Internal energy loss and momentum conservation question

[MoZeeba]

A uranium-238 atom can break up into a thorium-234 atom and a particle called an alpha particle, α-4. The numbers indicate the inertias of the atoms and the alpha particle in atomic mass units (1 amu = 1.66 × 10−27 kg). When an uranium atom initially at rest breaks up, the thorium atom is observed to recoil with an x component of velocity of -2.6 × 105 m/s. How much of the Uranium atom's internal energy is released in the breakup?

I know that this is an explosive separation problem and that the initial velocities are zero but I'm confused on how to approach this problem.

 

[BvU]

Hello MoZeeba,

but I'm confused

Clearly. This is obviously homework and should be posted in a homework forum. That has a template:

Homework Statement

Homework Equations

The Attempt at a Solution

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and the guidelines forbid us to help if the poster shows no attempt at solution. So, please indulge us...

For starters: energy equivalent of U ? Th ? $\alpha$ ?