Thursday 11 July 2013, Strathblane & Cromdale Halls, 16:30-18:30
Poster session C - Targets, moderators and beam components
P.202 Optimization of a beamline neutronic background
S Ansell, F Burge and G Skoro
Rutherford Appleton Laboratories, UK
Many instruments are critically dependent on their signal to noise ratio (S/N), however calculation of this quantity is
often extremely difficult or unreliable. In this instance, we have carried out a complete MCNPX simulation of the new
ISIS SANS beamline, ZOOM, from protons on target to neutrons at detector.
In order to determine an accurate S/N, an extremely detailed model of the beamline and target station was
produced, in excess of 10,000 objects and extending out to the detector tank and including choppers and guide.
Normally this is prohibitively expensive to compute but by combining an automated software optimization coupled
with a full parametric description of the model, the background could be calculated sufficiently quickly, to allow
neural-network pattern learning software to optimize the background.
This showed that despite the original designed having used normalneutron ray tracing simulation packages, key
areas of background contributions had been missed. These including a significant photon-neutron background due
to a direct view of a target shine point, and a large albedo transport component that cross-scattered into the guide.
These area were primarily addressed by designing a multi-step shutter collimation and by re-optimizing the bender
direction and shielding, and increased the S/N ratio by several orders of magnitude.
P.203 Neutron moderator development research at the low energy neutron source
D Baxter
Indiana University, USA
The Low Energy Neutron Source at Indiana University was constructed as a model University-scale pulsed neutron
source suitable for conducting materials research, educating students in the neutron sciences, and the development
of novel neutron instrumentation. Specific aspects of the source design make it particularly well-suited to the
experimental exploration of neutron moderation. Over the past 5 years we have conducted a number of experiments
in this arena, and in this presentation I will review a number of these in order to highlight the facility’s capabilities.
Specifically, I will present results from measurements of total neutron cross sections at energies as low as 0.050
meV, emission time distribution measurements with a dynamic range of almost 3 orders of magnitude, and angleresolved measurements of moderator intensity on convoluted moderators.
P.204 New thermal neutron scattering kernels for light and heavy based on molecular dynamics simulations
J J Blostein1, J R Granada2, J I Marquez Damian1 and D Malaspina3
1
CONICET, Argentina, 2 CNEA, Argentina, 3Northwestern University, USA
Calculations of moderators require scattering kernels that are accurate in both the energetics and angular
distribution of outgoing neutrons. Currently, scattering cross sections available in ENDF format to be used in Monte
Carlo and deterministic calculations rely on water models that do not utilize the up-to-date knowledge of its
structure and dynamics.
In this work we present a new model to compute the scattering kernels for light and heavy water based on molecular
dynamics simulations. Using the molecular dynamics program GROMACS and a flexible SPC model we obtained the
ICNS 2013 International Conference on Neutron Scattering
frequency spectra of hydrogen, deuterium and oxygen, bound in light and heavy water. With those spectra we
computed the scattering laws using the LEAPR module of NJOY, which uses the incoherent approximation. Scattering
laws for D and O in D2O are corrected using the Sköld approximation and partial structure factors obtained by
Soper.
Using those kernels we computed double differential and integral cross sections over a wide range of neutron
energies (1e-5 1 eV). These results represent an improvement over existing models when compared with
experimental values, especially for low incident neutron energies.
P.205 Lujan center; a national user facility for neutron scattering – overview and opportunities
M Bourke
Los Alamos National Laboratory, USA
The Lujan Center is a Basic Energy Sciences (BES) user facility for neutron scattering science at Los Alamos
National Laboratory. Neutrons are produced by spallation in a split tungsten target by 800-MeV protons produced
from the LANSCE accelerator. Distinguishing aspects of the source are 20-Hz operation and a short proton pulse
width. The former offers broad bandwidth well suited to studies of soft, condensed matter and pair distribution
function analysis. The latter enables resonance imaging using epithermal neutrons, for which the pulse width of the
incident proton beam is critical. Eight instruments are currently accessible through the user program. Opportunities
on eight others exist by mutual interest. More than 50 sample environments are available including for example an
11 T magnet with a 300-mK capability; a 10 GPa, 1500 K pressure cell; a humidity-controlled pressure cell; a 250
kN, 1800 K load frame; and a 2700 K furnace. This talk will provide an overview of the facility status and address
opportunities for developing flight paths that are not currently in the BES user program.
P.206 High energy particle background shielding concept for spallation neutron sources
N Cherkashyna1, K Kanaki1, U Filges2, P Deen1, K Herwig3, B Winn3, G Ehlers3, G Greene3, M Hagen3, R Connatser1, R
Hall-Wilton1 and P Bentley1
1
European Spallation Source ESS AB, Sweden, 2Paul Scherrer Institute, Switzerland, 3Oak Ridge National Laboratory
(Spallation Neutron Source), USA
Low energy particle background shielding is well understood for reactor sources of neutrons, typically below 20
MeV. However, modern spallation neutron sources are driven by proton beams with GeV energies.
Shielding solutions for such high energy particles are not fully explored for use at neutron scattering facilities.
We present measured data from a number of spallation neutron sources around the world, which illustrate the
experimental backgrounds that result from interactions of high energy particles with shielding and instrumentation,
and the particle showers that are subsequently created. We use detailed, high energy physics models of several
materials to identify promising combinations in laminated shielding solutions. We propose several options that are
new to the neutron scattering community, including copper alloys as used in hadronic calorimeters in high energy
physics laboratories.
It is envisaged that these materials can be complementary to the steel, concrete, boron and hydrocarbons that are
traditionally used in shielding. The new options have very attractive energy absorption characteristics
when considering the particle showers as a whole. Simulations predict that the background suppression could be
improved by one or two orders of magnitude.
We also suggest applications of these solutions by presenting minor modifications and their impact to neutron
beam delivery solutions and facility layouts that are specifically addressing background suppression. These
solutions are expected to be of great benefit not only to the European Spallation Source, but also to existing
spallation sources. The issue of activation of the proposed materials will also be addressed.
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P.207 A first measurement result of a polarizing neutron supermirror fabricated by KAERI
S J Cho and S A Kim
Korea Atomic Energy Research Institute, Korea
Based on the project of neutron guide development, which started in 2005, KAERI has possessed the techniques
such as supermirror coating, guide element assembly, guide alignment, special tool development and guide
maintenance. With help of multilayer coating from supermirror fabrication, a project called ‘polarizing supermirror
development’ started early 2011. To begin with, most used coating materials were investigated, and for using
polarized neutron, GT-S located at CG1 beam line (Guide Test Station: Reflectometer) was modified with adding
spin flipper, polarizer, analyzer and magnetic sample holder. The first polarizing neutron supermirror fabricated last
year by KAERI was measured at the modified GT-S, which has a reflectivity of 80% and a polarization of 95%. At
this presentation, the polarizing neutron supermirror fabricated by KAERI and GT-S upgrade status will be
discussed.
P.208 The restart of the user program at the IBR-2 reactor: results of the first year of operation after the reactor
modernization
O A Culicov1, A Belushkin2 and D Kozlenko2
1
Joint Institute for Nuclear Research, Russia and INCDIE ICPE-CA, Romania, 2Joint Institute for Nuclear Research,
Russia
At present, the IBR-2 pulsed reactor has resumed its operation ranking among the world’s leading neutron sources.
The installation of the first moderator out of the three cold neutron moderators has been completed and its physical
start-up has been successfully performed. The cold neutron flux from the surface of the cryogenic moderator has
increased by a factor of up to 13 as compared to that from the surface of a water moderator.
The produced neutrons are now available for the world-wide scientific community for research purposes. The mean
power of 2MW provides an average thermal neutron flux at the surface of the moderator of 1013 n/cm2/s and a
maximum flux of 1016 n/cm2/s in burst. A more detailed description of the parameters of the modernized IBR-2
reactor, current status and prospects for the development of its instrumentation, as well as the principles of the user
policy of the Frank Laboratory of Neutron Physics (FLNP JINR) and basic information for users are given. The main
conclusions concerning the restart of the user program after the first year of operation following the modernization of
the reactor are presented as well.
P.209 Design and commissioning of new spin manipulation devices for RESEDA
W Häußler1, N Martin1, J Kindervater1, J Repper2 and P Böni1
1
Technische Universität München, Germany, 3Paul-Scherrer-Institut, Switzerland
Precise manipulation of the neutrons' polarization by means of Larmor precession devices requires highly
homogeneous magnetic fields. In the neutron resonance spin-echo (NRSE) technique, the spin flippers are based
on a combination of static and radio frequency (RF) magnetic field coils. For the NRSE spectrometer RESEDA at
FRM II, six of these NRSE-coils are installed before and after the sample position. In addition, RESEDA uses also
magnetic field coils around the sample to perform polarisation analysis experiments and to control the spin
precession plane. The manufacturing of coils, which deliver stable and homogenous magnetic fields is one of the
challenges in NRSE instrumentation.
In this contribution we present the conceptual details and first experimental results of recently developed NRSE and
spin manipulation coils. The dimensions of the NRSE coils allow for rotating them by more than 70° with respect to
the neutron beam direction. Equipped with new NRSE-coils, RESEDA opens the field of applications to Larmor
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diffraction experiments as well as to inelastic neutron scattering experiments using cold neutrons. At zero rotation
angle, the RF coils serve as resonant spin flippers used in MIEZE-I experiments. Finally, if operated in combination
with the magnetic field coils near the sample region of RESEDA, they serve as spin turners for spherical spin
polarization analysis experiments. We give a short description of these experimental options, and show results of
first experiments.
P.210 Form invariant volume transformation in phase space by focusing neutron guides
T Hofmann and N Stüßer
Helmholtz-Zentrum Berlin, Germany
Tapered guides with supermirror coating are frequently used to focus neutron beams on specimens. The divergence
distribution in the focussed beam is of great importance for the quality of neutron instrumentation. We derive the
tapering, which is needed to achieve a form invariant phase space transformation of a rectangular phase volume,
basically for a monochromatic beam. When a neutron beam with a homogeneous profile characterized by a spatial
beam width and a width in the divergence enters the focusing module, it will reduce the beam width and enlarge the
beam divergence so that the profile is still homogeneous at the exit. The inverted operation of the module expands
the width and reduces the beam divergence. From the calculated geometry of the module one can derive neutron
optical elements which allow a simultaneous expansion of the beam and its rotation. An attractive application is e.g.
a ballistic guide system without a direct view to the source. These and other applications will be presented.
P.211 Designing and utilizing elliptical guide split set-ups for ESS
S Holm1, N Rasmusen1, L Høpfner2, K Andersen2, J Voigt3 and K Lefmann1
1
Niels Bohr Institute, Denmark, 2European Spallation Source & ESS AB, Sweden, 3Forschungszentrum Jülich GmbH,
Germany
With ESS the field of neutron scattering is on the verge of entering a new era. As the world’s first long-pulsed source,
ESS offers a great number of new possibilities. However the long pulse also requires long instruments. Therefore new
neutron guide design ideas are necessary.
Since the first straight guides of the sixties the design of guides has gone many transformations. The realization that
a removal of the sample from the line of sight leads to a significant reduction of the background noise from fast
neutrons and gamma radiation, made a slightly curved version of the straight guide the standard of contemporary
guide design. With the addition of the super mirror coating in the seventies, another vital step in the improvement of
neutron guides was taken. In the recent years ballistic guides with straight tapering, parabolic tapering and full
elliptical geometries have all been investigated with the aim of reducing transport losses in guide systems.
We present a new guide system concept with which it is possible to increase the instrument capacity of a neutron
source. The design of our guide system is to have two elliptical guides in series, where the second guide is slightly
rotated around a point near to their closely spaced focal points. In turn, this rotation enables the possibility of
placing several secondary guides. Simulations of a two-, four-, and eight-split option were performed using McStas.
We have showed that the sibling instruments on the secondary guides all have high brilliance transfer (∼90%) for
neutrons with wavelengths above 2.5Å. This is possible due to the fact that the sibling instruments exploit different
parts of the phase space transported by the primary guide.
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P.212 Neutron beam fundamentals development in Japan - utilization of steady state and pulsed neutrons
K Kakurai1, T Oku1, H Hayashida1, K SakaiI1, T Shinohara1, M Nakamura1, S Wakimoto1, D Yamazaki1, K Sakasai1, K
Soyama1, M Arai1, Y Endoh1, H Kira2, Y Sakaguchi2, J Suzuki2, H Ueno3, T Kamiyama3, M Furusaka3, Y Kiyanagi3, K
Ohoyama4, H Hiraka4, Y Arimoto5, T Ino5, K Yamada5,4, K Fujiwara6, H Takahashi6, J Parker7, T Tanimori7, L J Chang8,1
and H M Shimizu9,5
1
JAEA, Japan, 2CROSS, Japan, 3Hokkaido University, Japan, 4IMR, Tohoku University, Japan, 5KEK, Japan, 6University
of Tokyo, Japan, 7Kyoto University, Japan, 8National Cheng Kung University, Taiwan, 9Nagoya University, Japan
We would like to report the development efforts in neutron beam techniques for both the steady state and pulsed
neutron source instruments at JRR-3 research reactor and J-PARC/MLF spallation source,both located on the site of
Japan Atomic Energy Agency (JAEA), Nuclear Science Research Institute in Tokai. Especially the recent
developments of polarized neutron techniques, neutron focusing and detecting devices achieved within the
'Neutron Beam Fundamentals Development' project supported by the Quantum Beam Technology Program of MEXT
will be presented.
The state-of-the-art instrumentations, which can be realized based on these developments both at JRR-3 and JPARC/MLF, will be presented with examples of materials and life science investigations being conducted there.
Acknowledgement: The developments of polarized neutron techniques, neutron focusing and detecting devices are
in part supported by the Quantum Beam Technology Program of the Ministry of Education, Culture, Sport, Science
and Technology (MEXT), Japan.
P.213 Supermirror coating optimisation for long neutron guides
K H Klenø, K Lefmann and M Bertelsen
Niels Bohr Institute, Denmark
Modern supermirror coating for neutron guides can be manufactured to a very high standard. However it is also
expensive enough that generous use of very high quality coating in a long neutron instrument can be prohibitively
expensive.
In this work we present several methods for optimising the use supermirror coating in a neutron guide, both in terms
of guide transport performance as well as cost.
We find that a non-uniform supermirror coating distribution can drastically reduce the cost of a guide, while having
little to no impact on the transmission of neutrons to the sample, when comparing with a uniform coating
distribution.
We will present recent examples, including e.g. a long ballistic guide considered for the ESS.
P.214 Applications of the MCNPX-McStas interface for shielding and background calculations at ESS
E Klinkby1, U Filges2, P Willendrup3, E Nonbøl1, E Bergbäck3, B Lauritzen1 and P Bentley4
1
DTU Nutech, Denmark, 2Paul Scherrer Institut, Switzerland, 3DTU Physics, Denmark, 4ESS, Sweden
Recently, an interface between the Monte Carlo code MCNPX and the neutron ray-tracing code McStas was
developed [1].
The present study constitutes the first application of the combined MCNPX-McStas code to calculate dose rates
along neutron beam guides and background at the instruments. The simulations are performed based on the
expected neutronic performance and guide geometries relevant for the ESS.
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Neutron generation and moderation are simulated using a full scale MCNPX model of the ESS target monolith and
upon entering the beam extraction region, the individual neutron states are handed to McStas via the MCNPXMcStas interface.
McStas accounts for the transport of neutrons through the beam guide and by using newly developed event logging
capability, the neutron state parameters corresponding to un-reflected neutrons are recorded at each scattering.
This information is handed back to MCNPX where it serves as neutron source input for a second MCNPX simulation.
This simulation enables calculation of nuclear heating in shielding material and of dose rates in the vicinity of the
guide. In a second application of the same technique, the first estimates of gamma background at the instruments
will be presented.
In addition the logging mechanism employed to record the scatterings along the guides is exploited to simulate the
supermirror quality requirements (i.e. m-values) needed at different positions along the beam guide to transport
neutrons in the same guide/source setup.
[1]
E. Klinkby et. al., Developing an interface between MCNPX and McStas for simulation of neutron
moderators, Nucl. Instr. and Meth. in Physics Research A700 (February 2013) 106-110
P.215 The neutron beam expansion program at the Bragg Institute
F Klose
ANSTO, Australia
Over the past few years, the Bragg Institute went through a large instrumentation expansion phase, doubling the
number of instruments from 7 to 14.
The funding for the program came from the Australian government through ANSTO internal funding for the TOF
inelastic spectrometer PELICAN, the ultra-small-angle neutron scattering instrument KOOKABURRA, the Laue
diffractometer JOEY, the Be Filter chemical spectrometer and 3He Polarisation Project. The Super Science – Future
Industries government initiative which was established as a stimulus package in 2009 as reaction to the global
financial crisis provided funding for construction of the TOF-based small-angle neutron scattering instrument BILBY,
the backscattering spectrometer EMU, the radiography/tomography instrument DINGO, two new cold neutron
guides as well as new sample environment equipment, including a 12 Tesla split-coil high-field magnet. In addition
to this, the Taiwanese government invested at the Bragg Institute and funded the cold triple-axis spectrometer SIKA.
The choice of the new instruments was based on earlier requests by the scientific users of the Bragg Institute (e.g.
the Blue Mountains Workshop) and more detailed specifications were developed at the NBI2 Scoping Workshop in
2009. During the peak period from 2011 to 2013, well over 40 staff were working on the program.
Major installations of the new instruments started early in 2009 and major changes to the OPAL reactor (i.e. the
insertion of the new cold guides) were completed in December 2012.
Now in the first half of 2013, PELICAN, SIKA and JOEY are in the hot-commissioning stage and major components of
KOOKABURRA are installed. Over 2013, these instruments and DINGO will obtain their operational licenses and
from there both BILBY and EMU will complete their installation work in order to transition to hot-commissioning and
operations in 2014.
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P.216 The neutron guide upgrade project at HZB
T Krist, A Rupp, N Stüsser and A Tennant
Helmholtz Zentrum Berlin, Germany
The Helmholtz-Zentrum Berlin has exchanged its cold source. At the same time the complete neutron guide system
from the extraction part to the instruments in neutron guide hall 1 was rebuilt.
The state-of-the-art neutron guide system was designed using advanced neutron optics in order to fully exploit the
new cold source and to reduce the beam losses during transport. Most guides are coated with m=3 supermirrors.
In this process an additional guide was created which is used as a test beam line for the ESS upgrade project.
The change of the guide system offered the unique chance to relocate some of the instruments and bring them to
optimal positions. Especially the cold triple axis instrument FLEX and the imaging instrument CONRAD profit from an
end position and the cold time-of-flight instrument NEAT will have an extended flight path ending in a new building.
Since the total guide cross section is doubled and the guide coating is changed from 58Ni to supermirrors with m=3
the radiation has strongly increased. Also, due to the doubled width of three guides the direct line of sight extends
to more than half the guide hall. Based on MCNP calculations a shielding system was designed which is close to the
neutron guides and consists of heavy concrete and a sandwich system. Measurements verify that the required
radiation levels are kept.
P.217 Neutron beam polarization and focusing by means of periodic magnetic fields
C Mondelli3, A Prodi1 and L Paolasini2
1
CNR-ISM-IOM, Italy, 2 European Synchrotron Radiation Facility, France, 3CNR-IOM, Italy and Institut Laue Langevin,
France
Advancement in the applications of polarised neutron diffraction critically relies on efficient techniques to produce
and analyze neutron beams with polarization properties. In the past various methods have been proposed: Heusler
alloys; supermirrors; 3He filters; field gradient devices [1]. In the latter method, neutrons in the two spin states, get
spatially separated by experiencing oppositely directed forces, in the presence of a magnetic field gradient. Tailoring
the field gradient allows not only to optimize the deflection but also to achieve beam focusing by affecting its
spectral dispersion. Focusing devices with cylindrical symmetry as multipole magnetic lenses and magnetic
refractive lenses have been demonstrated [2,3]. A new design exploits the periodicity along the beam propagation
direction of the magnetic field obtained by the periodic rotation of magnetization of an array of permanent magnets
[4]. In this way, a continuous refraction gradient perpendicular to the magnet surface is generated which provides
large deflection over long distances and line focusing on a parallel plane in the drift space with focal distance that
increases with neutron energy. Here we present results from magnetic field simulations for several periodic
permanent magnet configurations and Monte Carlo ray tracing simulations of such field gradient devices as part of
neutron instruments with realistic beam parameters at continuous and pulsed sources.
[1]
[2]
[3]
[4]
W. Gavin Williams, Polarized Neutrons, 1988 Cladendon Press, Oxford.
H. M. Shimizu et al, 1999 Nucl. Instrum. Methods Phys. Res. A 430, 423.
K. C. Littrell et al, 2007 Rev. Sci. Inst, 78 035101.
J. T. Cremer et al, 2010 Rev. Sci. Inst, 81 013902.
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P.218 Performance evaluation test of radial collimators for chopper spectrometer at J-PARC/MLF
M Nakamura1, W Kambara1, Y Yamauchi1, R Kajimoto2, K Ikeuchi2, S Ji2, Y Inamura1, K Nakajima1, S OhiraKawamura1, T Kikuchi1 and Y Kawakita1
1
Japan Atomic Energy Agency, Japan, 2Comprehensive Research Organization for Science and Society, Japan
In order to obtain the good quality data in neutron scattering experiments using sample environmental apparatus, a
countermeasure against the background is necessary. Radial collimator has been conventionally used to suppress
the off-sample parasitic scattering without perturbing the sample scattering.
Recently, inelastic neutron scattering measurements under high temperature or high magnetic field have been
frequently requested. In chopper spectrometers at J-PARC/MLF, all the detectors are installed inside the vacuum
scattering chamber. Thus, we started the research and development of a radial collimator for chopper
spectrometers. The design and assembling work were done by in-house staff. Our radial collimators are designed to
be operated in vacuum and oscillate to avoid the shadow of shielding blades.
Based on the evaluation results of shielding performance test, two kinds of shielding blades are applied for radial
collimator according to the neutron energy range. Gd2O3 sheets are used as a shielding blade in AMATERAS (BL14)
which achieves the best performance in the energy range between 1 and 20 meV. On the other hand, Cd-coated
thin plates are chosen for 4SEASONS (BL01) where the incident energy range is relatively higher (10 -- 300 meV).
In this study, we will introduce the specification of two radial collimators, and report the results of evaluation tests
performed at BL01 and BL14.
P.219 Monte Carlo simulation of accelerator-based epithermal neutron beams for neutron capture therapy
I Porras1, P L Esquinas2, J Praena3,4,and M Sabaté3
1
Departamento de Física Atómica, Molecular y Nuclear, Facultad de Ciencias, Universidad de Granada, Spain,
Department of Physics and Astronomy, University of British Columbia, Canada, 3Departamento de Física Atómica,
Molecular y Nuclear, Universidad de Sevilla, Spain, 4Centro Nacional de Aceleradores (CNA), Spain
2
Boron Neutron Capture Therapy (BNCT) [1] is an experimental form of radiotherapy based on the selective uptake of
a boron compound by tumor cells and the subsequent irradiation of the tumor with a low energy neutron beam
producing a thermal neutron field in the tumor. Thermal neutrons are captured by the boron atoms by means of a
neutron-alpha reaction in which high energy particles are delivered locally to the tumor. These particles have a
significantly higher energy transfer to the medium (tumor) than photons or electrons, and therefore can be more
biologically effective than conventional radiotherapy.
Up to now, all clinical trials of BNCT have been performed from research reactor neutron sources. These neutron
sources are scarce and are not practical for construction in hospitals. For this reason, accelerator-based neutron
sources (ABNS) are in development in several countries, and in Japan, an ABNS is ready for medical applications
[2].
The ABNS in Japan is based on collisions of high energy protons from a cyclotron with a Be target. Another option,
which requires a lower energy proton beam, is based on the (p,n) reaction on 7Li near the threshold. This produces a
less energetic neutron beam thus requiring minor moderation for use in patient irradiation [3].
For BNCT, the spectrum of the neutron beam is critical. The neutrons should have enough energy to penetrate
deeply in the body, but not so high as to produce a large background radiation dose, while also being able to
thermalize within a large volume within the body. These features require an initial epithermal spectrum for the
neutrons, but the exact requirements need to be determined with Monte Carlo simulations.
In this work we will perform calculations of an entire procedure for an accelerator-based BNCT application staring
from the 7Li(p,n) reaction. Using an adequate energy for the proton beam near the threshold and a particular exit
ICNS 2013 International Conference on Neutron Scattering
angle, we obtain a epithermal spectrum which produced a depth-dose distribution in a body model appropriate for
a BNCT treatment. In particular, the dose calculcated in the tumor with this procedure is double that produced in the
healthy tissue.
[1]
[2]
[3]
R.F. Barth, J.A. Coderre, M.G.H. Vicente and T.E. Blue, Clin. Cancer Res.11, 3987 (2005).
H. Tanaka, Y. Sakurai, M. Suzuki, S. Masunaga et al., Appl. Radiat. Isot. 69, 1642 (2011).
T. Kobayashi, G. Bengua, K. Tanaka and Y. Nakagawa, Phys. Med. Biol. 52, 645 (2007).
P.220 High-Tc YBCO films as neutron spin manipulation devices
R Pynn1, F Li1, T Wang1, S Parnell1, A Washington1, W Hamilton2 and D Baxter1
1
Indiana University Bloomington, 2Oak Ridge National Laboratory, USA
The Meissner effect has been used in the past to create a non-adiabatic transition between regions containing noncollinear magnetic fields and thereby to facilitate neutron spin manipulation. Superconducting niobium sheets are
used for this purpose in both spin flippers and to define spin precession regions in spherical neutron polarimeters.
Because of its low superconducting transition temperature, niobium effectively mandates the use of liquid helium as
a cryogen. To escape from this constraint, we have begun several projects using 300-nm-thick films of high-Tc YBCO
on single-crystal sapphire substrates. This material has the advantages of providing a very well defined, planar fieldtransition and of having very low neutron absorption and scattering. We have built and tested two devices using
these films: a spin flipper and neutron spin precession device. In the latter case, the magnetic field that generates
the spin precession is produced by coils wound with YBCO tape. For both devices, we have compared our test
results with simulations using the commercial, finite-element software MagNet© and found good agreement. The
flipper is more than 99% efficient over a large range of neutron wavelengths and the neutron depolarization
produced by the precession device is dominated by the relatively long (600 msec) neutron pulse length used in our
tests. Our results indicate that these films provide adequate flux exclusion for neutron spin-manipulation purposes
even when cooled by simple closed-cycle refrigerators. These and other devices promise to make the use of
polarized neutrons more straightforward in future.
P.221 Optimization of cold neutron beam extraction at ESS
T Schönfeldt1, K Batkov2, E Klinkby3, A Takibayev2, P Willendrup3, L Zanini2 and B Lauritzen3
1
DTU – NuTech, Denmark / ESS, Sweden, 2ESS, Sweden, 3DTU, Denmark
The neutron flux at the ESS beam guide entrance depends on their position and orientation relative to the moderator
surface. This knowledge can be utilized to optimize neutron guide geometry, with the theoretical possibility to
enhance (in certain cases almost a factor 2) the effective neutron luminosity in the phase-space range accepted by
the neutron instrument/experiment. This analysis is based on proton on target simulations using MCNPX in
preliminary models of ESS target station. Individual neutron states are propagated from the moderator surface to
beam extraction areas, where their distributions are analyzed from different instruments point of view. One of the
more important observations in this analysis is that the neutron distributions are not only anisotropic at a specific
beam extraction position, but also changing for different positions w.r.t. the moderator surface.
This detailed mapping of neutron emission can be applied for a more efficient beam extraction. For instance,
instruments could be optimized according to the wanted footprint and divergence range required by the experiment.
Commonly used ray tracing code, such as McStas, generally assumes that neutrons originate isotropic on the
moderator surface and that no correlations between position, momentum or emittance time exist and therefore does
not allow position, orientation, instrument arrangement or guide geometry optimization. Therefore a component for
McStas is being developed, using parameters and continues analytic functions obtainedby fitting the phase-space
and time distributions found in this analysis.
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P.222 Status of China Spallation Neutron Source and perspectives of neutron research
F Wang, T Liang, X Jia, Y Chen, L Ma and H Chen
Chinese Academy of Sciences, China
The China Spallation Neutron Source (CSNS) is an accelerator based multidiscipline user facility started its
construction in Dongguan, Guangdong, China, in October 2011. The facility will be initially operated in a beam
power of 100 kW at a repetition rate of 25 Hz and is upgradable to 500 kW. The CSNS target station will be
composed of a piece-stacked tungsten target with tantalum cladding to produce pulsed neutrons with peak flux of ~
2×1016n/cm2/s (@ 100 kW). Three wing moderators, decoupled H2O (300K), decoupled and poisoned H2(20K)
and coupled H2(20K), will supply four different characteristic neutron spectrums. Neutrons are extracted from 20
beam ports for neutron diffraction and scattering applied in multidisciplinary fields, such as material, physics,
chemistry and biology. Only three day-one neutron scattering instruments, a general-purpose powder diffractometer
(GPPD), a small angle neutron scattering spectrometer (SANS) and a magnetic reflectometer (MR), will be
constructed at the first step due to the stressed budget. The status, design, R&D, and upgrade outlook of the CSNS
will be reported here, and perspectives of neutron research are also discussed.
ICNS 2013 International Conference on Neutron Scattering