# Questions about activation energy for fission

## Main Question or Discussion Point

Hi,
I hope someone can help me with these question I have about fission?
Where can I find a list of what the activation energy is between the normal state of the nucleus and the state where it splits. In my book it says the activation energy for U-235 is 5.3 MeV(The energy required to fission U-235). And to see if a fission will occur when U-235 absorbs a neutron and converts to U-236 I’m given the following formula:

Q=-(mU-236 - mU-235 - mneutron)*931,5MeV/u

And with numbers from wikipedia( http://en.wikipedia.org/wiki/Isotopes_of_uranium ) I put in the numbers:

Q=-(236.045568u - 235.0439299u - 1.0086649156u) * 931.5 MeV/u = 6.54548 MeV

And since 6.54548 MeV is greater than the required activation energy for U-235 on 5.3 MeV fission is possible. But where can I find the activation energy for other isotopes?
The only other activation energy number mentioned in my book is for U-238 which is 5.5 MeV, and doing the same calculation as before with the numbers from wikipedia I get the following:

Q=-(239.0542933u - 238.05078u - 1.0086649156u) * 931.5 MeV/u = 4.80637 MeV

Which is lower than the required 5.5 MeV, and therefor fission is not possible with a neutron. But I’ll like to do calculate on other isotopes of Uranium.

Why is it hard to fission even number nucleus, like U-234 and U-238, when it’s easier to fission odd number nucleus, like U-233 and U-235?