共查询到20条相似文献,搜索用时 15 毫秒
1.
Fedorov V. V. Kuznetsov I. A. Lapin E. G. Semenikhin S. Yu. Voronin V. V. 《JETP Letters》2004,80(9):575-579
JETP Letters - A doubled effect of a neutron spin rotation in a noncentrosymmetric quartz crystal for the Bragg reflected neutrons from the deformed exit crystal side is first observed. The effect... 相似文献
2.
A. I. Frank 《Physics of Particles and Nuclei》2016,47(4):647-666
The present review is focused on the problem of interaction of neutron waves with moving matter. The validity of the 1/v law for ultracold neutrons and the possibility to characterize the interaction of neutrons with matter using the effective potential were verified in the so-called null Fizeau experiments. A neutron wave in such experiments propagates through a flat sample that moves parallel to its edges. The observation of effects caused by this motion provides evidence that the concept of constant effective potential is not correct. The second part of the review deals with the prediction and the first observation of the accelerated matter effect (a change in the energy of neutrons in passing through a refractive sample that moves with an acceleration directed along or opposite the direction of neutron propagation). The characteristic features of this phenomenon in the case of birefringent material are considered. In conclusion, the problem of propagation of neutron waves in matter moving with giant acceleration is discussed. 相似文献
3.
A simple additive formula is given which, for neutron energies in the range 10-4 < E<10 eV, permits calculation of the nuclear capture, thermal diffuse and Bragg scattering cross-sections of a crystalline material as a function of its crystal constants and temperature. Computer codes PUO and SUO were developed to calculate the total attenuation of reactor neutrons through poly- and mono-crystalline samples, respectively. The codes were applied to calculate the total cross-section of polycrystalline uranium and thorium dioxides in the energy range from 4 meV to 1 eV. The obtained agreement between the calculated values and available experimental values justifies the applicability of the used formula and the computer codes. A feasibility study on using depleted polycrystalline uranium dioxide as a cold neutron filter and the single crystal as a thermal neutron filter is given. The optimum crystal parameters and thickness for efficiently transmitting the thermal reactor neutrons while strongly attenuating both fast neutrons and -rays accompanying the thermal ones is also given. 相似文献
4.
5.
We have derived analytic expressions for the deflection as well as transmitted fraction of monochromatic neutrons forward
diffracted by a single crystal prism. In the vicinity of a Bragg reflection, the neutron deflection deviates sharply from
that for an amorphous prism, exhibiting three orders of magnitude greater sensitivity to the incidence angle. We have measured
the variation of neutron deflection and transmission across a Bragg reflection, for several single crystal prisms. The results
agree well with theory.
相似文献
6.
V. V. Voronin Yu. V. Borisov A. V. Ivanyuta I. A. Kuznetsov S. Yu. Semenikhin V. V. Fedorov 《JETP Letters》2013,96(10):609-612
The features of the propagation of a neutron through a crystal at nearly Bragg energies has been studied within the framework of the preparation of an experiment on the search for the electric dipole moment of a neutron by the crystal diffraction method. The time of passage of the neutron through the crystal has been studied as a function of the deviation from the Bragg condition. The anomalous behavior of the dispersion of the neutron, i.e., the energy dependence of its average velocity, has been observed. It has been shown that the derivative dv/dE for the diffracting neutron at nearly Bragg energies can be three or four orders of magnitude larger than this derivative for a free neutron. This opens new possibilities in precision neutron spectroscopy. 相似文献
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8.
Apoorva G. Wagh 《Pramana》2008,71(4):797-807
Bragg reflections from single crystals yield angular widths of a few arcsec for thermal neutron beams. The Bonse-Hart proposal to attain a sharp, nearly rectangular profile by Bragg reflecting neutrons multiply from a channel-cut single crystal, was realized in its totality three and a half decades later by achieving the corresponding Darwin reflection curves for 5.23 Å neutrons. This facilitated SUSANS (Super USANS) measurements in the Q ~ 10?5 Å?1 range. The polarized neutron option was introduced into the SUSANS set-up by separating the up- and down-spin neutron beams by ~10 arcsec with a magnetic (air) prism. The neutron angular width has recently been reduced further by an order of magnitude to ~0.6 arcsec by diffracting 5.3 Å neutrons from a judiciously optimized Bragg prism. This constitutes the most parallel monochromatic neutron beam produced to date. I present the first SUSANS spectra probing the Q ~ 10?6 Å?1 domain, recorded with this beam. 相似文献
9.
