[Neutron] New Reflectometer - Canadian Neutron Beam Centre
McIvor, Alastair - NRC
Alastair.McIvor at nrc.gc.ca
Thu Sep 6 17:43:05 CDT 2007
National Research Council Canada
NRC-CNBC - Call for Proposals
The NRC Canadian Neutron Beam Centre is operated on a continuous proposal
basis. Proposals for experiments may be submitted at any time. Experiments
are given beam time on the basis of peer review.
All the details are available on line:
The Centre is based at the 135 MW NRU reactor at Chalk River Laboratories,
with a thermal flux of 3.5E14 n/cm2/s.
The laboratory currently operates six thermal neutron spectrometers:
C2, High Resolution Powder Diffractometer
C5, Polarized Beam Triple-Axis Spectrometer
D3, Neutron Reflectometer
E3, Materials Science and Triple Axis Spectrometer
L3, Strain-Scanning Diffractometer
N5, Triple-Axis Spectrometer
OLE_LINK2The D3 Neutron Reflectometer is the latest addition Operating in
the horizontal scattering plane, D3 is a thermal instrument using a fixed
wavelength, l = 2.37Å. At this energy range, using thermal neutrons
(instead of cold neutrons) it is a facility of international calibre thanks
to several unique features.
It has a pyrolytic graphite monochromator that is 300 mm tall and
vertically-focused, creating an intense image of the source 45 mm high at
the sample position. The collimator between the source and the
monochromator is tapered oppositely in two directions: diverging vertically
(needed to illuminate the tall monochromator) and converging horizontally
(to keep the fast-neutron background down to an absolute minimum). This
feature alone leads to a factor of 6 improvement in the signal-to-background
ratio compared to the C5 setup. A sapphire filter, placed as far up the
beam line as possible, rejects fast-neutrons at the earliest opportunity.
Space is reserved if this filter needs to be thickened in the future in
order to improve signal-to-background further. A slit with vertical
adjustment allows the reduction of the monochromator height if a particular
experiment requires a smaller vertical divergence of the beam.
Immediately downstream from the monochromator (hence furthest away from the
sample in this leg) the beam passes through a pyrolytic graphite filter for
l/2 and l/3 rejection, another feature that reduces unwanted neutrons as
early as possible. All the slits downstream from the monochromator are
driven by high-precision translation stages, with the critical ones having 2
Neutrons reflected off the sample are captured by a 300 mm tall 3He
detector, consisting of individually recorded 32 signal wires. Although not
part of the original proposal, a high-resolution area detector will be
implemented in the near future. Another feature that will be implemented
shortly is the polarized neutron capability using magnetized super-mirrors.
In additions to these features, this "full-time" reflectometer will maintain
alignment and calibration, ensuring reliability and repeatability of data
over prolonged research campaigns requiring multiple measurement sessions,
say, over the duration of research for a Ph.D. candidate.
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