Steven Lamoreaux
Yale University
Friday, February 8, 2008
4:00 pm in SPL 57
The Oklo Natural Reactor and the Time Variation of the Fundamental Constants of Nature
Abstract: Two billion years ago, a uranium deposit in Oklo, Gabon, Africa achieved criticality and a nuclear chain reaction was sustained in the deposit for about 100,000 years. Such a reactor was possible because the relative isotopic abundance of U-235 was much greater in the past. By analyzing the isotopic abundances of stable fission products in the deposit, it is possible to determine whether low energy neutron absorption resonance energies were different in the past, and thereby determine whether the fundamental constants of physics have changed. A precise recent analysis of isotopic abundances implied that the fine structure constant has fractionally changed by as much as 45 parts per billion,with six sigma confidence. However, additional modeling of the reactor indicates that this should interpreted as an upper limit on a possible change, and at present is the most restrictive limit. A review of laboratory measurements, both completed and planned, will also be presented, along with a brief discussion of the underlying theoretical motivation for raising the question of time variability of the "constants" that determine the fundamental interactions of physics.
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