Page 108 - Neutrons for Sciences and Society

Neutrons for Science
• IN4 a time-of-flight spectrometer with a rotating crystal monochromator
• IN5 a multi-chopper time-of-flight spectrometer on a guide from the cold source
The first of these instruments, IN1, was built at Saclay by Bernard Hennion et al. The first ILL responsible was Defendente Tochetti assisted by Alain Castets.
IN2 was constructed at Jülich by Bruno Dorner and Georg Duesing, who both came to the ILL, Duesing in 1970, and Dorner in 1972.
IN4 was the responsibility of Winfried Drexel at Kahrlsruhe. He joined the ILL in 1971.
The other two instruments were more complicated, and were designed at the ILL. The idea of IN5 came from Scherm while still at Jülich in 1965. It was a much improved version of a Saclay instrument. The monochromatic beam is produced by a
set of four disks with slits (or choppers) which spin at high speed about a horizontal axis. These disks absorb neutrons except at
the windows. By synchronising these rotors only neutrons of a chosen velocity pass through the four choppers. The use of four rather than two serves to eliminate harmonics. Guy Gobert and Francis Douchin led the project; the mechanical construction was entrusted to the Bertin Company while the electronics came from Ispra where the specialised know-how already existed.
The triple axis spectrometers IN2 and IN3 were different from the classic IN1 design by incorporating the possibility to vary the distance between the sample and monochromator and analyser crystals. This enables focussing to be optimised. This is actually achieved by mounting the tables bearing the crystals on air
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