Development of Experimental Techniques/Facilities at JAEA R&D Centers

J-PARC Center

13-4 Development of Ultraprecise Focusing Supermirrors with Elliptical Surface－ Focusing Gain of 52 Achieved for Advanced Instrumentation at J-PARC －(a) unfocused direct beam(b) focused beam

A’

5 mm05100400 mm
B50B’lnset

5 mm

00A

10050FWHM = 0.128 mm
Gain = 520B

A’

2012/2/9

Neutron intensity (a.u.)A

Neutron intensity (a.u.)

100B’

2012/2/91Fig.13-7 Neutron focusing images obtained by large-scale elliptical supermirror ((a): unfocused direct beam; (b): focused beam)
The FWHM of the focused beam was 0.128 mm, and a focusing gain of 52 was observed using an imaging plate. Inset photographshows elliptical NiC/Ti supermirror with m = 4 coated on 400-mm-long substrate.

Slow neutrons, which exhibit quantum mechanical wave
properties, are used to investigate crystal and molecular
structures and dynamics in solid-state physics, polymer andbiological sciences, and so on.
Neutron focusing devices play the important roles offocusing neutrons on samples and increasing the available
neutron intensities or improving the experimental resolutions
in various experiments such as small-sample diffraction andsmall-angle scattering. Therefore, high-performance focusing
mirrors have been aggressively developed to accelerate
the exploration of new scientific phenomena at neutron
experimental facilities worldwide, such as J-PARC.
We successfully developed focusing supermirrors with alarge critical angle, high reflectivity, and low diffuse scatteringby using ion beam sputtering (IBS). A precise surface figure
was obtained on the focusing mirror by using the numericallycontrolled local wet etching (NC-LWE) on the mirror
substrate. The NC-LWE technique enables an asphericalshape to be figured deterministically with sub-micrometer
form accuracy because it uses a noncontact chemical removal
process that is insensitive to external disturbances such as
vibration and/or thermal deformation.

We designed and fabricated one-dimensional neutron
focusing with a large beam divergence by a 400-mm-longelliptical supermirror. A NiC/Ti supermirror with 1200 layers
was deposited on the substrate using the IBS instrument.
We successfully obtained a figure error of 0.43 μm peak-tovalley with a surface roughness of less than 0.2 nm root meansquare. The neutron reflectivity was measured using the BL17SHARAKU instrument at J-PARC/MLF. The reflectivity ofthe m = 4 supermirror was ≃0.6.
The focusing performance of the fabricated ellipticalsupermirror was evaluated at BL10 NOBORU. The wavelengthof the neutron beam was varied from 3.5 to 10 Å. The upstream
width of the slit in this experiment was 0.10 mm.
Fig.13-7 shows neutron profiles of the unfocused direct
beam and the focused beam. The full width at half-maximum(FWHM) of the focused beam was 0.128 mm, and a focusing
gain of 52 in terms of the peak intensity was achieved
compared with the unfocused direct beam. Note that the tail ofthe focused beam is no larger than that of the unfocused beamprofile, which suggests that the focusing mirror produces little
diffuse scattering.

Reference
Nagano, M., Yamazaki, D. et al., One-Dimensional Neutron Focusing with Large Beam Divergence by 400mm-Long Elliptical Supermirror, Journal ofPhysics: Conference Series, vol.340, 2012, p.012034-1-012034-6.
JAEA R&D Review 2013113