 Descriptions of collisions among sub-atomic particles such as the bombardment of Lithium make it seem as though one must admit that mass is converted into energy. However, influenced perhaps by the widely-known discussion of mass-energy equivalence by Bondi and Spurgin (1987) (see  Section 2.3.1),  physicists now explain such reactions not as cases of mass being converted into energy, but merely as cases where energy has changed forms. Typically, in these types of reactions, the potential energy that “contributes” to the rest-mass of one (or possibly) more of the reactants is transformed in a non-controversial way to the kinetic energy of the products. As Baierlein (2007, p. 322) explains, in the case of the bombardment of \({^7}\Li\) with protons and its subsequent decomposition into two \(\alpha\)-particles, the apparently “excess” kinetic energy of the \(\alpha\)-particles did not simply “appear” out of nowhere. Instead, that energy was there all along as the potential and kinetic energy of the nucleons. In other words, one can explain the change in mass and energy in the bombardment reaction by saying (i) that the potential and kinetic energies of the nucleons that make up the \({^7}\Li\) nucleus contribute to its rest-mass and (ii) that the vast amount of energy of the \(\alpha\)-particles was not “created” in the reaction, or “converted” from mass, but was simply transformed from the various forms of energy the nucleons possess.