Background of the original experiment. The artificial disintegration of the Lithium nucleus producing 8.58 + million volt alpha particles hitting them with 150,000 volt protons.

 In 1932   Cockroft and Walton, at the Cavendish Laboratory, Cambridge  employed a number of kenotrons.

 in series multiplying circuit, succeeded in producing high voltage to accelerate protons to energies of 100,000  to 700,000 electron-volts. (Kenotrons are vacuum rectifying hot cathode tubes of the diode type). Their power supply was very large and very expensive.

With this power supply they  bombarded lithium and produced the first transmutation by means of artificially produced projectiles (protons), as follows: They ionized hydrogen giving them protons which they shot at a Lithium target. with the high voltage power supply. The result was  8,530,000  electron volt alpha particles. The equation of the reaction is

_{{ 1}H¹ + ₃Li⁷ }  --->  ₂He ⁴ + ₂He⁴ + E.   equation (1) p435

The hydrogen nucleus (proton) combined with the lithium nucleus to produce two helium nuclei (alpha particles). These two helium nuclei are shot out in opposite directions with the great kinetic energy of  8.53 X 10 ⁶ electron volts each See Fig. 1.

The reaction was an important test of Einstein's theory of mass and energy.

Figure (1) shows a drawing of a cloud chamber picture of three such pairs. This energy, less the initial kinetic energy of 150,000 ev of the proton, is represented in equation (1) by E. From the magnitude of the energies of the alphas, it is seen that the reaction is in the nature of an explosion.

The question of whence came this enormous energy exhibited by the alphas in the  transmutation of mass and energy. One of the conclusions from Einstein's theory of relativity was that mass should be changeable into energy or energy into mass according to the relation:

 E = mc²     

where
 m is the mass in question
 c is the velocity of light
E is the energy equivalent to mass m.

This prediction of the relativity theory is verified in a highly satisfactory way by the reaction of Eq. (2). Taking atomic masses in terms of eV of the mass of an oxygen atom as a unit, to which the name Dalton has been given, we have the following values: Writing these masses for the nuclei in Eq. (2), we have

 _iH¹ + ₃L⁷ --->  ₂He⁴ + ₂He⁴ + E gives 1.0075 + 7.0132 = 2(4.0011) + E

where E=0.0185

 Hence, if the laws of conservation of mass and of energy hold true, the energy E must equal 0.0185 Dalton.

It may be shown that

1 Dalton = 927 X 10⁶ electron-volts.

Therefore

0.0185 Dalton = 0.0185 X 927 X 102 = 17.15 mev

The observed value of the energy of the two alphas in their experiment  was 17.06 mev. The calculated and experimental values are in excellent agreement and offer strong confirmation of theory. In the foregoing we have an example of the transformation of matter into energy.

FIG. (1). Transmutation of Lithium into Helium shown in a drawing of a cloud chamber event.

Ref.1, Physics by Frank L. Robeson Macmillan Co New York 1942

Ref, 2 Procedures in Experimental Physics by John Strong etal.1938-1956 Prentice- Hall, Inc.

Ref 3,  The Particles of Modern Physics by J.D. Stranathan 1943-1946 Blakiston Co. Philadelphis . Toronto p 435---