Artificial Production of Fast Protons

J. D. Cockcroft and E. T. S. Walton

Editor’s Note

To study the structure of the atomic nucleus, physicists in the early 1930s needed to accelerate probe particles to high energies. Among the first to develop such techniques were John Cockcroft and Ernest Walton in Cambridge. Here they report initial studies using a device for accelerating protons. An electrical discharge in hydrogen gas produced protons, which were then accelerated by high-voltage electrodes in a vacuum tube nearly one metre long, and detected at a fluorescent screen. Cockcroft and Walton measured proton velocities of up to 1.16×109 cm/s. The two physicists later used the device to achieve the first artificial splitting of the atom, or “transmutation” of the nucleus, for which they won the 1951 Nobel Prize for physics.　　中文

A high potential laboratory has been developed at the Cavendish Laboratory for the study of the properties of high speed positive ions. The potential from a high voltage transformer is rectified and multiplied four times by a special arrangement of rectifiers and condensers, giving a working steady potential of 800 kilovolts. Currents of the order of a milliampere may be obtained at a potential constant to 1–2 percent.　　中文

Protons from a discharge in hydrogen are directed down the axis of two glass cylinders 14 in. in diameter and 36 in. long, and accelerated by the steady potentials of the rectifier. They are then passed into an experimental chamber at atmospheric pressure through a mica window having a stopping power of about 1mm. air equivalent. Luminescence of the air can easily be observed.　　中文

The ranges of the protons in air and hydrogen have been measured using a fluorescent screen as a detector. The range in air at S.T.P. of a proton having a velocity of 109 cm./sec. is found to be 8.2 mm., whilst the corresponding range for hydrogen is 3.2 cm. The observed ranges support the general conclusions of Blackett on the relative ranges of protons and α-particles, although the absolute values of the ranges are lower for both gases. The ranges and stopping power will be measured more accurately by an ionisation method.　　中文

The maximum energy of the protons produced up to the present has been 710 kilovolts with a velocity of 1.16×109 cm./sec. and a corresponding range in air of 13.5 mm. at S.T.P. We do not anticipate any difficulty in working up to 800 kilovolts with our present apparatus.　　中文

(129, 242; 1932)

J. D. Cockcroft and E. T. S. Walton: Cavendish Laboratory, Cambridge, Feb. 2.