re-enable S(a,b) w/ forced iso lab scattering
re-enable S(a,b) w/ forced iso lab scattering

johnnyliu27/openmc,smharper/openmc,wbinventor/openmc,samuelshaner/openmc,kellyrowland/openmc,bhermanmit/openmc,liangjg/openmc,smharper/openmc,amandalund/openmc,mit-crpg/openmc,johnnyliu27/openmc,mit-crpg/openmc,samuelshaner/openmc,shikhar413/openmc,mjlong/openmc,amandalund/openmc,shikhar413/openmc,paulromano/openmc,johnnyliu27/openmc,mit-crpg/openmc,mit-crpg/openmc,smharper/openmc,shikhar413/openmc,paulromano/openmc,paulromano/openmc,walshjon/openmc,johnnyliu27/openmc,smharper/openmc,walshjon/openmc,mjlong/openmc,samuelshaner/openmc,shikhar413/openmc,wbinventor/openmc,kellyrowland/openmc,amandalund/openmc,liangjg/openmc,wbinventor/openmc,wbinventor/openmc,samuelshaner/openmc,paulromano/openmc,walshjon/openmc,bhermanmit/openmc,liangjg/openmc,walshjon/openmc,liangjg/openmc,amandalund/openmc