Universität zu Köln

Dunai, T. J., Binnie, S. A., Hein, A. S. and Paling, S. M. (2014). The effects of a hydrogen-rich ground cover on cosmogenic thermal neutrons: Implications for exposure dating. Quat. Geochronol., 22. S. 183 - 192. OXFORD: ELSEVIER SCI LTD. ISSN 1878-0350

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Abstract

We present results of thermal neutron flux measurements in experimental granite piles that were tailored to study the effect of hydrogen-rich covers on that flux. We find that hydrogen-rich covers (polyethylene, water), used as proxies for snow, dead and/or live plant matter, increase the thermal neutron flux in an underlying rock surface significantly, as compared to the state without cover. The rock serves as the main source for thermal neutrons, the hydrogen-rich cover as a neutron reflector. In situations where the thickness of such a cover would be negligible in terms of high-energy neutron (>10 MeV) attenuation, e.g. 2-3 cm water equivalent cover, a significant enhancement of the thermal neutron flux (factor >2.5 +/- 0.5) can be achieved. This increase is made up of three components (Masarik et al., 2007): (1) reflected thermal neutrons (albedo neutrons), (2) moderated fast neutrons from the ground, and (3) moderated fast neutrons from the atmospheric cascade (Masarik et al., 2007). The higher thermal neutron flux increases the production rates of those cosmogenic nuclides that have a significant thermal neutron production pathway (He-3, Cl-36, Ca-41) Ignoring this effect in situations where target nuclei (Li-6, Cl-36, Ca-40) are abundant will severely underestimate production rates. The effect of hydrogenrich ground cover on the thermal neutron flux has the potential to be used for studies that are aimed at reconstructing the persistence of past plant/snow cover. Isotopic ratios of spallogenic versus predominantly thermal neutron produced nuclides, would reveal the presence or absence of hydrogen-rich cover in the past as compared to the present-day situation. (C) 2013 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Dunai, T. J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Binnie, S. A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hein, A. S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Paling, S. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-433467
DOI:	10.1016/j.quageo.2013.01.001
Journal or Publication Title:	Quat. Geochronol.
Volume:	22
Page Range:	S. 183 - 192
Date:	2014
Publisher:	ELSEVIER SCI LTD
Place of Publication:	OXFORD
ISSN:	1878-0350
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language ABOVEGROUND BIOMASS ESTIMATION; MOISTURE-CONTENT; ENERGY-SPECTRUM; WATER-CONTENT; HE-3; FOREST; NUCLEAR; BOREAL; CANOPY; ABOARD Multiple languages Geography, Physical; Geosciences, Multidisciplinary Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/43346