The transport of neutrons in long beamlines at spallation neutron sources presents a unique challenge for Monte-Carlo transport calculations. This is due to the need to accurately model the deep-penetration of high-energy neutrons through meters of thick dense shields close to the source and at the same time to model the transport of low-energy neutrons across distances up to around 150 m in length. Typically, such types of calculations may be carried out with MCNP-based codes or alternatively PHITS. However, in recent years there has been an increased interest in the suitability of Geant4 for such types of calculations. Therefore, we have implemented supermirror physics, a neutron chopper module and the duct-source variance reduction technique for low-energy neutron transport from the PHITS Monte-Carlo code into Geant4. In the current work, we present a series of benchmarks of these extensions with the PHITS software, which demonstrates the suitability of Geant4 for simulating long neutron beamlines at a spallation neutron source, such as the European Spallation Source, currently under construction in Lund, Sweden.
Development and extension of a monochromatic neutron beamline for neutron polarimetry device characterization at the Spallation Neutron Source
Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；University of Tennessee（田纳西大学）；Oak Ridge National Laboratory（橡树岭国家实验室）；Kellogg Radiation Laboratory, California Institute of Technology（加州理工学院凯洛格辐射实验室）
We describe the Fundamental Neutron Physics Beamline (FnPB) facility located at the Spallation Neutron Source at Oak Ridge National Laboratory. The FnPB was designed for the conduct of experiments that investigate scientific issues in nuclear physics, particle physics, astrophysics and cosmology using a pulsed slow neutron beam. We present a detailed description of the design philosophy, beamline components, and measured fluxes of the polychromatic and monochromatic beams.
The European Spallation Source is being constructed in Lund, Sweden and is planned to be the world's brightest pulsed spallation neutron source for cold and thermal neutron beams ($\le$ 1 eV). The facility uses a 2 GeV proton beam to produce neutrons from a tungsten target. The neutrons are then moderated in a moderator assembly consisting of both liquid hydrogen and water compartments. Surrounding the moderator are 22 beamports, which view the moderator's outside surfaces. The beamports are connected to long neutron guides that transport the moderated neutrons to the sample position via refle…
We report results of tests of the MISANS technique at the CG-1D beamline at High Flux Isotope Reactor (HFIR), Oak Ridge National Laboratory (ORNL). A chopper at 40 Hz simulated a pulsed neutron source at the beamline. A compact turn-key MISANS module operating with the pulsed beam was installed and a well characterised MnSi sample was tested. The feasibility of application of high magnetic fields at the sample position was also explored. These tests demonstrate the great potential of this technique, in particular for examining magnetic and depolarizing samples, under extreme sample environment…
This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline is to produce ultracold neutrons (UCN) for fundamental-physics experiments. It delivers up to 40 microA of 480 MeV protons from the TRIUMF cyclotron to a tungsten spallation target and uses a fast kicker to share the beam between the Center for Molecular and Materials Science and UCN. The beamline has been successfully commissioned and operated with a beam current up to 10 microA, facilitating first large-scale UCN production in Canada.
FINESSE: A Versatile Beamline for Fundamental Interactions with Neutrons at the European Spallation SourcE
Rio de Janeiro State University（里约热内卢州立大学）；University of Minnesota（明尼苏达大学）；European Spallation Source ERIC（欧洲散裂源）；The Grainger College of Engineering, University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校格兰格工程学院）；Lund University（隆德大学）；Columbia University（哥伦比亚大学）；Oak Ridge National Laboratory（橡树岭国家实验室）；Stockholm University（斯德哥尔摩大学）；Istituto Nazionale di Fisica Nucleare (INFN)（意大利国家核物理研究所）；National Research Council of Italy (CNR)（意大利国家研究委员会）；University of Milano-Bicocca（米兰比可卡大学）；Technical University of Munich（慕尼黑工业大学）；California Institute of Technology（加州理工学院）；Universidad Europea de Valencia（瓦莱西亚欧洲大学）；Polish Academy of Sciences（波兰科学院）；Universidad Autónoma de Zacatecas（萨卡特卡斯自治大学）；Jagiellonian University（雅盖隆大学）；Chalmers University of Technology（查尔姆斯理工大学）；University of Surrey（萨里大学）；University of Tennessee（田纳西大学）；Montclair State University（蒙特克莱尔州立大学）；Chinese Academy of Science（中国科学院）；China Spallation Neutron Source（中国散裂中子源）；Indiana University Bloomington（印第安纳大学伯明顿分校）
The construction of the European Spallation Source (ESS) faces many challenges from the neutron beam transport point of view: The spallation source is specified as being driven by a 5 MW beam of protons, each with 2 GeV energy, and yet the requirements in instrument background suppression relative to measured signal vary between 10$^{-6}$ and 10$^{-8}$. The energetic particles, particularly above 20 MeV, which are expected to be produced in abundance in the target, have to be filtered in order to make the beamlines safe, operational and provide good quality measurements with low background. We…
Activation analysis is used in this work to measure the flux of a fast neutron beamline at a spallation source over a wide energy spectrum, extending from thermal to hundreds of MeV. The experimental method is based on the irradiation of multiple elements and measurements of activation γ-lines using a High Purity Germanium detector. The method for data analysis is then described in detail, with particular attention to the evaluation of uncertainties. The reactions have been chosen so to cover the whole energy range, using mainly (n,γ) for thermal and epithermal neutrons, and threshold reaction…
Ray effects are the inherent problem of discrete ordinates method. RAY3D, a functional module of ARES which is a discrete ordinates code system, employs a semi-analytic first collision source method to mitigate ray effects. This method decomposes the flux into uncollided and collided components, and then calculates them with analytical method and discrete ordinates method respectively. In this article, RAY3D is validated by the Kobayashi benchmarks and applied to the neutron beamline shielding problem of China Spallation Neutron Source (CSNS) target station. Numerical results of the Kobayashi …
