Disk chopper time-of-flight spectrometer

ILL7 building, Cold neutron guide H16

(Vertical Cold Source)


6 counter-rotating choppers

Chopper velocity Vo
(revolution per minute)

2000 rpm to 17000 rpm

Incident wavelength λo

1.8 Å to 20 Å


elastic energy resolution
at 5.0 Å, 8500rpm

~ 100 µeV

max neutron energy loss

ωmax 0.6×Eo
Emin ≈ 0.4×Eo (λmax = 1.5λo)

max energy gain for the neutrons

Emax ~ ∞  . . .

max momentum transfer Qmax

11.48/λo Å-1

horizontal divergence (no collim.)

~ 0.1×2×λo [°]

vertical divergence (no collim.)

~ 0.1×3×λo [°]

Collimation before sample

- / 30' / 60'

beam size at the sample

~ 15×50 mm2

flux at the sample at 5.0 Å

6.83×105 [n/cm2/s]


detector shape


detector surface [m2]


fight path (radius of reading) [m]


effective detection height [m]


scattering angular range [°]

-12° to 135°

vertical angular range [°]e


solid angle covered

1.8 sr (~0.6π)

min. & max. momentum transfer [Å-1]

0.2/λ [Å] - 11.8/λ [Å]

spatial resolution [cm2]

2.6 x 2.6

angular resolution [° / rad / ']

0.37° / 6.10-3 rad / 22

detector type

position sensitive 3He counters

gas mixture

4.75 bar 3He +1.25 bar CF4

detector efficiency

~ 80% for Eo = 3.27 meV (5 Å)

dead time / max. count rate (per tube)

≤ 10 µs / ≥ 100 kHz


stainless steel

number of detectors units (32 tubes/unit)


tubes diameters [inches/cm]

1' / 2.54


nb. of pixels per tube / per unit / total

256 / 8192 / ~105

time channel / pixel

≤ 1024

max. raw data volume / spectrum

≤ 768 Mb

Sample environment

accommodating samples with 69 mm Ø

dilution fridge (LT1)

≤ 50mK ... 1.6K

vertical cryomagnet S(MV)

0 ... 2.5 Tesla and 0 ... 10 Tesla

ILL orange cryostat (CO)

1.5 ... 310 K

cryofurnace (CF)

2.5 ... 600 K

furnace (F2)

300 ... 1600 °C

heating and cooling loop (CL)

100 ... 620 K

Instrument description

IN5 is a general purpose direct geometry Time of Flight (ToF) spectrometer. It is used to study low-energy transfer processes as a function of momentum transfer. Typically this instrument is used for measurements in the small energy and momentum transfer region with values of the order of δE/E  = 1 % for the energy resolution (e.g. quasi-elastic scattering in solids, liquids, molecular crystals and inelastic scattering with small energy transfers in the order of magnitude 0.1 - 250 meV). It offers total flexibility of wavelength selection and chopper speed which permits considerable optimisation of the energy range, energy resolution, momentum-transfer range and countrate.

Primary spectrometer:
the chopper system provides an extremely well defined resolution function which remains nearly gaussian (counter-rotating disks) down to 1/10 000 of its height.

Secondary spectrometer:
it consists in an large cylindrical array of pixelated position sensitive detector (PSD) mounted inside a vacuum time-of-flight chamber 4m from the sample. PSDs cover  a large gapless detection surface (30m2) with a spatial resolution comparable to triple-axis instruments. With the new detector, the instrument has a large solid-angle for powder and amorphous systems experiments and is fully equipped for single-crystal spectroscopy. 

Sample area:
a large sample chamber (max diameter = 80cm, depth ~ 130cm) allows hosting the broad range of IN5 sample environments but also user-designed equipments (contact instrument responsibles before). The non-magnetic material surrounding the sample allows the use of either high magnetic field (limited to 2.5T at the moment it is foreseen to purchase a specific magnet for higher fields - equal or above 10T) or neutron polarisation devices (still to come).