Neutron Time of Flight facility takes off smoothly at CERN

1 July 2001


There was a new arrival among CERN’s family of particle beams when the laboratory’s first intense beam of neutrons was produced at the new neutron Time Of Flight (nTOF) facility. The nTOF opens the door to many corridors of research, ranging from fundamental science to new forms of energy generation, and it is complementary to CERN’s existing ISOLDE radioactive-beam facility.

The goal of the nTOF is to provide unprecedented precision in neutron kinetic energy determination, which will in turn bring much-needed precision in neutron-induced cross-section measurements. Such measurements are vital for a range of studies in fields as diverse as nuclear technology, astrophysics and fundamental nuclear physics. The nTOF will provide neutron rates some three orders of magnitude higher than existing facilities, allowing measurements to be made more precisely and more rapidly than in the past.

The lineage of the nTOF can be traced back to work that was carried out by CERN’s 1984 Nobel prizewinner Carlo Rubbia on a new, safe and clean way of extracting energy from the atomic nucleus. Rubbia’s Energy Amplifier is an example of an Accelerator Driven System (ADS) in which the thorium cycle would be put to work. Since thorium fission does not release sufficient neutrons to sustain a chain reaction, an accelerator would be used to produce the neutrons that drive the reactions.

In 1994, in a European Union-backed experiment at CERN, Rubbia’s team showed that the energy produced by fission is about 30 times that injected by the accelerated particle beam, giving a strong impetus to the Energy Amplifier concept. Then, in 1997, the Transmutation by the Adiabatic Resonance Crossing experiment used lead moderated neutrons to induce the transmutation of long-lived fission fragments from conventional reactors, and of elements yielding isotopes useful in nuclear medicine.

These early experiments demonstrated the viability of the Energy Amplifier concept and showed that ADS technology could have an impact on society that involved much more than energy generation. Experiments at the nTOF, which is financially supported by the European Union’s EURATOM programme, will now turn to the more technological issues of an ADS, measuring neutron cross-sections on structural and coolant materials as well as on fuel and fission products. In line with one of EURATOM’s main goals, special emphasis will be placed on the elimination of nuclear waste.

The nTOF collaboration, which consists of almost 150 scientists from 40 institutes, began its scientific programme by precisely calibrating the neutron spectrum. From there, the collaboration moved on to its first approved experiments, both of which are in the domain of astrophysics. One will provide neutron capture data needed for computing stellar reaction rates – data that will help to improve calculations of the age of the universe. The other will measure cross-sections important for understanding nucleosynthesis by slow neutron-capture, or the s-process, which is important for generating elements heavier than iron. For the future, a rich and varied range of proposals has been submitted to CERN’s ISOLDE and nTOF committee, promising an intense hive of scientific activity for many years to come.

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