NEUTRON-PRODUCTION IN EXTENDED CU-TARGET IRRADIATED WITH RELATIVISTICC-12-IONS AT DUBNA, AS STUDIED WITH SSNTD AND NUCLEAR CHEMISTRY

An extended Cu-target was irradiated with 22 and 44 GeV carbon ions, T he target was in contact with a (CH2)(n)-block for the moderation of s econdary neutrons. Small holes in the moderator were filled with eithe r lanthanium salts or uranium oxide. The reaction La-139 (n,gamma) La- 140 -->/(beta) was studied via the decay of La-140 (40 h), and the rea ction U-238 (n, gamma) U-239 -->/(beta) Np-239 -->/(beta) was studied via the decay of Np-239 (2.3 d). In addition, a variety of solid state nuclear track detectors (SSNTD) were used. Results will be presented. The yields for the formation of (n, gamma) products agree essentially with other experiments on extended targets carried out at the Synchro phasotron LHE, JINR (Dubna). To a first approximation, the breeding ra te of (n, gamma) products, as well as the specific track density, seen with several SSNTDs, doubles when the carbon energy is increased from 22 to 44 GeV. If, however, results at 44 GeV are compared in detail t o those at 22 GeV, we observe an excess of (37 +/- 9) % in the experim entally observed Np-239-breeding rate over theoretical estimations. Ex periments using solid state nuclear track detectors are giving similar results. We also observed in the past such excess in the yield of oth er secondary particles in relativistic heavy ion interactions above a total energy of approximately 35-40 GeV.