Questions about activation energy for fission

[dotdkay]

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=-(m_U-236 - m_U-235 - m_neutron)*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?

 

[mfb]

Uranium has 92 protons, so odd mass numbers are odd neutron numbers. Even numbers are bound more tightly (pair term), so going from odd to even can often result in an excited state which can then fission.

Finding these numbers for isotopes that are not easily fissile and have no practical application can be difficult - the energy required might be very large and/or poorly measured.