Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Time-variability of alpha from realistic models of Oklo reactors   We reanalyze Oklo $^{149}$Sm data using realistic models of the natural
nuclear reactors. Disagreements among recent Oklo determinations of the time
evolution of $\alpha$, the electromagnetic fine structure constant, are shown
to be due to different reactor models, which led to different neutron spectra
used in the calculations. We use known Oklo reactor epithermal spectral indices
as criteria for selecting realistic reactor models. Two Oklo reactors, RZ2 and
RZ10, were modeled with MCNP. The resulting neutron spectra were used to
calculate the change in the $^{149}$Sm effective neutron capture cross section
as a function of a possible shift in the energy of the 97.3-meV resonance. We
independently deduce ancient $^{149}$Sm effective cross sections, and use these
values to set limits on the time-variation of $\alpha$. Our study resolves a
contradictory situation with previous Oklo $\alpha$-results. Our suggested $2
\sigma$ bound on a possible time variation of $\alpha$ over two billion years
is stringent: $ -0.24 \times 10^{-7} \le \frac{\Delta \alpha}{\alpha} \le 0.11
\times 10^{-7}$, but model dependent in that it assumes only $\alpha$ has
varied over time.

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The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
4
The categories of this paper are: cond-mat
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: solv-int
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The categories of this paper are: physics
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The categories of this paper are: econ
28
The categories of this paper are: alg-geom