Bi-spectral beam extraction combines neutrons from two different kind of moderators into one beamline, expanding the spectral range and thereby the utilization of an instrument. This idea can be realized by a mirror that reflects long wavelength neutrons from an off-axis colder moderator into a neutron guide aligned with another moderator emitting neutrons with shorter wavelengths which will be transmitted through the mirror. The mirror used in such systems is typically several meters long, which is a severe disadvantage because it reduces the possible length of a focusing device in design con…
We present the development of a specialized concrete for neutron shielding at neutron research facilities, based on the addition of hydrogen atoms in the form of polyethylene and also B$_{4}$C for enhancing the neutron capture properties of the concrete. We show information on the mechanical properties of the concrete and the neutronics, in particular it's relevance to modern spallation neutron sources, such as the European Spallation Source (ESS), currently under construction in Lund, Sweden. The new concrete exhibits a 15% lower mass density, a compressible strength of 50% relative to a stan…
The white neutron beamline at the China Spallation Neutron Source will be used mainly for nuclear data measurements. It will be characterized by high flux and broad energy spectra. To exploit the beamline as a neutron imaging source, we propose a liquid scintillator fiber array for fast neutron resonance radiography. The fiber detector unit has a small exposed area, which will limit the event counts and separate the events in time, thus satisfying the requirements for single-event time-of-flight (SEToF) measurement. The current study addresses the physical design criteria for ToF measurement, …
Existing limits on the electric dipole moment (EDM) of the free neutron have provided critical constraints on new sources of CP violation for more than 60 years. A new round of searches are actively underway with the goal of improving the sensitivity to CP violation by up to two orders-of-magnitude. The status of these new searches will be discussed, including recent progress on the nEDM experiment to be carried out at the Fundamental Neutron Physics Beamline at the Oak Ridge National Laboratory's Spallation Neutron Source.
Development and Application of an eV Neutron Polarization for Parity Violation Studies at CSNS Back-n Beamline
Sun Yat-Sen University（中山大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；Spallation Neutron Source Science Center（散裂中子源科学中心）；University of Chinese Academy of Sciences（中国科学院大学）；China Institute of Atomic Energy（中国原子能科学研究院）；Great Bay University（大湾区大学）；National Synchrotron Radiation Laboratory, University of Science and Technology of China（中国科学技术大学国家同步辐射实验室）；Dongguan University of Technology（东莞理工学院）；Indiana University（印第安纳大学）；Xi’an Jiaotong University（西安交通大学）；Shandong University（山东大学）
An instrument and software algorithm is described for the purpose of characterization of large single crystals at the Alignment Facility (ALF) of the ISIS spallation neutron source. We describe a method for both characterizing the quality of the sample and also aligning it in a particular scattering plane. We present a software package written for this instrument and demonstrate its utility by way of an example of the structural characterization of large singles crystals of Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$. We suggest extensions and modifications of characterization instruments for future impro…
An accurate characterization of the neutron fields at spallation sources is crucial for many applications based on neutron irradiations, such as radiation damage tests that need a precise dose estimate. In this work we present the neutron flux measurements performed with the multi-foil activation technique in the ROTAX and ChipIr beamlines of the ISIS spallation source, characterized by moderated and unmoderated spectra, respectively. We selected many different activation reactions to cover a wide energy range, from thermal to very fast neutrons up to about 100 MeV. By applying a Bayesian unfo…
The Cryogenic Apparatus for Precision Tests of Argon Interactions with Neutrino (CAP- TAIN) program is designed to make measurements of scientific importance to long-baseline neutrino physics and physics topics that will be explored by large underground detectors. The CAPTAIN detector is a liquid argon TPC deployed in a portable and evacuable cryostat. Five tons of liquid argon are instrumented with a 2,000 channel liquid argon TPC and a photon detection system. Subsequent to the commissioning phase, the detector will collect data in a high-energy neutron beamline that is part of the Los Alamo…
Expanding Neutron Capacity at the ESS through Symbiotic Instruments: SLEIPNIR & Remora
Department of Physics, Technical University of Denmark（丹麦技术大学物理系）；Data Management & Scientific Computing, European Spallation Source ERIC（欧洲散裂源ERIC数据管理与科学计算部）；Spectroscopy Division, European Spallation Source ERIC（欧洲散裂源ERIC光谱学部）；Jülich Centre for Neutron Science（朱利希中子科学中心）；Heinz Maier-Leibnitz Zentrum, Technical University of Munich（慕尼黑大学海因茨·迈尔-莱布尼茨中心）
The boron-10 based Multi-Grid detector is being developed as an alternative to helium-3 based neutron detectors. At the European Spallation Source, the detector will be used for time-of-flight neutron spectroscopy at cold to thermal neutron energies. The objective of this work is to investigate fine time- and energy-resolved effects of the Multi-Grid detector, down to a few $μ$eV, while comparing it to the performance of a typical helium-3 tube. Furthermore, it is to characterize differences between the detector technologies in terms of internal scattering, as well as the time reconstruction o…
Evaluation of a method for time-of-flight, wavelength and distance calibration for neutron scattering instruments by means of a mini-chopper and standard neutron monitors
Canada recently lost its major supply of neutron beams with the closure of the National Research Universal reactor at Chalk River Laboratories in March 2018. This issue is further exacerbated by the closure of other reactors abroad, which also served as centers for neutron research. Consequently, there is a demand for new sources, both for Canada and internationally, as the global supply shrinks. Compact accelerator driven neutron sources provide an avenue to realize an intense source of pulsed neutron beams, with a capital cost significantly lower than spallation sources. In an effort to clos…
