INVESTIGATION OF SURFACE LAYERS USING A COUNTER

In one of the previous issues of the journal¹ an abstract was published in which it was pointed out that electronic emission from metals at room temperature arises as a result of mechanical treatment of the surface of these metals². With the aid of a point counter it was shown that this electronic emission decreases with time and depends on the temperature of the metal under investigation. These experiments were repeated and confirmed by other authors³.

Kramer, who discovered this phenomenon, connects it with phase transformations in the surface layer of a metal, assuming that mechanical treatment of the metal surface leads to the formation in the surface layer of an amorphous phase, which with time passes back into the normal metallic phase; the energy released in this transformation ensures the escape of electrons from the metal.

The authors of the paper under review⁴ carried out, with the aid of a Geiger–Müller counter, a number of new experiments which enabled them to give a new explanation of the phenomenon mentioned. They believe that mechanical treatment, like a glow discharge in hydrogen, which produces the same effect, reduces the degree of coverage of the metal surface by an oxide layer. After treatment (or after the discharge) the layer is restored. In this process, in the opinion of these authors, the combination of an oxygen atom with an unsaturated metal atom creates the possibility of emission of one electron. The energy released in this chemical adsorption is compared with the work function of the electron.

The theoretical calculation carried out by the authors shows that the temperature dependences of the electronic emission are explained if it is assumed that the probability of formation of the chemical compound is connected with the presence of a certain activation energy, which is supplied to the atoms participating in the reaction by thermal motion.

In connection with the effect found for metals, it is of interest to note that a similar phenomenon was also found for comminuted nonmetallic crystalline substances⁵. A point counter into which these substances were introduced after comminution recorded a very large number of pulses, which rapidly decreased with time. Later it was discovered⁶ that these comminuted substances retain for several hours the ability to restore the activity mentioned as a result of irradiation by sufficiently short-wave radiation. Some substances had to be irradiated for this purpose with X-rays, whereas for other substances irradiation with visible light was sufficient. The activity could also be restored by means of a glow discharge. The law governing the decrease in the number of counter pulses with time proved in all cases to be one and the same.

It has not been possible to establish experimentally the physical nature of the indicated activity; however, there are grounds for assuming that in this case, as in the case of metals, the particles emitted by the substance are electrons.

V. Bredel

CITED LITERATURE

1. UFN 40, 325 (1950).
2. J. Kramer, Zeits. f. Physik 125, Nos. 11–12 (1949).
3. Louw J. D. a. S. M. Nande, Phys. Rev. 76, 571 (1949).
4. O. Haxel, F. G. Houtermans u. K. Seeger, Zeits. f. Physik 130, 109 (1951).
5. J. Kramer, Zeits. f. Physik 128, 538 (1950).
6. J. Kramer, Zeits. f. Physik 129, 34 (1951).