

The Nail as a Noninvasive Indicator of Methylmercury Exposures and Mercury/Selenium Molar Ratios in Brain, Kidney, and Livers of Long-Evans Rats

Animal studies indicate that the toxic effects of methylmercury (MeHg) exposures increase when selenium (Se) status is low. Toxicity is directly proportional to Hg/Se molar ratios in critical tissues such as brain and increase dramatically as molar ratios exceed 1:1. In this study, we examined the nail as a biomonitor of Hg/Se molar ratios in kidney, liver, and brain tissues of weanling male Long-Evans rats fed controlled diets containing varying amounts of Se and MeHg. Linear regression analyses indicate that the natural log transform of the Hg/Se ratio in the nails is strongly related to the Hg/Se molar ratio in kidney, liver, and brain (p < 0.01 in all cases). The nail appears to be a reliably accurate noninvasive biomonitor of the Hg/Se molar ratio in tissues and should, therefore, be considered for use in human studies.

Fast and reliable method for As speciation in urine samples containing low levels of As by LC-ICP-MS: Focus on epidemiological studies

The speciation analysis of As in urine samples can provide important information for epidemiological studies. Considering that these studies involve hundreds or thousands of samples, a fast and reliable method using a simple LC system with short-length mixed bed ion exchange chromatographic column coupled to ICP-MS for As speciation in human urine samples was developed in this work. Separation of AB+TMAO, DMA, AC, MMA and AsIII+AsV was accomplished within 5min with good resolution when ammonium carbonate solutions were used as mobile phases and H2O2 was added to samples to quantitatively convert AsIII-AsV. Repeatability studies yielded RSD values from 2.0% to 4.8% for all species evaluated. Limits of detection (LOD) for As species ranged from 0.003 to 0.051ngg-1. Application of the method to human urine samples from a non-contaminated area showed that the sum of species measured corresponded to 62-125% of the total As in the sample. The recovery values for these species in urine SRM 2669 were in the range of 89-112% and demonstrated the suitability of the proposed method for epidemiological studies.

Spectral performance of a composite single-crystal filtered thermal neutron beam for BNCT research at the University of Missouri

Parameter studies, design calculations and initial neutronic performance measurements have been completed for a new thermal neutron beamline to be used for neutron capture therapy cell and small-animal radiobiology studies at the University of Missouri Research Reactor. The beamline features the use of single-crystal silicon and bismuth sections for neutron filtering and for reduction of incident gamma radiation. The calculated and measured thermal neutron fluxes produced at the irradiation location are 9.6 x 10(8) and 8.8 x 10(8)neutrons/cm(2)s, respectively. Calculated and measured cadmium ratios (Au foils) are 217 and 132. These results indicate a well-thermalized neutron spectrum with sufficient thermal neutron flux for a variety of small animal BNCT studies.

Measurement of U and Pu isotope ratios in hair and nail samples using extraction chromatography and multi-collector inductively coupled plasma mass spectrometry

A bioassay capable of monitoring occupational or environmental exposure to special nuclear materials would be a useful tool for nuclear nonproliferation programs. Hair and nail are potential biomonitors of exposure to U and Pu. A method is described to measure isotope ratios of ultra-trace concentrations of U and Pu in hair and nail samples. The method uses multiple extraction chromatography resins to separate U and Pu fractions from the sample matrix. The U recovery was quantitative while the Pu recovery ranged from 81% to 109%, with a U decontamination factor of 5×10(4). Following the separation (234)U/(238)U, (235)U/(238)U and (240)Pu/(239)Pu were measured in human hair and hair and nail samples using multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS). The human hair and nail samples had elevated ratios of (234)U/(238)U which could reflect exposure to naturally fractionated U.

Analysis of k0 neutron activation analysis at the University of Missouri Research Reactor.

k(0) Instrumental Neutron Activation Analysis (k(0) INAA) was evaluated at the University of Missouri Research Reactor (MURR). The MURR, unlike many other research reactors that employ k(0) INAA, is refueled on a weekly basis. To determine if the neutron spectrum is stable enough for routine k(0) INAA analysis, the neutron spectrum parameters alpha and f were measured over a 9 month period. The average values of f and alpha measured using the Cd ratio multi monitor technique were 57.4+/-4.5 and 0.039+/-0.012, respectively. It was determined that k(0) INAA could be used at the MURR by employing the average value of alpha and f. However, significant measurement bias could occur for elements with high Q(0) values if the true spectral parameters deviate by more than 10% from the average value.

Intercalibration of physical neutron dosimetry for the RA-3 and MURR thermal neutron sources for BNCT small-animal research

New thermal neutron irradiation facilities to perform cell and small-animal irradiations for Boron Neutron Capture Therapy research have been installed at the Missouri University Research Reactor and at the RA-3 research reactor facility in Buenos Aires, Argentina. Recognizing the importance of accurate and reproducible physical beam dosimetry as an essential tool for combination and intercomparisons of preclinical and clinical results from the different facilities, we have conducted an experimental intercalibration of the neutronic performance of the RA-3 and MURR thermal neutron sources.

Development of ammonium bifluoride fusion method for rapid dissolution of trinitite samples and analysis by ICP-MS

Field deployable dissolution techniques are needed to decrease response time following a nuclear event. This study tested the capability of NH4HF2 fusion to dissolve trinitite. Dissolution of trinitite by NH4HF2 fusion was compared to conventional microwave digestion. Following digestion, trace elements were measured using ICP-MS. This work demonstrates that low temperature fusion with NH4HF2 is capable of dissolving trinitite samples. The low purity of the NH4HF2 resulted in a higher limit of detection for several elements when compared to microwave digestion with high purity acids.