A multi-anode photomultiplier with position sensitivity

We have measured the properties of a specially developed photomultiplier with proximity dynodes and 10 wire anodes. This design allows us to determine the position of emission of the photoelectrons from the cathode with an accuracy of 1.3 mm fwhm. This tube is also extremely fast due to the short transit time and the geometry of its dynodes.     

脉冲磁场传感器的设计与灵敏度修正方法

在武器设计研究中,对客体做闪光照相时需要用到脉冲磁场对某一个或几个用于聚焦打靶的电子束团进行调节。为清楚脉冲磁场的强度,分析时变聚焦的效果,基于法拉第电磁感应定律研制用于测量脉冲磁场的脉冲磁场传感器;同时,在分析传统传感器采用固定比例尺寸绕制的特点基础上,根据被测磁场源幅频特性,设计合理尺寸的单匝线圈作为传感器的探头线圈,克服了传统线圈中热噪声电压和由于匝数较多导致的对二次仪表不良影响,并提出解决单匝线圈在测量时"点"性不好的方法。通过实验数据和理论值的对比,验证了方法的有效性。     

Performance of a photomultiplier tube with transmissive dynodes in a high magnetic field

The performance of a photomultiplier tube with transmissive dynodes was examined. We found that the amplification gain was higher than 10⁴ even in a magnetic field of 7.8 kG. The energy resolution for 662 keV gamma rays from ¹³⁷Cs was 12% fwhm measured using a NaI crystal at 7.8 kG. The time resolution was as good as about 200 ps at 7.8 kG for the light generated by 2 GeV pions when they passed through a 1 cm thick scintillator mounted on the tube.     

Bimetallic cylinder in a pulsed magnetic field

The magnetic field diffusion into a bimetallic cylinder comprising a central rod and the outer shell made of different conducting materials is analytically described. In the case of an external field pulse representing a half-wave B _e = B _msin(πt/T), the cylinder exhibits delamination, which is caused by the shell expansion under the action of a residual magnetic field present in its internal cavity. The pressure of this residual field nonmonotonically depends on the conductivity of the rod.     

Optical response of nematic droplets in a polymer matrix to a strong pulsed magnetic field

A change in the optical transmission of an ordered single-layer ensemble of nematic liquid crystal (NLC) droplets of 4-n-pentyl-4′-cyanobiphenyl (5CB) in a poly(vinyl butyral) (PVB) matrix in response to a magnetic field pulse with an amplitude of H = 9 × 10⁶ A/m was observed. Since the leading pulse front duration (τ_onH = 5 ms) significantly exceeded the theoretically calculated NLC response time (τ_onLC = 0.8 ms), the dynamics of transformations of the NLC director orientation and the optical response were analogous to those in the case of a stationary or slowly varying magnetic field. In contrast, the field decay time (τ_offH = 25 ms) was much shorter than the NLC relaxation time (τ_offLC = 300 ms) and, hence, the trailing front of the optical response was not influenced by the oscillatory character of the magnetic field decay during capacitor discharge via an RL chain.     

Cellular uptake of protein-bound magnetic nanoparticles in pulsed magnetic field

A method for fast delivery of proteins conjugated to superparamagnetic iron oxide nanoparticles (SPION) into mammalian cells by applying a strong magnetic field in pulses was proposed. Firstly, SPION were prepared from an alkaline solution of divalent and trivalent iron ions and covalently bound with protein through the activation of N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC). After fluorescently labelling, the protein-nanoparticle conjugate was mixed with mammalian cell line and exposed to a pulsed magnetic field for short durations of few milliseconds. Results suggested that superparamagnetic nanoparticles were able to carry proteins into living cells immediately. Cellular internalization of the fluorescently labelled protein-nanoparticle conjugate was proved by the observation of cell fluorescence in a fluorescent microscopy, as well as cell analysis by a flow cytometer. We found that the cellular uptake was accomplished dominantly by the process of bombardment of magnetic nanoparticles.     

脉冲磁场作用于钢液熔体的电磁场数值模拟

为了解脉冲磁场的电磁力特性,利用ANSYS软件,脉冲电源波形采用梯形波,对脉冲磁场作用下钢液的电磁场进行了模拟,得到了电磁力周期变化规律,脉冲频率和脉冲波型对脉冲电磁力的影响规律.结果表明:脉冲磁场作用下,电磁力瞬时发生变向,往复振荡熔体;在研究的脉冲放电频率范围内,脉冲放电频率的改变对电磁场、力场的分布影响不大;对于采用的梯形脉冲波形,电磁力随着脉冲上升沿和下降沿宽度的减小而显著增大,而当脉冲宽度增大时,脉冲电磁力呈现减小的趋势.     

