O interesse sobre o papel dos elementos traço na gênese de doenças, na mortalidade e na manutenção da saúde vem sendo cada vez maior. Este trabalho tem como objetivo determinar as concentrações séricas dos elementos: Br, Ca, Cl, Fe, Na, Rb, Se e Zn e correlacioná-las com os aspectos clínicos de uma população de idosos saudáveis. Foram considerados saudáveis os idosos sem senilidade sistêmica e sintomática, sendo selecionamos 101 idosos saudáveis, 33 (32,67%) homens e 68 (67,33%) mulheres com idade média de 71,7 ± 7,1 (60-98). O nível sérico de Se foi significativamente menor em pacientes mais idosos (p < 0.001). Em comparação com os valores de referência, o Br, Cl e Na apresentaram médias menores. Em relação ao sexo, os homens tiveram menores níveis de Br (p < 0,001) e de Se (p = 0,005) com maiores níveis de Fe (p < 0,001). Menores níveis de Se foram relacionados com menor escolaridade (p= 0.013). Os valores de Br estiveram muito abaixo dos valores de referência e a prática da atividade física correlacionou-se com menores níveis de Br (p= 0,008). Poderíamos questionar se os altos níveis de Br seriam prejudiciais ao envelhecimento saudável, se níveis baixos de bromo seriam marcadores de saúde em idosos ou até se existe relação entre hábitos de vida saudáveis com os níveis de Br. A partir dos 71,2 anos, os níveis séricos de selênio começam a cair mesmo em indivíduos saudáveis. Estudos adicionais deverão determinar se o monitoramento dos níveis séricos de selênio pode ser utilizado como marcador precoce do desenvolvimento de doenças e mortalidade / Concern about the role of trace elements in the genesis of disease, mortality and health maintenance has been increasing. This study aims to determine serum concentrations of the elements: Br, Ca, Cl, Fe, Na, Rb, Se and Zn and correlate them with clinical features of a population of healthy elderly. Were considered healthy elderly people without senile systemic symptoms. We selected 101 healthy elderly, 33 (32.67%) men and 68 (67.33%) women with a mean age of 71.7 ± 7.1 (60-98). The serum level of Se was significantly lower in older patients (p <0.001). Compared with the reference values Br, Cl and Na diminished. Longer averages about sex men had lower levels of Br (p <0.001) and Se (p = 0.005) with higher levels of Fe (p <0.001). If lower levels were associated with less education (p = 0.013). Br values were well below the reference values and physical activity correlated with lower levels of Br (p = 0.008). One might question whether high levels of Br would be detrimental for healthy aging, if low levels of bromine were markers of health in the elderly or even if there is a relationship between healthy lifestyle habits with the levels of Br. From 71.2 years, serum levels of selenium begin to fall even in healthy individuals. Additional studies will determine if monitoring of serum levels of selenium can be used as a marker of early development of disease and mortality

<p>Aluminum (Al) is the third most abundant metal on the earth’s surface. An association of Al with Alzheimer’s disease has been suggested, but, given limited human evidence, is controversial. It is possible that exploration of long-term, or cumulative, exposure to Al will help clarify this debate. Therefore, our study hypothesis was that occupational exposure to Al, particularly long-term exposure, is associated with adverse cognitive and olfactory outcomes. </p><p>Biomarkers are important tools in epidemiologic research; however, the reliability and quality of various biomarkers may vary. Therefore, in Chapter 2, we reviewed current evidence on Al biomarkers with the goal to synthesize current understanding regarding their utility for use in research. Our review evaluated 78 papers which discussed various biomarkers of Al exposure. Limited evidence is currently available for Al in nails, hair, breastmilk, saliva and semen. Although they have more daily variation than other biomarkers, blood Al concentrations may differentiate between exposed and non-exposed groups. Unlike blood Al, Al concentrations in both urine and bone are not subject to daily fluctuations. Bone Al appears able to quantify long term Al exposure. Therefore, the use of <i>in vivo</i>neutron activation analysis (IVNAA), a