Recent results of the study of ADS with 500 kg natural uranium target aßembly QUINTA irradiated by deuterons with energies from 1 to 8 GeV at JINR NUCLOTRON

The study of basic properties of the ADS presented in the previous Baldin seminar [1] was continued during the 2011-2012. For these experiments, uranium target aßembly has been upgraded: the entrance window was created to reduce the albedo of the incident beam and a section was added to keep the effective maß of uranium to the beam axis. The new target aßembly with a maß of 500 kg of natural uranium metal (diameter ∼30cm and length ⁶⁵cm) was named QUINTA. During the three runs of JINR NUCLOTRON the target aßembly (TA) QUINTA was irradiated by deuterons with energies from 1 to 8 GeV and the total number of deuterons on the target of (3-5) 10¹³ for each energy. The the energy spectra of prompt neutrons inside and outside the target aßembly and the time spectra of delayed neutrons (DN) between accelerator bursts were measured. Beside that the spatial distributions of fißion rates inside TA have been measured with aid of solid state track detectors and independently by activation method. The last method was used for measurements of ²³⁹Pu nuclei production. All these measurements were made with the original TA QUINTA as well as with TA surrounded by a 10 cm thick lead blanket. Total numbers of fißions and produced ²³⁹Pu nuclei were obtained by integration over QUINTA volume and normalized to one incident deuteron and one GeV. Both these numbers were constant within experimental errors of about 15 % for the deuteron energy range (1-8) GeV. In measurements with a lead blanket the absolute amount of produced ²³⁹Pu nuclei increased by about 50% but staying constant in studied deuteron energy range, while the numbers of fißions remained virtually unchanged The group analysis of DN time spectra indicates a growth in the average energy of the neutrons initiating fißion of target nuclei from 15 to ∼ 40 MeV with an increase in energy of the incident deuterons from 1 to 8 GeV. This result should be verified by experiments planned at the end of 2012.