Other types of particle accelerators were also being developed at this time. The most famous was the one built in 1930 by the American physicist Ernest Orlando Lawrence (1901-1958). In this device a magnet was used to make the protons move in gradually expanding circles, gaining energy with each lap until they finally moved out beyond the influence of the magnet and then hurtled out of the instrument in a straight line at maximum energy. This instrument was called a “cyclotron”. [Illustration: _Inventors of one of the first accelerators, Ernest T. S. Walton, left, and John D. Cockcroft, right, with Lord Ernest Rutherford at Cambridge University in the early 1930s._] [Illustration: _The bombardment of lithium-7 with protons was the first nuclear reaction caused by man-made particles._] Lithium-7 (4N,3P) + Hydrogen-1 (Proton) → Helium-4 (2N,2P) (Alpha particle) + Helium-4 (2N,2P) (Alpha particle) Neutron=N, Proton=P The cyclotron was rapidly improved, using larger magnets and increasingly sophisticated design. There are now, at this time of writing, “proton synchrotrons” (descendants of that first cyclotron) that produce particles with over a million times the energy of those produced by Lawrence’s first cyclotron. Of course, the first cyclotron was only a quarter of a meter wide, while the largest today has a diameter of some 2000 meters. As particle accelerators grew larger, more efficient, and more powerful, they became ever more useful in studying the structure of the nucleus and the nature of the subatomic particles themselves. They did not serve, however, to bring the dream of useful nuclear energy any closer. Though they brought about the liberation of vastly more nuclear energy than Rutherford’s initial bombardments could, they also consumed a great deal more energy in the process. It is not surprising that Rutherford, the pioneer in nuclear bombardment, was pessimistic. To the end of his days (he died in 1937) he maintained that it would be forever impossible to tap the energy of the nucleus for use by man. Hopes that “nuclear power” might some day run the world’s industries were, in his view, an idle dream. [Illustration: _Ernest O. Lawrence holds a model of the first cyclotron in 1930, a year after its conception._] THE NEUTRON Nuclear Spin What Rutherford did not (and could not) take into account were the consequences of a completely new type of nuclear bombardment involving a type of particle unknown in the 1920s (though Rutherford speculated about the possibility of its existence). The beginnings of the new path came about through the reluctant realization that there was a flaw in the apparently firmly grounded proton-electron picture of nuclear structure.