novel bone biomarker, can potentially represent cumulative Al exposure. </p><p>In Chapter 3, we evaluated the hypothesis that the correlation between bone and CEI measurements will be higher than the correlation between bone with fingernail. A cross-sectional cohort of 61 ferroalloy and manufacturing factory workers from Zunyi, China were used in this secondary analysis. Correlations of bone Al with other Al measures (fingernail and cumulative exposure index (CEI)) were assessed for 43 of the factory workers who had bone Al samples. Fingernail samples were analyzed using inductively coupled plasma mass spectrometry. Bone measurements were taken with a compact IVNAA developed by our research team. CEI was calculated as CEI_i=, where C_iis estimated Al exposure based on job title (low/medium/high) and Y_iis the years employed. The CEI was calculated for the prior 5, 10, 15, 20 years and lifetime work history. Median Al values were: 34.4 mg/g (IQR=46) fingernail; 15 mg/g (IQR=28) bone; and 26 (IQR=21) total CEI. Adjusting for age and education, the linear regression model suggests that bone Al is reflective of 15 years of exposure based off the significant association between bone Al and 15-year CEI (b=0.91, <i>p</i><0.02). Other models with CEI were not statistically significant.</p><p>In Chapter 4, we evaluated the association between bone, CEI and fingernail Al measurements with olfactory and cognitive function. The relationship between cognitive and olfactory function was compared with bone Al (N=43), fingernail Al (FnAl) (N=56), 5 year Al CEI and lifetime Al CEI (N=61) measurements. Olfactory function was assessed with the University of Pennsylvania Smell Identification Test and cognitive function was assessed with the WHO/UCLA Auditory Verbal Learning Test (AVLT). Verbal fluency was assessed using Fruit Naming and Animal Naming. Additional variables were assessed via questionnaire. Linear regression models, adjusted for age, education, current alcohol consumption and current smoking status, showed a significant association between higher BnAl and higher recall on the AVLT interference list (b=0.04, 95% Confidence interval (CI)=0.01, 0.08) and higher 5-year CEI with higher recall on the fifth AVLT trial (b=-0.23, 95% CI=-0.45, -0.01). No significant association between FnAl and lifetime CEI with olfactory and cognitive function was observed. </p><p>In Chapter 5, we explored the potential for interactions of Al with another metal to impact the potential association of Al with cognitive and olfactory function. Interaction models used the natural log of fingernail Al with each of copper (Cu), manganese (Mn), lead (Pb) and zinc (Zn) for the 56 male workers. The linear regression models controlled for age, education current alcohol consumption, current smoking status, and all five fingernail metals. Higher ln(FnMn) was associated with lower recall for several AVLT trials. The interaction term for ln(FnAl) and ln(FnZn) was significantly associated with AVLT Trial 1 (β= 1.99, 95% CI=0.07, 3.93), AVLT Trial 5 (β= 2.71, 95% CI= 0.02, 5.41) and AVLT average (β=2.11, 95% CI=0.01, 4.21). </p>Overall, this research presents valuable information regarding noninvasive, <i>in vivo</i>assessment of BnAl and its relationship with other Al biomarkers and measures of cognitive function. To the best of our knowledge, this is the largest study to use INVAA BnAl measurements to quantify long-term aluminum exposures within an occupational population, the first to compare BnAl with an estimate of cumulative Al exposure. Additionally, we are not aware of prior studies which have examined the interaction of fingernail metals, including Al, with olfactory and cognitive tests. Our results suggest BnAl is significantly associated with the prior 15-years of Al exposure and that IVNAA to assess BnAl can be used in field epidemiology studies. For our study, there was limited evidence of an association of BnAl and 5-year CEI with cognitive function. Most comparisons did not show any evidence of an association of Al with cognitive or olfactory function, but a statistically significant interaction between Al and Zn with some measures of cognitive function was observed. It is recommended that our findings be confirmed with larger studies.

O controle da composição dos elementos presentes nos suplementos nutricionais é de grande importância devido ao crescente consumo e a comercialização de diversos tipos e marcas destes produtos. A determinação da quantidade de elementos nos suplementos torna – se necessária para comparar com os valores declarados nos seus rótulos. Neste trabalho, a ativação com nêutrons foi aplicada à análise de 11 amostras de suplementos, adquiridos em farmácias e em lojas de produtos naturais. As amostras, adquiridas nas formas de cápsulas ou comprimidos foram moídas para se obter as na forma de pó homogêneo. As amostras e os padrões sintéticos dos elementos foram irradiados no reator nuclear de pesquisas IEA-R1. Irradiações de 8 h sob um fluxo de nêutrons térmicos de 5x1012 n cm –2 s-1 foram realizadas para a determinação dos elementos Ca, Co, Cr, Fe, Se e Zn e para a determinação dos elementos As, Cu, Fe, K, Na as amostras foram irradiadas por 1 h sob fluxo de nêutrons térmicos da ordem de 1x1012 n cm –2 s-1. As medidas das atividades gama induzidas foram realizadas usando um detector de Ge hiperpuro acoplado a um espectrometro de raios gama. Os resultados das quantidades obtidas nas amostras de suplementos foram em geral, concordantes com os valores apresentados nos seus respectivos rótulos. Elementos tóxicos como As, Cd, Hg e Sb não foram detectados em nenhuma das amostras. Para o controle da qualidade dos resultados analíticos com relação à exatidão e precisão foram analisados os materiais certificados de referência NIST 1400 Bone Ash e NIST 1633b Coal Fly Ash ambos da National Institute of Standards and Technology (NIST). Os resultados obtidos nestes materiais de referência apresentaram uma boa precisão e exatidão e os valores de Z score ou diferença padronizada obtidos das análises, foram menores que 2 indicando que os resultados obtidos são satisfatórios e estão dentro da faixa dos valores dos certificados a um nível de confiança de 95%. / The control of element composition in nutritional supplements is of great interest due to increasingly high consumption and a large diversity and brands of these products offered in market. Therefore, there is the necessity to evaluate the element contents in the supplements and to compare with those values declared on the labels. In this study neutron activation analysis (NAA) was applied to evaluate the element composition of 11 commercial nutritional supplement brands bought in natural product drugstores and pharmacies. These samples acquired in capsule or tablet forms were ground to a homogeneous powder. The samples were irradiated together with the elemental standards in the IEA-R1 nuclear research reactor. Irradiations of 8 h under a thermal neutron flux of 5x1012n cm-2s-1 were carried out for Ca, Co, Cr, Fe, Se and Zn determinations. For Cu, K and Na determinations thermal neutron flux of 1x1012n cm-2s-1 was used and, the exposure time was 1h. The induced gamma activities were measured using a hyperpure Ge detector coupled to a gamma ray spectrometer. The obtained results compared with the values of the labels of nutritional supplements presented good agreement for most of the elements. Toxic elements such as As, Cd, Hg and Sb were not detected in the samples. For quality control of the analytical data, certified reference materials NIST 1400 Bone Ash and NIST 1633b Coal Fly Ash provided by the National Institute of Standards and Technology were also analysed. Accuracy and precision of these results were evaluated. The obtained Z score values were lower than 2 indicating that the data are within the ranges of certified values at 95% confidence level.

No presente estudo valores de referência para Br (0,0008 - 0,0056 gL-1), Ca (0,089 - 0,369 gL-1), Cl (2,10 - 3,26 gL-1), Fe (0,381 - 0,689 gL-1), I (0,00018 - 0,00266 gL-1), K (1,14 - 2,74 gL-1), Mg (0,030 - 0,074 gL-1), Na (1,36 - 2,80 gL-1), P (<1,99 gL-1), S (0,99 - 2,79 gL-1) e Zn (0,0012 - 0,0048 gL-1) bem como a matriz de correlação em sangue de eqüinos da Raça Crioula foram determinados utilizando metodologia nuclear (técnica de Análise por Ativação com Nêutrons). Estes dados permitiram identificar alterações fisiológicas relacionadas ao gênero e regime de exercício em que se enquadram estes animais (produção de soros hiperimunes no Instituto Butantan, São Paulo, Brasil). Para realização dessas análises foram utilizados 20 cavalos adultos (8 machos e 12 fêmeas) sadios, na faixa etária de 1 a 3 anos e peso médio de 350 kg, mantidos na Fazenda São Joaquim do Instituto Butantan (São Paulo). Outro grupo recém imunizados, composto por 6 cavalos machos (mesmo peso e idade) foram também analisados. Estes dados auxiliaram na interpretação das funções fisiológicas desses elementos no sangue destes animais durante o processo de imunização para produção de soros. / In this study the reference value for Br (0,0008 - 0,0056 gL-1), Ca (0,089 - 0,369 gL-1), Cl (2,10 - 3,26 gL-1), Fe (0,381 - 0,689 gL-1), I (0,00018 - 0,00266 gL-1), K (1,14 - 2,74 gL-1), Mg (0,030 - 0,074 gL-1), Na (1,36 - 2,80 gL-1), P (<1,99 gL-1), S (0,99 - 2,79 gL-1) and Zn (0,0012 - 0,0048 gL-1) as well as the correlation matrix in blood of Crioulo breed horses were determined using nuclear methodology (Neutron Activation Analysis Technique). These data allowed to identifying physiological alterations related to the sex and regime of exercise (hyperimmune sera production at Butantan Institute, São Paulo, Brasil). To perform these analyses was used 20 adult horses (8 males and 12 females), with average mass 350 kg, without clinical signs of disease, 1-3 years old, kept on pasture in São Joaquim Farm at Butantan Institute (São Paulo city). Other group just immunized, composed by 6 equines males (same age and weight), were also analyzed. These data are an important support to understand the physiological functions of these elements in blood during the process of sera production.

