Thermal neutron three-axis spectrometer IN8

Reactor hall, thermal beam H10

Beamtube diameter Ø = 200 mm


Virtual source at 2284 m before monochromator matching the monochromator-sample distance



W x H (mm2)ki/Å-1

flux/108 n cm-2s-1

PG (002) double focusing,
three faces



Cu (200) variable double-focusing,
anisotropic mosaic (h:25', v:10')



Si (111) bent perfect crystals, fixed horiz. curvature optimized for k=3.5Å-1




Compatible with wide range of sample environment (cryostats, displex, furnaces, cryomagnet, vacuum box). Sample position radiologically shielded.

Analyser (interchangeable)

PG (002) double-focusing, fixed vertical aperture
active area: 230 mm x 100 mm (W x H)

Si (111) bent perfect crystals, double-focusing, fixed vertical aperture
active area: 160 mm x 120 mm (W x H)

Cu (111) flat
active area: 160 mm x  80 mm (W x H)


nine Ge (111) plastically bent analysers
active area 360 mm x 120 mm (W x H)


Single 3He detector, vertically mounted
or position sensitive detector (PSD) consisting in 54 3He-filled tubes ;  Ø = 9 mm


Instrument description

IN8 is installed on beamtube H10 (diameter F = 200 mm).

The incident wavelength selection is obtained through a double focusing monochromator , which has three faces equipped with PG002, Cu200 and bent perfect Si111 crystals, respectively. Horizontal focusing allows increasing the monochromatic flux at the expense of momentum but not energy resolution when the horizontal virtual source (an adjustable entrance slit) is introduced at a distance before the monochromator which matches the monochromator-sample distance.

The aperture of the horizontal virtual source can be varied but is typically kept below 50 mm. This reduces the background level of the instrument. Converging collimators as well as diaphragms can be placed in the beam path before and after the monochromator to optimize the beam dimension and definition. For special high-resolution experiments using a flat monochromator, Soller collimators are available.

The shielding drum allows varying the monochromator take-off angle in the range 10° < 2θM < 90°. The secondary spectrometer has heavy borated polyethylene shielding installed around the analyzer and detector elements. The scattering angle at the sample position is in the range 0° < 2θs < 130° independent of the monochromator take-off angle.

The design of the secondary spectrometer allows one to working in a standard TAS configuration or as multiplexed spectrometer (IMPS):

  • for the TAS configuration, PG002, Si111 and Cu111 analysers are used with a single type detector. PG filter and collimators are available.
  • the multiplexed spectrometer allows to measure nine different (Q,ω) points simultaneously by using a multiblade analyser consisting in nine crystal blades of plastically-bent Ge111 together with a two-dimensional PSD consisting in 54 He-filled tubes of 9 mm diameter.

The instrument allows using a wide range of sample environment equipment such as high field magnets. For low scattering angle experiments the sample to analyzer distance can be increased to host a vacuum box to reduce air scattering.