Neutron Scattering

the diffraction plane) two further rotation axes x and (p, which are perpendicular to each other .
The x-axis is also perpendicular to the ù)-axis . Together with the rotation axis of the detector
20 ( I 1 te, the (o-axis) this mechanical unit is called 4-circle goniometer (leading te, the narre
4-circle diffractometer for this type of single crystal diffractometers) . The measurement of
integrated intensities 1(H) of individual Bragg-reflections is performed according te, the
o)/n .20-scan techniques described in chapter 7 .2 . For a computer-controlled automatic data
collection a detailed knowledge of the crystal lattice is needed. Therefore, a single clystal
diffraction experiment starts by a systematic search of reflections in varying x and cp, with the
restriction ca = 0 (bisected condition) . From the accurate angular positions of typically 20
indexed reflections the lattice constants and the orientation matrix are determined .
As an example for a single crystal neutron diffractometer the Pl10/5C2-instrument installed
at the hot neutron source of the ORPHEE-reactor in Saclay (F) is shown in Fig . 10 . The
monochromatic neutron flux at the sample position is increased by a monochromator system
with vertical focussing . The use of small wavelengths allows the measurement of Braggintensities
up to large H -values ( H maX = 2sin0 maX/;, = 2 .8 L1
Fig . 10 .
Single crystal diffractometer P110/5C2 at the hot neutron source of the ORPHEEreactor
in Saclay (F)
Attention : The lengths of both the vector H ofthe reciprocal lattice used in clystallography
and the scattering vector (~ of solid state physics are expressed in  -1 . But there is a factor of
271 which means that 1 H = 2 .8 A-1 corresponds to 1 Q 1 = 17 .6 A-1 .
7- 1 2