In the previous reading selection, taken from the first half of his 1932 article on The Existence of a Neutron, Chadwick described his experiments with the recently discovered highly-penetrating beryllium radiation. First, a beryllium target was bombarded with \(\alpha \)-particles from a silver disk coated with polonium. When a sheet of paraffin wax was held near the beryllium, protons were ejected from the paraffin. These protons had high enough energies that they could travel significant distances through air and still be detected by an ionization counter. Earlier investigators (Curie and Joliot) had supposed that the protons were being ejected from the paraffin by \(\gamma \)-particles—high-frequency light quanta—which had been emitted by the beryllium target. Chadwick rejected this hypothesis for two reasons. First, the scattering of protons from paraffin by light quanta should, according to theoretical considerations, produce far fewer protons than were actually being observed. Second, the hypothesized light quanta produced by the bombarding \(\alpha \)-particles would not have the requisite energy to eject protons from the paraffin which could survive such long flights though air and still be detected by an ionization counter. So Chadwick instead proposed that the protons were being ejected from the paraffin by close collisions with uncharged particles whose masses are the same as a proton. These uncharged particles from the beryllium, he argued, were quite possibly the long-sought neutrons which Chadwick’s mentor, Ernest Rutherford, had predicted years before. In the reading selection that follows (the second half of his 1932 article) Chadwick continues to explore the nature of the neutron and how it interacts with other materials. Neutron scattering would later become one of the most important techniques for condensed matter physics research and radioactive isotope production for both medical and industrial purposes.