Comparison of protons and electrons in the excitation of x-rays by impact

Abstract

The experimental investigation of the laws governing the excitation of x-rays by electron impact appears to be near completion. However, the existence of the proton, with its mass of 1,846 times that of the electron, provides the possibility of introducing anew variable—the mass—into collision experiments. Previous investigations have led to inconclusive results except that it is known that when fast α-particles fall on an element, its characteristic x-ray spectrum is excited. In the writer's experiments, a mass spectrograph is used to bring either protons or electrons, of same energy in the range from 15 kv. to 25 kv., onto a copper target. The arrangement eliminates several known sources of error. X-radiation produced passed into an argon filled Geiger counter.The procedure was to compare two currents: (1) the current composing an electron beam just intense enough to produce detectable x-rays; and (2) that composing the strongest proton beam which certainly produced less radiation.The ratio of these currents is a minimum value for p, the ratio of the efficiencies for excitation of electrons and protons respectively. The results were that (1) no radiation from proton impacts was observed, (2) the minimum value of p from three sets of experiments was 740; 237,000; and 6,400.In view of the directness of the experiment, the order of magnitude of the highest figure is presented as the result, i.e. ϱ = 10 5. This may be compared with ( M/m = 1,846, W/m) 3 2 = 79,310, (M/m) 2 = 3,408,000 . Wave mechanical considerations of impact processes indicate that radiation should be produced by proton impacts of energy greater than the critical energy (for copper, 8.86 kv.) but intensity formulas have not been derived.If they can be derived the present results offer the possibility of checking the wave mechanics of impact processes.