Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 112-116).

Made available in DSpace on 2014-10-09T12:38:13Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:33Z (GMT). No. of bitstreams: 1 05657.pdf: 4842908 bytes, checksum: 494ca773331866a32eca85a48d2e214c (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The relative abundances of the stable and long-lived Isotopes of rubidium, cesium, strontium, cerium, neodymium, and samarium resulting from the ther­mal neutron fission of U^235 and Pu^239 were determined mass spectrometrically. Special precautions were taken to eliminate or at least minimize contamination of the sub-microgram quantities of fission products with the naturally occurring elements. By using isotope dilution the yields of isotopes of different elements were related with very good precision. Sufficient information was available to evaluate from such results the absolute cumulative yields of twenty-seven mass chains for U^235 fission. It was possible from the results of the present study of make a quantitative comparison between the yields of the heavy fragments for U^235 and Pu^239 fission, with special attention being given to the fine structure supposedly resulting from the influence of nuclear shells involving 50 and 82 neutrons. / Thesis / Master of Science (MS)

Made available in DSpace on 2014-10-09T12:23:24Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:19Z (GMT). No. of bitstreams: 1 00033.pdf: 604992 bytes, checksum: bd0adbafb06db10f288569995b703e3f (MD5) / Dissertacao (Mestrado) / IEA/D / Faculdade de Medicina Veterinaria e Zootecnia, Universidade de Sao Paulo - FMVZ/USP

Made available in DSpace on 2014-10-09T12:32:40Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:55Z (GMT). No. of bitstreams: 1 11287.pdf: 2299583 bytes, checksum: 3a52dfa78e40aea5f1af99afce1b85a5 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:23:24Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:19Z (GMT). No. of bitstreams: 1 00033.pdf: 604992 bytes, checksum: bd0adbafb06db10f288569995b703e3f (MD5) / Dissertacao (Mestrado) / IEA/D / Faculdade de Medicina Veterinaria e Zootecnia, Universidade de Sao Paulo - FMVZ/USP

Made available in DSpace on 2014-10-09T12:32:40Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:55Z (GMT). No. of bitstreams: 1 11287.pdf: 2299583 bytes, checksum: 3a52dfa78e40aea5f1af99afce1b85a5 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Applications of in situ cosmogenic nuclides to problems in Quaternary geology require increasingly accurate and precise knowledge of nuclide production rates. Production rates depend on the terrestrial cosmic-ray intensity, which is a function of the elevation and geomagnetic coordinates of a sample site and the geomagnetic field intensity. The main goal of this dissertation is to improve the accuracy of cosmogenic dating by providing better constraints on the spatial variability of production rates.In this dissertation I develop a new scaling model that incorporates the best available cosmic-ray data into a framework that better describes the effects of elevation and geomagnetic shielding on production rates. This model is based on extensive measurements of energetic nucleon fluxes from neutron monitor surveys and on more limited data from low-energy neutron surveys. A major finding of this work is that neutron monitors yield scaling factors different from unshielded proportional counters. To verify that the difference is real I conducted an airborne survey of low-energy neutron fluxes at Hawaii (19.7° N 155.5° W) to compare with a nearby benchmark neutron monitor survey. Our data confirm that the attenuation length is energy dependent and suggest that the scaling factor for energetic nucleons is 10% higher between sea level and 4000 m than for low-energy neutrons at this location. An altitude profile of cosmogenic 36Cl production from lava flows on Mauna Kea, Hawaii, support the use of neutron flux measurements to scale production rates but these data do not have enough precision to confirm or reject the hypothesis of energy-dependent scaling factors.

Made available in DSpace on 2014-10-09T12:24:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:28Z (GMT). No. of bitstreams: 1 00288.pdf: 1133493 bytes, checksum: cc3bee26beefe753c5695b8f356ce09e (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Made available in DSpace on 2014-10-09T12:24:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:28Z (GMT). No. of bitstreams: 1 00288.pdf: 1133493 bytes, checksum: cc3bee26beefe753c5695b8f356ce09e (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP