547 research outputs found
Neutron Moderation in the Oklo Natural Reactor and the Time Variation of alpha
In the analysis of the Oklo (gabon) natural reactor to test for a possible
time variation of the fine structure constant alpha, 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 non-zero change in alpha, over the last two billion years
since the reactor was operating, of \Delta\alpha/\alpha\geq 4.5\times 10^{-8}
(6\sigma confidence). Issues regarding the interpretation of the shifts of the
low energy neutron resonances are discussed.Comment: 7 pages, 4 figures; version 2 included reference to Flambaum/Shuryak
work and corrects error in abstract version three corrects a few points and
adds discussion on hydrogen and impurity concentration
Variation of the Fine-Structure Constant from the de Sitter Invariant Special Relativity
There are obvious discrepancies among various experimental constraints on the
variation of the fine-structure constant, . We attempt to discuss the
issue in the framework of de Sitter invariant Special Relativity () and to present a possible solution to the disagreement. In
addition, on the basis of the observational data and the discussions presented
in this Letter, we derive a rough theoretical estimate of the radius of the
Universe.Comment: 8 pages, no figure
Natural Nuclear Reactor Oklo and Variation of Fundamental Constants Part 1: Computation of Neutronics of Fresh Core
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 Sm-149 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} < d alpha/dt/alpha < 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.Comment: 25 pages, 14 figures, 12 tables, minor corrections, typos correcte
Models of quintessence coupled to the electromagnetic field and the cosmological evolution of alpha
We study the change of the effective fine structure constant in the
cosmological models of a scalar field with a non-vanishing coupling to the
electromagnetic field. Combining cosmological data and terrestrial observations
we place empirical constraints on the size of the possible coupling and explore
a large class of models that exhibit tracking behavior. The change of the fine
structure constant implied by the quasar absorption spectra together with the
requirement of tracking behavior impose a lower bound of the size of this
coupling. Furthermore, the transition to the quintessence regime implies a
narrow window for this coupling around in units of the inverse Planck
mass. We also propose a non-minimal coupling between electromagnetism and
quintessence which has the effect of leading only to changes of alpha
determined from atomic physics phenomena, but leaving no observable
consequences through nuclear physics effects. In doing so we are able to
reconcile the claimed cosmological evidence for a changing fine structure
constant with the tight constraints emerging from the Oklo natural nuclear
reactor.Comment: 13 pages, 10 figures, RevTex, new references adde
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