The first neutron beam hits EAR2

On 25 July 2014, about a year after construction work began, the Experimental Area 2 (EAR2) of CERN’s neutron facility n_TOF recorded its first beam. Unique in many aspects, EAR2 will start its rich programme of experimental physics this autumn.


The last part of the EAR2 beamline: the neutrons come from the underground target and reach the top of the beamline, where they hit the samples.

Built about 20 metres above the neutron production target, EAR2 is in fact a bunker connected to the n_TOF underground facilities via a duct 80 cm in diameter, where the beamline is installed. The feet of the bunker support pillars are located on the concrete structure of the n_TOF tunnel and part of the structure lies above the old ISR building. A beam dump located on the roof of the building completes the structure.

Neutrons are used by physicists to study neutron-induced reactions with applications in a number of fields, including nuclear waste transmutation, nuclear technology, nuclear astrophysics and medical physics. “The research programme that will be carried out at EAR2 is very broad and very important for CERN,” confirms Sergio Bertolucci, CERN’s Director for Research and Computing. “By combining the existing n_TOF facility and the new EAR2, CERN is now able to provide a unique infrastructure to the neutron physics community, which can be enriched by its contribution.”

At EAR2, the neutron-induced reactions will be studied with very high accuracy and in very good experimental conditions thanks to the very high instantaneous neutron flux provided by the facility. The facility also includes a room, isolated by a concrete wall from the main experimental area, in which scientists will prepare the samples to be measured and where the data acquisition stations are located. “The first experiments will be installed this autumn and our schedule is full until the end of 2015,” says Enrico Chiaveri, spokesperson of the n_TOF collaboration.

The reactions that will be studied at EAR2 sometimes require unencapsulated radioactive samples, which is why the whole facility is designed to be in class A, the most stringent standard for radiation protection currently in use. In particular, the dump comprises three different layers: the first one – made of borated polyethylene – to stop thermal neutrons, the second one – made of iron – to stop faster neutrons and the last one – concrete – to make everything radiation-tight. “The beam line of EAR2 is also well shielded and equipped with collimators and a large-aperture magnet for shaping the neutron beam and reducing the background caused by other particles produced in the spallation process,” adds Christina Weiss, n_TOF run coordinator and CERN fellow from the Vienna University of Technology.

The first signal recorded by the various detectors at n_TOF's EAR2 on 25 July.

On 25 July, the much awaited moment came when the detectors – a combination of silicon sensors, MicroMegas and diamond detectors – measured the first neutron beam in EAR2. “It was a low-intensity beam,” says Frank Gunsing, n_TOF physics coordinator and a CERN scientific associate from CEA Saclay, “but it showed that the whole chain – from the spallation target to the experimental hall, including the sweeping magnet and the collimators – is working well and that we are ready to complete and commission this exciting new facility.”

by Antonella Del Rosso