
In order to unify several different processing tasks, GROUPR
uses the concept of a generalized group integral
where the integrals are over all initial neutron energies in
group g, σ(E) is a cross section at E,
and φ(E) is an estimate of the flux
at E. We call fancy F of Ethe "feed function". It alone
changes for different data types. To average a neutron cross section,
fancy F is set to 1. To average a ratio quantity like fission mubar
with respect to elastic scattering, fancy F is set to mu.
For photon production, fancy F is the photon yield. For matrices,
it is the lth Legendre component of the normalized
probability of scattering into secondary energy group g' from initial
energy E. This definition is clearly independent of whether the
secondary particle is a neutron or a photon.
The question of integration grid or quadrature scheme is important for
the evaluation this equation. Each factor in the integrands has its own
characteristic features, and it is important to account for them all.
First, a grid must be established for each factor. As an example, the
grid of σ(E) is generated in RECONR and BROADR
such that sigma can be obtained to within a given tolerance
by linear interpolation. GROUPR contains a subroutine
GETSIG which carries out
this interpolation at E and also returns the next grid energy in
ENEXT . Subroutines GETFLX and
GETFF perform similar functions for the flux and
feed function. It is now easy to generate a union grid for the
threefactor integrand by just selecting the next closest
ENEXT from all the factors at each step of the
integration.
