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Title: Cosmogenic {sup 36}Cl accumulation in unstable landforms 1. Effects of the thermal neutron distribution

Abstract

Cosmogenic nuclides produced in situ within minerals at the surface of the Earth are proving to be an effective means of assessing geomorphic histories. The use of multiple cosmogenic nuclides permits both exposure times and erosion rates to be determined. However, if two nuclides are produced only by spallation reactions, the systematic differences in their accumulation rates depend only on the differences in their production rates and half-lives. The relatively small differences that result require a high degree of analytical precision to yield useful results. In contrast to other spallogenic nuclides, {sup 36}Cl is also produced by low-energy neutron, absorption, which creates a different pattern of production as a function of depth. We have measured the thermal flux with depth in a concrete block using {sup 3}He-filled neutron detectors. The measured thermal neutron profile agrees well with predictions from a simple diffusion-based thermal neutron distribution model. Calculations of {sup 36}Cl production using the model suggest that the use of {sup 36}Cl along with a purely spallogenic nuclide to determine erosion rates and exposure times should be less sensitive to analytical error than are determinations from two purely spallogenic nuclides. 31 refs., 7 figs., 3 tabs.

Authors:
; ;  [1]; ;  [2]
  1. New Mexico Tech., Socorro, NM (United States)
  2. Los Alamos National Lab., NM (United States)
Publication Date:
OSTI Identifier:
41798
Resource Type:
Journal Article
Journal Name:
Water Resources Research
Additional Journal Information:
Journal Volume: 30; Journal Issue: 11; Other Information: PBD: Nov 1994
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 66 PHYSICS; COSMIC RADIATION; NEUTRON FLUX; GEOLOGIC FORMATIONS; GEOMORPHOLOGY; ISOTOPE DATING; EROSION; NEUTRON DETECTORS; SPALLATION; CHLORINE 36; THERMAL NEUTRONS; GEOLOGIC HISTORY

Citation Formats

Liu, B, Phillips, F M, Stone, W D, Fabryka-Martin, J T, and Fowler, M M. Cosmogenic {sup 36}Cl accumulation in unstable landforms 1. Effects of the thermal neutron distribution. United States: N. p., 1994. Web. doi:10.1029/94WR00761.
Liu, B, Phillips, F M, Stone, W D, Fabryka-Martin, J T, & Fowler, M M. Cosmogenic {sup 36}Cl accumulation in unstable landforms 1. Effects of the thermal neutron distribution. United States. https://doi.org/10.1029/94WR00761
Liu, B, Phillips, F M, Stone, W D, Fabryka-Martin, J T, and Fowler, M M. 1994. "Cosmogenic {sup 36}Cl accumulation in unstable landforms 1. Effects of the thermal neutron distribution". United States. https://doi.org/10.1029/94WR00761.
@article{osti_41798,
title = {Cosmogenic {sup 36}Cl accumulation in unstable landforms 1. Effects of the thermal neutron distribution},
author = {Liu, B and Phillips, F M and Stone, W D and Fabryka-Martin, J T and Fowler, M M},
abstractNote = {Cosmogenic nuclides produced in situ within minerals at the surface of the Earth are proving to be an effective means of assessing geomorphic histories. The use of multiple cosmogenic nuclides permits both exposure times and erosion rates to be determined. However, if two nuclides are produced only by spallation reactions, the systematic differences in their accumulation rates depend only on the differences in their production rates and half-lives. The relatively small differences that result require a high degree of analytical precision to yield useful results. In contrast to other spallogenic nuclides, {sup 36}Cl is also produced by low-energy neutron, absorption, which creates a different pattern of production as a function of depth. We have measured the thermal flux with depth in a concrete block using {sup 3}He-filled neutron detectors. The measured thermal neutron profile agrees well with predictions from a simple diffusion-based thermal neutron distribution model. Calculations of {sup 36}Cl production using the model suggest that the use of {sup 36}Cl along with a purely spallogenic nuclide to determine erosion rates and exposure times should be less sensitive to analytical error than are determinations from two purely spallogenic nuclides. 31 refs., 7 figs., 3 tabs.},
doi = {10.1029/94WR00761},
url = {https://www.osti.gov/biblio/41798}, journal = {Water Resources Research},
number = 11,
volume = 30,
place = {United States},
year = {Tue Nov 01 00:00:00 EST 1994},
month = {Tue Nov 01 00:00:00 EST 1994}
}