Abstract
The neutron-induced fission cross section of 235U, a standard at thermal energy and between 0.15 MeV and 200 MeV, plays a crucial role in nuclear technology applications. The long-standing need of improving cross section data above 20 MeV and the lack of experimental data above 200 MeV motivated a new experimental campaign at the n_TOF facility at CERN. The measurement has been performed in 2018 at the experimental area 1 (EAR1), located at 185 m from the neutron-producing target (the experiment is presented by A. Manna et al. in a contribution to this conference). The 235U(n,f) cross section from 20 MeV up to about 1 GeV has been measured relative to the 1H(n,n)1H reaction, which is considered the primary reference in this energy region. The neutron flux impinging on the 235U sample (a key quantity for determining the fission events) has been obtained by detecting recoil protons originating from n-p scattering in a C2H4 sample. Two Proton Recoil Telescopes (PRT), consisting of several layers of solid-state detectors and fast plastic scintillators, have been located at proton scattering angles of 25.07° and 20.32°, out of the neutron beam. The PRTs exploit the ΔE-E technique for particle identification, a basic requirement for the rejection of charged particles from neutron-induced reactions in carbon. Extensive Monte Carlo simulations were performed to characterize proton transport through the different slabs of silicon and scintillation detectors, to optimize the experimental set-up and to deduce the efficiency of the whole PRT detector. In this work we compare measured data collected with the PRTs with a full Monte Carlo simulation based on the Geant-4 toolkit.
Highlights
The 235U(n,f) cross section is considered as standard at thermal neutron energy and between 0.15 MeV and 200 MeV [1]
To measure n-p scattering in presence of an intense γ flash and a continuous neutron energy distribution, three Proton Recoil Telescopes (PRTs) were designed
To measure n-p scattering, three PRT detection systems were placed in front of Polyethylene targets as shown in figure 1
Summary
The 235U(n,f) cross section is considered as standard at thermal neutron energy and between 0.15 MeV and 200 MeV [1]. Its importance in nuclear reactor applications is overwhelming and, typically, it is employed as a reference in fission cross section measurements, see Ref. Despite its widespread use in many fields, only two measurements are available between 20 and 200 MeV [3, 4], and no experimental points exist for neutron-induced fission cross sections above 200 MeV. To measure n-p scattering in presence of an intense γ flash and a continuous neutron energy distribution, three Proton Recoil Telescopes (PRTs) were designed. Since fission fragments and recoil protons have been measured by different experimental set-ups, efficiencies must be precisely known and a fully characterization of the detectors is mandatory. Some preliminary results and comparisons to experimental data for the two of the three PRT detectors of INFN conception are shown
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