Instrument description

D16 - Cold neutron diffractometer
horizontal cold source
beam tubeH5
neutron guideH521 (150 x 60 mm2)
Focussing PG monochromator
7 vertically bending HOPG(002) crystals d = 3.355 Å or 3 Rb-intercalated graphite crystals
area per element17 x 80 mm2
total area122 x 60 mm2
wavelengths (take off)4.5 Å and 7.5 Å (83°)
5.6 Å and 9 Å (115°)
mosaicity0.4° (HOPG) and 1.5° (Rb-int)
Beryllium filter
coolingliquid nitrogen
cut-off3.95 Å
path length100 mm
efficiencyλ/2 < 0.1 %
Collimation
2 variable slits:
S1 (mono)max. 150 x 40 mm2
S2 (sample)

max. 150 x 40 mm2

monochromator-to-
sample distance

2.8 m
Sample area
max flux at sample 107cm-2 s-1
typical sample size 30 x 10 mm2 (diffraction)
7 x 7 mm2 (HighRes SANS)
He detector (MILAND)
distances 0.3 to 1.0 m
rotation -5° < 2Θ <125°
area 320 x 320 mm2
resolution (pixel size)1 x 1 mm2
max. counting rate 100 kHz (less than 1% dead time)
beamstopvariable size, typically 20 x 20 mm2
X/Y motorized
2-circle mode
sample rotation (Θ)-180° ... +180° +/- 0.002°
detector rotation (2Θ)-5° ... +130° +/- 0.01°
4-circle mode
sample rotation (Θ)-180° ... +180°
sample rotation (φ)-180° ... +180°
sample rotation (χ)-180° ... +180°

D16 is a two-circle diffractometer that evolved from the first "biological membrane diffractometers" built in Brookhaven and Harwell in the early seventies. Its original specifications were defined for the study of structures of about 5 nm periodicity diffracting to a real space resolution of a fraction of nanometer. Because of its special characteristics, D16 remains unequalled for the study of a wide range of systems in biology, physics and physical chemistry. These include large unit-cell lamellar organisations such as membranes or clays, two-dimensional membrane and surface lattice structures, colloidal structures and magnetic systems.

 

The primary white beam is reflected by a focussing pyrolytic graphite monochromator providing an important flux at the sample. The monochromator housing has two beam holes at take-off angles of 90° and 115°, corresponding to 4.7 Å and 5.6 Å beams and incorporates the slit systems and cooled Beryllium filter in a way that optimises the beam optics within space and health physics constraints.

 

In the last decade D16 has undergone several major upgrades: in 1999 with a new design and the move from H16 to H17, in 2002 with a new 3He PSD and in 2007 with the move to H53. The design revisited in 2007 allows for much easier and rapid wavelength changes by simple rotation of the diffractometer around the monochromator axis.

 

Since 2006, a high-resolution SANS setup is used routinely in experiments requiring the 1% wavelength band width and the high angular resolution of the instrument.

 

The sample environment includes controlled temperature and humidity chambers, cryostats, furnaces, magnets, cryomagnets, high pressure cryostats, high pressure cells and an automatically positioned, temperature controlled horizontal sample changer.

 

In terms of Q-space and Q-resolution, D16 nicely fills the gap between the small angle instruments and classical diffractometers.