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Merge pull request #337 from paulromano/evaporation

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Improved evaporation spectrum sampling algorithm
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Jon Walsh 2014-12-14 01:06:50 -05:00
commit 2f07c0371e
2 changed files with 18 additions and 10 deletions
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17
docs/source/methods/physics.rst
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@ -682,17 +682,20 @@ nuclear temperature, which is a function of the incoming energy of the
neutron. The ACE format contains a list of nuclear temperatures versus incoming
energies. The nuclear temperature is interpolated between neighboring incoming
energies using a specified interpolation law. Once the temperature :math:`T` is
determined, we then calculate a candidate outgoing energy based on rule C45 in
the `Monte Carlo Sampler`_:
determined, we then calculate a candidate outgoing energy based on the algorithm
given in LA-UR-14-27694_:
.. math::
:label: evaporation-E
E' = -T \log (\xi_1 \xi_2)
E' = -T \log ((1 - g\xi_1)(1 - g\xi_2))
where :math:`\xi_1, \xi_2` are random numbers sampled on the unit
interval. The outgoing energy is only accepted according to a specified
restriction energy as in equation :eq:`maxwell-restriction`.
where :math:`g = 1 - e^{-w}`, :math:`w = (E - U)/T`, :math:`U` is the
restriction energy, and :math:`\xi_1, \xi_2` are random numbers sampled on the
unit interval. The outgoing energy is only accepted according to the restriction
energy as in equation :eq:`maxwell-restriction`. This algorithm has a much
higher rejection efficiency than the standard technique, i.e. rule C45 in the
`Monte Carlo Sampler`_.
ACE Law 11 - Energy-Dependent Watt Spectrum
+++++++++++++++++++++++++++++++++++++++++++
@ -1591,6 +1594,8 @@ References
.. _Monte Carlo Sampler: https://laws.lanl.gov/vhosts/mcnp.lanl.gov/pdf_files/la-9721_3rdmcsampler.pdf
.. _LA-UR-14-27694: http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-14-27694
.. _MC21: http://www.osti.gov/bridge/servlets/purl/903083-HT5p1o/903083.pdf
.. _Sutton and Brown: http://www.osti.gov/bridge/product.biblio.jsp?osti_id=307911