Consider the fission of `._(92)^(238)U` by fast neutrons. In one fission event, no neutrons are emitted and the final end products, after the beta decay of the primay fragments, are `._(58)^(140)Ce` and `._(44)^(99)Ru`. Calculate Q for this fission process. The relevant atomic and particle masses are
`m(._(92)^(238)U)=238.05079 u`
`m(._(58)^(140)Ce)=139.90543 u`
`m(._(44)^(99)Ru)=98.90594 u`

Explanation

1.The disintegration energy Q is the energy transferred from mass energy to kinetic energy of the decay products. 2. `Q=-Deltamc^(2)`, where `Deltam` is the change in mass.
Calculation : Because we are to include the decay of the fission fragments, we combine Eqs. 40 -36 , 40 -37 and 40-38 to write to overall trasformation as
`""^(235)Uto""^(140)Ce+""^(94)Zr+n` (40-42)
Only the single neutron appears here because the initiating neutron on the left side of Eq. 40-36 cancels one of the two neutrons on the right of that equation. The mass difference for the reaction of Eq. 40-42 is
`Deltam=(139.9054u+93.9063j+1.00866u)`
`-(235.0439u)`
`=-0.22354u`
and the corresponding disintegration energy is
`Q=-Deltamc^(2)=-(-0.22354u(931.494013MeV//u)`
`=208MeV`
which is in good agreement with our estimate of eq. 40-41.
If the fission event takes place in a bulk solid, most of this disintegration energy, which first goes into kinetic energy of the decay products, appears eventually as an increase in the internal energy of that body, revealing itself as a rise in temperature. Five or six percent or so of the disintegration energy, however, is associated with neutrinos that are emitted during the beta decay of the primary fission fragments. This energy is carried out of the system and is lost.