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Improved knowledge of the real part of the neutron scattering length of 3He is important for further development of nuclear few-body theory, as well as for a thorough understanding of neutron scattering off quantum liquids. The real part of the bound incoherent neutron scattering length b i' has recently been measured directly with an experimental uncertainty of better than 1% by means of spin echo spectrometry. The uncertainty of the more fundamental bound multiplet scattering lengths b ±' is thus limited by today's 1.2% uncertainty of the spin-independent coherent part b c'. Employing the skew-symmetric perfect crystal Si-interferometer at the S18 experimental site at ILL, Grenoble, we have re-measured the real part of the bound coherent neutron scattering length b c' of 3He. Our result b c' = 6.010(21)fm exhibits a significant deviation compared to the latest accepted value b c' = 5.74(7)fm (H. Kaiser, H. Rauch, G. Badurek, W. Bauspiess, U. Bonse, Z. Phys. A 291, 231 (1979)). Including the known value of the incoherent neutron scattering length, we obtain new values for the real parts of the free singlet and triplet scattering lengths, a -' = 7.573(30)fm and a +' = 3.480(18)fm. Our result contravenes by more than 7 standard deviations the measurement of the same physical quantity that has recently been performed by a group at NIST in a very similar experiment (P.R. Huffman, D.L. Jacobson, K. Schoen, M. Arif, T.C. Black, W.M. Snow, S.A. Werner, Phys. Rev. C 70, 014004 (2004)) which yielded b c' = 5.853(7)fm. [ABSTRACT FROM AUTHOR]

Free neutron decay is the prototype for nuclear beta decay and other semileptonic weak particle decays. It provides important insights into the symmetries of the weak nuclear force. Neutron decay is important for understanding the formation and abundance of light elements in the early universe. The two main experimental approaches for measuring the neutron lifetime, the beam method and the ultracold neutron storage method, have produced results that currently differ by 9.8 ± 2.0 s. While this discrepancy probably has an experimental origin, a more exciting prospect is that it may be explained by new physics, with possible connections to dark matter. The experimental status of the neutron lifetime is briefly reviewed, with an emphasis on its implications for cosmology, astrophysics, and dark matter. [ABSTRACT FROM AUTHOR]

Fast neutron beams (E n > 1 MeV) are of relevance for many scientific and industrial applications. This paper explores fast neutron production using a TANDEM accelerator at the Legnaro National Laboratories, via an energetic ion beam (90 MeV 14 N ) onto a lithium target. The high energy models for nuclear collision of FLUKA foresee large neutron yields for reactions of this kind. The experiment aimed at validating the expected neutron yields from FLUKA simulations, using two separate and independent set-ups: one based on the multi-foil activation technique, and the other on the time of flight technique, by using liquid scintillator detectors. The results of the experiment show clear agreement of the measured spectra with the FLUKA simulations, both in the shape and the magnitude of the neutron flux at the measured positions. The neutron spectrum is centered around the 8 MeV range with mild tails, and a maximum neutron energy spanning up to 50 MeV. These advantageous results provide a starting point in the development of fast neutron beams based on high energy ion beams from medium-sized accelerator facilities. [ABSTRACT FROM AUTHOR]

There exists a puzzling disagreement between the results for the neutron lifetime obtained in experiments using the beam technique versus those relying on the bottle method. A possible explanation of this discrepancy postulates the existence of a beyond-Standard-Model decay channel of the neutron involving new particles in the final state, some of which can be dark matter candidates. We review the current theoretical status of this proposal and discuss the particle physics models accommodating such a dark decay. We then elaborate on the efforts undertaken to test this hypothesis, summarizing the prospects for probing neutron dark decay channels in future experiments. [ABSTRACT FROM AUTHOR]

The neutron capture cross section of 232 T h has been measured with the time-of-flight technique in the energy range from 10 to 200 keV at the back-streaming white neutron beam-line (Back-n) of China Spallation Neutron Source (CSNS). The pulse height weighting technique (PHWT) was applied with four C 6 D 6 liquid scintillators to measure the prompt gamma-ray energy release following neutron capture. The measurement data, corrected with the PHWT, have been normalized to the saturated resonances at 21.8 eV. The background was determined by a lead sample measurement and detailed Monte Carlo simulations. The 232 T h (n , γ) average cross sections have been determined relative to the 197 A u (n , γ) reaction cross sections. The results are consistent with the evaluation values of CENDL-3.2 and JENDL-5. The total uncertainties, including the PHWT, normalization, background subtraction, corrections, and relative measurement, are in the range of 4.5–4.8%. [ABSTRACT FROM AUTHOR]

Prompt gamma rays of cerium and chlorine were investigated with the FaNGaS (Fast Neutron-induced Gamma-ray Spectrometry) instrument operated at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching. The gamma radiation was emitted from (n,n'), (n,p) and (n,α) reactions induced by the irradiation of a cerium(III) chloride (CeCl3) sample with a beam of fission neutrons. Additionally, a polyvinylchloride (PVC, (C2H3Cl)n) sample was irradiated to verify possible interferences between gamma lines of cerium and chlorine. We identified 87 prompt gamma lines of cerium and chlorine. From these, we assigned 58 lines to the (n,n') reaction in cerium (one for 136Ce, 41 for 140Ce and 16 for 142Ce), 23 to the (n,n') reaction in chlorine (15 for 35Cl and 8 for 37Cl), 5 lines to the 35Cl(n,p)35S reaction and 1 line to the 35Cl(n,α)32P reaction. We present relative intensities and fast-neutron spectrum-averaged partial cross sections of the aforementioned gamma lines and compare them with available literature data. Identification of new lines and discussion of possible errors adds important value to the literature data found to be consistent with our results. In addition, for a counting time of 12 h we estimate the detection limits for cerium and chlorine as 1 and 2 mg, respectively. [ABSTRACT FROM AUTHOR]

The precise modeling of the de-excitation of Gd isotopes is of great interest for experimental studies of neutrinos using Gd-loaded organic liquid scintillators. The FIFRELIN code was recently used within the purposes of the STEREO experiment for the modeling of the Gd de-excitation after neutron capture in order to achieve a good control of the detection efficiency. In this work, we report on the recent additions in the FIFRELIN de-excitation model with the purpose of enhancing further the de-excitation description. Experimental transition intensities from the EGAF database are now included in the FIFRELIN cascades, in order to improve the description of the higher energy part of the spectrum. Furthermore, the angular correlations between γ rays are now implemented in FIFRELIN, to account for the relative anisotropies between them. In addition, conversion electrons are now treated more precisely in the whole spectrum range, while the subsequent emission of X rays is also accounted for. The impact of the aforementioned improvements in FIFRELIN is tested by simulating neutron captures in various positions inside the STEREO detector. A repository of up-to-date FIFRELIN simulations of the Gd isotopes is made available for the community, with the possibility of expanding for other isotopes which can be suitable for different applications. [ABSTRACT FROM AUTHOR]

The 10 Hz/0.5 MW AUSTRON neutron spallation source is dedicated for high-resolution structural and dynamical investigations of condensed matter and for new fundamental research with neutrons. New magnetic focusing and bunching systems are under development, which create additional intensity-gain factors of 10-20. Clean-room conditions including vibration, temperature and humidity control will improve the standard of neutron optical and neutron reflectometry experiments considerably. Narrow band neutron perfect crystal resonators and storage systems are foreseen for a novel beam tailoring. A dedicated new ultra-cold neutron station will open a new horizon for experiments in the sub-neV region. Recently, the project secured additional support of the Austrian Governmental Board for Research and Technological Development, which recommended the forced continuation of the project, the installation of a professional project group and the cooperation with the European Spallation Source (ESS) project and with the neighboring countries. [ABSTRACT FROM AUTHOR]

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors. [ABSTRACT FROM AUTHOR]

Emission of prompt gamma rays following (n,n'), (n,p) and (n,α) reactions induced by irradiation of a calcium carbonate (CaCO3) sample with a beam of fission neutrons was investigated with a modified version of the FaNGaS (Fast Neutron-induced Gamma-ray Spectrometry) instrument operated at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching. The neutron spectrum has an average energy of 2.30 MeV and at sample position the fast neutron flux was (1.13 ± 0.04) × 108 cm−2 s−1. The measurement was performed at an angle of 90° between neutron beam and detector. In total, we claim the identification of 38 prompt gamma lines, from which we have assigned 12 to the (n,n') reaction in calcium (7 for 40Ca, 1 for 42Ca and 4 for 44Ca), 1 to the 12C(n,n')12C reaction, and 2 to the (n,n') reaction in oxygen (1 for 16O and 1 for 18O). The other observed gamma lines are attributed to the 40Ca(n,p)40K reaction (20 lines) and to the 40Ca(n,α)37Ar reaction (3 lines). Relative intensities and fast neutron spectrum averaged partial cross sections of the gamma lines are presented and compared with available literature data. Our results were found to be in good agreement with available literature data but also improved and complemented it, as we have pointed out possible errors and identified new lines. Additionally, for a counting time of 12 h the detection limits of calcium, carbon and oxygen were determined as 5, 13 and 64 mg, respectively. [ABSTRACT FROM AUTHOR]

Franz Käppeler and collaborators showed in the 1980's that the 7 Li(p, n) 7 Be reaction can be used to produce a flux of neutrons having a stellar-like energy distribution, closely similar to that contributing to the slow (s) neutron capture process in massive stars. The Liquid-Lithium Target (LiLiT) at Phase I of the Soreq Applied Research Accelerator Facility (SARAF) was designed following the same physical principle. Owing to the high proton beam intensity of SARAF and the power dissipation of LiLiT, the facility provided a neutron intensity more than one order of magnitude higher than available with conventional solid Li targets. We review here our first collaboration with Franz Käppeler and his group, the LiLiT design and nuclear astrophysics research accomplished in recent years at the SARAF-LiLiT facility. An outlook to the research program with SARAF Phase II, currently in construction, is presented. [ABSTRACT FROM AUTHOR]

This article describes the studies’ results aimed at the gas turbine combined cycle (CCGT) with the pressurized heat recovery steam generator (PHRSG) modernization scheme for the existing steam-power unit. It is shown that this scheme meets the energy development program's formal requirements. It reduces the reconstruction costs due to the equipment parts preservation. The heat transfer study has shown the possibility of heat exchange process simulation with boiler designer software. It was shown that the optimal flue gas pressure in PHRSG is 4–5 bar. Raising the flue gas pressure up to this level gives the largest increase in heat transfer coefficient. The greatest decrease in metal consumption occurs in the same area. The inlet velocity range from 10 to 20 m/s is optimal in this scheme. Several modernization schemes for popular Russian T-100 and K-300 steam turbines and GTE-160 and GT-25PA gas turbines are presented. The promising equipment unification potential of these schemes is shown. Several challenging schemes based on the researched scheme are proposed. [ABSTRACT FROM AUTHOR]

The neutron lifetime anomaly has been used to motivate the introduction of new physics with hidden-sector particles coupled to baryon number, and on which neutron stars provide powerful constraints. Although the neutron lifetime anomaly may eventually prove to be of mundane origin, we use it as motivation for a broader review of the ways that baryon number violation, be it real or apparent, and dark sectors can intertwine and how neutron star observables, both present and future, can constrain them. [ABSTRACT FROM AUTHOR]

Swelling behavior of cotton, dissolving wood pulp (DWP), viscose staple fiber, and Tencel staple fiber in varying sodium hydroxide (NaOH) concentration were investigated by means of optical microscopy and were characterized by molecular mass distribution, X-ray diffractometer, and dynamic vapor sorption. The effect of temperature (20–45 °C) and duration (0–120 min) was studied. The results reveal that the swelling ratio of fiber in alkali solution depends on fiber accessibility and NaOH concentration. Viscose staple fiber exhibited the highest swelling ratio and lowest swelling ratio observed for dissolving wood pulp fiber among all the materials. The cotton or DWP fibers provide maximum swelling during alkaline steeping (18wt % lye) at higher temperatures, i.e., 45 °C. As for viscose staple fiber and Tencel staple fiber, using 12 wt% lye concentration and steeping at lower temperatures, i.e., 20 °C maximum swelling behavior. [ABSTRACT FROM AUTHOR]

Diamond is widely studied and used for the detection of direct and indirect ionizing particles because of its many physical and electrical outstanding properties, which make this material very attractive as a fast-response, high-radiation-hardness and low-noise radiation detector. Diamond detectors are suited for detecting almost all types of ionizing radiation (e.g., neutrons, ions, UV, and X-ray) and are used in a wide range of applications including ones requiring the capability to withstand harsh environments (e.g., high temperature, high radiation fluxes, or strong chemical conditions). After reviewing the basic properties of the diamond detector and its working principle detailing the physics aspects, the paper discusses the diamond as a neutron detector and reviews its performances in harsh environments. [ABSTRACT FROM AUTHOR]

We report a neutronics study of a blanket mock-up using a discharge-type compact fusion neutron source. Deuterium–deuterium fusion neutrons were irradiated to the mock-ups composed of tritium breeder and neutron reflector/moderator. The tritium production rate (TPR) per source neutron was measured by a single-crystal diamond detector with a 6Li-enriched lithium fluoride film convertor after the calibration process. Despite the low neutron yield, energetic alpha and triton particles via 6Li(n, t)α neutron capture as well as 12C via elastic scattering were successfully detected by the SDD with high signal to noise ratios. The TPRs were experimentally evaluated with errors of 8.4%–8.5% at the 1σ level at the positions with high thermal neutron fluxes where the errors were dominantly introduced by uncertainties in the monitoring of the neutron production rate. The calculated to experimental (C/E) values of TPR were evaluated to be 0.91–1.27 (FENDL-2.1) and 0.94–1.28 (FENDL-3.1). As the neutron source can generate 14 MeV neutrons using a mixed gas of deuterium and tritium, this approach provides more opportunities for blanket neutronics experiments. [ABSTRACT FROM AUTHOR]

The neutron imaging instrument CONRAD was operated as a part of the user program of the research reactor BER-II at Helmholtz-Zentrum Berlin (HZB) from 2005 to 2020. The instrument was designed to use the neutron flux from the cold source of the reactor, transported by a curved neutron guide. The pure cold neutron spectrum provided a great advantage in the use of different neutron optical components such as focusing lenses and guides, solid-state polarizers, monochromators and phase gratings. The flexible setup of the instrument allowed for implementation of new methods including wavelength-selective, dark-field, phase-contrast and imaging with polarized neutrons. In summary, these developments helped to attract a large number of scientists and industrial customers, who were introduced to neutron imaging and subsequently contributed to the expansion of the neutron imaging community. [ABSTRACT FROM AUTHOR]

The neutron lifetime has been measured by comparing the decay rate with the reaction rate of |$^3$| He nuclei of a pulsed neutron beam from the spallation neutron source at the Japan Proton Accelerator Research Complex (J-PARC). The decay rate and the reaction rate were determined by simultaneously detecting electrons from the neutron decay and protons from the |$^3$| He(n,p) |$^3$| H reaction using a gas chamber, the working gas of which contains diluted |$^3$| He. The measured neutron lifetime was |$898\,\pm\,10\,_{\rm stat}\,^{+15}_{-18}\,_{\rm sys}\,$| s. [ABSTRACT FROM AUTHOR]

We report a neutron beam polarization P = [99.9982 ± 0.0024]%, which means an improvement of two orders of magnitude compared to known values. Actually, one can assume this neutron beam to be 100% polarized, because due to the special beam guidance the overlap of spin-up neutrons and spin-down neutrons could be suppressed down to 1.2 × 10−12 [rel. units]. These values are about four orders of magnitude below the detection limit of a monochromatic neutron flux of 108n· cm−2s−1. [ABSTRACT FROM AUTHOR]

The question of the nature of dark matter is one of the major challenges of elementary particle physics. Not surprisingly, the recent suggestion of a dark decay channel as a solution to persisting discrepancies in neutron lifetime measurements has initiated substantial research activity. We discuss the accurate measurement of the parity violating β-asymmetry using Perkeo III. The result is about five times more precise than the current world average and resolves a long-standing discrepancy. Based on this, we largely rule out the dark decay mode interpretation. We derive a new world average of the weak axial coupling and obtain a competitive value of the first element of the quark mixing matrix Vud from neutron decay. [ABSTRACT FROM AUTHOR]

We report on first experimental tests of a neutron magnetic spin resonator at a very cold neutron beam port of the high flux reactor at the ILL Grenoble. When placed between two supermirror neutron polarizers and operated in a pulsed traveling-wave mode it allows to decouple its time- and wavelength-resolution and can therefore be used simultaneously as electronically tunable monochromator and fast beam chopper. As a first 'real' scientific application we intend its implementation in the PERC (p roton and e lectron r adiation c hannel) project related to high-precision experiments in neutron beta decay. [ABSTRACT FROM AUTHOR]

