Experimental determination of the neutron channeling length in a planar waveguide

In neutron waveguides, the neutron wave is confined inside the guiding layer of the structure and can escape from the layer edge as a microbeam. The channeling within the guiding layer is accompanied by an exponential decay of the neutron wave function density inside the waveguide. Here, we report direct determination of the corresponding decay constant, termed the neutron channeling length. For this, we measured the microbeam intensity as a function of the length of a neutron absorbing layer of variable length placed onto the surface of a waveguide structure. Such planar neutron waveguides transform a conventional neutron beam into an extremely narrow but slightly divergent microbeam, which can be used for the investigation of nanostructures with submicron spatial resolution.     

单离子微束离子入射点定位

 为满足辐射实验的定位精确度要求,提出了一种对微束离子入射点进行捕捉和定位的方案。该方案根据离子束流轰击闪烁体能激发出光信号的特性,结合单离子微束装置的显微图像采集系统,通过对离子激发出的光斑进行图像采集分析实现了对离子入射点的定位。验证实验通过一种CR39膜记录离子辐射径迹, 采用的毛细玻璃管瞄准器内径为5 μm,长度为980 μm。实验得出了运用该方案进行入射点定位时装置的整体定位精度。     

Design of the IMP microbeam irradiation system for 100 MeV/u heavy ions

A state-of-the-art high energy heavy ion microbeam irradiation system is constructed at the Institute of Modern Physics of the Chinese Academy of Sciences. This microbeam system operates in both full current intensity mode and single ion mode. It delivers a predefined number of ions to pre-selected targets for research in biology and material science. The characteristic of this microbeam system is high energy and vertical irradiation. A quadrupole focusing system, in combination with a series of slits, has been designed to optimize the spatial resolution. A symmetrically achromatic system leads the beam downwards and serves simulta-neously as an energy analyzer. A high gradient quadrupole triplet finally focuses a C6+ ion beam to 1 μm in the vacuum chamber within the energy range from 10 MeV/u to 100 MeV/u. In this paper, the IMP microbeam system is described in detail. A systematic investigation of the ion beam optics of this microbeam system is presented together with the associated aberrations. Comparison is made between the IMP microbeam system and the other existing systems to further discuss the performance of this microbeam. Then the optimized initial beam parameters are given for high resolution and high hitting efficiency. At last, the experiment platform is briefly introduced.     

Application of a cryogenic moderator in the REMUR neutron reflectometer

Examples of the application of a cryogenic moderator in the REMUR time-of-flight neutron reflectometer of the IBR-2 pulsed reactor (Dubna) are given. The results of two experiments are presented: spatial beam splitting upon reflection from a magnetically noncollinear film and the recording of a microbeam formed by a layered waveguide. A conclusion concerning the efficiency of the cryogenic moderator for experiments of this type is made.     

Neutron diffraction analysis of a compositionally modulated alloy of nickel-copper

A compositionally modulated Ni_0.4Cu_0.6 alloy, made in a thin film of 1.8 μm thickness, was examined by polarized neutron diffraction. The results show that the material is ferromagnetic, with a large enhancement of the magnetic moment (0.3μ_B/Ni) with respect to a disordered alloy. The behaviour of the magnetic moments gives strong evidence of chemical clustering.     

毛细管准直微束过程模拟与微束品质分析

利用GEANT4程序对复旦大学单粒子微束的毛细管准直过程进行了蒙特卡罗模拟。计算结果表明:当前采用的1 m孔径、1 mm长度的毛细玻璃管准直器能够引出峰值能量2.2 MeV、能量分辨130 keV、束径2.4 m的质子微束,可达到装置对微束能量与束径分辨的设计指标,从理论上明确了毛细管准直微束引出的可行性。针对影响入射目标细胞微束品质的主要因素,分析了微束品质与准直系统和入射束流各状态参数的依赖关系,为毛细管准直微束的引出与优化提供了必要的理论依据。     

Neutron storage in a magnetic field

The motion of neutrons in magnetic traps is considered for various cases of neutron polarization. The results of implementing such traps in practice and special features of experiments studying magnetic neutron storage are discussed. The problem of neutron losses during injection via magnetic valves can be solved by conjoining a magnetic trap with a converter of cold neutrons into ultracold ones or with a source of ultracold neutrons. Prospects for expanding neutron-storage experiments by invoking a correlation analysis of neutron decay and by using the transport properties of charged particles in a nonuniform magnetic field are analyzed. In such an investigation, the recording of the storage time of neutrons proper can be supplemented with the detection of decay protons and electrons and with a parallel measurement of the asymmetries of proton and electron emission with respect to the magnetic field. A set of relative measurements permits improving the accuracy of an experimental determination of the neutron lifetime and combining this determination with the determination of correlation coefficients. On this basis, it is possible to find directly the ratio of the weak-interaction constants and the constants themselves. The application of the most advanced reactor and accelerator technologies to subcritical electric nuclear devices optimized for generating cold and ultracold neutrons, along with the use of solid deuterium and superfluid helium, creates preconditions for developing a neutron plant and for launching neutron studies at accelerators. Thus, the work that has been done as a development of V.V. Vladimirsky's proposals on magnetic neutron storage is analyzed, and the potential of a further use of ultracold neutrons and magnetic devices for deploying a full-scale precision experiment to study the beta decay of polarized neutrons is demonstrated.     

Neutron resonances in planar waveguides

We report on the results of the experimental investigation of the spectral width of neutron resonances in planar waveguides using the time-of-flight method and recording the microbeam emerging from the waveguide end. Experimental data are compared with the results of theoretical calculations.     

Dynamics and instability of current-carrying microbeams in a longitudinal magnetic field

The dynamics and instability of current-carrying slender microbeams immersed in a longitudinal magnetic field is investigated by considering the material length scale effect of the microbeam. On the basis of modified couple stress theory, a theoretical model considering the effect of Lorentz forces is developed to analyze the free vibration and possible instability of the microbeam. Using the differential quadrature method, the governing equations of motion are solved and the lowest three natural frequencies are determined. The obtained results reveal that the electric current and the longitudinal magnetic field tend to reduce the microbeam's flexural stiffness. It is therefore shown that the lowest natural frequencies would decrease with increasing magnetic field parameter. The mode shapes of the microbeam are found to be generally three-dimensional spatial in the presence of the longitudinal magnetic field. It is interesting that buckling instability would concurrently occur in the first mode or in the higher-order modes when the magnetic field parameter becomes sufficiently large.     

Fabrication of LIGA masks for microfluidic analytical systems

Preliminary results of fabrication and testing of LIGA mask samples for deep x-ray lithography in the spectral range of 3.5–13.5 keV are presented. The mask fabrication method is based on direct mask patterning with minimum element sizes of ≥ 10 μm by a synchrotron radiation x-ray microbeam. Such a method does not require an intermediate mask, which significantly simplifies fabrication and reduces the laboriousness and cost of LIGA masks.     

Construction of a positron microbeam in JAEA

We have developed a positron microbeam using magnetic lenses based on the commercial scanning electron microscope (SEM). A slow positron beam was generated using a handmade source with ²²Na and a solid neon moderator. The beam diameter was 3.9 μm on a target. Two-dimensional image of S parameter was successfully obtained. By introducing a beam pulsing section, positron lifetime measurement beam is also available.     

新型热中子敏感微通道板探测效率的蒙特-卡罗模拟研究

基于microchannel plates (MCP)的中子探测技术近年来发展迅速, 因其具有较高的空间分辨率和中子探测效率以及优异的时间分辨能力, 可用于高分辨率中子照相和能量选择中子成像. 本文利用蒙特-卡罗(MC)程序, 对栅格为15 μm的热中子敏感MCP板进行MC模拟计算, 获得了不同几何结构和材料组成情况下, 掺杂型和镀膜型热中子敏感MCP板的探测效率. 计算结果表明, 增加中子敏感材料的比例可以获得更高的中子阻挡效率, 但同时也加大了次级粒子发射进入MCP板通道的难度, 掺杂型MCP 板的通道直径和镀膜型MCP板的镀膜厚度均存在最优值. MCP板厚度为0.4 mm时, 对¹⁰B₂O₃材料, 掺杂型MCP板的热中子探测效率可以超过40%, 镀膜型MCP板的热中子探测效率可以接近60%.     

Magnetic and magnetocaloric properties of the high-temperature modification of TbTiGe

The high-temperature form (HT) of the ternary germanide TbTiGe was prepared by melting. The investigation of HT-TbTiGe by x-ray and neutron powder diffractions shows that the compound crystallizes in the tetragonal CeScSi-type structure (space group I4/mmm; a?=?404.84(5) and c?=?1530.10(9)?pm as unit cell parameters). Magnetization and specific heat measurements as well as neutron powder diffraction performed on HT-TbTiGe reveal a ferromagnet having T(C)?=?300(1)?K as the Curie temperature; the Tb-moments are aligned along the c-axis. This magnetic ordering is associated with a modest magnetocaloric effect around room temperature. The isothermal magnetic entropy change ΔS(m) was determined from the magnetization data; ΔS(m) reaches, respectively, a maximum value of -?4.3 and -?2.0?J?K(-1)?kg(-1) for a magnetic field change of 5 and 2?T.     

Asymmetry of neutrino emission from neutron beta decay in superdense matter and a strong magnetic field

The probability of neutron beta decay in the presence of degenerate magnetized matter consisting of electrons, protons, and neutrons is calculated by using exact solutions to the Dirac equation for charged particles in a uniform magnetic field. The asymmetry of the angular distribution of the momentum carried away by product antineutrinos is studied with allowance for the effect of a strong magnetic field. The values of basic parameters (magnetic-field strength, matter density, and matter temperature) that affect the reaction being considered are chosen in such a way as to render this investigation applicable to an analysis of the cooling of a neutron star.     

