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Changed sampling of Watt spectrum to direct (unpublished) scheme.

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This commit is contained in:
Paul Romano 2011-07-24 21:06:13 -04:00
parent 15ecc0c227
commit a29c7d8db4
1 changed files with 5 additions and 10 deletions
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15
src/physics.f90
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@ -1734,7 +1734,8 @@ contains
! WATT_SPECTRUM samples the outgoing energy from a Watt energy-dependent fission
! spectrum. Although fitted parameters exist for many nuclides, generally the
! continuous tabular distributions (LAW 4) should be used in lieu of the Watt
! spectrum
! spectrum. This direct sampling scheme is an unpublished scheme based on the
! original Watt spectrum derivation (See F. Brown's MC lectures).
!===============================================================================
function watt_spectrum(a, b) result(E_out)
@ -1743,16 +1744,10 @@ contains
real(8), intent(in) :: b ! Watt parameter b
real(8) :: E_out ! energy of emitted neutron
real(8) :: g ! from sampling scheme R28
real(8) :: r1, r2 ! random numbers
real(8) :: w ! sampled from Maxwellian
g = sqrt((1 + a*b/8)**2 - 1) + (1 + a*b/8)
do
r1 = log(rang())
r2 = log(rang())
E_out = -a*g*r1
if (((1 - g)*(1 - r1) - r2)**2 < b*E_out) exit
end do
w = maxwell_spectrum(a)
E_out = w + a*a*b/4. + (2.*rang() - ONE)*sqrt(a*a*b*w)
end function watt_spectrum