Cosmogenic nuclides as a surface exposure dating tool: improved altitude/latitude scaling factors for production rates

Persistent Link:
http://hdl.handle.net/10150/195651
Title:
Cosmogenic nuclides as a surface exposure dating tool: improved altitude/latitude scaling factors for production rates
Author:
Desilets, Darin Maurice
Issue Date:
2005
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
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.
Type:
text; Electronic Dissertation
Keywords:
cosmogenic nuclides; chlorine-36; cosmic rays; production rates; isotope dilution
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Hydrology; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Zreda, Marek
Committee Chair:
Zreda, Marek

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleCosmogenic nuclides as a surface exposure dating tool: improved altitude/latitude scaling factors for production ratesen_US
dc.creatorDesilets, Darin Mauriceen_US
dc.contributor.authorDesilets, Darin Mauriceen_US
dc.date.issued2005en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractApplications 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.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectcosmogenic nuclidesen_US
dc.subjectchlorine-36en_US
dc.subjectcosmic raysen_US
dc.subjectproduction ratesen_US
dc.subjectisotope dilutionen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineHydrologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorZreda, Mareken_US
dc.contributor.chairZreda, Mareken_US
dc.contributor.committeememberBaker, Victor R.en_US
dc.contributor.committeememberJull, Timothyen_US
dc.contributor.committeememberEkwurzel, Brendaen_US
dc.contributor.committeememberDamon, Paul E.en_US
dc.identifier.proquest1125en_US
dc.identifier.oclc137354089en_US
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