Of great benefit, but not limited to seafloor mineral exploration, is a technique that fairly rapidly determines the composition of a drilled vibracore (in a time comparable to the time involved in obtaining the core). The rapid assessment is desired to predict whether a given region warrants further exploration by coring. A proposed monitoring system, based on neutron capture gamma ray analysis, consists of a container tank filled with water and tubular extensions that house a Cf-252 neutron source and a detector positioned within the tank. The core sample is passed through the system in stop and count steps. The net count rates, due to "signature" capture gamma rays from neutron capture in elements in the core sample, are proportional to the amount of the element responsible for emitting the capture gamma ray. The proposed system was modeled and simulated by the Monte Carlo method to predict the relationship between the response of the detector and the elemental concentrations within the sample. Accurate and detailed treatment of neutron transport and gamma ray production and attenuation within the system were employed not only to predict the relationship of the photopeak responses with respect to elemental concentrations, but also to permit investigation of the design parameters and structural material changes in the system. The developed Monte Carlo code utilizes a variety of variance reduction techniques, such as implicit absorption with Russian Roulette and deterministic production of the gamma rays of interest, along with a form of correlated sampling to predict simultaneously the responses over a range of interest of the elemental concentrations. The predicted results were compared with predictions obtained from a well established general purpose Monte Carlo code (MCNP). / Graduation date: 1990

With new radioactive isotope accelerators coming online in the next decade, the problem of extracting reliable nuclear structure information from reactions with unstable nuclei deserves considerable attention. A method has been proposed to determine spectroscopic factors (SFs) using the asymptotic normalization coefficient (ANC) to fix the external contribution of a nonperipheral reaction, reducing the uncertainty in the SF. The ¹⁵C[left right arrow]¹⁴C+n system was chosen as a test case for this new method. The direct neutron capture rate on ¹⁴C is important for a variety of topics of interest in astrophysics, and the ANC for ¹⁵C[left right arrow]¹⁴C+n was also used to calculate this reaction rate. The objective of the first part of this work was to find the ANC for ¹⁵C[left right arrow]¹⁴C+n. This was done in two independent experiments. First, the heavy ion neutron transfer reaction ¹³C(¹⁴C,¹⁵C)¹²C was measured at 12 MeV/nucleon. Second, the inverse kinematics reaction d(¹⁴C,p)¹⁵C was measured using the new Texas Edinburgh Catania Silicon Array (TECSA). The next phase of the experimental program was to measure a reaction with a non-negligible interior contribution, for which ¹⁴C(d,p)¹⁵C at 60 MeV deuteron energy was used. This reaction turned out to be more peripheral than anticipated, and as a result, the ANC for the ground state was extracted from this measurement as well. The final results for the three measurements are C²2s1/2 = 1.96±0.16 fm⁻¹ for the ground state and C²1d5/2 = (4.23±0.38)·10⁻³ fm⁻¹ for the first excited state. Because the 60 MeV ¹⁴C(d,p)¹⁵C reaction turned out to have a very weak dependence on the interior, the SF could not be determined for the ¹⁴C+n ground state in ¹⁵C using the new method. A lower limit of 1.05 was found for the first excited state. It is possible that other reactions might turn out to be more suitable for this method, however, the difficulty encountered at this relatively high deuteron energy highlights a substantial problem likely to be seen in other applications. Using the ANCs determined in this work, the astrophysical ¹⁴C(n,γ)¹⁵C reaction rate was calculated. The resulting value for the cross section for capture to the ground state at 23 keV was σgs(23 keV)=5.1±0.4 μb and to the first excited state was σexc(23 keV)=0.2±0.02 μb.

The seabed is envisaged to meet the increased future demands for minerals from the rapidly growing industrialized societies of the world. Shipboard analysis of cores can significantly reduce the cost and time spent at the exploratory drilling stage by obviating the need to go back to land for analysis. It can further speed the exploration process by enabling a quick modification of the exploration plan based on the results of the shipboard analysis. A ²⁵²Cf-based analyzer utilizing the prompt gamma neutron activation analysis technique has been designed. The analyzer is a spherical iron shell with the source at its center. The seabed core is passed through a hollow composite tube which is positioned a short distance directly below the source and the resulting prompt gamma rays are collimated to a HPGe detector. The rest of the sphere is filled with paraffin. The gamma ray flux at the detector is converted into a count rate by using a semi-empirical detector response function. This count rate data are then used to determine the sensitivity and detection limits for the chosen elements (Mg, Al, Ti, Cr, Mn, Fe, Ni and Cu). Monte Carlo simulations using the Monte Carlo neutron photon coupled transport code, MCNP, were carried out for a parametric study of important variables influencing the design of the analyzer. These parameters included the moderator type, source to sample distance and sample porosity. MCNP was then used to model the analyzer and to generate the neutron flux profiles in the sample and the prompt gamma flux at the detector. Due to the non-availability of the prompt gamma data for most of the elements of economic interest in the ENDF/B-V cross section libraries associated with MCNP, the point kernel photon transport code ISOSHLD-II (modified for high energy gamma rays) was used to generate the gamma flux at the detector for specific elements. The ISOSHLD-II source term was calculated based on known gamma production data (thermal capture only) and the thermal neutron flux in the sample obtained from MCNP computations. The sensitivity and detection limits obtained from the isotopic source based analyzer were compared for the case of aluminum with values reported from reactor facilities. The results obtained indicate that the analyzer designed in this work could prove suitable for the on-line analysis of many elements of economic interest in seabed cores at the 1 weight percent level. / Graduation date: 1992

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 146-151). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 146-151). Also available on the Internet.

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

abstract: This thesis deals with the first measurements done with a cold neutron beam at the Spallation Neutron Source at Oak Ridge National Laboratory. The experimental technique consisted of capturing polarized cold neutrons by nuclei to measure parity-violation in the angular distribution of the gamma rays following neutron capture. The measurements presented here for the nuclei Chlorine ( 35Cl) and Aluminum ( 27Al ) are part of a program with the ultimate goal of measuring the asymmetry in the angular distribution of gamma rays emitted in the capture of neutrons on protons, with a precision better than 10-8, in order to extract the weak hadronic coupling constant due to pion exchange interaction with isospin change equal with one ( hπ 1). Based on theoretical calculations asymmetry in the angular distribution of the gamma rays from neutron capture on protons has an estimated size of 5·10-8. This implies that the Al parity violation asymmetry and its uncertainty have to be known with a precision smaller than 4·10-8. The proton target is liquid Hydrogen (H2) contained in an Aluminum vessel. Results are presented for parity violation and parity-conserving asymmetries in Chlorine and Aluminum. The systematic and statistical uncertainties in the calculation of the parity-violating and parity-conserving asymmetries are discussed. / Dissertation/Thesis / Ph.D. Physics 2012

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Made available in DSpace on 2014-10-09T12:26:53Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:05Z (GMT). No. of bitstreams: 0 / Neste trabalho as principais características dosímetricas da solução Fricke Xilenol Gel (FXG) foram estabelecidas para futura aplicação clínica na dosimetria de elétrons. As curvas de dose resposta para feixes de nêutrons térmicos para pesquisa em Terapia por Captura de Nêutrons (BNCT) e feixes elétrons de aplicação industrial também foram determinadas. A técnica padrão de leitura utilizada foi espectrofotometria. Para o feixe clínico as reprodutibilidades intra e inter-lotes da solução FXG são melhores que 1,4 % e 5,1 % respectivamente, o comportamento da resposta para o intervalo de dose entre 0,2 e 40 Gy é linear e independente da energia e da taxa de dose para o intervalo estudado. Devido aos efeitos da oxidação natural do FXG o tempo ótimo entre o preparo e a irradiação é de 24h e o comportamento da curva de dose resposta não se altera no período estudado para a variação da absorvância líquida do dosímetro. Para o estudo com o campo de nêutrons as curvas de dose resposta do FXG apresentaram comportamento linear em todo intervalo de dose estudado, e para campos industriais de elétrons o comportamento é exponencial decrescente. De acordo com os resultados obtidos para os feixes de radiação estudados, não houve alteração na posição das bandas características do espectro de absorção do FXG. Como testes adicionais, foi determinada a viabilidade do uso do método de leitura do FXG por imagens fotográficas digitais e aplicação do FXG na dosimetria para braquiterapia intracavitária. O bom desempenho do dosímetro FXG nos testes realizados indica que este pode ser utilizado na avaliação tridimensional da dose em tratamento radioterápicos. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP