Ernest O. Lawrence

During the 1920s, the only available method for probing nuclei was that developed by Ernest Rutherford, which consisted of bombarding the nuclei with alpha particles. A major problem with this technique was overcoming the repulsive forces between the positively charged alpha particle and the target's positively charged nucleus. The relatively low energies possessed by alpha particles compounded the problem. Rutherford's method worked reasonably well with light elements, whose nuclear charges were small, but failed with elements of high atomic numbers. To overcome this problem, a number of machines were developed for accelerating charged particles to higher energies, but the cyclotron of Ernest Lawrence would prove the most important tool in high-energy physics. Lawrence conceived the idea for the cyclotron in 1929 after coming across an article by Rolf Wideröe. The article described an accelerator that employed a pair of linearly arranged cylinders and an alternating electric field. Lawrence's inspiration was to reconfigure Wideröe's cylinders as D-shaped chambers and position them between the poles of a magnet. Within the "dees," ions (e.g., protons) were accelerated in a series of steps over a spiral path. As such, the cyclotron could be small yet capable of generating very high energy ions. Even Lawrence's first machine, only 4.5" in diameter, accelerated protons to 80,000 eV. Later, Lawrence used improved versions of the cyclotron to investigate nuclear processes and to produce a variety of new and medically important isotopes (e.g., the phosphorus-32 used in early attempts to treat leukemia). For this work, Lawrence received the 1939 Nobel Prize in physics. Today, descendants of this first cyclotron continue to play an important role in the treatment of cancer and have proven to be the physicist's most useful tool for exploring the nature of matter.

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