Specific features of the reflection of infrared radiation by crystalline dielectrics in a magnetic field

Magnetic-field-induced variations in the reflection spectra R(λ) of the crystalline dielectrics Al₂O₃, LiF, and MgO in the infrared band (λ = 2.5–25 μm) are investigated. It is found that the reflection spectra exhibit specific features in the neighborhood of wavelengths corresponding to the excitation of optical phonon modes in the above-mentioned crystals and that a magnetic field causes an appreciable variation in the reflectivity at these wavelengths. To qualitatively describe the effect of a magnetic field on the reflection of light, the magnetoreflection spectra ΔR/R are investigated. The spectra ΔR/R exhibit sharp peaks in the neighborhood of wavelengths at which the materials under investigation are characterized by minimal reflectivity. The values of ΔR/R for p-polarized infrared radiation in a magnetic field of about 12 kOe amount to about 0.5% for Al₂O₃ at λ ≈ 9.6 μm, 7% for LiF at λ ≈ 11.1 μm, and 0.07% for MgO at λ ≈ 11.7 μm.     

Characterisation of novel magnetic materials using the USANSPOL technique

USANSPOL is a novel ultra-small-angle scattering technique with polarised neutrons for investigation of magnetic materials. It represents a polarised neutron extension to traditional USANS which works with unpolarised neutrons. The high angular resolution of this technique relies on the narrow reflection width of perfect crystal reflections and is employed in a double-crystal diffractometer. Corresponding to the μrad resolution of the set-up, micro-structures of the order of a few tenths of a micrometre up to a few tens of micrometres may be investigated. Neutron polarisation is achieved by insertion of birefringent magnetic prisms between the monochromator crystal and the sample. Rocking the analyser crystal produces a scattering pattern for both neutron spin states in a single measurement but well separated in reciprocal space. By this technique, we have recently studied various amorphous Galfenol soft-magnetic ribbons which were produced by spinning from melt at different manufacturing conditions. USANSPOL allows for a determination of domain sizes of the non-magnetised samples and a study of the growing of magnetically homogeneous regions with increasing externally applied magnetic field. The manufacturing process of the ribbons is reflected in the magnetic micro-structure of the different specimens.     

Efficient extraction of hydrogen ions from high-velocity plasma bunches by a pulsed electric field

The systematized results are presented of an investigation of the process of the efficient extraction of ions, by a pulsed electric field, from the surface of a plasma moving at a velocity of 10⁴ m/sec under the conditions of small accelerating diodes. A mathematical model is analyzed of the propagation of a plasma bunch formed by a laser pulse (E _las<1 J) in a quasicylindrical diode system. The possibilities are considered of increasing the current of the extracted ions by utilizing the phenomenon of magnetic confinement of electrons, and diode systems with a transparent anode. The designs of small acceleration tubes for generating neutron pulses are presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 65–74, April, 1996.     

微束技术在放射生物学中的应用

微束装置可以为生命科学研究提供微米定位、剂量特定的电离辐射,在生物体内的电离辐射靶物质及其敏感度、靶物质的损伤及修复机制研究中具有独特的作用。概述了生物微束装置和实验技术的发展及其在低剂量辐射效应、旁观者效应、信号传导研究中的主要应用;介绍了中国科学院近代物理研究所（IMP）重离子微束装置,该装置可以提供能量7~ 80 MeV/u、传能线密度为30~ 3000 keV/μm的重离子微束,实现了活细胞辐照和在线观察、小鼠定位辐照的实验技术;利用IMP微束装置在重离子诱导旁效应实验、小鼠下丘脑重离子辐照效应和DNA损伤快速修复动态等方面取得了一些实验成果。The microbeam facility can provide micrometer scale localized and predefined ionizing radiation in the life science study, and the microbeam techniques play a unique role in determining the target substances of ionizing radiation, as well as in the study of radiation sensitivity, mechanisms of radiation damage response and repair. This paper summarizes the technical developments of biological microbeam facilities and their applications in the studies of low-dose radiation effect, bystander effect and cellular signaling. This paper also introduces the recent developments at the heavy-ion microbeam facility in the Institute of Modern Physics (IMP), which can provide heavy ion microbeam irradiation with energy of 7~80 MeV/u and LET of 30~3000 keV/μm. The facility can perform radiobiological irradiation and online investigation in living cells and mice, including bystander effect study, sleeping system influence after irradiation to mice hypothalamus and the recruitment dynamics of XRCC1 protein.     

Polarized neutron channeling as a tool for the investigations of weakly magnetic thin films

We present and apply a new method to measure directly weak magnetization in thin films. The polarization of a neutron beam channeling through a thin film structure is measured after exiting the structure edge as a microbeam. We have applied the method to a three-layer thin film structure acting as a planar waveguide for polarized neutrons. The middle guiding layer is a rare earth based ferrimagnetic material TbCo₅ with a low magnetization of about 20 mT. We demonstrate that the channeling method is more sensitive than the specular neutron reflection method.     

Channeling of Neutrons in a Planar Waveguide

The propagation of neutrons in the middle layer of a planar waveguide in the form of a three-layer thin film has been investigated. The microbeam from the end face of the film has been registered. The neutron channeling length has been measured as a function of the thickness of the upper waveguide layer and the resonance order. The experimental data have been compared with theoretical results.