Wednesday 10 July 2013, Fintry Room, 14:30-16:30
Neutron optics
Lenses for focusing and imaging of thermal neutrons
S O Poulsen1, H F Poulsen1, T Panzner2 and U Filges2
1
Technical University of Denmark (DTU), Denmark, 2Paul Scherrer Institut, Switzerland
Compound refractive lenses (CRL) have become widely used in high energy X-ray experiments in recent years.
There, CRLs are used both for focussing broad beams to small spot sizes, and as imaging objectives, i.e. allowing
microscopy. This technology has not yet found widespread use in thermal neutron experiments, despite the
similarities between these, and experiments with high energy X-rays. The broad energy range of typical thermal
neutron beams have been a factor impeding the use of CRLs, as the optical power of CRLs is highly energy
dependent. Several strategies for extending the use of CRL technology to broad energy beams of thermal neutrons,
e.g. for TOF experiments, will be presented and discussed, with the main emphasis on a passive solution. Strategies
for employing this lens technology to extend well-known thermal neutron experiments will be presented and
discussed, as will some novel microscopy experiments with thermal neutron beams. Specifically, we introduce dark
field microscopy as a novel neutron imaging concept, and discuss its potentials and limitations for crystallographic
imaging of microstructure, strain and texture.
Development of focusing supermirors by means of ultra-precise surface figuring and ion beam sputtering
D Yamazaki1, H Hayashida1, R Maruyama1, K Soyama1, M Nagano2, K Yamamura2, K Yoshimi1, M Naoki2 and T
Takaaki2
1
J-PARC Center, Japan, 2Osaka University, Japan
Neutron beam focusing is essential to perform measurements on small areas of a sample as well as small angle
scattering (SANS) measurements in that focusing can both enhance beam intensity at the sample and reduce
backgrounds. When it comes to pulsed neutrons, a focusing optics must be free from chromatic aberration. Hence a
reflective optics based on total reflection is preferable.
We have been developing focusing supermirrors by depositing a supermirror on a precisely figured aspheric surface
[1-4]. Surface of a substrate is figured using “numerically controlled local wet etching” technique. The figured
surface shows a figure error of less than 1 micrometer p-v and an rms roughness of less than 0.2 nm. Deposition of
NiC/Ti supermirror (m=4) with ion beam sputtering keeps the figure error within a several micrometers p-v but and
the roughness almost unchanged.
A one-dimensional elliptic supermirror of 400mm in length was developed and achieved focused peak width
(FWHM) of 0.128 mm and peak intensity 52 times that of unfocused (divergent) beam. Thin elliptic supermirrors of
1.5mm in thickness were also developed for multiple stacking and achieved focused peak width (FWHM) of 0.21
mm and peak intensity 12 times that of unfocused beam.
We will also present measurement results of a multiply-stacked mirror, two-dimensional focusing with a KirkpatrickBaez configuration and several applications to sample measurements including SANS and prompt-gamma
spectroscopy.
[1]
[2]
[3]
[4]
K. Yamamura et al., Opt. Express 17, 6414 (2009)
D. Yamazaki et al., J. Phys. Conf. Series 251, 012076 (2010)
M. Nagano et al., J. Phys. Conf. Series 340, 012034 (2012)
M. Nagano et al., J. Phys. Conf. Series 340, 012016 (2012)
ICNS 2013 International Conference on Neutron Scattering
(invited) Focusing on small samples
J Stahn1, U Filges1, T Panzner1, E Rantsiou1 and U Hansen2
1
Paul Scherrer Institute, Switzerland, 2Niels Bohr Institute, Denmark
In many areas of neutron scattering there is a growing demand to measure small samples. Reasons are the
limited space in extreme environments, that the sample material is not available in higher quantities, or that the
sample cannot be grown larger. By focusing one can trade resolution for intensity and thus advance smaller
volumes.
Experiences we made at the reflectometer Amor at SINQ with an elliptical reflector based on the REFOCUS concept
[1,2] led to the development of the \textsl{Selene} guide concept, which is a truly focusing, aberration-corrected
optics. We built and tested a prototype to be used as an add-on to probe sub-mm$^2$ area.[3] Scaled up, it
forms an entire neutron guide.
The \textsl{Selene} guide consists of two subsequent, collinear planar-elliptic reflectors, sharing a focal point. The
phase space characteristics of the beam within the guide allows for new optical elements. E.g. all beams originating
from a small slit intersect a surface shaped like a logarithmic spiral with the same angle. This can be used for
lambda-filtering or polarisation. The beam spot size and its divergence can be adjusted independently.
Within the guide direct or garland-like trajectories are blocked, meaning that all neutrons are focused. This is
in contrast to conventional elliptic guides where only down to 5% are focused.
