138 BELL SYSTEM TECHNICAL JOURNAL 



diverge at mutual angles of 120° from a point in a boron target bom- 

 barded by protons, and Dee and Walton have noticed a number of 

 trios of paths springing from such a target, but without being quite 

 sure that they are not mere coincidences.^^ 



Having now met with a case in which there may not be a balance 

 between the two sides of such an equation as (6), we should now 

 pause to inquire what can be done about such cases. Of course, 

 such a disagreement might mean that the actual process is something 

 entirely different from the one postulated in the equation, but it may 

 not be necessary to make such a complete surrender of the theory. 

 In equations (1) to (6), it is everywhere assumed that all the energy is 

 retained by the material particles, in the form of kinetic energy or of 

 rest-mass. Suppose that the process described by one of these 

 equations, (6) for instance, is confirmed in every respect excepting 

 that the final kinetic energy of the fragments is found to be less, by 

 some amount Q, than the value of Ti computed from the equation. 

 One might then assume that the missing energy Q is radiated away 

 in the form of one or more photons. Alternatively one might assume 

 that the missing energy is retained by one of the material fragments 

 in the form of "energy of excitation"; the rest-mass of the fragment, 

 so long as it retained this energy and remained in the excited state, 

 would then be correspondingly greater than its normal rest-mass, and 

 the equation would be balanced if this abnormal value of mass were 

 inserted into it in place of the normal one. Such explanations are 

 frequently offered nowadays. They suffer, of course, from the 

 disadvantage of being too easy ; one can always postulate the necessary 

 photons or excited states to explain any observed positive value of Q. 

 But if they can ever be supported by independent proof of these 

 excited states or photons, they will become much more convincing. 



Lithium and boron are by far the best-studied of nuclei, in respect 

 to their interactions with protons and deutons. It is true that our 

 knowledge of the distribution-in-range curves of the fragments is still 

 confined to comparatively low values of the energy of the bombarding 

 particles, values less than 300,000 electron-volts. With higher energies 

 it is to be presumed that the steps at the right-hand ends of the 

 curves in Figs. 8 and 9 would move to the right, to the extent pre- 



^^ If in the case of boron bombarded by protons it be assumed that two of the He 

 nuclei fly off in directions making symmetrical angles (tt — 0) and (tt + 6) with the 

 direction of the third, the distribution-in-0 of the disintegrations can be deduced from 

 the curve of Fig. 14; it turns out that the most probable cases are those in which 

 6 = 60° nearly, and ail the three particles have nearly the same energy. A like 

 deduction may be made for lithium bombarded by deutons, the neutron playing the 

 part of third alpha-particle in the foregoing case; it is inferred that again the most 

 probable types of disintegration are those in which all three share almost equally in the 

 energy. 



