Abstract
The neutron induced fission of 235U is extensively used as a reference for neutron fluence measurements in various applications, ranging from the investigation of the biological effectiveness of high energy neutrons, to the measurement of high energy neutron cross sections of relevance for accelerator driven nuclear systems. Despite its widespread use, no data exist on neutron induced fission of 235U above 200 MeV. The neutron facility n_TOF offers the possibility to improve the situation. The measurement of 235U(n,f) relative to the differential n-p scattering cross-section, was carried out in September 2018 with the aim of providing accurate and precise cross section data in the energy range from 10 MeV up to 1 GeV. In such measurements, Recoil Proton Telescopes (RPTs) are used to measure the neutron flux while the fission events are detected and counted with dedicated detectors. In this paper the measurement campaign and the experimental set-up are illustrated.
Highlights
Neutron cross section standards are fundamental ingredients for both measurements and evaluations of neutroninduced reaction cross sections
Despite its importance in fundamental nuclear physics and its widespread use as reference for neutron fluence measurements, only two data sets are available in the energy range between 20 and 200 MeV and two absolute experimental measurements have been performed in the high energy region, above 200 MeV [3, 4]
The Parallel Plate Avalanche Counters consist of 3 electrodes, a central anode surronded by two cathodes; the 3 mm gaps between electrodes are filled with forced flow of C3F8 maintained at low-pressure (4 mbar)
Summary
Neutron cross section standards are fundamental ingredients for both measurements and evaluations of neutroninduced reaction cross sections. No cross section standard exists for neutron energies above 200 MeV. An effective choice for the reaction to be studied is the 235U(n,f) reaction, already one of the most important standard cross section at thermal neutron energy and between 0.15 MeV and 200 MeV [2]. Despite its importance in fundamental nuclear physics and its widespread use as reference for neutron fluence measurements, only two data sets are available in the energy range between 20 and 200 MeV and two absolute experimental measurements have been performed in the high energy region, above 200 MeV [3, 4] (figure 1). A dedicated measurement campaign was carried out with the aim of providing accurate and precise cross section data of the 235U(n,f) reaction in the high energy region
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