Experimentelle Untersuchungen zur Bestimmung der thermischen Neutronenflüsse an einem Target-Moderator-Reflektorsystem einer Spallationsquelle

• Main Author: Pohl, Christoph
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 2003
• Subjects: Methane hydrate
• Online Access: https://juser.fz-juelich.de/record/33779; https://juser.fz-juelich.de/search?p=id:%22PreJuSER-33779%22

In this thesis the neutron time-of-flight spectra of a target-moderator-reflektor-system of a spallation neutron source was investigated. With these results questions concerning nuclear technology and radiation protection issues both for the design of a target-moderator-reflectorsystem of a high intensive spallation neutron source and the operation of foreseen experiments could be answered. With the JESSICA-experiment ($\underline{J}$ülich $\underline{E}$xperimental $\underline{S}$pallation Target $\underline{S}$et-up $\underline{I}$n $\underline{C}$OSY $\underline{A}$rea) installed at the Jülich proton accelerator COSY the neutron time-of-flight spectra were measured. In accompanying Monte Carlo simulations the neutron generation, the particle transport, and the interaction of neutrons with moderator materials over a broad energy range -from 1.334 GeV incident energy of the protons down to the meV range of the cold neutrons- was simulated. Both the experimental and theoretical results allow to optimise the efficiency of moderators and increasing the safety regarding radiation protection. As moderator materials water and polyethylene at T = 300 K and ice at 70 K and 20 K were used. For the first time the neutron time-of-flight spectra of methane-hydrate at 20 K was measured. By applying a methane-hydrate moderator the expected advantages due to the spectral characteristic of the thermal and cold neutrons was observed. The time response of the wavelength dependent neutrons was determined by investigating the decay time and pulse width with an accuracy of about 10 %. The gathered data of the JESSICA experiment were used to validate neutron transport- and scattering cross sections for Monte Carlo systems. Whereas for water and polyethylene experimental results and simulations are in a good agreement, for the cold ice moderator systems at 70 K and 20 K spectral differences were observed. The relevance of the experiment for radiation safety issues of a high power spallation neutron source will be discussed.