Regenerated cellulose fibers are produced using two industrially dominant technologies: the viscose and lyocell processes. Here, we compare commercially available fibers, prepared using the viscose and lyocell processes. Single fibers are subjected to a variety of mechanical deformations to obtain stress–strain, stress relaxation and stress recovery data. These are fitted to a phenomenological model, whose parameters are interpreted in terms of the fiber semicrystalline microstructure. This simple model does not incorporate the complexities of semicrystalline microstructure. Rather, it represents structure in a semicrystalline polymer fiber in terms of an elastic crystalline phase that coexists with a viscoelastic Voigt-like glassy amorphous phase. Lyocell fibers are characterized by higher values of crystalline modulus relative to viscose. Lyocell fibers also have a higher amorphous phase modulus and a wider relaxation spectrum than viscose, suggesting that amorphous and crystalline phases are dispersed in close connectivity in lyocell. Viscose and lyocell fibers exhibit qualitative similarities in their mechanical response. On stretching, there is a transition in the stress–strain curve from a low strain elastic response at a critical value of strain. This critical strain has been incorrectly attributed to yielding of the fiber. We establish that this critical value corresponds to an apparent yield. When subjected to strains higher than this apparent yield point, the fibers develop a memory of the mechanical deformation. This memory decays slowly, logarithmically with time and is lost over about a day as the fiber structure transitions back to the original as spun fiber. Finally, we demonstrate that on wetting the fibers with water, there is an increase in the apparent yield strain for viscose fibers, but not for lyocell. We interpret these results in terms of the semicrystalline microstructure of the fibers. [ABSTRACT FROM AUTHOR]

The knowledge of the neutron capture cross sections of s-process branching point isotopes represents a basic requirement for the understanding of star evolution. Since such branching point isotopes are by definition radioactive, the measurement of their cross sections from thermal to stellar energies becomes a challenging task. Considerable amounts of material have to be produced, representing a significant radioactive hazard. We report here on the production and separation of 3.5 mg 171Tm from 240 mg 170Er2O3 and 72 μg 147Pm from 100 mg 146Nd2O3 irradiated at the ILL high flux reactor. Thin targets were prepared with high chemical and radioisotopic purity suitable for neutron capture measurements at n_TOF CERN and the SARAF-LiLiT facility. [ABSTRACT FROM AUTHOR]

Water diffusion in cellulose was studied via two-phase Kärger model and the propagator method. In addition to ruling out anomalous diffusion, the mean squared displacements obtained at different diffusion times from the Kärger model allowed to characterize the system's phases by their average confining sizes, average connectivity and average apparent diffusion coefficients. The two-phase scheme was confirmed by the propagator method, which has given insights into the confining phase-geometry, found consistent with a parallel-plane arrangement. Final results indicate that water in cellulose is confined in two different types of amorphous domains, one placed at fiber surfaces, the other at fiber cores. This picture fully corresponds to the phenomenological categories so far used to identify water in cellulose fibers, namely, free and bound water, or freezing and non-freezing water. [ABSTRACT FROM AUTHOR]

For Th and U, the (n ,γ) reaction cross-sections at the neutron energies of 2.45 and 14.8 MeV as well as the (n,2n) reaction cross-sections at 14.8 MeV have been determined using activation and off-line γ-ray spectrometric technique. The (n ,γ) and (n,2n) reaction cross-sections of Th and U were also calculated theoretically using the TALYS 1.6 computer code. The present data and literature data in a wide range of neutron energies were compared with the evaluated data of ENDF/B-VII.1, JENDL-4.0, JEFF-3.1/A and CENDL-3.1 and theoretical value of TALYS to examine the systematics of (n ,γ) and (n,2n) reaction cross-sections. [ABSTRACT FROM AUTHOR]

The geometric phase has found a broad spectrum of applications in both classical and quantum physics, such as condensed matter and quantum computation. In this paper, we introduce an operational geometric phase for mixed quantum states, based on spectral weighted traces of holonomies, and we prove that it generalizes the standard definition of the geometric phase for mixed states, which is based on quantum interferometry. We also introduce higher order geometric phases, and prove that under a fairly weak, generically satisfied, requirement, there is always a well-defined geometric phase of some order. Our approach applies to general unitary evolutions of both non-degenerate and degenerate mixed states. Moreover, since we provide an explicit formula for the geometric phase that can be easily implemented, it is particularly well suited for computations in quantum physics. [ABSTRACT FROM AUTHOR]

Three regenerated cellulosic fiber types: lyocell, viscose, and modal were subjected to repetitive wet-dry treatments. Simulated treatments showed reorganization of the internal fiber structure which could be determined by accessibility studies. The reduction in liquid water retention capacity was found to be greater for lyocell than that for modal and viscose, sorption of iodine, and water vapor reduced for all studied fibers. The wet-dry treatment did not have influence on chemical reactivity of cellulosic fibers characterized by complexation of iron under highly alkaline conditions. The effect of wet-dry treatment on the tenacity, elongation at break, abrasion resistance, and molecular weight distribution of fibers was also explored in this study. The reduced strength in treated specimens was not accompanied by changes in molecular weight distributions. Based on these results, the changes observed in wet-dry-treated specimens were observed mainly owing to polymer reorganization in amorphous parts of the fibers. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]