D1A, a high resolution neutron powder diffractometer with a bank of mylar collimators

This paper describes a first attempt at following the design criteria set out earlier for a high resolution conventional powder diffractometer. An existing machine, D1A, has been modified using a bank of ten high pressure 3He counters and almost perfect 10minutes of arc mylar foil collimators. The system is more successful than earlier multicollimator arrangements because each of the collimator/counters is virtually identical; this permits automatic addition of the intensities so that a single high resolution profile, up to X40 times as intense as on the original diffractometer, is obtained just as easily as on a single counter machine. A comparison is made with the other powder diffractometers, D1B and D2 at the ILL. (Auth.)