From 477da9b47dd7aec81c5ada5056559cc004b7db7f Mon Sep 17 00:00:00 2001
From: Qingming He <906459647@qq.com>
Date: Tue, 11 Oct 2016 14:35:09 -0400
Subject: [PATCH] add energy_cutoff

Kill particles under certain energy
---
 src/global.F90    |  1 +
 src/input_xml.F90 | 11 +++++++++--
 src/physics.F90   |  7 +++++++
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/global.F90 b/src/global.F90
index a5720464de..042d530f37 100644
--- a/src/global.F90
+++ b/src/global.F90
@@ -304,6 +304,7 @@ module global
 
   logical :: survival_biasing = .false.
   real(8) :: weight_cutoff = 0.25_8
+  real(8) :: energy_cutoff = ZERO
   real(8) :: weight_survive = ONE
 
   ! ============================================================================
diff --git a/src/input_xml.F90 b/src/input_xml.F90
index c92ceee8c5..18af461a79 100644
--- a/src/input_xml.F90
+++ b/src/input_xml.F90
@@ -659,8 +659,15 @@ contains
     ! Cutoffs
     if (check_for_node(doc, "cutoff")) then
       call get_node_ptr(doc, "cutoff", node_cutoff)
-      call get_node_value(node_cutoff, "weight", weight_cutoff)
-      call get_node_value(node_cutoff, "weight_avg", weight_survive)
+      if (check_for_node(node_cutoff, "weight")) then
+        call get_node_value(node_cutoff, "weight", weight_cutoff)
+      end if
+      if (check_for_node(node_cutoff, "weight_avg")) then
+        call get_node_value(node_cutoff, "weight_avg", weight_survive)
+      end if
+      if (check_for_node(node_cutoff, "energy")) then
+        call get_node_value(node_cutoff, "energy", energy_cutoff)
+      end if
     end if
 
     ! Particle trace
diff --git a/src/physics.F90 b/src/physics.F90
index 232effebf3..842540d166 100644
--- a/src/physics.F90
+++ b/src/physics.F90
@@ -127,6 +127,13 @@ contains
       if (.not. p % alive) return
     end if
 
+    ! Kill neutron under certain energy
+    if (p % E < energy_cutoff) then
+      p % alive = .false.
+      p % wgt = ZERO
+      p % last_wgt = ZERO
+    end if
+
   end subroutine sample_reaction
 
 !===============================================================================