Spin polarization and production rate studies of surface muons in a novel solenoid capture system based on CSNS

A novel surface muon capture system with a large acceptance was proposed based on the China spallation neutron source(CSNS).This system was designed using a superconducting solenoid where a long graphite target was put inside it.Firstly,the spin polarization evolution was studied in a constant uniform magnetic field.As the magnetic field can interact with the spin of the surface muon,both the spin polarization and production rate of the surface muons collected by the new capture system were calculated by the G4beamline.Simulation results showed that the surface muons could still keep a high spin polarization([90%)with different magnetic fields(0–10 T),and the larger magnetic field is,the more surface muons can be captured.Finally,the proton phase space,Courant–Snyder parameters,and intensities of surface muons of different beam fractions were given with magnetic fields of 0 and 5T.The solenoid capture system can focus proton and surface muon beams and collect p?and l?particles.It can also provide an intense energetic positron source.     

Measurements of neutron emission induced by muons stopped in metal deuteride targets

An 80-MeV/c negative muon beam from the Alternating Gradient Synchrotron at Brookhaven National Laboratory was used to investigate the stopping of muons inside Pd, Ti, and Y targets saturated with deuterium. Neutron emission from the targets was measured with an array of³He detectors, and in some runs, the temperature of the target was monitored as a function of time, with and without a flux of muons on the target. The neutron rates were also measured for Pd cathodes in an active electrochemical cell similar in design to those used in so-called “cold fusion” experiments, and the electrolyte solution was analyzed for excess tritium. No evidence was found for muon-catalyzed fusion at rates consistent with those claimed in “cold fusion” experiments. Neutron production from catalyzed fusion due to the presence of deuterium in palladium deuteride, PdD_0.7, exposed to muons was determined to be 0.0±0.03 (stat.) ±0.25 (syst.) neutrons per stopped muon.     

Geant4 simulation of production and interaction of muons

A set of models for Monte Carlo simulation of production and interaction of high energy muons is developed in the framework of the Geant4 toolkit. It describes the following physics processes: ionization of high energy muons with radiative corrections, bremsstrahlung, electron-positron pair production, muon induced nuclear reactions, gamma annihilation into muon pair, positron annihilation into muon pair, and into pion pair. These processes are essential for the LHC experiments, for the understanding of the background in underground detectors, for the simulation of effects related with high-energy muons in cosmic ray experiments and for the estimation of backgrounds in future colliders. The applicability area of the models extends to 1 PeV. The major use-cases are discussed.     

Improvement of photonuclear reaction model below 140 MeV in the PHITS code

The photonuclear reaction model in the particle and heavy ion transport code system (PHITS) code is improved for incident photon energies below 140 MeV. Japanese Evaluated Nuclear Data Library (JENDL) Photonuclear Data File 2004 (JENDL/PD-2004) is adopted to determine the total reaction cross section. The statistical decay model after excitation of the nucleus in PHITS is improved by modifying the decay widths for light nuclei under the isospin selection rule to reasonably reproduce the proton and neutron emission in the de-excitation process. The quasideuteron disintegration process is newly introduced into PHITS to handle the photonuclear reaction up to 140 MeV of incident photon energy. The accuracy of the improvements was verified by comparison with the experimental literature data. The improved PHITS can contribute to various practical applications such as neutron dose estimation in X-ray therapy.     

不同测量条件下μ子源项特征模拟

采用CRY宇宙射线模拟软件包,获取不同测量条件下μ子的特征信息,研究不同条件下宇宙射线中μ子的通量、能谱、角分布等特征规律。研究结果表明:太阳活动极大时会使μ子通量降低;地磁场的影响使得赤道附近的μ子通量比极地地区要小且能谱蓝移;海拔升高则会显著增大μ子通量,但总体能量均值降低。模拟结果与相关实验结果具有很好的一致性。     

Some thoughts on the production of muons for fusion catalysis

For muon-catalyzed fusion to be of practical interest, a very efficient means of producing muons must be found. We describe here some schemes for producing muons that may be more energy efficient than any heretofore proposed. There are, in particular, some potential advantages of creating muons from collisions of high-energy tritons confined in a magnetic mirror configuration. If one could catalyze 200 fusions per muon and employ a uranium blanket that would multiply the neutron energy by a factor of ten, one might produce electricity with an overall plant efficiency (ratio of electric energy produced to nuclear energy released) approaching 30%.     

宇宙线缪子散射成像模拟与算法研究

本文验证了基于Micromegas探测器的宇宙线缪子散射成像系统进行快速核材料检测的可行性,并对实验室宇宙线缪子成像系统原型进行参数估算。基于Geant4程序开发了用于模拟宇宙线缪子物理过程、传输径迹及Micromegas探测器响应的模拟程序。在模拟数据的基础上,实现并改进了两种主要的宇宙线缪子散射成像算法。根据模拟和成像结果,1 m×1 m成像系统可在10 min内检测到被重元素屏蔽的核材料。10 cm×10 cm成像系统的缪子事例触发率为0.16 s^-1,要获得较为清晰的成像结果,要求探测器位置分辨率达到300 μm,探测器增益为1 000时实际测量事例至少需要20 h。     

A segmented conical electric lens for optimization of the beam spot of the low-energy muon facility at PSI: a Geant4 simulation analysis

The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures, and near-surface regions. The low-energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential. In LE-μSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies(0.5–30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.     

A segmented conical electric lens for optimization of the beam spot of the low-energy muon facility at PSI: a Geant4 simulation analysis

The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the keV range to carry out muon spin rotation (LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures,and near-surface regions.The low-energy muon beam is focused and transported to the sample by electrostatic lenses.In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction,a special electrostatic device has been implemented close to the sample position.It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential.In LEμSR experiments,an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies (0.5-30 keV).Additionally,a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments.The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations.Some experimental tests were also performed and show that the simulation well describes the experimental setup.     

Features of Particle and Heavy Ion Transport code System (PHITS) version 3.02

We have upgraded many features of the Particle and Heavy Ion Transport code System (PHITS) and released the new version as PHITS3.02. The accuracy and the applicable energy ranges of the code were greatly improved and extended, respectively, owing to the revisions to the nuclear reaction models and the incorporation of new atomic interaction models. Both condense history and track-structure methods were implemented to handle the electron and positron transport, although the latter is reliable only for simulations in liquid water. In addition, several user-supportive functions were developed, such as new tallies to efficiently obtain statistically better results, radioisotope source-generation function, and software tools useful for applying PHITS to medical physics. Owing to the continuous improvement and promotion of the code, the number of registered users has exceeded 3,000, and it is being used in diverse areas of study, including accelerator design, radiation shielding and protection, medical physics, and cosmic-ray research. In this paper, we summarize the basic features of PHITS3.02, especially those of the physics models and the functions implemented after the release of PHITS2.52 in 2013.     

Benchmark study of the recent version of the PHITS code

We performed a benchmark study for 58 cases (22 cases reported in this paper and 36 cases reported in online as supplementary materials of this paper) using the recent version (version 2.88) of the Particle and Heavy-Ion Transport code System (PHITS) in the following fields: (1) particle production cross-sections for nuclear reactions from 20 MeV to 1 GeV, (2) thick-target neutron yields and neutron shielding, (3) depth–dose distribution in water using ¹²C beam, and (4) electron and photon transportation over a wide-energy range from keV to GeV. Overall agreements were found to be sufficiently satisfactory; however, several discrepancies are observed, particularly in particle productions with energies below 100 MeV, neutron production for ⁷Li(p,n)⁷Be, and photonuclear reactions. To overcome these inaccuracies and to further improve the code, it will be necessary to incorporate a high-energy version of the evaluated nuclear data library JENDL-4.0/HE and the photonuclear data file JENDL-PD in the PHITS package.     

A data-based photonuclear simulation algorithm for determining specific activity of medical radioisotopes

For simulating more accurately neutron or proton production from photonuclear reactions,a data-based photonuclear reaction simulation algorithm has been developed.Reliable photonuclear cross sections from evaluated or experimental database are chosen as input data.For checking the validity of the use of the data-based photonuclear algorithm,benchmarking simulations are presented in detail.We calculate photonuclear cross sections or reaction yield for ~9Be,~(48)Ti,~(133)Cs,and ~(197)Au and compare them with experimental data in the region of incident photon energy below ~30 MeV.While Geant4 can hardly reproduce photonuclear experimental data,results obtained from the data-based photonuclear algorithm are found in good agreement with experimental measurements.Potential application in estimation of specific activity of radioisotopes is further discussed.We conclude that the developed data-based photonuclear algorithm is suitable for an accurate prediction of photoninduced neutron or proton productions.     

Design principles for efficient muon production in muon-catalyzed fusion reactors

The two major schemes for a fixed-target muon production system in muon-catalyzed fusion reactors are analyzed and compared using Monte Carlo simulation techniques. Starting with a careful optimization of the pion production target we next consider the complete system where pion conversion losses and muon losses in the target and the pressure vessel are taken into account. A simple but realistic design for the pion-muon converter is introduced. Problems and inefficiencies are identified to provide a basis for future inventions.     

142~146,148,150Nd光核反应理论计算

基于我国自主研制的核反应理论计算程序MEND G,针对200 MeV能量范围内光子诱发142~146,148,150Nd的核反应数据开展了系统的理论计算研究。首先分析了现有的多种光核反应测量数据,筛选出以实验数据作为理论计算依据;利用8种经典的光子强度函数模型和准氘模型,描述光子吸收截面;在此基础上,采用MEND G程序对142~146,148,150Nd开展光核反应理论计算,并通过优化6个Gilbert Cameron能级密度参数,得到适用于Nd天然稳定同位素的普适能级密度,同时针对142,143Nd得到与实验结果符合更好的定域能级密度参数。通过对分光中子出射截面的系统分析,建立了ENDF 6格式的光核反应数据。结果表明,推荐的光核数据合理,与实验测量数据一致性较好,该数据已收录在CENDL 32光核子库中。     

Differential cross sections on fragment (2 ≤ Z ≤ 9) production for carbon,aluminum and silicon induced by tens-of-MeV protons

The double-differential cross sections (DDXs) for the inclusive reactions producing heavy nuclei with Z = 2–9 (fragments) from carbon, aluminum, and silicon targets induced by 50 and 70 MeV protons are systematically measured at several angles (30°, 60°, 90°, and 135°) using a specially developed Bragg curve counter and the energy-time-of-flight method. The DDXs of a silicon target for the proton-induced reaction producing fragments heavier than lithium were measured for the first time. The present results are compared with past experimental data, the LA150 evaluated data by the Los Alamos group and several intranuclear cascade models (Bertini and ISOBAR), and the JAEA-version quantum molecular dynamics model (JQMD) coupled with the Generalized Evaporation Model (GEM), which are implemented in the Particle and Heavy Ion Transport code System (PHITS). The present results agree well with the past experimental data and LA150 data for α -particle production. For the fragments heavier than lithium, the present results show forward-peak angular distributions rather than isotropic ones stored in LA150. Calculations with the ISOBAR and GEM models well reproduced our experimental results except for light fragments especially in the high-energy region.     

缪子科学技术前沿及未来发展

缪子物理和缪子应用技术研究是涉及粒子物理、材料科学、凝聚态物理、生物分子、考古学等众多学科的国际前沿交叉研究领域。目前北美、欧洲及日本均在这一领域做出了众多重要成果。由于加速器条件限制,目前国内尚未系统开展加速器缪子方面的实验,相关领域的研究团队主要依托国外装置或参与国际合作开展研究。本文综述性报道了近年国际上开展的几项主要缪子物理科学研究与缪子应用技术进展,并展望了国内在缪子源设计、建设及应用方面的科学前景。     

Feasibility of the hardware muon trigger track finder processor inCMS

This paper describes a feasibility study for the design of the muon trigger track finder processor in the high-energy physics experiment compact muon solenoid (CMS), planned for 2005, at CERN. It covers the specification, proposed method, and a prototype implementation. Comparison between several other measurement methods and the proposed one are carried out. The task of the processor is to identify muons and measure their transverse momenta and locations within 350 ns. It uses data from almost 200000 detector cells of drift tube muon chambers. The processor searches for muon tracks originating from the Interaction point by joining the track segments provided by the drift tube muon chamber electronics to full tracks. It assigns transverse momentum to each reconstructed track using the track's bend angle     

Proton-induced activation cross section measurement for aluminum with proton energy range from 0.4 to 3 GeV at J-PARC

We have started an experimental program to measure activation cross sections systematically in the proton-induced spallation reaction in structural materials commonly used in high-intensity proton accelerator-based facilities, such as Japan Proton Accelerator Research Complex (J-PARC). As the first step of the program, aluminum (Al) was chosen to verify the adequacy of the measurement technique implemented in a J-PARC proton beam environment because data of Al have been relatively well studied both by experimental measurement and simulation. Activation cross sections of ⁷Be, ²²Na, and ²⁴Na in Al were measured at proton energy points from 0.4, 1.3, 2.2 to 3.0 GeV, which could be delivered smoothly from the synchrotron. The validity of experimental data has been verified by introducing an effective proton numbers determination procedure. We compared the measured data with existing experimental data, the evaluated data (JENDL-HE/2007), and the calculations with several intra-nuclear cascade models by the Particle and Heavy Ion Transport code System (PHITS) code. Although the experimental data agreed with JENDL-HE/2007, the calculations underestimated about 40%. This could come from the evaporation model (generalized evaporation model) being implemented in the PHITS code. We found that the calculations agreed with the experimental data by an upgraded PHITS code.     

Research Status and Prospect of Muon Physics and Technique

Muon physics and the application of muon technique is an interdisciplinary research which involves particle physics, material science, condensed matter physics, biomolecular science, and archaeology. Many important researches have been done and published in these areas by scientists from North America, Europe, and Japan. Due to the lack of accelerator-based muon source in China, Chinese research groups in these fields mainly rely on overseas muon facilities or on joining international collaborations. Some recent major progress on muon physics and muon technique application, and the prospects of the design, construction, and application of the accelerator-based muon source in China were reported in this paper.     

See inside: The development of a cosmic ray muon imaging system to aid the clean up of the UK’s nuclear waste legacy

In recent years the use of non-intrusive and non-invasive imaging techniques to safely interrogate non-nuclear (industrial) storage vessels or process units has seen a significant increase. The nature of material found within active ‘legacy waste’ storage vessels and other radiation shielded vessels coupled with the distinct lack of access makes representative sampling or visual inspection of the vessel extremely problematic and in some cases impossible. However, until recently, the radiation shielding which is commonplace on all nuclear sites has rendered existing remote non-intrusive imaging techniques useless. This is due to the limiting penetrative power of X-rays and gamma-rays as well as lack of access for other semi-invasive techniques such as electrical and acoustic imaging. Cosmic ray muon based imaging systems have great potential. This is because muons have very high energies (up to 10¹² GeV) and therefore, offer a superior penetrative power which provides a means to ‘peer through’ objects which otherwise would be inaccessible. Such objects may include lead lined silo or vessels as well as various intermediate material transport modules. Because muons only show detectable interactions with high atomic number material they also offer a means to detect the quantity and location of heavy metal elements and their associated compounds. In this work the first attempts at two-dimensional muon attenuation mapping are described. More specifically multiple plane prototype muon detection system has been used to image the resultant attenuation maps for a number of lead phantoms. This opens up possibilities for the collation of muon trajectory data which in turn can be used to track muon events both entering and leaving the object of interest allowing attenuation based image processing. It is believed that future work in this area will serve to significantly improve both the coverage area and the spatial resolution of the system though improved detector technology providing a powerful tool for the rendering of either large or dense objects.