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Cosmogenic 36 Cl accumulation in unstable landforms: 1. Effects of the thermal neutron distribution
Author(s) -
Liu Beiling,
Phillips Fred M.,
FabrykaMartin June T.,
Fowler Malcolm M.,
Stone William D.
Publication year - 1994
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/94wr00761
Subject(s) - nuclide , cosmogenic nuclide , neutron , spallation , neutron temperature , neutron flux , erosion , nuclear physics , radiochemistry , geology , physics , chemistry , cosmic ray , geomorphology
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, 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 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 36 Cl production using the model suggest that the use of 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.