Natural nuclear reactor at Oklo and variation of fundamental constants: Computation of neutronics of a fresh core

Abstract

Using modern methods of reactor physics we have performed full-scale calculations of the natural reactor Oklo. For reliability we have used recent version of two Monte Carlo codes: Russian code MCU REA and world wide known code MCNP (USA). Both codes produce similar results. We have constructed a computer model of the reactor Oklo zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities and neutron fluxes were calculated. We have estimated also the temperature and void effects for the fresh core. As would be expected, we have found for the fresh core a significant difference between reactor and Maxwell spectra, which was used before for averaging cross sections in the Oklo reactor. The averaged cross section of 149 62 Sm and its dependence on the shift of resonance position (due to variation of fundamental constants) are significantly different from previous results.Contrary to results of some previous papers we find no evidence for the change of the fine structure constant in the past and obtain new, most accurate limits on its variation with time: −4 · 10 −17 year −1 ≤α/α ≤ 3 · 10 −17 year −1 . A further improvement in the accuracy of the limits can be achieved by taking account of the core burnup. These calculations are in progress.

Effects of the variation of fundamental constants on Population III stellar evolution

“…That the typical correction to the resonant energies is of the order of 10 MeV (×δ NN ), compared to the resonant energies themselves which are around 0.1 MeV, allows one to put relatively strong constraints on any variation. This is reminiscent of the case of the resonance producing an excited state of 150 Sm of importance in setting constraints on the variation in couplings using the Oklo reactor (Shlyakhter 1976;Damour & Dyson 1996;Fujii et al 2000;Olive et al 2002;Petrov et al 2006). In that case, the resonant energy is 0.1 eV compared to corrections of about 1 MeV due to changes in the fine structure constant, leading to limits on Δα em /α em of the order of 10 −7 .…”

“…This is the case for the fine structure constant for which the constraintα em /α em = (−1.6 ± 2.3) × 10 −17 yr −1 at z = 0 has been obtained from comparing aluminium and mercury single-ion optical clocks (Rosenband et al 2008). On a longer timescale, it was demonstrated that α em cannot have varied by more than 10 −7 over the last 2 Gyr from the Oklo phenomenon (Shlyakhter 1976;Damour & Dyson 1996;Fujii et al 2000;Olive et al 2002;Petrov et al 2006;Flambaum & Wiringa 2009) and over the last 4.5 Gyr from meteorite dating (Dicke 1959;Dyson 1972;Fujii & Iwamoto 2003;Olive et al 2004). At higher redshift, 0.4 < z < 3.5, there are conflicting reports of an observed variation of α em from quasar absorption systems.…”

On the Absence of Antimatter From the Universe, Dark Matter, the Fine Structure Parameter, the Fluctuations of the Cosmic Microwave Background Radiation and the Temperature Difference Between the Northern and Southern Hemisphere of the Universe

“…For t = 2×10 9 yr, a time interval of the order of magnitude of the operation of the Oklo natural nuclear reactor, we get: This variation is extremely small and it is difficult to measure (Petrov et al, 2006;Meshik et al, 2004;Gauthier-Lafaye, 2002;De Laeter et al, 1980). We expect that the processing of the cosmological data we possess, as well as the improvement of the observational instruments, will give us a more accurate value for the fundamental parameter W. However, this more accurate measurement cannot considerably affect the theoretical prediction about Oklo's reactor, since Equation 72 gives an extremely small value for the ratio α α ∆ .…”

Primordial nucleosynthesis as a probe of fundamental physics parameters

“…Other limits on the values of particle couplings and masses at (relatively) recent epochs arise from nuclear physics effects in the Oklo natural reactor at z ≃ 0.2 [20,21] and from long-lived β decay isotopes in meteorites [22]. Direct comparisons of atomic clocks at periods of a few years in the laboratory have also led to strong bounds at the level of 10 −15 per year fractional variation [23].…”