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Added description of ACE Law 61 in documentation.

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Paul Romano 2012-07-25 19:05:03 -04:00
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docs/source/methods/physics.rst
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@ -524,6 +524,28 @@ outgoing angle is
ACE Law 61 - Correlated Energy and Angle Distribution
+++++++++++++++++++++++++++++++++++++++++++++++++++++
This law is very similar to ACE Law 44 in the sense that the outgoing angle of
the neutron is correlated to the outgoing energy and is not sampled from a
separate distribution. In this case though, rather than being determined from an
analytical distribution function, the cosine of the scattering angle is
determined from a tabulated distribution. For each incident energy :math:`i` and
outgoing energy :math:`j`, there is a tabulated angular distribution.
The calculation of the outgoing energy of the neutron proceeds exactly the same
as in the algorithm described in :ref:`ace-law-4`. In that algorithm, we found
an interpolation factor :math:`f`, statistically sampled an incoming energy bin
:math:`\ell`, and sampled an outgoing energy bin :math:`j` based on the
tabulated cumulative distribution function. Once the outgoing energy has been
determined with equation :eq:`ace-law-4-energy`, we then need to decide which
angular distribution to use. If histogram interpolation was used on the outgoing
energy bins, then we use the angular distribution corresponding to incoming
energy bin :math:`\ell` and outgoing energy bin :math:`j`. If linear-linear
interpolation was used on the outgoing energy bins, then we use the whichever
angular distribution was closer to the sampled value of the cumulative
distribution function for the outgoing energy. The actual algorithm used to
sample the chosen tabular angular distribution has been previously described in
:ref:`angle-tabular`.
ACE Law 66 - N-Body Phase Space Distribution
++++++++++++++++++++++++++++++++++++++++++++