Extended Bonner Spheres spectrometer was used to measure the angular distribution of neutron spectral fluence around NYLON6 phantom irradiated with pencil beam of 100, 150 and 200 MeV protons at the Proton Therapy Center Praha. Measurements were supplemented by a calculation of neutron spectral fluences at different depths of the phantom. The calculation of neutron spectral fluence at different depth of the phantom demonstrated that the majority of high energy neutrons was generated at the beginning of the proton trajectory in the phantom and the neutron yield decreased with increasing depth, with a minimum at the depth corresponding to the Bragg peak. Therefore, attention should be paid not only to the tissue behind the irradiated volume, but also to the preceding tissue. However, the neutron spectral fluence in the vicinity of the treated tissue can only be determined by calculation, mainly due to the dimensions of the neutron spectroscopic instrumentation. This paper presents a suitable technique and experimental conditions to acquire reliable data necessary for the proper determination of neutron spectral fluence. From the measured spectral fluences, the neutron fluence in whole-range and partial energy intervals were determined together with the corresponding ambient dose equivalents at measurement positions. The obtained results indicate that high energy neutrons predominate at the direction of the proton beam and more neutrons are generated by higher energy protons. 相似文献
10.
Yu. N. Pokotilovski 《JETP Letters》2013,96(12):751-753
The chameleon scalar field is considered as a possible cause of accelerated expansion of the Universe. The chameleon field induces an interaction potential between particle and massive body. Previous experiments with falling cold neutrons intended to measure the neutron coherent scattering lengths and verification of the weak equivalence principle for the neutron are used to constrain the parameters characterizing the strength of the scalar chameleon fields. 相似文献
11.
G. L. Squires 《Contemporary Physics》2013,54(5):411-441
The present article describes some experiments with thermal neutrons to investigate a variety of properties of crystals. Elastic scattering of the neutrons, like Bragg scattering of X-rays, helps to determine the atomic structure of crystals, and is particularly useful for locating light atoms, such as hydrogen, where X-rays fail. It also gives information on the arrangement of electron spins and the density distribution of unpaired electrons in magnetic atoms. Measurement of the change in energy of the neutrons in inelastic scattering gives the frequencies of the normal modes of vibration of the crystal, which are related to the interatomic forces. For magnetic crystals, inelastic scattering also gives the frequencies of spin waves, which depend on the magnetic interactions between the atoms. The article concludes with an account of the experimental techniques of thermal neutron scattering. 相似文献
12.
Rotation of the spin of cold neutrons passing through a noncentrosymmetric single crystal is observed. This effect is caused by the Schwinger interaction of the magnetic moment of a moving neutron with the crystalline electric field in a noncentrosymmetric single crystal and depends both on the direction of neutron trajectory in the crystal and on its energy. It is shown that the characteristic magnitude of the effect for α-quartz is ?(1–2)×10?4 rad/cm over a wide wavelength range (from 2.8 to 5.5 Å) and is determined by the degree of beam monochromaticity [Δλ/λ=(2–5)×10?2 in our experiment]. This magnitude corresponds to an electric field of ?(0.5–1)×105 V/cm acting on a neutron. The measured value agrees well with the theoretical calculation. 相似文献
13.
A. R. Mkrtchyan A. G. Hayrapetyan B. V. Khachatryan R. G. Petrosyan 《Physics of Atomic Nuclei》2010,73(3):478-484
For the first time the high-energy neutrons scattering in a crystal is considered under the influence of an external laser
wave field. The process is inelastic with respect to the laser wave and at the same time it is elastic with respect to a crystal.
The possibility of high-energy neutron diffraction is illustrated—wavelength of neutrons is less than the lattice period.
The method is based on the multiphoton interaction of the neutron anomalous magnetic moment with the field of laser radiation
by using the Farri representation. The neutron-phonon interaction is considered to be a perturbation described by the Fermi
pseudopotential. 相似文献
14.
