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...2).

The name of this diffractometer is derived from the initials of `Powder Automatic Neutron Diffraction Apparatus'. It is one of the recent neutron powder diffractometers installed at Harwell, UK and has a very high resolution. It is fitted with a mechanism which allows continuous rotation and tilting of the monochromator. By using different monochromator crystals, varying the reflecting planes and the take-off-angle, the neutron wavelength can be continuously varied from 0.5 to 4 Å. This diffractometer has a bank of three BF₃ counters in the equatorial plane (instead of one counter in simple diffractometers). Three additional counters are mounted below and another three above the equatorial counters, making a total of nine counters altogether, but the data obtained from the non-equatorial counters are not exactly the same as those for equatorial ones, see Arzi (1975). Out of three tubes marked as collimator ($\alpha_2$) only one is used in a given diffraction experiment, the other two are blocked. The choice between the three tubes depends on the reflecting planes and the take-off-angle of the crystal monochromator.

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...ones.

Highly oriented pyrolytic graphite is also used as monochromator, see e.g. Dorner and Kollmar (1974).

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