diff --git a/reactions.cpp b/reactions.cpp
index 5812b2f..6ce7958 100644
--- a/reactions.cpp
+++ b/reactions.cpp
@@ -89,7 +89,7 @@ double SigmaR_Kox(int Ap, int Zp, double E, int At, int Zt){
     double Rs = r0 * ((a*Ap13*At13)/(Ap13+At13)-c)+D;
     double Rv = r0 * (Ap13 + At13);
     double Ri = Rv + Rs;
-    double Ecm = Ecm_from_T_relativistic(E,Ap,At);
+    double Ecm = Ecm_from_T(E,Ap,At);
     return 10.0*PI*Ri*Ri*(1-(Bc/Ecm));
     }
 #endif
diff --git a/reactions.h b/reactions.h
index f40de79..c0eadf9 100644
--- a/reactions.h
+++ b/reactions.h
@@ -58,6 +58,7 @@ double SigmaR_Kox(int Ap, int Zp, double E, int At, int Zt);
 inline double p_from_T(double T, double M=1.0){
     return M*sqrt(T*T + 2*T*atomic_mass_unit);
 }
+/*
 inline double Ecm_from_T_relativistic(double T, double Ap, double At){
     double mp = Ap*atomic_mass_unit;
     double mt = At*atomic_mass_unit;
@@ -67,6 +68,11 @@ inline double Ecm_from_T_relativistic(double T, double Ap, double At){
     double pcm = plab * mt / ecm;
     return sqrt(pcm*pcm+mp*mp)-mp;
 }
+*/
+/// calculates Ecm fom T, return in MeV units
+inline double Ecm_from_T(double T, double Ap, double At){
+    return T*Ap*At/(Ap+At);
+}
 
 #endif //NUREX
 #endif