M.J.A. De Voigt K. Maeda H. Ejiri T. Shibata K. Okada T. Motobayashi M. Sasao T. Kishimoto H. Suzuki H. Sakai A. Shimizu 《Nuclear Physics A》1982,379(1):160-172
Neutron time-of-flight spectra and γ-ray multiplicities were measured in coincidence with discrete γ-rays for specific exit channels in the 158Gd(α, xn) reactions at Eα = 70 MeV. The neutron energy spectra and angular distributions were analysed in terms of equilibrium and non-equilibrium decay processes. Significant emission of non-equilibrated neutrons was found, amounting to about 40 %, 25 % and 15 % of the total neutron emission in the 4n, 5n and 6n exit channels, respectively. The corresponding average kinetic energies in this precompound phase were around 12, 8 and 4.5 MeV. The angular momentum carried away by the neutrons was found to be rather constant for all exit channels and on the average about 3? units. It is found that the total energy and angular momentum removed by the neutrons and γ-rays agrees within the experimental errors with the calculated values for the compound nucleus. 相似文献
15.
The depolarization of a neutron beam executing Laue diffraction in a thick (~3.5 cm) noncentrosymmetric α-quartz crystal is observed. This effect was predicted by us earlier and suggested for measuring the electric dipole moment (EDM) of a neutron. The effect is due to an interaction of the magnetic moment of a moving neutron with a strong crystal electric field, as a result of which the neutron spin rotates in opposite directions for waves of two types excited in the crystal. The effect is studied for neutron diffraction by a system of crystallographic (110) planes at Bragg angles close to π/2, up to 87°. It is shown that, for a crystal of thickness L=3.5 cm, a direct beam initially polarized along the reciprocal lattice vector becomes depolarized upon diffraction, irrespective of the value of Bragg angle, whereas the beam polarized perpendicular to the diffraction plane retains its polarization. The Eτ value determining the sensitivity of the method to EDM is experimentally estimated. 相似文献
16.
Keishiro Yamashita Kazuki Komatsu Stefan Klotz Maria T. Fernández-Díaz Oscar Fabelo Tetsuo Irifune 《高压研究》2020,40(1):88-95
ABSTRACTA high-pressure cell for in-situ single-crystal neutron diffraction was developed. The cell uses nano-polycrystalline diamond anvils in a tubular load frame made of bulk metallic glass which is highly transparent to neutrons and does not produce Bragg reflections. Diffraction peaks from a sample can be measured from almost any direction and the simple geometry of the cell allows accurate attenuation corrections. We demonstrate the operation of the cell by ambient-pressure experiment using a single-crystal of NaCl on the D9 diffractometer at the Institute-Laue-Langevin. A high-pressure experiment was also carried out on a single crystal of ice VII at 2.35?GPa showing the potential to detect weak diffraction spots. The correct integration of weak reflections together with the simple attenuation correction will help to carry out precise structure analysis and address new scientific problems using neutron diffraction. 相似文献
17.
墙壁的反射中子会对快脉冲堆的波形产生明显的影响.堆芯中子泄漏后,经过墙壁的反射有一定的概率返回堆芯,由于能量的差异,泄漏中子的返回时间是一个连续的分布.传统的双区模型只考虑了相互作用概率,而没有时间信息,尽管可以很好地解决稳态问题,而无法解决瞬态问题.本文采用等效的方法,把泄漏中子等效为时间相关的堆芯本征源,建立了含有反射效应的时间关联双区模型.求解得到的脉冲波形与CFBR-Ⅱ的实验结果一致,从而合理解释了脉冲波形后沿衰减变慢和坪功率提高的实验现象. 相似文献
18.
An additive formula is given that permits the calculation of the nuclear capture, thermal diffuse and Bragg scattering cross-sections as a function of sapphire temperature and crystal parameters. We have developed a computer program that allows calculations of the thermal neutron transmission for the sapphire rhombohedral structure and its equivalent trigonal structure. The calculated total cross-section values and effective attenuation coefficient for single-crystalline sapphire at different temperatures are compared with measured values. Overall agreement is indicated between the formula and experimental data. We discuss the use of sapphire single crystal as a thermal neutron filter in terms of the optimum cystal thickness, mosaic spread, temperature, cutting plane and tuning for efficient transmission of thermal-reactor neutrons. 相似文献
19.
The magnetic dipolar interaction responsible for the neutron scattering due to magnetic moments in a crystal is affected by the persistent current in the superconducting state. From this effect, the small angle scattering of neutrons is strongly depressed, and the intensity maximum of the critical scattering appears at a finite scattering wave number even in ferromagnetic superconductors. 相似文献