Miniaturized magneto-optic sensor for pulsed magnetic field measurements

The design and performance of a miniaturized magneto-optic probe using a terbium doped paramagnetic glass are described. The compactness and simplicity of the device are achieved by using the polarizer sheets obtained from a commonly available liquid crystal display. Plastic optical fibers are used to transport the light. A pulsed magnetic field up to 48 T has been generated and measured using high-voltage capacitor discharge in single-turn coils. A rise time and magnetic field-dependent anomalous behavior is observed in the terbium glass characteristics at room temperature.     

Effect of a pulsed magnetic field on the luminescence of silver chloride single crystals

The phenomenon of a long-term (tens of hours) increase in the intensity of photoluminescence of silver chloride single crystals upon a short-term (tens of seconds) action of a weak (～4 kOe) pulsed magnetic field has been observed for the first time. The observed effect is probably related to the disappearance of vacancy defect complexes present in the initial crystal, which exhibit decomposition via the magnon mechanism under the action of an applied pulsed magnetic field.     

Structure refinement of pure Mg under pulsed magnetic field

Abstract

A pulsed magnetic field (PMF) was introduced into the solidification of pure Mg. Fine uniform equiaxed grains are acquired in the whole ingot from the PMF treatment, in contrast with the coarse columnar grains observed in conventional casting, and the average grain size is refined to 260 μm with a 200 V PMF treatment. Pulsed magnetic field increases melt convection during solidification, and the violent agitation causes warmer liquid to fracture the tip of columnar dendrites or to break off dendrite branches to promote the formation of an equiaxed structure, with the broken pieces transported into the bulk liquid acting as nuclei. In addition, the uniform temperature field resulting from the stirring increases the likelihood of nuclei survival. The Joule heat effect also participates in the structure refinement. The pure Mg produced with a 200 V PMF treatment exhibits improved mechanical properties, such as the ultimate compressive strength (227 MPa) and fracture strain (33·2%).     

Nonequilibrium solidification effects induced by a pulsed magnetic field in ionic crystals

A digital DTA study of the process of solidification in KCl pretreated in a weak pulsed magnetic field (PMF) reveals a latent decrease in the enthalpy of solidification, followed by recovery of the initial state 144 h after the treatment. A sharp drop in the enthalpy of solidification observed 72 h after the PMF treatment gives rise to an additional relaxation process (postsolidification effect) revealed by a long-term fluctuational evolution of dissipated heat. According to the X-ray diffraction data, the PMF action upon KCl induces an intracrystalline transformation manifested by a small decrease in the lattice parameter and a sharp increase in the reflection intensity.     

The effect of a pulsed magnetic field on the nuclear spin echo signal in ferrite

A pulsed magnetic field produces shifts of domain walls in a magnetically ordered material (ferrite) and thus affects the nuclear spin echo signal in this material. The suppression and restoration of a response signal have been observed using exciting sequences with pulses of different polarities. The established dependence of the spin echo suppression coefficient on the external constant magnetic field confirms the hypothesis that the observed phenomena are related to the domain walls.     

Microstructure and mechanical properties of Mg-Al-Zn alloy under a low-voltage pulsed magnetic field

Effect of a low-voltage pulsed magnetic field on the solidified microstructure and mechanical properties of Mg-Al-Zn alloy has been investigated. When the low-voltage pulsed magnetic field is applied during solidification, the as-cast microstructure is significantly refined and α-Mg is modified from developed dendrite to fine rosette. This morphology modification is caused by the accumulation of Joule heat on the dendrite tip. The yield strength is improved with the application of the low-voltage pulsed magnetic field under normal casting and semi-continuous casting conditions. The ultimate tensile strength is decreased slightly under normal casting condition due to the occurrence of plenty of shrinkage under the low-voltage pulsed magnetic field. The shrinkages are removed and the yield strength and ultimate tensile strength are increased under semi-continuous casting condition with low-voltage pulsed magnetic field.     

Effect of pulsed magnetic field on the thermal decomposition of zirconium hydroxide

An applied magnetic field was found to raise the rate and reduce the temperature of the dehydration, dehydroxylation, and crystallization of zirconium hydroxide. The role of water in the crystallization and aggregation of zirconium hydroxide was examined.