First, the alpha particles used in bombardment were positively charged and so were the atomic nuclei. This meant that the alpha particles and the atomic nuclei repelled each other and much of the energy of the alpha particles was used in overcoming the repulsion. For more and more massive nuclei, the positive charge grew higher and the repulsion stronger until for elements beyond potassium, no collision could be forced, even with the most energetic naturally occurring alpha particles. [Illustration: _Man-made transmutation._] Nitrogen-14 (7N,7P) + Helium-4 (2N,2P) (Alpha particle) → Oxygen-17 (9N,8P) + Hydrogen-1 (1P) Neutron=N, Proton=P Second, the alpha particles that are sprayed toward the target cannot be aimed directly at the nuclei. An alpha particle strikes a nucleus only if, by chance, they come together. The nuclei that serve as their targets are so unimaginably small that most of the bombarding particles are sure to miss. In Rutherford’s first bombardment of nitrogen, it was calculated that only 1 alpha particle out of 300,000 managed to strike a nitrogen nucleus. The result of these considerations is clear. There is energy to be gained out of nuclear reactions, but there is also energy that must be expended to cause these nuclear reactions. In the case of nuclear bombardment by subatomic particles (the only way, apparently, in which nuclear reactions can be brought about), the energy expended seems to be many times the energy to be extracted. This is because so many subatomic particles use up their energy in ionizing atoms, knocking electrons away, and never initiate nuclear reactions at all. It was as though the only way you could light a candle would be to strike 300,000 matches, one after the other. If that were so, candles would be impractical. In fact, the most dramatic result of alpha particle bombardment had nothing to do with energy production, but rather the reverse. New nuclei were produced that had _more_ energy than the starting nuclei, so that energy was absorbed by the nuclear reaction rather than given off. This came about first in 1934, when a French husband-and-wife team of physicists, Frédéric Joliot-Curie (1900-1958) and Irène Joliot-Curie (1897-1956) were bombarding aluminum-27 (atomic number 13) with alpha particles. The result was to combine part of the alpha particle with the aluminum-27 nucleus to form a new nucleus with an atomic number two units higher—15—and a mass number three units higher—30. The element with atomic number 15 is phosphorus so that phosphorus-30 was formed. The only isotope of phosphorus that occurs in nature, however, is phosphorus-31. Phosphorus-30 was the first man-made nucleus—the first to be manufactured by nuclear reactions in the laboratory. [Illustration: _Frédéric and Irène Joliot-Curie_]