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In-situ buildup of cosmogenic isotopes at the earth`s surface: measurement of erosion rates and exposure times

Abstract

Cosmic rays produce a number of nuclides in rocks that can be used to determine the geomorphic history of surfaces. The most useful are the radioactive isotopes {sup 10}Be (t{sub 1/2} = 1.5Ma), {sup 26}Al (0.7Ma) and {sup 36}Cl (0.3Ma). Within the top 2m of the surface, these are produced principally by fast neutrons. At greater depths, production is dominated by the capture of negative muons. Measurements of a single nuclide produced in situ can be used to determine total exposure times or erosion rates. The use of multiple nuclides with different half-lives makes it possible to determine more complex histories, such as exposures interrupted by periods of burial. At the ANU, all three of the isotopes above are being used to study a variety of problems in geomorphology and paleoclimatology, although to date, most of the work has concentrated on {sup 36}Cl. The accumulation of cosmogenic {sup 36}Cl in calcite (CaCO{sub 3}) provides a means of measuring erosion rates on limestone surfaces. Sensitivity is achieved over a wide range of erosion rates due to the high production rate of {sup 36}Cl in calcite (typically greater than 30 atoms/g/yr) and a detection limit of ca. 5000 atoms/g attainable with the  More>>
Authors:
Fifield, L K; Allan, G L; Stone, J O.H.; Evans, J M; Cresswell, R G; Ophel, T R [1] 
  1. Australian National Univ., Canberra, ACT (Australia)
Publication Date:
Dec 31, 1993
Product Type:
Conference
Report Number:
INIS-mf-15527; CONF-9311348-
Reference Number:
SCA: 540211; 400101; PA: AIX-28:025063; EDB-97:043859; SN: 97001752625
Resource Relation:
Conference: 8. Australian conference on nuclear techniques of analysis, Lucas Heights (Australia), 17-19 Nov 1993; Other Information: PBD: 1993; Related Information: Is Part Of Proceedings of the 8. Australian conference on nuclear techniques of analysis; PB: 194 p.
Subject:
54 ENVIRONMENTAL SCIENCES; 40 CHEMISTRY; CALCITE; CHLORINE 36; ISOTOPE RATIO; NUCLEAR REACTION ANALYSIS; ALPHA PARTICLES; AUSTRALIA; CALCIUM 40 TARGET; COSMIC NEUTRONS; EROSION; MUON REACTIONS; PAPUA NEW GUINEA; QUANTITATIVE CHEMICAL ANALYSIS; SPALLATION
OSTI ID:
445978
Country of Origin:
Australia
Language:
English
Other Identifying Numbers:
Other: ON: DE97616714; TRN: AU9715789025063
Availability:
INIS; OSTI as DE97616714
Submitting Site:
AUN
Size:
pp. 124-125
Announcement Date:
Mar 28, 1997

Citation Formats

Fifield, L K, Allan, G L, Stone, J O.H., Evans, J M, Cresswell, R G, and Ophel, T R. In-situ buildup of cosmogenic isotopes at the earth`s surface: measurement of erosion rates and exposure times. Australia: N. p., 1993. Web.
Fifield, L K, Allan, G L, Stone, J O.H., Evans, J M, Cresswell, R G, & Ophel, T R. In-situ buildup of cosmogenic isotopes at the earth`s surface: measurement of erosion rates and exposure times. Australia.
Fifield, L K, Allan, G L, Stone, J O.H., Evans, J M, Cresswell, R G, and Ophel, T R. 1993. "In-situ buildup of cosmogenic isotopes at the earth`s surface: measurement of erosion rates and exposure times." Australia.
@misc{etde_445978,
title = {In-situ buildup of cosmogenic isotopes at the earth`s surface: measurement of erosion rates and exposure times}
author = {Fifield, L K, Allan, G L, Stone, J O.H., Evans, J M, Cresswell, R G, and Ophel, T R}
abstractNote = {Cosmic rays produce a number of nuclides in rocks that can be used to determine the geomorphic history of surfaces. The most useful are the radioactive isotopes {sup 10}Be (t{sub 1/2} = 1.5Ma), {sup 26}Al (0.7Ma) and {sup 36}Cl (0.3Ma). Within the top 2m of the surface, these are produced principally by fast neutrons. At greater depths, production is dominated by the capture of negative muons. Measurements of a single nuclide produced in situ can be used to determine total exposure times or erosion rates. The use of multiple nuclides with different half-lives makes it possible to determine more complex histories, such as exposures interrupted by periods of burial. At the ANU, all three of the isotopes above are being used to study a variety of problems in geomorphology and paleoclimatology, although to date, most of the work has concentrated on {sup 36}Cl. The accumulation of cosmogenic {sup 36}Cl in calcite (CaCO{sub 3}) provides a means of measuring erosion rates on limestone surfaces. Sensitivity is achieved over a wide range of erosion rates due to the high production rate of {sup 36}Cl in calcite (typically greater than 30 atoms/g/yr) and a detection limit of ca. 5000 atoms/g attainable with the ANU AMS system. The method is simplified by the predominance of Ca reactions (principally spallation) over other sources of {sup 36}Cl in calcite, and the ease of sample preparation. This presentation discuss the results of measurements of {sup 36}Cl in calcite from limestone samples from Australia and Papua New Guinea. Erosion rates derived from these measurements range from 3 microns per year (Australia) to over 200 microns per year in the New Guinea highlands. 3 refs.}
place = {Australia}
year = {1993}
month = {Dec}
}