Mass-energy relations

The experiments of Cockcroft and Walton (Proc. Roy. Soc. A 1932, 137, 229) showed that the lithium isotope of mass number seven under bombardment by protons may capture a proton and the resulting nucleus may distintegrate into two o-particles. 

The a-particles of range 8.4 cm, which are produced by means of protons of 270 keV energy, have an energy of 8.62 MeV each. 

The atoms concerned haye masses determined bj the mass-spectrograph on the physical scale ( 0 = 16) as follows (Aston, Mass-spectra and isotopes , Arnold, 1942) 

According to the special theory of relativity, energy E and mass M are different aspects of the same entity their values being interrelated by 

We begin by obtaining a conversion factor from atomic nuclear energy to mass on the conventional atomic weight scale . Denoting the faraday by F we have for this factor 

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This is the most useful form of the mass-energy relation. 

Nuclear equation, 513 Nuclear masses, 521t Nuclear radiation. See Radioactivity Nuclear reactions biological effects, 527 equations, 513 fission, 523-526 fusion, 526-527,528 mass-energy relations, 520-523,... 

The condition that energy be released follows from the Einstein mass-energy relation ... 

Pair production involves the complete disappearance of the incident photon and the creation of an electron and a positron. It occurs only at incident energies larger than 1.02 MeV since an electron pair has to be created. Using the Einstein mass—energy relation E = me2, in fact, one finds that one electron mass is equivalent to 0.51 MeV. Energy in excess of 1.02 MeV is converted to kinetic energy of the pair. The probability of pair production increases slowly with energy and above 4 MeV it is proportional to log E and Z2. 

This mass-energy relation must dominate the whole question of the genesis of elements, the dynamics of stars, the origin of cosmic radiations, and other fundamental matters. The only respect in which it affects ordinary terrestrial chemistry is in connexion with the stability of atomic nuclei. The changes which occur in chemical reactions are too small to affect practically the traditional principle of mass conservation upon which so much of chemical theory has been based. 

Beta decay can take place only when one (or more) of the following mass-energy relations are fulfilled ... 

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