PHYS01200804001 Sohrab Abbas - Homi Bhabha National Institute

Fig.37 Bragg reflection from the θ S =53.5 o monochromator observed with prism diffraction (cf.
inset) of the optimal analyser.
alignment of the analyser whose Bragg reflection as well as prism diffraction were monitored
(Fig.38). The analyser rocking curve yielded the expected ~ 3.1 arcsec wide peak (circles) with a
peak intensity of about 468 neutrons/s. The monochromator was then translated to illuminate the
analyser with its prism diffraction alone. The corresponding analyser rocking curve of ~ 2.5 arcsec
FWHM (cf. Fig.39) agrees well with theory (smooth blue curve), displaying a peak intensity of
68.5 neutrons/s, After optimising the analyser alignment, the Cd sheet before the detector was
translated to stop Bragg reflected neutrons from the analyser. With these Bragg prism diffractions,
the analyser tilt adjustment became even more critical and had to be made in 0.9 arcsec steps, since
prism diffraction peaks are narrower and sharper than the Bragg reflections. The rocking curve
(Fig.40) consisting of a pair of 0.62 arcsec wide peaks separated by 2.2 arcsec (squares), is in fair
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