How to calculate the threshold energy of (n,n') reactions?

[dsaha]

Let us take the example of 89Y(n,n')89mY reaction. In the calculation of Q value we require mass of reactants and products. Both are same here. Then how to calculate the Q value of this reaction or how to calculate the threshold energy of this type of reactions?

 

[drvrm]

Then how to calculate the Q value of this reaction or how to calculate the threshold energy of this type of reactions?

see the data below
refer to the source - http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/36/116/36116089.pdf

Reaction - '89Y (n, n') 89m Y

gamma-ray energy 909.157

Q-value [keV] 909.15

one gets a low Q-value which is associated with gamma-ray production/absorption.