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Title:
Pressure- and chemistry-dependent electron capture radioactive decay
Authors:
Lee, K. K.; Steinle-Neumann, G.
Affiliation:
AA(California Institute of Technology, Division of Geological & Planetary Sciences 1200 E. California Blvd, Pasadena, CA 91125 United States ; Bayerisches Geoinstitut, Universitat Bayreuth, Bayreuth, 95440 Germany ; ), AB(Bayerisches Geoinstitut, Universitat Bayreuth, Bayreuth, 95440 Germany ; )
Publication:
American Geophysical Union, Fall Meeting 2005, abstract #V41F-1528
Publication Date:
12/2005
Origin:
AGU
AGU Keywords:
1040 Radiogenic isotope geochemistry, 1115 Radioisotope geochronology, 1150 Cosmogenic-nuclide exposure dating (4918), 1155 Extinct radionuclide geochronology, 3924 High-pressure behavior
Abstract Copyright:
(c) 2005: American Geophysical Union
Bibliographic Code:
2005AGUFM.V41F1528L

Abstract

The half-lives of radioactive isotopes are often considered constant and are determined to high precision. For this reason, many radioactive isotopes are used to date Earth processes at all time and length scales. Among important radioisotopes are those that decay by electron capture, namely 7Be (→ 7Li, t1/2 ~53 days), 26Al (→ 26Mg, t1/2 ~720 kyr) and 40K (→ 40Ar, t1/2 ~1.25 Gyr). Heat production due to the decay of 26Al and 40K were also important during the accretion process and current heat budget respectively. For electron capture decay schemes, external forces affect the half-life. These include chemical state, ionization, temperature and pressure. Here we investigate the change in decay constant for these radioisotopes due to pressure and chemistry by means of accurate total energy band-structure computations to determine the charge density at the nucleus of the respective atom as pure metals (Be, Al, K) and in oxides (BeO, Al2O3 and K2O). We use an all-electron density functional theory based method, implemented in the Linearized Augmented Plane Wave (LAPW) method, with both the local density (LDA) and generalized gradient (GGA) approximations to many electron interactions. We predict that pressure decreases the half-life of 7Be by ~0.2% (~0.1 days) and that of 40K by ~0.03% (~375 kyr) at 50 GPa, while the half-life of 26Al increases by ~0.01% (~72 years) at 50 GPa. The oxide forms of each element show a further decrease in the length of the half-life.
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