The IN6 monochromator bank consists of 3 monochromator arrays with variable take of angles allowing the choice of different incident wavelengths as well as a horizontal focussing of the neutron beam onto the sample. The monochromator arrays are displaced by 30 mm in respect to each other. Each array holds 7 pyrolytic graphite crystals arranged for vertical focussing of the beam. A fixed vertical focus radus of 3000 mm is applied. The crystals are of 29 mm x 54 mm (height x length) size with a mosaicity of about 0.4 degrees.
IN6 is designed to work in a wavelength range of 4.1-5.9 Angstroem. Hence, higher order (shorter wavelength) reflections from the monochromator are filtered out by a beryllium filter located in the reflected neutron beam after the monochromator. This filter is built of two blocks of beryllium with a total thickness of 120 mm. It is kept at liquid nitrogen temperatures for working conditions with an experimentally determined transmission of as high as 90 % at a wavelength of 4.6 Angstroem.
The IN6 chopper unit comprises two cylindirical choppers.
A so-called Fermi chopper, located as close as possible to the sample position (39.5 mm), forms the neutron pulses and determines, thus, the energy resolution of the instrument. The neutron pulses are shaped by a rotating slit collimator consisting of a sequence of 200 neutron transmitting aluminum (0.2 mm thick) sheets separated by neutron absorbing gadolinium (0.025 mm thick) foils. A full width at half maximum of 1.4 degrees has been established experimentally for the transmission function of the slit collimator. Depending on the experimenal condition chopper frequencies of 60-250 Hz are applied.
A so-called suppressor chopper is located between the berylium filter and the Fermi chopper. Its function is to clean the monitored sample signal from frame overlap effects, i.e., to suppress the spill-over of signals stemming from subsequent neutron pulses. The extent of spill--over effects is dependent on different conditions. It can be enhanced by the instrumental setup (e.g. high chopper frequencies for high resolution experiments), the physics of the sample (materials with a rich and extensive spread of excitations covering a wide range of energies) as well as by experimental requirements (materials at very high temperatures). The speed of the suppressor chopper is given by f/n with f the Fermi chopper frequency and n = 1, 2, 3, ..., thus, cutting out none of the pulses n = 1 (maximum flux), every second pulse n = 2, every third n = 3, etc.
The IN6 oscillating solar collimator comprises 60 blades of gadolinium covered steel blades.
The acceptance of the collimator is 1.5 degrees.
|characteristics||Stick length||Monte-et-baisse position|
1.5 ... 310 K
|2.5 ... 600 K||925||580|
|100 ... 620 K||fixed||623|
cryoloop He (cold finger)
|30 ... 620K||fixed||625|
|300 ... 1000 K||400||≥ 625|
|300 ... 1500 K||400||649 (≥ 625)|
'Another Time Of Flight Spectrometer IN5bis/IN6' a proposal by R. Scherm, C. Carlile, J. Dianoux, J.-B. Suck, and J. White
IN6 DesignStudy Scherm 1976.pdf (pdf - 1.24 Mi)
IN6 design study by Scherm et al. 1976