Determination of spatial and energy distributions of neutrons in experiments on transmutation of radioactive waste using relativistic protons

Transmutation of239Pu and other nuclides using spallation neutrons produced by relativistic protons reacting with massive U- and Pb-targets

“…Uncertainties of about ±12% are due to statistical uncertainties in the measurements and systematic uncertainties in the monitor reaction cross-sections. Fluences based on 24 Na determinations in Al-foils of monitor 2 at a distance of 35 cm upstream of the massive target give consistent results for the proton fluence with the other 3 monitor reactions: 7 Be and 22 Na in Al and 24 Na in Cu. These latter three reactions are insensitive to lowenergy secondaries [10].…”

“…The neutron spectra at the positions of 129 I, 237 Np, and 239 Pu on top of the moderator are different at various geometrical positions along the axis of the target system, as has been shown by the Minsk-group [6,24]. Neutron spectra become "harder" the further downstream along the target, as also shown in Fig.…”

“…Zhuk et al [24] carried out experiments with sandwiches containing artificial mica or Lavsan as SSNTDs and thick target foils with U natural , U-6.5% (6.5% enrichment of 235 U) and 232 Th as sensors, thus allowing the determination of the fission rates for 235 U and 232 Th as well as the spectral index σ 232 Th f /σ 235 U f . The fission process of 235 U is initiated by neutrons of all energies (however, mainly thermal neutrons in our setups with paraffin moderator) and the fission process Table 9 and in Fig.…”

“…These latter three reactions are insensitive to lowenergy secondaries [10]. As it is fairly straightforward to accurately measure 24 Na in thin Al-foils, we essentially used the proton fluence determined with 24 Na in Al (monitor 2). These fluences are experimentally most accurately determined.…”

“…The spallation targets were irradiated with 0.53 GeV and 1.0 GeV protons, in addition to another 1.5 GeV run for a. Fluences (E+13) of experiments 1998 in Dubna, measured via 24 Table 4; b: In these two Pb-target irradiations, no moderator was installed ("blank" targets). control purposes.…”