Iron assembly penetration and streaming by neutrons and protons

The fluence of fast neutrons in the magnet coils, the number of atomic displacements in the copper stabilizer, and the nuclear heating in the winding pack are parameters of the ITER shield design that are determined by the neutron and photon fluxes (φn φγ) penetrating the shield. As shown by a sensitivity analysis of the NET shields, the evaluated nuclear data are the main source of uncertainties of the calculated shield parameters, and there the main contribution arise from the Fe data. Therefore, the φn(E) and φγ(E) penetrating Fe benchmark assemblies are measured and compared with the calculated fluxes. Solid Fe slabs as well as the influence of gaps in the assembly are investigated. The D-T neutron source is operated in pulsed mode, and for each detector event the pulse height and the time-of-arrival are recorded. The liquid scintillator used as detector is sensitive to both neutrons and photons. Low-energy neutrons are detected by spherical proportional chambers filled with hydrogen. The pulse-height distributions obtained are transformed to φn(E) and φγ(E). φn(t) is used as additional test of the neutron nuclear data, whereas φγ(t) is needed for background reduction