Production of neutrons in thick targets by high-energy protons and nuclei
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oduction of Neutrons in Thick Targets by HighEnergy Protons and Nuclei V. I. Yurevich Joint Institute for Nuclear Research, Dubna, Moscow oblast, Russia Abstract—This article is dedicated to the physics of spallation neutron production by highenergy particles and applications thereof. This field of research is related to the rapidly developing branch of nuclear physics that is high energy neutron physics. The central part of this article is a review of experimental results obtained in different lab oratories of the world during the last more than a quarter of a century. Analysis of the characteristics of multiple neutron production in targets induced by protons and nuclei with energies higher than several hundreds of mega electronvolts per nucleon is performed. The results of measurements that were carried out at the Joint Institute for Nuclear Research with beams of protons, deuterons, and light nuclei are discussed. Natural and artificial sources of spallation neutrons and their role in uptodate studies are considered. PACS: 25.40.h; 28.20.v; 29.25.Dz DOI: 10.1134/S1063779610050060
INTRODUCTION Since the moment when it was shown that the atomic nucleus contains a great number of neutrons and that for heavy nuclei their number considerably exceeds the number of protons, physicists have faced a new problem, that is, production of free neutrons from nuclei. It became a subject of research of the special branch of science that is neutron physics. A large number of reactions were proposed and investigated as possible sources of neutrons that were widely adopted in scientific research in lowenergy neutron physics and in numerous applications, including nuclear power engineering. With the advent of accelerators of protons and deu terons, there arose the possibility of creating beams of high energy neutrons in p+Li and p+Be reactions and through spallation of deuterons on the target nuclei. At the same time, there was also proposed the idea of largescale production of neutrons at heavy targets (Ta, W, Hg, Pb, Pb–Bi, Th, U) by highenergy parti cles, for instance, hydrogen ions that were accelerated up to energies higher than several hundreds of mega electronvolts. The foundation of this idea is the phe nomenon of multiple neutron production in matter by hadrons and highenergy nuclei through spallation reaction of heavy nuclei and subsequent multiplica tion of neutrons in cascade process of interaction of secondary highenergy particles with the target nuclei. As shown by measurements, with an increase of the thickness of a target, the fraction of charged particles decreases rapidly compared with neutron yield and a heavy target of relatively small size is the uppermost source of neutrons. Hence, two essential consequences follow:
(i) neutrons are an important and frequently deter mining component of radiation fields that are formed by highenergy particles; (ii) spallation of heavy nuclei could be used for cre ation of powerful neutron sources, for instance, on the basis of highintensity proton accele
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