Artificial radioactivity produced by neutron bombardment—II

Abstract We describe in this paper some further results on artificial radioactivity induced by neutron bombardment, which have been obtained in the physical Laboratory of the University of Rome, after the publication of our first paper on the same subject. Preliminary reports containing the main results have been already published by several of us. By far the most interesting new result concerns the effect of hydrogenated substances on the activation of several elements by neutron bombardment (§1). We give an interpretation of this phenomenon by assuming that neutrons are slowed down by impacts against hydrogen slow nuclei (§2). Some anomalously large absorption cross-sections for slow neutrons are discussed in §3. In many cases the anomalous absorption is connected with the emission of γ-rays (§4). §5 describes some attempts to get information about the energy of the slow neutrons. Scattering experiments on slow neutrons are described in §6, while §7 deals with the production of slow neutrons through the action of non-hydrogenated substances. In §8 the above results are discussed from a theoretical point of view. §§9 and 10 are dedicated to chemical methods for the separation of radioactive isotopes, and to improvements in the technique of the measurements. Results of a systematic investigation of the different elements are given in §11. These results are collected in a table at the end of the paper.