Happy birthday n_TOF!

The “Neutron Time Of Flight” facility (n_TOF) has recently turned ten. A simple ceremony marked the date of the anniversary and provides a nice opportunity to retrace the successful history of this unique facility, whose scientific activity spans a range from astrophysics to the study of nuclear-waste transmutation processes.


From left to right: Enrique Gonzalez-Romero, Chairman of Collaboration Board, Enrico Chiaveri, Spokesperson of n_TOF Experiment, and Carlo Rubbia, the creator of the n_TOF experiment.

Ten years after its first beam, n_TOF is just approaching maturity. Revitalized by the recent renovation of its infrastructures that allowed it to gain the unique label of “Class A” in radio-protection standards, n_TOF has a rich and challenging scientific programme. “One year ago, the beam line and the experimental area were completely rebuilt to comply with the Class A radio protection requirements in order to safely use almost all radionuclides. This allowed us to carry on waste transmutation studies on radioactive elements that are produced, for example, in nuclear power plants,” says Enrico Chiaveri, spokesperson of the n_TOF Collaboration, which involves approximately 90 physicists from some 30 institutions worldwide.

These studies are particularly important for the development of the new generation of nuclear reactors and the so-called accelerator-driven systems, which use accelerator-produced neutron beams to trigger nuclear reactions. “The production and transmutation of the radioactive elements by these new reactors requires careful measurement of the capture and fission cross-section for the so-called ‘minor actinides’, which constitute the most radiotoxic component of radioactive waste,” explains Chiaveri. “The results obtained at n_TOF - in some cases for the first time in the world - are extremely accurate and provide important information for the possible in situ treatment of these elements and their re-use as an energy source.”

The celebration marking the ten years of n-TOF took place on 24 November in Restaurant n°1.

Neutrons are involved in virtually all nuclear processes, including star formation and evolution. “We have done very accurate measurements on the formation of some heavy elements such as osmium (Os) and rhenium (Re) ” says Chiaveri. Thanks to these studies, with a technique known as “Nuclear Cosmo-chronometry”, the n_TOF collaboration was able to obtain a new estimate of the age of the Universe. These important results earned a special mention as an example of excellent research by the journal Physical Review C.

The n_TOF facility has many distinctive features: an extremely high instantaneous neutron flux, equal to 8x105 neutrons per cm2, a very precise energy resolution, and a wide neutron spectrum with a very broad energy range from the thermal energies up to the GeV region. All together these characteristics make n_TOF extremely competitive in its fields of research. “Looking to the longer term, the n_TOF facility has great potential to further improve the neutron flux intensity by reducing the flight path to a second experimental area. The preliminary estimations made by the CERN n_TOF support team (EN-STI Group) show that the realistic configuration could allow samples with 10-100 lower mass to be used, opening the path to direct measurements that are not possible at any existing facility ,” adds Chiaveri. The future looks bright for this 10-year-old youngster!

The history of n-TOF

The first neutron beam was produced at n_TOF in November 2000. The beam is produced using a pulsed beam of protons delivered by the PS hitting a lead spallation target. The facility was born from an idea of Carlo Rubbia, Nobel Prize Laureate and former Director-General of CERN.

by Francesco Poppi