Alpha decay (two protons and two neutrons) changes the mass number of the element by -4 and the atomic number by -2 so the remaining nucleus will be \(_{90}^{234}?\). A periodic table shows that ...

They broke a lithium nucleus in two by bombarding it with protons, verifying Albert Einstein’s insight that mass and energy were one and the same, as expressed by the equation E = mc2.

Roosevelt urging the United States to start its own atomic bomb research program ... in the theory of relativity (particularly the famous equation E=mc²) laid the theoretical groundwork for ...