Other neutrons are multiply reflected and form a divergent beam right after the guide exit.[4]
The \textsl{Selene} guide requires the high quality (low waviness, high contour accuracy) of a neutron
optical element, and it must be aligned accordingly. The surface homogeneity of the prototype and its shape were
checked by interferometry. For the alignment several approaches are discussed and tested, among them the
possibility to adapt the shape dynamically.
[1]
[2]
[3]
[4]
F. Ott \textit{et al.}: NIM A \textbf{586}, 23 (2008)
J. Stahn \textit{et al.}: NIM A \textbf{634}, S12 (2011)
J. Stahn \textit{et al.}: EPJ-AP \textbf{58}, 11001 (2012)
P. Bentley \textit{et al.}: NIM A \textbf{693}, 268 (2012)
The first diamond neutron monochromator at ILL
P Courtois1, A Freund2, M-T Fernandez-Diaz1 and G Nénert1
1
Institut Laue Langevin, France, 2Via Cordis – Consulting and Movement, France
The first diamond neutron monochromator has been successfully built at I.L.L. It has been designed for the hot
neutron diffractometer D9 with the aim of improving significantly the instrument performances for short wavelengths
in the 0.3-0.9 Å wavelength range.
Diamond crystal plates with dimensions of 1.5 x 1.5 x 0.17 cm3 were synthesized by a research team at the
University of Augsburg. With a mosaic distribution of 0.15°, these crystals already exhibit excellent properties for
neutron diffraction. Because thicker crystals are difficult to produce, we have built composite diamond crystals by
stacking crystal plates on top of each other. Such a technique allows the production of sufficiently thick diamond
crystals with a controlled mosaic spread adapted to the instrument requirements. Preliminary experiments carried
out at the ILL have confirmed the predicted high reflectivity of these composite diamond crystals[1].
The new diamond monochromator works in transmission geometry using the (220) reflection. With an active area of
6 x 6 cm2, it consists of 4 columns of 4 composite crystals that are approximately 0.55 cm thick with a global
mosaic distribution of 0.3°. The crystals are mounted onto specific holders cut from a perfect silicon crystal in order
to reduce background.
ICNS 2013 International Conference on Neutron Scattering
The monochromator has been recently installed on D9, replacing the previous Cu(220) crystals that has the same
d-spacing. It should show the highest performance ever achieved at short wavelengths.We expect a gain in neutron
flux of more than a factor two at the sample position as compared to the previous set-up.
[1]
A.K. Freund et al. , Nucl. Instrum. Methods A 634 (2011) S28
Holographic gratings for long-wavelengths neutron optics
J Klepp1, Y Tomita2, C Pruner3, P Geltenbort4 and M Fally1
1
University of Vienna, Austria 2University of Electro-Communications, Tokyo, 3University of Salzburg, Austria, 4Institut
Laue Langevin, France
Previous experiments with holographic nanoparticle-polymer composite diffraction-gratings have demonstrated how
such gratings can be used as multi-port beam-splitters or mirrors for very-cold neutrons. Their coherent scattering
length density could -- to a certain extent -- be chosen by selecting the species of nanoparticles for development of
further applications such as polarizing beam splitters, for instance. However, the main disadvantage of nanoparticlepolymer composite gratings is their limited thickness, which is due to detrimental light-scattering during recording.
In recent neutron diffraction experiments, this problem could be overcome by tilting of gratings around an axis
parallel to the grating vector. With the aim to use even single holographic gratings as highly-stable interferometric
devices, more efficient materials combined with new recording techniques become necessary. We report on recent
tests of such gratings using very-cold neutrons.
Determination of the effective transverse coherence length of the neutron as employed in reflectivity studies of
condensed matter structures
C Majkrzak, C Metting, B Maranville, J Dura, S Satija, N Berk and T Udovic
NIST, USA
The primary purpose of this investigation is to determine the effective coherent extent of the neutron wave packet
transverse to its mean propagation vector k, as prepared in a typical reflectometer used to study the structure of
materials by elastic reflection or diffraction. There are two principal reasons for doing so. One has to do with the
fundamental physical interest in the characteristics of a free neutron as a quantum object while the other is of a
more practical nature, relating to the understanding of how to interpret scattering data when the neutron is
employed as a probe of condensed matter structure on an atomic or nanometer scale. In this study we describe a
semi-quantitative means of measuring the effective transverse coherence length of the neutron wavepacket by
specular reflection from a series of diffraction gratings of different spacings. Each grating was fabricated by lift-off
photolithography patterning of a nickel film (approximately 1000 Angstroms thick) formed by physical vapor
deposition on a flat silicon crystal surface. The grating periods ranged from 10 microns (5 microns Ni stripe, 5
microns intervening space) to several hundred microns. The effective transverse coherence length, modeled as the
width of the wavepacket, was determined from an analysis of the specular reflectivity curves of the set of gratings.
ICNS 2013 International Conference on Neutron Scattering