Collisions of neutrons with light nuclei.—Part II

Abstract

In a previous paper experiments were described in which collisions between neutrons and nitrogen nuclei had been investigated by stereoscopic photography of the tracks produced in an expansion chamber filled with nitrogen and traversed by the radiation from a source of polonium and beryllium placed at its centre. With this arrangement 1740 pairs of photographs were taken. The method has since been extended to neutrons-oxygen nucleus encounters, and a preliminary report of the results obtained in 1490 pairs of photographs has appeared. In the present paper these results are presented in greater detail and more recent experimental material, provided by 1460 stereoscopic pairs belonging to an oxygen-hydrogen series of photographs and 2210 pairs to an acetylene-helium series, is given for the first time. The analysis of this new material scarcely does more than provide preliminary data for this new material scarcely does more than provide preliminary data for the discussion of the general problem of the close collisions of neutrons with light nuclei, but its publication at this time may well be of interest. During the course of the work reports of similar experiments—in progress, or already productive of preliminary results—have been received from Auger; Meitner and Philipp§; Harkins, Gans, and Newson║; Kurie¶; and Rieder.** Reference will be made to their results at a later stage. It is necessary, however, to draw attention at the outset to a feature common to all such experiments, in which the expansion chamber is used. Although individual events may be studied and the angles involved in their description be determined directly, the kinetic energies concerned may be deduced only from measurements of lengths of cloud track. However extensive the experimental material may be, we are very seriously handicapped in interpreting it by the inadequacy of our knowledge of the researches of Blackett and his coworkers provided the only data for use in this connection. Now range-velocity curves are also available for the recoil atoms of fluorine and (less accurately) of carbon, these having recently been investigated by the writer.* Some of the earlier results must be considered in the light of this new knowledge.