CERN’s neutrons fly higher

The construction of a second experimental area for n_TOF – CERN’s neutron source – has just been approved by the CERN Council. The new facility will provide the scientific community with a higher neutron flux, which translates into a higher sensitivity for the experiments. The new neutron beam line will open the way to a wider variety of research fields including nuclear energy applications, nuclear astrophysics, basic nuclear physics, dosimetry and radiation damage.


The 4π calorimeter inside the n_TOF experimental area. Image courtesy of the n_TOF Collaboration.

The project involves building a vertical flight path roughly 20 m above the current neutron target and a new experimental hall – Experimental Area 2 (EAR-2) – in the current Building 559. EAR-2 will be located on top of the neutron production target and partially on top of the ISR building (see the image below of a model of the facility). “The hall will be housed in a bunker, which will be connected with the n_TOF underground facilities via a duct 60 cm in diameter,” explains Enrico Chiaveri, spokesperson for the n_TOF collaboration. “Due to the expected weight of the bunker, support pillars roughly 12 m high will have to be built with their feet located on the concrete structure of the n_TOF tunnel.”

Physicists use neutrons – created from a primary pulsed proton beam – in a broad energy range (from meV to GeV) to study neutron-induced reactions in samples, which are often radioactive. These same processes are in fact involved in a number of fields, including nuclear waste transmutation, nuclear technology, nuclear astrophysics and stellar evolution. Additional applications of wide energy neutron beams include basic research, medical applications, dosimetry and radiation damage. The enhanced capabilities provided by EAR-2 will allow experimentalists to study processes and isotopes with unprecedented accuracy that until now have remained out of reach in existing facilities. “Since the number of neutrons at the sample position is on average increased by a factor of 25, measurements can be performed on much smaller samples, in some cases less than 1 mg,” explains Enrico Chiaveri. “This feature is of key importance when dealing with unstable samples and in cases where the sample material is particularly rare. Indeed, limitations in sample mass are crucial in astrophysics as well as in the field of nuclear technologies. Depending on the isotope concerned, EAR-2 may enable us to perform some measurements for the very first time.”

3D model of the new EAR-2 facility.

EAR-2 and the existing EAR-1 (located around 200 m downstream of the production target) will run in parallel. “The n_TOF facility is already unique in the world in terms of its instantaneous neutron flux and low background, but the addition of the new neutron line will provide a 25 times higher flux per pulse delivered in 10 times less time. This will result in a substantial reduction of the background and an improved experimental sensitivity,” says Enrico Chiaveri.

The long shutdown of accelerators (LS1) scheduled during 2013-14 will see the construction of the new facility, which is expected to receive the first beams during the summer of 2014. The attractiveness of n_TOF, soon featuring two neutron beam lines, is growing within the scientific community: indeed seven new institutions have joined the n_TOF Collaboration over the past two years and more are likely to join soon. A bright future lies ahead.

by Antonella Del Rosso