Universität zu Köln

Lifton, Nathaniel ORCID: 0000-0002-6976-3298, Sato, Tatsuhiko and Dunai, Tibor J. (2014). Scaling in situ cosmogenic nuclide production rates using analytical approximations to atmospheric cosmic-ray fluxes. Earth Planet. Sci. Lett., 386. S. 149 - 161. AMSTERDAM: ELSEVIER SCIENCE BV. ISSN 1385-013X

Full text not available from this repository.

Abstract

Several models have been proposed for scaling in situ cosmogenic nuclide production rates from the relatively few sites where they have been measured to other sites of interest. Two main types of models are recognized: (1) those based on data from nuclear disintegrations in photographic emulsions combined with various neutron detectors, and (2) those based largely on neutron monitor data. However, stubborn discrepancies between these model types have led to frequent confusion when calculating surface exposure ages from production rates derived from the models. To help resolve these discrepancies and identify the sources of potential biases in each model, we have developed a new scaling model based on analytical approximations to modeled fluxes of the main atmospheric cosmic-ray particles responsible for in situ cosmogenic nuclide production. Both the analytical formulations and the Monte Carlo model fluxes on which they are based agree well with measured atmospheric fluxes of neutrons, protons, and muons, indicating they can serve as a robust estimate of the atmospheric cosmic-ray flux based on first principles. We are also using updated records for quantifying temporal and spatial variability in geomagnetic and solar modulation effects on the fluxes. A key advantage of this new model (herein termed LSD) over previous Monte Carlo models of cosmogenic nuclide production is that it allows for faster estimation of scaling factors based on time-varying geomagnetic and solar inputs. Comparing scaling predictions derived from the LSD model with those of previously published models suggest potential sources of bias in the latter can be largely attributed to two factors: different energy responses of the secondary neutron detectors used in developing the models, and different geomagnetic parameterizations. Given that the LSD model generates flux spectra for each cosmic-ray particle of interest, it is also relatively straightforward to generate nuclide-specific scaling factors based on recently updated neutron and proton excitation functions (probability of nuclide production in a given nuclear reaction as a function of energy) for commonly measured in situ cosmogenic nuclides. Such scaling factors reflect the influence of the energy distribution of the flux folded with the relevant excitation functions. Resulting scaling factors indicate He-3 shows the strongest positive deviation from the flux-based scaling, while C-14 exhibits a negative deviation. These results are consistent with a recent Monte Carlo-based study using a different cosmic-ray physics code package but the same excitation functions. (C) 2013 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Lifton, Nathaniel UNSPECIFIED orcid.org/0000-0002-6976-3298 UNSPECIFIED Sato, Tatsuhiko UNSPECIFIED UNSPECIFIED UNSPECIFIED Dunai, Tibor J. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-448479
DOI:	10.1016/j.epsl.2013.10.052
Journal or Publication Title:	Earth Planet. Sci. Lett.
Volume:	386
Page Range:	S. 149 - 161
Date:	2014
Publisher:	ELSEVIER SCIENCE BV
Place of Publication:	AMSTERDAM
ISSN:	1385-013X
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language BE-10 PRODUCTION-RATE; PRODUCTION-RATE CALIBRATION; LATITUDE SURVEY; GEOMAGNETIC-FIELD; SOLAR MODULATION; CRITICAL REEVALUATION; INTENSITY VARIATIONS; INDUCED NEUTRONS; ENERGY-SPECTRUM; SEA-LEVEL Multiple languages Geochemistry & Geophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/44847