Speaker
Description
The n_TOF facility at CERN is a pulsed neutron source for time-of-flight measurements, first conceptualised by Carlo Rubbia in 1998 [1]. It is designed to study neutron induced reactions bearing importance for fundamental research, nuclear astrophysics [2,3], nuclear technology applications [4] as well as nuclear medicine [5]. During its first two operation phases, n_TOF consisted of a single beam-line of 185 m length, while for its third phase in 2014, a vertical 20 m beam-line was constructed.
The facility’s 185 m flight path provides an excellent energy resolution, reaching as low as ΔE/E ~ 10-4 for the eV region [6], enabling high precision measurements that can significantly contribute to standard neutron cross section evaluations [7]. The energy range it covers stretches from a few meV up to the GeV region, allowing for significant extension of cross section data, especially for fission measurements. Furthermore, the high instantaneous neutron flux, provided by a high intensity 20 GeV/c proton beam impinging on a lead spallation target allows to measure highly radioactive samples.
Throughout CERN’s Long Shutdown 2, the n_TOF facility has been largely upgraded. The biggest change was the replacement of the water-cooled, single block lead spallation target, with a new nitrogen-cooled target consisting of several slabs of lead and optimised also for n_TOF’s vertical beam-line. After this major change, it must be ensured that the performance of the horizontal beam-line still fulfills its high standards and has not significantly changed. Additionally, the performance of the new target must be inspected thoroughly.
During the Commissioning in 2021, several detection systems, such as a fission and charged particles setup for the measurement of the neutron flux and beam profile. The energy resolution of the beam-line was investigated with neutron capture detectors complimented by extensive Monte Carlo simulations.
In this work, the characterisation of the horizontal beam-line after the facility’s spallation target replacement will be summarised. The preliminary results on the neutron flux will be presented along with a comparison with simulations as well as with the flux of the previous spallation target. Characteristics such as the energy resolution and the background conditions will also be discussed and compared to the beam-line’s previous performance.
References
[1] C. Rubbia et al., A high resolution spallation driven facility at the CERN-PS to measure neutron cross sections in the interval from 1 eV to 250 MeV, CERN/LHC/98-02 (EET), 1998
[2] U. Abbondanno et al., Neutron Capture Cross Section Measurement of 151Sm at the CERN Neutron Time of Flight Facility (n_TOF), Phys. Rev. Lett. 93, 161103 (2004)
[3] C. Lederer et al., Neutron Capture Cross Section of Unstable 63Ni: Implications for Stellar Nucleosynthesis, Phys. Rev. Lett. 110, 022501 (2013)
[4] N. Colonna, A. Tsinganis, R. Vlastou, et al. The fission experimental programme at the CERN n_TOF facility: status and perspectives. Eur. Phys. J. A 56, 48 (2020)
[5] J. Praena et al., Measurement and resonance analysis of the 33S(n,α)30Si cross section at the CERN n_TOF facility in the energy region from 10 to 300 keV, Phys. Rev. C 97, 064603 (2018)
[6] Guerrero, C., Tsinganis, A., Berthoumieux, E. et al. Performance of the neutron time-of-flight facility n_TOF at CERN. Eur. Phys. J. A 49, 27 (2013)
[7] S. Amaducci, L. Cosentino, M. Barbagallo, et al. Measurement of the 235U(n, f) cross section relative to the 6Li(n, t) and 10B(n,a) standards from thermal to 170 keV neutron energy range at n_TOF. Eur. Phys. J. A 55, 120 (2019)