The equivalence of mass and energy

✍ Scribed by K.T. Bainbridge

• Publisher: Elsevier Science
• Year: 1933
• Tongue: English
• Weight: 103 KB
• Volume: 216
• Category: Article
• ISSN: 0016-0032
• DOI: 10.1016/s0016-0032(33)91147-3

✦ Synopsis

An experimental test of the relationship AE = C2zim is possible for two modes of nuclear disintegration when the results of recent mass-spectrograph measurements of the masses of the lithium isotopes i are considered in conjunction with the disintegration experiments of Coekcroft and Walton 2 and of Lewis, Livingston and Lawrence?

The experiments of Cockcroft and Walton with lithium show that the lithium isotope of mass number seven under bombardment by high energy protons may capture a proton and that the resulting nucleus may disintegrate into two a-particles. The a-particles of range 8.4 cm. which appear for protons of 27o kilo-volts energy have an energy of 8.6. N Io 6 electron-volts. The gain in energy in the reaction is I6.97 N IO 6 e-volts, an energy equivalent to o.oi82 mass units on the o 16 scale if AE = C2Am. Taking Aston's values for the mass of helium and hydrogen and the author's value, 7.oi46 -4-o.ooo6 for Li 7, the mass change is o.oI81 4-o.ooo6 in the reaction which may be represented as Li z -4-P ~ 2a. Within the probable error of the measurements the equivalence of mass and energy is satisfied.

Recently Lewis, Livingston, and Lawrence have reported some remarkable disintegration experiments wherein the H "~ nucleus was the bombarding particle. In the case of lithium, a-particles of two ranges, 8.2 and ~4.8 centimeters, were observed as the products of disintegration. The bombarding particles were H 2 nuclei of 1.33 X Io 6 e-volts energy. Extrapolation of the range-energy data for a-particles secured by Rutherford, Ward, and W. B. Lewis ~ yields I2.5 × I() 6 e-volts for the energy of the a-particles of greatest range.