O controle da composição dos elementos presentes nos suplementos nutricionais é de grande importância devido ao crescente consumo e a comercialização de diversos tipos e marcas destes produtos. A determinação da quantidade de elementos nos suplementos torna – se necessária para comparar com os valores declarados nos seus rótulos. Neste trabalho, a ativação com nêutrons foi aplicada à análise de 11 amostras de suplementos, adquiridos em farmácias e em lojas de produtos naturais. As amostras, adquiridas nas formas de cápsulas ou comprimidos foram moídas para se obter as na forma de pó homogêneo. As amostras e os padrões sintéticos dos elementos foram irradiados no reator nuclear de pesquisas IEA-R1. Irradiações de 8 h sob um fluxo de nêutrons térmicos de 5x1012 n cm –2 s-1 foram realizadas para a determinação dos elementos Ca, Co, Cr, Fe, Se e Zn e para a determinação dos elementos As, Cu, Fe, K, Na as amostras foram irradiadas por 1 h sob fluxo de nêutrons térmicos da ordem de 1x1012 n cm –2 s-1. As medidas das atividades gama induzidas foram realizadas usando um detector de Ge hiperpuro acoplado a um espectrometro de raios gama. Os resultados das quantidades obtidas nas amostras de suplementos foram em geral, concordantes com os valores apresentados nos seus respectivos rótulos. Elementos tóxicos como As, Cd, Hg e Sb não foram detectados em nenhuma das amostras. Para o controle da qualidade dos resultados analíticos com relação à exatidão e precisão foram analisados os materiais certificados de referência NIST 1400 Bone Ash e NIST 1633b Coal Fly Ash ambos da National Institute of Standards and Technology (NIST). Os resultados obtidos nestes materiais de referência apresentaram uma boa precisão e exatidão e os valores de Z score ou diferença padronizada obtidos das análises, foram menores que 2 indicando que os resultados obtidos são satisfatórios e estão dentro da faixa dos valores dos certificados a um nível de confiança de 95%. / The control of element composition in nutritional supplements is of great interest due to increasingly high consumption and a large diversity and brands of these products offered in market. Therefore, there is the necessity to evaluate the element contents in the supplements and to compare with those values declared on the labels. In this study neutron activation analysis (NAA) was applied to evaluate the element composition of 11 commercial nutritional supplement brands bought in natural product drugstores and pharmacies. These samples acquired in capsule or tablet forms were ground to a homogeneous powder. The samples were irradiated together with the elemental standards in the IEA-R1 nuclear research reactor. Irradiations of 8 h under a thermal neutron flux of 5x1012n cm-2s-1 were carried out for Ca, Co, Cr, Fe, Se and Zn determinations. For Cu, K and Na determinations thermal neutron flux of 1x1012n cm-2s-1 was used and, the exposure time was 1h. The induced gamma activities were measured using a hyperpure Ge detector coupled to a gamma ray spectrometer. The obtained results compared with the values of the labels of nutritional supplements presented good agreement for most of the elements. Toxic elements such as As, Cd, Hg and Sb were not detected in the samples. For quality control of the analytical data, certified reference materials NIST 1400 Bone Ash and NIST 1633b Coal Fly Ash provided by the National Institute of Standards and Technology were also analysed. Accuracy and precision of these results were evaluated. The obtained Z score values were lower than 2 indicating that the data are within the ranges of certified values at 95% confidence level.

