CHAPTER<br > ONE<br > A HALF-CENTURY<br > OF PARTICLE<br > ACCELERATORS<br >The moment was one of high excitement for M. Stanley<br >Livingston. A turn of the dial would soon tel this gradu-<br >ate student in physics if he was to make scientific his-<br >tory. His advisor， Ernest O. Lawrence， had proposed<br >this machine as a way of breaking apart atomic nuclei.<br >But would the idea actually work in practice?<br > Livingston turned the dial and . . . success! The<br >maclgne worked. The world s first circular particle accel-<br >erator， or cyclotron， was in operation.<br > This historic scene took place on the Berkeley cam-<br >.Pus of the University of California in early 1932. The<br >cyclotron opened a new era in our study of the atom.<br > During the first two decades of the twentieth cen-<br >tury， scientists had made enormous strides in learning<br >about the atom. They had found that atoms consist of<br >two parts: a dense， positively charged core called the<br >11<br >