From 2f3bbef81cd7199f0f345f1f16f3ac15891f776e Mon Sep 17 00:00:00 2001
From: Paul Romano <romano7@gmail.com>
Date: Sun, 1 Apr 2012 20:25:26 -0400
Subject: [PATCH] Fixed subtle bug with S(a,b) cross section calculation.

---
 src/cross_section.F90 | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/cross_section.F90 b/src/cross_section.F90
index aa155eefe7..be8f009a7b 100644
--- a/src/cross_section.F90
+++ b/src/cross_section.F90
@@ -187,8 +187,13 @@ contains
        end if
     end if
 
-    ! Set last evaluated energy
-    if (index_sab == 0) micro_xs(index_nuclide) % last_E = p % E
+    ! Set last evaluated energy -- if we're in S(a,b) region, force
+    ! re-calculation of cross-section
+    if (index_sab == 0) then
+       micro_xs(index_nuclide) % last_E = p % E
+    else
+       micro_xs(index_nuclide) % last_E = ZERO
+    end if
 
   end subroutine calculate_nuclide_xs