Neutron generation in massive Cu-targets during the irradiation with 22 and 44 GeV carbon ions

Abstract

An extended Cu-target was irradiated with 22 and 44 GeV carbon ions for about 11.3 and 14.7 hours, respectively. The upper side of the target was in contact with a paraffin-block for the moderation of secondary neutrons. Small holes in the moderator were filled with either lanthanum salts or uranium oxide. The reaction${}^{139}La(n,\gamma ){}^{140}La\mathop \to \limits^{\beta - }$ was studied via the decay of¹⁴⁰La(40h) using radiochemical methods, as has been published. The reaction${}^{238}U(n,\gamma )^{239} U\mathop \to \limits^{\beta - } {}^{239}Np\mathop \to \limits^{\beta - }$ was studied via the decay of²³⁹Np(2.3 d) as well as the reaction U(n,f) using radiochemical methods. In addition, solid state nuclear track detectors were used for fission studies in gold. The yields for the formation of (n,γ) products agree essentially with other experiments on extended targets carried out at the Dubna Synchrophasotron (LHE, JINR). To a first approximation, the breeding rate of (n, γ) products doubles when the carbon energy increases from 22 to 44 GeV. If, however, results at 44 GeV are compared in detail to those at 22 GeV, we observe an excess of (37±9)% in the experimentally observed²³⁹Np-breeding rate over theoretical estimations. Experiments using solid state nuclear track detectors give similar results. We present a conception for the interpretation of this fact: There is the evident connection between anomalies we observe in the yield of secondary particles in relativistic heavy ion interactions above a total energy of approximately 30–35 GeV and increased yield of neutrons in this energy region.