Abstract
The study of the resonant structures in neutron-nucleus cross-sections, and therefore of the compound-nucleus reaction mechanism, requires spectroscopic measurements to determine with high accuracy the energy of the neutron interacting with the material under study.To this purpose, the neutron time-of-flight facility n_TOF has been operating since 2001 at CERN. Its characteristics, such as the high intensity instantaneous neutron flux, the wide energy range from thermal to few GeV, and the very good energy resolution, are perfectly suited to perform high-quality measurements of neutron-induced reaction cross sections. The precise and accurate knowledge of these cross sections plays a fundamental role in nuclear technologies, nuclear astrophysics and nuclear physics.Two different measuring stations are available at the n_TOF facility, called EAR1 and EAR2, with different characteristics of intensity of the neutron flux and energy resolution. These experimental areas, combined with advanced detection systems lead to a great flexibility in performing challenging measurement of high precision and accuracy, and allow the investigation isotopes with very low cross sections, or available only in small quantities, or with very high specific activity.The characteristics and performances of the two experimental areas of the n_TOF facility will be presented, together with the most important measurements performed to date and their physics case. In addition, the significant upcoming measurements will be introduced.
Highlights
The time-of-flight facility of CERN, called n_TOF, became operative in 2001 based on an idea by Rubbia et al [1], and since it occupies a major role in the field of neutron cross-section measurements
Since July 2014 a second experimental area (EAR2) has been built 20 m above the spallation target, with unique characteristics which made it a powerful tool for measurements of highly radioactive and of low-mass samples, and of very low cross sections. This new measuring station is complementary to the existing first experimental area (EAR1), and the characteristics of both are extremely competitive in terms of flux intensity, energy range covered and energy resolution
Depending on the requirements of the reaction under study precise and accurate results can be achieved, and several detection systems are available to investigate (n,γ), (n,cp) and (n, f ) reactions. These cross sections play a fundamental role in nuclear technologies, nuclear astrophysics and fundamental nuclear physics, and significant results have been attained, relating to new reactor designs, to stellar and primordial nucleosynthesis models and to the investigation of the compound nucleus
Summary
The time-of-flight facility of CERN, called n_TOF, became operative in 2001 based on an idea by Rubbia et al [1], and since it occupies a major role in the field of neutron cross-section measurements. The resolution function changes significantly from EAR1 and EAR2, because of its strong dependance on the neutron transport within the target and on the neutron propagation to the experimental areas Since these effects cannot be experimentally measured, the two resolution functions for the spallation target-moderator assembly have been simulated with FLUKA [9] and MCNP [10] Monte Carlo codes for both the configuration with normal and borated water as moderator material, and neutrons have been propagated through the two different beam lines. Depending on the requirements of the reaction under study (e.g. the need of high energy resolution or rather of high neutron flux), the two experimental areas of the n_TOF facility provide a remarkable flexibility to select the best configuration for successful measurement To fully exploit this potential, different detection systems are available and will be described
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