Feasibility study of a strong ultra cold neutron source

The heat that would be produced in a superthermal ultra-cold neutron source proposed by Golub and Pendlebury is evaluated when it is placed in a cold neutron field. The source strength achievable in the present technology is also discussed.Paper based on the KEK Internal Report 83-7 (Dee), p 223, and 84-2 (Dec), p 139, by H.Y. and M.U.     

Analysis of lithium and hydrogen movement in functional solid materials by neutron radiography

The principle and availability of Neutron Radiography are demonstrated. The technique is actually applied to obtain the images as to lithium in the oxide lithium ion conductors and/or hydrogen in the hydrogen storage alloys. From analysis of the lithium or hydrogen distribution, the ionic transport number and the diffusion coefficient can be calculated and the hydrogenation process is discussed. In the case imaging the special cross-section in the sample, Neutron Computed Tomography is more favorable. Here, it will be demonstrated using our actual experimental results that the NCT technique is also useful in the field of Solid State Ionics to clarify the ion distribution and movement. Paper presented at the Patras Conference on Solid State Ionics, Patras, Greece, Sept. 14–18, 2004.     

Measurement of the ultra cold neutron production rate in an external liquid helium source

Ultra Cold Neutrons have been produced by down scattering of cold neutrons $\text{(λ = 10}\text{A}\text{?}\text{)}$ on liquid helium. The measured production rate is in agreement with the calculated value.     

New installation for measuring a neutron lifetime with a big gravitational trap of ultra cold neutrons

At present the highest precision of neutron lifetime measurements has been achieved by the experiment made in Petersburg Nuclear Physics Institute (PNPI) with a gravitational trap of ultracold neutrons (UCN). A new installation with a big gravitational trap is an advanced development of methods and approaches applied in the previous experiment. We are planning to attain the measurement precision of 0.2 s which is four times better than the existing level of precision. A model of the experiemnt has been made for simulation by the Monte Carlo method. This model allows one to imply the concrete value of the neutron lifetime, then to reproduce an experiemental procedure and to see if there is any difference between the implied value and the measured one. As a result of modelling one has determined systematic uncertainty related to the procedure of calculating the efficient frequency of collisions of UCNs. It is equal to 0.1 s. We have also carried on modeling of different construction units of the installation.     

超快中子探测器闪烁体性能计算

超快中子探测器是ICF聚变反应速率测量系统的核心部件。利用蒙特卡罗粒子输运工具包Geant4模拟了一种超快中子探测器——BC-422型闪烁探测器的中子探测过程,计算出了几种厚度的BC-422型闪烁体的探测效率、输出光信号强度和时间分辨力;对比了闪烁体的2种不同反射表面对输出光信号强度和时间分辨力的影响。计算的结果显示：设计适当的BC 422型闪烁探测器能够测量的最低中子产额在108量级,对DT中子的信号时间分辨力好于20 ps,对DD中子的信号时间分辨力达到30 ps,能够用于大型激光装置及其原型的聚变反应速率测量。     

中子散射在磁性材料研究中的应用

中子具有天然磁矩,穿透能力强且对轻元素敏感等独特的优势,是目前研究材料中磁结构最有力的工具。发展中子散射技术对开发新型磁性材料和研究磁性物理机理等方面具有重大意义。文章介绍了几种常用的中子散射技术(如粉末衍射、小角散射、反射等),并通过典型的实例来说明它们在磁性材料研究中的具体应用。针对国内介绍中子反射技术的资料相对较少,尤其是极化中子反射技术在精确定量表征薄膜磁性大小和分布方面的研究极度匮乏的现状,文章重点介绍了这一特色技术以及应用实例。     

基于冷中子谱的紧凑型中子自旋倒相器设计

为节省极化中子散射谱仪传输光路的空间,实现特定冷中子谱的极化中子高效率自旋翻转,使用在空间上自然衰减的前端多层膜极化器静磁场作为中子自旋倒相器的导向磁场,在空间上形成了紧凑型冷中子自旋倒相器设计模型。介绍了实际模型物理参数的计算方法。对前端极化器静磁场在空间上的自然衰减进行了实验测试,根据测试结果及拟使用冷中子波段,针对设计的紧凑型中子自旋倒相器的相关参数进行了优化计算。模拟了极化中子在实际复合磁场中的自旋翻转图像,计算了自旋倒相器的翻转效率。对设计的紧凑型中子自旋倒相器进行了翻转效率物理实验测试,测试结果表明：设计的中子自旋倒相器翻转效率可在99.2%以上,达到了预期设计指标,可用于极化冷中子散射谱仪。     

Study of hydrogen chemisorbed on Raney-nickel by neutron inelastic spectroscopy

The motion of chemisorbed hydrogen on the Raney-nickel surface was studied by neutron inelastic spectroscopy. The peaks found at low energy transfers (below 320 cm^?1) are nearly identical to the spectrum of lattice frequencies of pure nickel. This means that each hydrogen atom is bound to only one nickel atom. The mean square amplitude of the bound proton was found to exceed that of nickel by 0.04 ± 0.02 Ų. A broad band found at 1120 cm^?1 (800 cm^?1 in the case of deuterium) is attributed to motions of hydrogen atoms relative to the nickel surface. An interpretation of this band is given in terms of harmonic approximation. An analysis of the shape of the elastic line has shown that no broadening could be detected with our instrument. This leads to an upper limit for the diffusion constant of the protons, D<5×10^?7 cm²/s, at room temperature.     

A study of cold cathodes for the plasma sources of hydrogen ion beams

Two types of cold cathodes (the hollow and magnetron) of a duoplasmatron used for the production of proton beams are comparatively studied.     

The study of mobile adsorption by cold neutron scattering

The scattering of 4.14 Å neutrons by methane adsorbed at room temperature on indicates that the migration on the surface should be described by a diffusive model. The absence of an inelastic peak specific for vibrations perpendicular to the surface is commented on.     

液氢容器复温周期确定方法研究

液氢容器在频繁加转注的移动罐中很容易积累固空,因此需要经常复温,清除其内部累积的杂质,防止容器被严重污染。通过对某液氢容器在转注过程中氧氮含量的测量,研究液氢容器氧氮杂质积累规律,得出了固氧、固氮累积量的计算公式。对该容器在现行复温周期下的合理性进行了核算,将正常使用情况下到复温周期时液氢容器内的氧氮含量与安全值进行了比较。给出了一定的使用时间、加转注频次下的液氢容器复温周期计算方法,初步建立了一套液氢容器复温周期确定方法。     

Effect of AlN coating on hydrogen permeability and surface structure of VT6 alloy by vacuum arc ion plating

We study the absorption of hydrogen of metal by the permeability method. With the help of the gas reaction controller(GRC), the absorptive capacity of hydrogen, which is a function of time, temperature and pressure, can be recorded. The effect of the performance of the hydrogen permeability of AlN coating on the titanium alloy surface structure is studied.In the research, the AlN is selected to be added to the titanium alloy sample VT6, and the properties of the titanium alloy are investigated, and the hydrogen absorption rate of the coating is calculated by performing the hydrogen saturation of the test sample. The results show that under 600℃ the AlN film reduces the hydrogen absorption rate of titanium alloy and improves the surface properties of VT6 alloy.     

Interphase microstress measurements in IN 718 by cold neutron diffraction

The linear energy–momentum relation results in more high-energy electrons in 2D (two-dimensional) graphene FETs (field-effect transistor) than those in silicon FETs that features parabolic energy–momentum relation if the same surface electron density has been assumed in all FETs. The numerical calculations demonstrate that, under such assumption, the gate leakage currents in graphene FETs are much larger than that in silicon FETs. The results illustrate that if the conduction band offset between graphene and gate oxide is lower than 3.55 eV, the gate leakage currents in graphene electronics are more significant than those in the silicon electronics.     

Molecular motions in liquid ethane studied by cold neutron scattering

In a previous work we report a comparative study of the molecular motions in gaseous and liquid methane and argon. In the present work we present the results of a study of the molecular motions in liquid ethane at three widely different temperatures. The aim is to study the rotational-translational motions of the rigid molecule. The unknown scattering from the librational and other motions of the CH₃ group is experimentally determined from a high-temperature run by a procedure of isolation of this scattering by use of successive approximations in which also the corrections for multiple scattering are involved.It is found that the translational motions are very nearly described by a cross section based on simple Langevin diffusion. The effects of encaging in ethane well below the critical point seem to influence the cross section only rather modestly. The scaling of the “encaging part” of the translational motion from liquid argon to ethane by use of the law of corresponding states is not successful. The rotational motions are equally well described by the Langevin rotational-diffusion model or by the step model. It is observed that certain degrees of rotational freedom tend to be frozen when the freezing point is approached.     

Phonon- and libron-excitation with ortho-para conversions by neutron scattering on solid hydrogen

The cross section for incoherent neutron scattering on solid ortho hydrogen in the ordered phase is investigated for processes where ortho-para conversions take place in combination with the excitation of phonons and librons. The phonon part of the cross section is calculated and compared with the experimental results of Stein, Stiller and Stockmeyer [2]. The coupling of the librons to the ortho-para conversion is discussed. We show that librons give a contribution to the cross section in the vicinity of both the ortho → para and the para → ortho conversion line.     

Secondary ion mass spectrometry for quantitative surface and in-depth analysis of materials

Secondary ion mass spectrometry (SIMS) is a technique based on the sputtering of material surfaces under primary ion bombardment. A fraction of the sputtered ions which largely originate from the top one or two atomic layers of the solid is extracted and passed into a mass spectrometer where they are separated according to their mass-to-charge ratios and subsequently detected. Because the sputter-yields of the individual species, coupled with their ionization probabilities, can be quite high and the mass spectrometers can be built with high efficiencies, the SIMS technique can provide an extremely high degree of surface sensitivity. Using a particular mode like static SIMS where a primary ion current is as low as 10^?11 amp, the erosion rate of the surface can be kept as low as 1 Å per hour and one can obtain the chemical information of the uppermost atomic layer of the target. The other mode like dynamic SIMS where the primary ion current is much higher can be employed for depth profiling of any chemical species within the target matrix, providing a very sensitive tool (～ 1 ppm down to ppb) for quantitative characterization of surfaces, thin films, superlattices, etc. The presence of molecular ions amongst the sputtered species makes this method particularly valuable in the study of molecular surfaces and molecular adsorbates. The range of peak-intensities in a typical SIMS spectrum spans about seven to eight orders of magnitude, showing its enormously high dynamic range; an advantage in addition to high sensitivity and high depth-resolution. Furthermore, the high sensitivity of SIMS to a very small amount of material implies that this technique is adaptable to microscopy, offering its imaging possibilities. By using this possibility in static SIMS or dynamic SIMS mode of analysis, one can obtain a two-dimensional (2D) surface mapping or a three-dimensional (3D) reconstruction of the elemental distribution, respectively within the target matrix. Secondary ion yields for elements can differ from matrix to matrix. These sensitivity variations pose serious limitations in quantifying SIMS data. Various methods like calibration curve approach, implantation standard method, use of relative sensitivity factor, etc. are presently employed for making quantitative SIMS analysis. The formation of secondary ions by ion bombardment of solids is relatively a complex process and theoretical research in this direction continues in understanding this process in general. The present paper briefly reviews the perspective of this subject in the field of materials analysis.     

Compatibility of organic latent heat storage materials and plastic container materials

Plastic container materials are evaluated for use in macroencapsulation of latent heat storage materials, with special emphasis on fatty acids. Different platics have been tested. With the most promising container material and a mixture of two fatty acids a laboratory model of a storage unit was built; first results of the experiments are presented.