Range of Radiation from Samarium

Abstract

In NATURE of December 3 we announced the discovery of radiation of α-ray type emitted by samarium. Recently we have determined the range of this radiation. The apparatus used, to which Prof. H. Geiger had kindly directed our attention, consisted of a perforated Geiger-Müller tube, surrounded by a cylindrical brass tube, the inside of which was coated with samarium oxide. The whole system could be evacuated, and the pressure could be varied until no more α-particles reached the counter. From the air pressure and the distance between the samarium oxide layer and the counter, the range of the particles could be determined. The value for the range of the samarium radiation in air at atmospheric pressure was found to be 1.1₃ cm. at 15° C. The reliability of the method was checked by determining the range of the α-rays of radium F and a value of 3.90 cm. was found. Making use of the known relation between range and velocity of α-particles, we can conclude that particles having the velocity of 1.05 × 10⁹ cm. sec.¹ are emitted by samarium. That samarium emits α-particles and not H-particles could be proved by comparing the magnitude of the electrometric deflections obtained when counting the number of α-particles emitted by samarium, and also the magnitude of the deflections which polonium radiation produced, when the range of the particles was cut down to 1.1₃ cms.