The neutron time-of-flight facility, nTOF, has been operating at CERN since 2001. nTOF is a pulsed neutron source coupled to a 200-metre flight path. It is designed to study neutron-nucleus interactions for neutron energies ranging from a few meV to several GeV. The wide energy range and high-intensity neutron beams produced at nTOF are used to make precise measurements of neutron-related processes.
To produce neutrons, a pulsed beam of protons from the Proton Synchrotron (PS) is directed at a lead target. When the beam hits, every proton yields about 300 neutrons. The initially fast neutrons are slowed down, first by a lead target, and then by a slab containing water. Some neutrons slow more than others as they pass through the targets, which creates a range of neutron energies (a "neutron spectrum") from the meV region up to the GeV region.
These neutrons are guided through an evacuated beam pipe to an experimental area 185 metres from the target. In a typical experiment, a sample is placed in the neutron beam and the reaction products detected. This allows the team to reconstruct the reaction probability as a function of the incident neutron energy.
Neutron time-of-flight measurements contribute in an important way to understanding nuclear data. Only a few time-of-flight facilities exist worldwide, each with its own characteristics. The strength of nTOF is the large energy range it can cover, and the high number of neutrons per pulse.
Data produced by nTOF are used in astrophysics to study stellar evolution and supernovae. Intense neutron beams are also important in hadrontherapy (the treatment of tumors with beams of hadrons) and studies of how to incinerate radioactive nuclear waste.