Slow Neutrons

Abstract

FOR some months past we have been investigating the influence of the temperature of hydrogen containing material on the activity of silver irradiated by slow neutrons. In our experiments we have cooled down paraffin wax to the temperature of liquid air. Under these conditions, no increase of activity of silver has been observed. Moon and Tillman¹ and also Fermi² have shown that the activity of silver increases to about 10–30 per cent when paraffin wax is cooled through the same range of temperatures as in our experiments. The only difference in the experimental conditions consisted in the fact that Tillman and Moon used a layer of cooled paraffin wax 1.7 cm. thick while in our experiments the thickness of this layer was about 10 cm. The discrepancy of the results may be explained by the assumption that the process of slowing down neutrons is accompanied by the absorption. In fact, if cooled paraffin wax absorbs slow neutrons more strongly than the paraffin at room temperature, then the decrease of the number of neutrons reaching the target in the case of a thick layer of cooled paraffin wax may counterbalance the increase of activity of neutrons.