The nuclear interaction at Oklo 2 billion years ago

We re-examine the effort to constrain the time variability of the coupling constants of the fundamental interactions by studying the anomalous isotopic abundance of Sm observed at the remnants of the natural reactors which were in operation at Oklo about 2 billion years ago, in terms of a possible deviation of the resonance energy from the value observed today. We rely on new samples that were carefully collected to minimize natural contamination and also on a careful temperature estimate of the reactors. We obtain the upper bound (-0.2 +/- 0.8) X 10(-17) y(-1) on the fractional rate of change of the electromagnetic as well as the strong interaction coupling constants. Our result basically agrees with and even suggests some improvement of the result due recently to Damour and Dyson. Strictly speaking, however, we find another choice of the resonance energy shift indicating a non-zero time variation of the constants. However, we find a rather strong but still tentative indication that this non-null range can be ruled out by including Gd data, for which it is essential to take the effect of contamination into account. (C) 2000 Elsevier Science B.V, All rights reserved.