# Critical fission energy question

1. May 6, 2007

### andybham

I have a fission exam next week, can someone help me with this past paper question:

If you know the masses of two nuclei (A)Z and (A+1)Z, (say masses are (A) and (A+1)) and you know the 'critical fission energy' of (A+1)Z, how do you determine if (A)Z is fissile? if it is not fissile, at what neutron energy would you expect fission to be possible.

2. May 6, 2007

### Astronuc

Staff Emeritus
How about comparing the binding energy of the compound nucleus (A+1)Z with the critical energy?

3. May 6, 2007

### andybham

is this done by calculating the separation energy? E = m(n) + m(A) - m(A+1)

4. May 6, 2007

### Astronuc

Staff Emeritus
http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html

yes - it is the mass-energy difference between the reactants and product(s). The energy is released as prompt gamma or as the kinetic energy if there are two or more products.

Calculate the mass-energy difference between U235+n and U236.