Monte Carlo simulations and n-p differential scattering data measured with Proton Recoil Telescopes

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.

Trends in particle and nuclei identification techniques in nuclear physics experiments

“…the accumulation of events with ΔE and E of about 12 and 60 MeV respectively). The n+C reactions are characterized by a negative Q value, therefore the protons emitted An extensive study through Monte Carlo simulations with neutrons impinging on a realistic setup was performed to estimate the performances of the techniques used in the analysis [237]. The correlation between ΔE − E and TOF enables a selection of proton events at the level of 1% accuracy, for protons with energy up to 180 MeV.…”

Recoil Proton Telescopes and Parallel Plate Avalanche Counters for the 235U(n,f) cross section measurement relative to H(n,n)H between 10 and 450 MeV neutron energy

“…A step-by-step comparison of the results from the two toolkits was performed to validate Geant4 and MCNP simulations. For each step it was verified that the two codes provided the same results after the adoption of the correct physics models for the n-p elastic scattering [27]. In particular, the energy deposited in each stage of the counter telescope and the number of recorded events resulted to be compatible, within the uncertainties, between the two MC simulations.…”

“…This evaluation is accepted by the Committee on Standards NEANDC/INDC as a primary standard for cross section measurements in the 20-350 MeV range [1], and included in the evaluated nuclear data files ENDF/B-VII.0 and JENDL-4.0 [33,34] evaluations in the low energy range, below 20 MeV, and in the JENDL/High Energy file [35] up to 3 GeV. Since all the reference physics list classes -9 - already defined in Geant4 do not contain the VL40 interaction, a detailed Monte Carlo model [27] was specifically developed for using the Geant4 toolkit [25].…”

Riptide: a proton-recoil track imaging detector for fast neutrons

“…neutron-proton interaction has previously been tested within the framework of other experiments and it is considered as validated in this context and reliable in the current energy range (see for instance [19]).…”