Neutron Reflection

Three important Bronze Age copper-alloy artefacts from the permanent exhibition of the National Museum of Antiquity in Leiden (NL) have been studied by neutron-based methods. These artefacts are known as the Buggenum sword, the Jutphaas dirk, and the Escharen double axe. All three objects have been studied with neutron resonance capture analysis (NRCA), a non-destructive method to determine the bulk elemental compositions. The Buggenum sword is also studied with time-of-flight neutron diffraction (TOF-ND) giving additional information about crystalline properties and internal material structures, and neutron tomography (NT), showing details of the construction of this sword and voids inside the material. The composition of the Jutphaas dirk is compared with the compositions of two other dirks belonging to the group of six Plougrescant-Ommerschans (PO) ceremonial dirks. The Escharen double axe, identified as being of the Zabitz type, variant Westeregeln, is a rare object in the Low C...

Neutron resonance capture analysis (NRCA) has been applied to determine the elemental compositions of three valuable, precious and very well preserved ancient bronze objects from the National Museum of Antiquities in Leiden (NL). For this study it was not allowed to use analytical methods, for which samples should be taken from objects. For this reason they were studied by NRCA using epithermal neutron beams from the pulsed neutron source of the GELINA facility of the EC-JRC-IRMM in Geel (Belgium). Neutrons can penetrate thick layers of materials, and therefore this method provides bulk compositions. NRCA is a fully non-destructive method. Since thermal neutrons are removed from the beam, the activation of the objects is low already directly after the measurement and fully negligible after a short waiting period. This research is part of the European ANCIENT CHARM project.

The design and characteristics of a double-supermirror monochromator for neutron instrumentation at the Laboratoire Léon Brillouin are described. The aim of this monochromator is to reduce the intense γ radiation produced by conventional velocity selectors and to avoid a direct view of the guide while keeping a comparable neutron transmission (70%). The monochromator offers a continuous choice of wavelength selection in the range 0.5–2 nm.

Tribological phenomena usually occur at a solid surface or an interface of solids. To carefully examine a tribological phenomenon, information on the state at the surface or the interface must be tried to be gotten from different angles. Estimations of the state, however, are generally considered to be difficult because there are few methods suit for adequately picking up the information on profiles and/or properties of the only nearest region to the surface. Especially for the case that the target is at the interface of metals, the estimation is more difficult because a standard electron beam cannot penetrate into either of the metal. The authors have, accordingly, developed a new estimation method applying a 'neutron reflectometry' to such a metal surface or a metal-metal interface. The reflectometry is suitable for analysis of vertical structures of the nearest regions to a surface as less than 1µm. In addition, since a neutron beam can penetrate into many kinds of common metals, the estimation by the neutron reflectometry can be useful even for the metal-metal interface. In this paper, we report some results obtained by some of several basic experiments on neutron reflectometry. Surface profiles and ultra-thin film thickness of PFPE lubricant at a metal surface and/or a metal-metal interface were estimated in the study. BASIC CHARACTERISTICS OF A NEUTRON BEAM Prior to outlining our experiments, we will firstly introduce some characteristics of a neutron beam. A neutron beam, as is well known, can either behave as a wave or a particle, like visible light or X-rays. The main characteristics of a neutron favorable for tribological studies are as follows: •

It falls to me to summarise the third and very successful workshop in the series. I suppose that, as a worldwide activity, the field is now over forty years old, coming into being, as it did, with the completion of the first generation of nuclear reactors providing neutrons for research. Some people here, such as Professor Ramsey and several others, have been active par

Neutron and associated secondary photon line-beam response functions (LBRFs) for point monodirectional neutron sources are generated using the MCNP Monte Carlo code for use in neutron skyshine analysis employing the integral line-beam method. The LBRFs are evaluated at 14 neutron source energies ranging from 0.01 to 14 MeV and at 18 emission angles from 1 to 170deg, as measured from the source-to-detector axis. The neutron and associated secondary photon conical-beam response functions (CBRFs) for azimuthally symmetric neutron sources are also evaluated at 13 neutron source energies in the same energy range and at 13 polar angles of source collimation from 1 to 89 deg. The response functions are approximated by an empirical three-parameter function of the source-to-detector distance. These response function approximations are available for a source-to-detector distance up to 2500 m and, for the first time, give dose equivalent responses that are required for modern radiological assessments. For the CBRFs, ground correction factors for neutrons and secondary photons are calculated and also approximated by empirical formulas for use in air-over-ground neutron skyshine problems with azimuthal symmetry. In addition, simple procedures are proposed for humidity and atmospheric density corrections.

The lowest stationary quantum state of neutrons in the Earth's gravitational field is identified in the measurement of neutron transmission between a horizontal mirror on the bottom and an absorber/scatterer on top. Such an assembly is not transparent for neutrons if the absorber height is smaller than the ''height'' of the lowest quantum state.

Over a decade ago, it was confirmed that detonation nanodiamond (DND) powders reflect very cold neutrons (VCNs) diffusively at any incidence angle and that they reflect cold neutrons quasi-specularly at small incidence angles. In the present publication, we report the results of a study on the effect of particle sizes on the overall efficiency of neutron reflectors made of DNDs. To perform this study, we separated, by centrifugation, the fraction of finer DND nanoparticles (which are referred to as S-DNDs here) from a broad initial size distribution and experimentally and theoretically compared the performance of such a neutron reflector with that from deagglomerated fluorinated DNDs (DF-DNDs). Typical commercially available DNDs with the size of ~4.3 nm are close to the optimum for VCNs with a typical velocity of ~50 m/s, while smaller and larger DNDs are more efficient for faster and slower VCN velocities, respectively. Simulations show that, for a realistic reflector geometry, th...

We present a summary description of the 8th annual international Design and Engineering of Neutron Instruments Meeting (DENIM) which was held in North Bethesda, MD, USA, September 17–19, 2019. DENIM VIII was organized by the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) in combination with the University of Maryland (UMD). DENIM specifically addresses the unique field of neutron instrument engineering, a subcategory of neutron scattering science. DENIM is organized by engineers for engineers who share openly about what works and what doesn’t work in the life cycle design of an instrument used to analyze materials with neutrons. DENIM is held under the patronage of the International Society of Neutron Instrument Engineers which was formed in 2017. At DENIM VIII, there were 3 keynote talks, 29 additional presentations and 13 posters (presented to the plenary in a poster slam session). Attendees toured the unique labs at NIST including the NCN...

Polarised neutron scattering is the method of choice to study magnetism in condensed matter. Polarised neutrons are yet typically very low in flux and complex experimental configurations further reduce the count rate, neutron polarisation corrections would therefore be needed. Here we analytically derive formulae of the corrected partial differential scattering cross sections. The analytical method is designed for the longitudinal polarisation analysis, and the correction generally holds for time-independent polarised neutrons with a triple-axis spectrometer. We then applied the correction to recent results of our $P_x$ experiment on Y$_3$Fe$_5$O$_{12}$. Although there is a difficulty with experimental determination of inefficiency parameters of neutron spin polarisers and flippers, the correction appears to work properly.

Neutron radiation offers significant advantages for the study of biological molecular structure and dynamics. A broad and significant effort towards instrumental and methodological development to facilitate biology experiments at neutron sources worldwide is reviewed.

Realizations of the TOF technique for neutron reflectometers at steady flux reactors are compared. Beam choppers for neutron reflectometers divide into choppers of type 1 (= const) and 2 (∕ = const). It follows from Monte-Carlo simulations that choppers of type 1 do not yield to more intricate choppers of type 2, widely used at neutron reflectometers. Because of a very fast drop of neutron reflectivities with the momentum transfer , non-optimality of measurements with a chopper of type 1 is fully compensated by better statistics at large , and is not so much essential at small. To vary the TOF resolution with choppers of type 1, a phasing of two discs and a turning of the system of two discs are suggested. The fluxes of neutrons with wavelengths beyond the working range and the efficiencies of their elimination by means of a bandwidth limiting prechopper are evaluated.

The paper contains recent contributions to cold and ultracold neutron physics by groups at Garching and Grenoble, and, in a second part. by a group at the University, of Rhode Island. We describe first results in neutron microscopy obtained at the ILL and (}arching reactors. Two versions of a two-mirror neutron microscope were used: one employing uhracold neutrons and total-reflecting mirrors, and the other utilizing very cold neutrons in conjunction with muhilayer mirrors. We then describe the essential features of the new source of ultracold and cold neutrons which ls presently being set up :it the HFR. Grenoble. and discuss the novel all-metallic neutron mirrors and guides which were developed in connection with this project. Finally a proposal by the University of Rhode Island for application of high-resolution neutron optical techniques to the stud~, of critical phenomena in liquids is presented.

Long pulsed neutron sources are being actively developed as small university based sources and are being considered for the next generation of high powered sources, such as the European Neutron Source (ESS) and the Spallation Neutron Source (SNS) second target station. New instrumentation concepts will be required to effectively utilize the full spectrum of neutrons generated by these sources. Neutron diffractometers, which utilize time-of-flight (TOF) techniques for wavelength resolution, are particularly problematic. We describe an instrument for a long pulsed source that provides resolution comparable to that obtained on short pulsed sources without the need of long incident flight paths. We accomplish this by utilizing high speed choppers to impose a time structure on the spectrum of incident neutrons. By strategically positioning these choppers the response matrix assumes a convenient form that can be deconvoluted from the measured TOF spectrum to produce the diffraction pattern of the sample. We compare the performance of this instrument to other possible diffraction instruments that could be utilized on a long pulsed source.

Neutron reflectivity is a powerful technique for characterizing interfaces in many areas of science. The traditional method of time of flight for measuring the wavelength of neutrons in a white beam is extremely wasteful, as the vast majority of neutrons must be absorbed in the choppers in order to produce a pulsed beam. A prism operates continuously, with a transmission up to two orders of magnitude higher than choppers. The wavelength-dependent deflection of the beam by the prism, coupled with a high spatial resolution detector, results in excellent wavelength resolution. The theory of how the resolution is considerably enhanced by curving the surface of the prism is described in detail for a real experimental arrangement. It is demonstrated how this can be used for faster neutron reflectometry, including the merging of different angles and subtraction of background. The technique shows considerable promise for neutron reflectivity, opening up new areas of science particularly in ...

The neutron resonances in the LiF(200 A s)/Ti(2000 A s) /Cu(1000 A s)/glass layered structure have been observed simultaneously by neutron re#ectivity and Li(n,) H nuclear reaction. A ionization chamber was used to register the alpha and triton particles emitted after the neutron capture in Li nuclei. The observation of the neutron density resonant character in the spacer needs a neutron absorber layer which, for the present experiment, was the cap layer itself. For de"nite wavelengths one looks for minima on the re#ectivity curve which corresponds to maxima on the-spectra and H-spectra. The charged particle normalized intensity re#ects the resonant behavior of neutron density in the cap layer Li which is a result of the realization of the resonances in the spacer layer (Ti). The decreasing of the enhancement factor with the increasing of the resonance order is directly seen on both registration channels. Fitting of charged particles and neutron data helps signi"cantly in characterizing the depth pro"le of the sample and leads to the idea that the Ti spacer layer could be used as a medium for sensitive investigation.

Results of experiments aimed at observing the change in the energy of a neutron traversing an accelerated refractive sample are reported. The experiments were performed with ultracold neutrons, the energy transfer in these experiments being ±(2−6) × 10 −10 eV. The results suggest the existence of the effect and agree with theoretical predictions to a precision higher than 10%. A similar effect was previously predicted for the change in the frequency of an electromagnetic wave traversing an accelerated dielectric slab. In all probability, the effect has a very general nature, but it is presently observed only in neutron optics.

MERLIN is designed to be a high intensity, medium energy resolution spectrometer. As such, it will complement the high-resolution MAPS spectrometer at ISIS. MERLIN will utilise all the latest advances in technology with a supermirror guide to enhance flux as well as 3 m long position-sensitive detectors in a vacuum making it ideal for single-crystal users. The detector bank will cover a massive p steradians of solid angle with an angular range from À451 to +1351 degrees in the horizontal plane and 7301 degrees in the vertical plane. This will allow large swathes of Q,o space to be accessed in a single run. The instrument will be ready for commissioning in February 2006. This paper presents details of design and performance of this new instrument.

Neutron radiation offers significant advantages for the study of biological molecular structure and dynamics. A broad and significant effort towards instrumental and methodological development to facilitate biology experiments at neutron sources worldwide is reviewed.

Neutron Resonance Transmission Analysis (NRTA) uses resonant absorption of neutrons to infer the absolute isotopic composition of a target object, enabling applications in a broad range of fields such as archaeology, enrichment analysis of nuclear fuel, and arms control treaty verification. In the past, NRTA involved large user facilities and complex detector systems. However, recent advances in the intensity of compact neutron sources have made compact neutron imaging designs increasingly feasible. This work describes the Monte Carlo (MC) based design of a compact epithermal NRTA radiographic instrument which uses a moderated, compact deuterium-tritium (DT) neutron source and an epithermal neutron detector. Such an instrument would have a wide range of applications, and would be especially impactful for such scenarios as nuclear inspection and arms control verification exercises, where system complexity and mobility may be of critical importance. The MC simulations presented in this work demonstrate accurate time-of-flight (TOF) reconstructions for transmitted neutron energies, capable of differentiating isotopic compositions of nuclear material with high levels of accuracy. A new generation of miniaturized and increasingly more intense neutron sources will allow this technique to achieve measurements with greater precision and speed, with significant impact on a variety of engineering and societal problems.

The total scattering cross sections for slow neutrons with energies E in the range 300 neV to 3 meV for gaseous and liquid ortho-2 H 2 have been measured. The cross sections for 2 H 2 gas are found to be in excellent agreement with both the Hamermesh and Schwinger and the Young and Koppel models. For liquid 2 H 2 , we confirm the existing experimental data in the cold neutron range and the discrepancy with the gas models. We find a clear 1= E 0 p dependence at low energies for both states. A simple explanation for the liquid 2 H 2 cross section is offered.

We prove that, under the condition of validity of the Fresnel approximation, diffraction and interference for a wave traveling in the z-direction may be described in terms of the spreading in time of the transverse (x,y)-wave packet. The time required for the evolved wave packet to yield identical patterns as given by standard optics corresponds to the time for the quantum to cross the optical apparatus. This point of view may provide interesting cues in wave mechanics and quantum physics education.

Резюмируется опыт работы сектора нейтронного активационного анализа (НАА) по применению эпитепловой активации в науках о жизни и материаловедении. Обсуждаются потенциальные возможности комбинации эпитепловой активации и подавления комптоновского рассеяния и вклада от элементов с каскадным высвечиванием γ-квантов для выхода на новый уровень аналитических работ в НАА.

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The reciprocity principle is that, when an emitted wave gets scattered on an object, the scattering transition amplitude does not change if we interchange the source and the detector - in other words, if incoming waves are interchanged with appropriate outgoing ones. Reciprocity is sometimes confused with time reversal invariance, or with invariance under the rotation that interchanges the location of the source and the location of the detector. Actually, reciprocity covers the former as a special case, and is fundamentally different from - but can be usefully combined with - the latter. Reciprocity can be proved as a theorem in many situations and is found violated in other cases. The paper presents a general treatment of reciprocity, discusses important examples, shows applications in the field of photon (M\"ossbauer) scattering, and establishes a fruitful connection with a recently developing area of mathematics.