CBSE Class 12-science Answered

When nucleons of nucleus are separated apart from each other then the sum of the nucleons is greater than the mass of nucleus.This is direct mass defeat of nucleus. Some mass has been converted into energy which holds the nucleous together.

Given : Atomic mass of ²³⁸U = 238.0580 u

           Atomic mass of ^234Th = 234.04363 u

           Atomic mass of alpha-particle = 4.00260 u

           1u =  931 MeV

Mass defect = 238.0580-(234.04363 + 4.00260)

                 = 238.05080 - 238.04623 = 0.00457 u

Emitted energy will be = 0.00457 x 931 = 4.25 MeV