What is the energy q released in the first step of the thorium-232 decay chain? the atomic mass of 232 90th is 232.038054 u and the atomic mass of 228 88ra is 228.0301069 u. express your answer numerically in megaelectron volts?

Using Einstein's equivalence, the energy released in the decay is equal to the variation of mass between the initial state and the final state:
(1)
where c is the speed of light.

In the first step of the decay, an alpha particle (2 protons+2 neutrons) is emitted, with atomic mass 4.001506179 u. The variation of mass in the decay therefore is


and since 1 u is equal to the mass of the proton: 

The mass difference of the decay in kg is


And so by using (1) the energy released in the decay is


And since , we can convert this energy into eV: