C1-2 Small-Angle Neutron Scattering Instrument, University of Tokyo (SANS-U)
Instrumental Overview
The SANS-U, installed at the guide-hall C1-2 beam port, is a small-angle neutron scattering instrument with a 65 cm-wide 2-dimensional position-sensitive detector. The SANS-U is designed for studies of nano-order structure, miscibility and conformation of polymers, micelles, gels, protein, DNA, polysaccharides, and magnetic inhomogeneties in materials in 1 to 100 nm ranges. The layout of the SANS-U is schematically shown in Fig. 1. The sample-to-detector distance (SDD) can be continuously varied from 1 to 16 m, which covers the Q-range from 0.03 to 2.7 nm-1 as was determined from the flat scattering region of polyethylene standard. The effective source-to-sample distance (collimation length, CL) can be chosen from 1, 2, 4, 8, 12, or 16 m by arranging the collimator system consisting of pinholes of 20 mmf and neutron guide tubes of 20 mm x 50 mm. Normally, a symmetric optical arrangement, i.e., CL = SDD, is recommended to optimize the flux and divergence of the beam. The most-commonly used neutron wavelength is 0.7 nm.
Fig.1 The layout of the SANS-U spectrometer.
| Monochromator |
| mechanical velocity selector (Astrium) |
| wavelength range: 0.65 < l < 1.0 nm |
| wavelength resolution(Dl/l): 10% (for lambda = 0.7 nm) |
| Q-range (when l = 0.7 nm is used) |
| 0.4 to 2.7 nm-1(2 x 1; 2m CL x 1m SDD) |
| 0.2 to 1.4 nm-1(2 x 2) |
| 0.10 to 0.73 nm-1(4 x 4) |
| 0.05 to 0.47 nm-1(8 x 8) |
| (12 x 12)0.03 to 0.25 nm-1 |
| Detector |
| 65 x 65 cm2 3He 2D-detector(ORDELA model 2660N) |
| 0.5 x 0.5 cm2 resolution |
| Sample equipment |
| automatic multi-specimen sample changer |
| max. number of cells: 10 |
| temperature range: 0 to 80 degC |
| furnace (300 to 450 K) |
| pressure cell (0.1 to 400 MPa) |
| shear cell (10-3 to 10 3 s-1) |
A 500 mmf diameter sample stage is located between the pre- and post-sample flight paths. A variety of sample environments can be mounted on this stage, such as an automatic sample changer, an inner cell-type high-pressure cell (HP cell), in situ rheological measurement apparatus, a furnace for high temperature, and a cryostat with electromagnets. Except for the shear cell, the temperature of the sample can be controlled precisely by using TEMCON system with an accuracy of less than 0.01 degC. The HP cell has recently been designed to carry out high-pressure experiments for polymer solution or microemulsion systems. The accessible pressure is 400 MPa. A typical experimental result is shown in Fig. 2.1
Fig.2 Pressure dependence of the scattering profile for poly(N-isopropylacrylamide) aqueous gel. The scattering intensity increases with pressure due to the appearance of the phase separation between the polymer and water.
Recently, the SANS-U has been upgraded in order to expand the applicable conditions of experiments and to improve the reliability of the control system. The major upgrades are 1) a replacement of the two dimensional area detector, 2) a renewal of the operating system from a VAX and sequencers to an integrated PXI system controlled by LabVIEW-RT software, and (3) a focusing collimation system.
The new detector is a multi-wired PSPC (model 2660N, ORDELA). Because of the multi-wired cathodes for both the horizontal (X) and vertical (Y) directions and a lower 3He gas pressure, the maximum count rate is 106 cps/detector (catalogue base), which is ten times higher than that of the old detector. For safety use, the upper limit of counting rate is regulated to be 7000 cps/detector and 200 cps/pixel.
The optical system of the SANS-U is controlled by LabVIEW-RT running on a integrated PXI (PCI eXtensions for Instrumentation) system. LabVIEW-RT is an operating system, which has good compatibility with LabVIEW applications and guarantees a long-run stability. The PXI system is handled by commands from the control panel or a control PC connected via local area network, which enables a remote control.
The LabVIEW environment also realizes easy integration of data acquisition. The control system contains a real time circular averaging function, which converts an original two-dimensional scattering intensity pattern to a circularly averaged one-dimensional profile. By simply typing the center channel of the profile and the rate of re-flushing, users are able to watch the evolution of the scattering profile during measurement. The resulting one-dimensional data and the original two-dimensional data are stored automatically to the control PC. Users are allowed to transfer the data to their own computers any time.
A focusing collimation system consisting of 54 of biconcave material lenses, which are kindly provided by NOP group at RIKEN, can be mounted by remote control from the control panel. Here, the specification of the lens is as follows; the curvature radius = 25.0 mm, the center thickness = 1.00 mm, and the outer diameter = 30.0 mm. When the beam size of 16 mmf is used, both the center beam intensity and the sharpness of the profile is improved by the factors of 1.4 and 1.3, respectively. Hence, it is recommended to employ this setup when a large sample is available.
Reference
[1] M. Shibayama et al.: Macromolecules, 37 (2004) 2909.
Contact person:
Mitsuhiro SHIBAYAMA
NSL, ISSP, The University of Tokyo
Tel: +81-29-287-8904
Fax: +81-29-283-3922
e-mail: sibayama@issp.u-tokyo.ac.jp
