Updated:
17.11.2010
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SANS-II, the former Risø-SANS instrument, has
been installed at SINQ in middle of the year 2002. It has been upgraded
in several details, e.g. by the installation of a new velocity selector
and is in the routine operation since August 2002.
As for the other PSI-Risø instruments, half of the
beamtime time is reserved for the Danish user community ,
whereas the other half is scheduled via the SINQ proposal system.
Instrument Description
Main characteristics of this Small-Angle Neutron Scattering instrument
(see Fig.) are as follows:
· neutron wavelength range 4.5 - 20 Å
· beam collimation 1-6 m (moveable one-meter
sections)
· sample-to-detector distance (SDD) 1-6 m
· area detector, diameter 64 cm, 128×128
pixels
· accessible Q -range: 0.002
– 0.35 Å -1
(i.e. inhomogeneity-size range 15 – 1500 Å)
· flux in the sample position for 4 m
collimation and l=4.5 Å: 30000
n/s/cm 2 /mrad 2 /mA
Beam formation
SANS-II facility is installed at SINQ neutron guide RNR 12. The
incoming neutrons are monochromized by a mechanical velocity selector.
Collimation is performed in the six meter long collimation section. It
consists of one fixed and five moveable one-meter sections in which
nickel-coated neutron guides can be inserted individually by
computer-controlled pneumatic cylinders allowing the neutron source
pin-hole to be moved from one to six meters in steps of one meter away
from the sample position.
Sample environment
The whole system, i.e. collimators, sample chamber and detector tank
can be operated in a single vacuum system without windows in order to
lower background. In that case, 7-position sample exchanger (with
temperature control in the range 6-80ºC), or 2-position furnace
(up to 300ºC) can be employed. The sample chamber can be, however,
also fully removed and a rotation table can be installed instead. This
option enables to use of bulky and heavy equipment such as cryomagnet
or shear devices. The new SANS-II sample table is under construction,
another table can be however used (standard equipment at SANS-I). The
sample environment available at SINQ is gradually integrated to SANS-II
systems.
Detection of scattered neutrons
The area-sensitive multi-wire proportional neutron detector has been
developed at Risø National Laboratory. The active volume is 64
cm in diameter and 4.5 cm thick and the total gas volume is 15.2
litres. The normal filling is 1 atmosphere 3 He plus 1.5 atmosphere
argon and methane, which combines high efficiency, high spatial
resolution and low ?-ray sensitivity. The gas is purified by convective
circulation through an activated alumina filter, which is mounted in an
enclosed space on the back of the detector together with the
preamplifiers. The detector can be used in an evacuated space. The
xy-positioning of the detected neutron is based on the difference in
rise-times for pulses arriving at the two ends of the wire-grids. The
anode grid is used for one coordinate and the two cathode grids,
coupled in parallel after the preamplifiers, are used for the other
coordinate.
The detector can be moved continuously from one to six meters away from
the sample position.
Q -range
The accessible range is 2.10 -3 Å -1 < Q < 0.35 Å -1 .
The full Q -range can be obtained by
measuring at three geometries:
1) SDD= 6 m, l= 19.6
Å: 0.002 Å -1 < Q < 0.014
Å -1
2) SDD= 5 m, l= 4.55
Å: 0.010 Å -1 < Q < 0.075
Å -1
3) SDD= 1 m, l= 4.55
Å: 0.050 Å -1 < Q < 0.35
Å -1 .
Intensity at sample position
Compared to SANS-I:
A) for identical resolution: SANS-II = 0.7 of
SANS-I
B) for relaxed resolution and maximum flux: SANS-II = 0.2
of SANS-I
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