O Laboratório de Análise por Ativação com Nêutrons (LAN-IPEN) vem analisando amostras geológicas, tais como rochas, solos e sedimentos, há vários anos, empregando o método de análise por ativação com nêutrons comparativa, visando estudos geoquímicos e ambientais. Este trabalho apresenta os resultados obtidos na implementação do método de padronização k0-INAA no LANIPEN, para a análise de amostras geológicas, utilizando o programa k0-IAEA, fornecido pela Agência Internacional de Energia Atômica (IAEA). A razão do fluxo de nêutrons térmico-epitérmico f e o fator &alpha; da distribuição de fluxo de nêutrons epitérmicos do reator IEA-R1 do IPEN foram determinados na estação pneumática de irradiação, e em uma posição de irradiação selecionada, para irradiações curtas e longas, respectivamente. Para obter esses fatores, foi utilizado o chamado método bare triple-monitor com 197Au-96Zr-94Zr. Para avaliar a exatidão e precisão do método, foram analisados os materiais geológicos de referência basalto JB-1 (GSJ) e BE-N (IWG-GIT), andesito AGV-1 (USGS), granito GS-N (ANRT), SOIL-7 (IAEA) e sedimento Buffalo River Sediment (NIST BRS-8704), que representam diferentes matrizes geológicas. Os resultados obtidos para até 30 elementos concordaram com os valores recomendados, com erros relativos (bias) menores que 10%, exceto no caso do Zn no AGV-1 (11,4%) e Mg no GS-N (13,4%). Os critérios estatísticos z-score, zeta-score e U-score foram aplicados para avaliação dos resultados. Pelo critério do z-score, os resultados obtidos puderam ser considerados satisfatórios (z<2), com exceção dos resultados obtidos para Mg no GS-N e no JB-1, e para Yb no Soil-7. O critério estatístico zeta-score se mostrou o mais restritivo, obtendo-se resultados questionáveis (2 < zeta < 3) para Mg no BE-N, Mn no GS-N e Yb no Soil-7, e resultados insatisfatórios (zeta>3) para Mn no BE-N, Mg, Ce e La no GS-N, Mg no JB-1, e Th e Eu no Buffalo River Sediment. Os valores de U-score mostraram que todos os resultados, com exceção do valor para Mg no JB-1, estão dentro de um intervalo de confiança de 95% (se for considerado 1,96 o valor limite para o Uteste para um nível de probabilidade de 95%). Estes resultados indicam excelentes possibilidades para o uso deste método paramétrico no LAN-IPEN para a análise de amostras geológicas em estudos geoquímicos e ambientais. / The Neutron Activation Analysis Laboratory (LAN-IPEN) has been analysing geological samples such as rocks, soils and sediments, for many years with the INAA comparative method, for geochemical and environmental research. This study presents the results obtained in the implementation of the k0-standardization method at LANIPEN, for geological sample analysis, by using the program k0- IAEA, provided by the International Atomic Energy Agency (IAEA). The thermal to epithermal flux ratio f and the shape factor &alpha; of the epithermal flux distribution of the IPEN IEA-R1 nuclear reactor were determined for the pneumatic irradiation facility and one selected irradiation position, for short and long irradiations, respectively. To obtain these factors, the bare triple-monitor method with 197Au- 96Zr-94Zr was used. In order to validate the methodology, the geological reference materials basalts JB-1 (GSJ) and BE-N (IWG-GIT), andesite AGV-1 (USGS), granite GS-N (ANRT), SOIL-7 (IAEA) and sediment Buffalo River Sediment (NISTBRS-8704), which represent different geological matrices, were analysed. The concentration results obtained agreed with assigned values, with bias less than 10% except for Zn in AGV-1 (11.4%) and Mg in GS-N (13.4%). Three different scores were used to evaluate the results: z-score, zeta-score and Uscore. The z-score showed that the results can be considered satisfactory (z<2), except for Mg in GS-N and JB-1, and for Yb in Soil-7. Zeta-score was the most restrictive criterion, indicating questionable results (2 < zeta < 3) for Mg in BE-N, Mn in GS-N and Yb in Soil-7, and unsatisfactory results (zeta>3) for Mn in BE-N, Mg, Ce and La in GS-N, Mg in JB-1, and Th and Eu in Buffalo River Sediment. The U-score test showed that all results, except Mg in JB-1, were within 95% confidence interval. These results indicate excellent possibilities of using this parametric method at the LAN-IPEN for geological samples analysis in geochemical and environmental studies.

