CERN’s neutrons fly higher

A new experimental facility and neutron beamline will provide nTOF with its highest neutron flux yet – good news for experiments downbeam

CERN’s neutrons fly higher

nTOF's 4π calorimeter in its experimental area (Image: nTOF)

The CERN council has approved construction of a second experimental area for CERN’s neutron source, nTOF. The new facility will open up a variety of research fields from nuclear physics and astrophysics to dosimetry and radiation damage.

Physicists at nTOF use a broad energy range (from meV to GeV) of neutrons created from a primary, pulsed proton beam to study neutron-induced reactions in various samples. A new beamline will provide a higher neutron flux – a measure of the total length travelled by all neutrons in a given volume per unit time – which should translate into higher sensitivity to physics phenomena for experiments using the neutron beam.

nTOF will build a vertical flight path 20 metres above the current neutron target in Building 559, and a new hall – Experimental Area 2 (EAR-2) – will sit partially on top of the ISR building. “The hall will be housed in a bunker connected with the nTOF underground facilities by a duct 60 centimetres in diameter,” says nTOF spokesperson Enrico Chiaveri. “Due to the expected weight of the bunker, 12-metre support pillars will have to be built with their feet on the concrete structure of the nTOF tunnel.”

EAR-2 will allow experimentalists to study processes and isotopes with unprecedented accuracy: “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 miligram,” says Chiaveri. The feature is important when dealing with unstable or rare samples, he says. "Limitations in sample mass are crucial in astrophysics as well as in nuclear technologies. EAR-2 may enable us to perform some measurements for the first time.”

The nTOF facility is already unique 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 improved experimental sensitivity,” says Chiaveri. The existing EAR-1 facility, located around 200 metres downstream of the production target, will run in parallel with EAR-2.

The new facility – which will be built during the 2013-14 long shutdown of accelerators – is already attracting interest from the high-energy-physics community: seven new institutions have joined the collaboration over the past 2 years. 

First beams are expected in summer 2014.