Lamoreaux S.K., Torgensen J.R. Neutron Moderation in the Oklo Natural Reactor and the Time Variation of Alpha. — Phys. Rev, June 2004. — Vol. 69, Paper 121701
In previous analyses of the Oklo (Gabon) natural reactor to test for a possible time variation of the fine-structure constant α, a Maxwell-Boltzmann low energy neutron spectrum was assumed. We present here an analysis where a more realistic spectrum is employed and show that the most recent isotopic analysis of samples implies a decrease in α, over the last 2×109 years since the reactor was operating, of (αpast−αnow)/α>~4.5×10−8 (6σ confidence). Issues regarding the interpretation of the shifts of the low energy neutron absorption resonances are discussed.