High-energy ion beam based proton induced x-ray (PIXE) is an ideal analytical tool suitable for simultaneous quantification of trace elements with high accuracy. The quantification of trace elements in solids using PIXE has been well established for over two decades. The main objective of this study is to extend this capability to solids with an inhomogeneous internal structure. In this study, pure GAC and PAC samples were soaked in known concentration of arsenic (As) solution and the trace amount of As uptake was determined during these exposures using PIXE, neutron activation analysis (NAA) and atomic absorption spectroscopy (AAS). There is a good agreement between the values and adsorption mechanisms derived from the NAA and pelletised PIXE measurements and some AAS measurements. Micro-PIXE was used to understand the discrepancies in the As adsorption on the pore and flat surfaces of GAC samples. / Master of Science (Hons) (Physics)

14.8-MeV neutrons from a Cockcroft-Walton type accelerator/neutron generator have been used to irradiate particulate and ionic samples prepared from river water. Five-minute irradiations were performed in a flux of order 109 neutrons/cm2/sec at target position. Gamma-ray spectra resulting from the activated products were recorded with a spectrometer system consisting of a high resolution Ge(Li) detector (2.5% efficiency at 1330 keV) and multichannel analyzer. Trace elements present in the samples were identified by the characteristic gamma-ray energies and half lives associated with the decay products. Standards of known concentration were used to make relative determinations of the quantities of trace elements present in the water. Elements observed in samples with parts per million concentrations include Al, Ba, Ca, Cl, Cr, Fe, K, Mg, Na, Si, and Sr. Sensitivities for elements not observed in the water samples were also determined for As, Cd, Hg, Ni, Ti, Zn, and Zr.Ball State UniversityMuncie, IN 47306

Various samples of ultra-pure germanium were lithium diffused for approximately one day at temperatures ranging from 300° to 4500 C under an inert atmosphere. Lithium precipitation kinetics were characterized utilizing D-C electrical conductivity measurements at room temperature. Selected samples were subsequently exposed to an estimated total integratedfast-neutron flux of order 1012 /cm2. Following the irradiation process, lithium precipitation subsequent to annealing at various temperatures was studied, again through the eletrical conductivity. It was noted that the presence of the fast-neutron generated disordered regions can initiate precipitation in lithium -diffused germanium in which no post-diffusion precipitation was observed.Utilizing Frank S. Ham's Theory of Diffusion -Limited Precipitation for spherical precipitate centers, and the precipitation kinetics data obtained, the density of precipitate centers was calculated as a function of annealing temperature. The variations in the density of precipitate centers with annealing temperature suggest this method as possibly useful in studies of annealing behavior of disordered regions in germanium.Ball State UniversityMuncie, IN 47306

The dissolution of the Soviet Union coupled with the growing sophistication of international terror organizations has brought about a desire to ensure that a sound infrastructure exists to interdict smuggled nuclear material prior to leaving its country of origin. To combat the threat of nuclear trafficking, radiation portal monitors (RPMs) are deployed around the world to intercept illicit material while in transit by passively detecting gamma and neutron radiation. Portal monitors in some locations have reported abnormally high gamma background count rates. The higher background data has been attributed, in part, to the concrete surrounding the portal monitors. Higher background can ultimately lead to more material passing through the RPMs undetected. This work is focused on understanding the influence of the concrete surrounding the monitors on the total gamma ray background for the system. This research employed a combination of destructive and nondestructive analytical techniques with computer simulations to form a model that may be adapted to any RPM configuration. Six samples were taken from three different composition concrete slabs. The natural radiologcal background of these samples was determined using a high-purity germanium (HPGe) detector in conjunction with the Canberra In-Situ Object Counting System (ISOCS™) and Genie™ 2000 software packages. The composition of each sample was determined using thermal and fast neutron activation analysis (NAA) techniques. The results from these experiments were incorporated into a Monte Carlo N-Particle (MNCP) photon transport simulation to determine the expected gamma ray count rate in the RPM due to the concrete. The results indicate that a quantitative estimate may be possible if the experimental conditions are optimized to eliminate sources of uncertainty. Comparisons of actual and simulated count rate data for 137Cs check sources showed that the model was accurate to within 15%. A comparison of estimated and simulated count rates in one concrete slab showed that the model was accurate to within 4%. Subsequent sensitivity analysis showed that if the elemental concentrations are well known, the carbon and hydrogen content could be easily estimated. Another sensitivity analysis revealed that the small fluctuations in density have a minimal impact on the gamma count rate. The research described by this thesis provides a method by which RPM end users may quantitatively estimate the expected gamma background from concrete foundations beneath the systems. This allows customers to adjust alarm thresholds to compensate for the elevated background due to the concrete, thereby increasing the probability of intercepting illicit radiological and nuclear material.