High-frequency magnetic modulation of recoilless gamma radiation of57Fe

Radio-frequency (rf) magnetic modulation has been used to generate sidebands in⁵⁷Fe Mössbauer spectra of Fe_0.18Ni_0.82 Permalloy foils which have the smallest constant of magnetostriction among Fe?Ni alloys. Sidebands in Mössbauer spectra were observed at 30 MHz and 55 MHz. In addition to the generation of sidebands, the external rf magnetic field was found to alter the line positions of the original six line spectrum. An attempt was made to study acoustic vibrations in the foil by means of X-ray diffraction. The rf magnetic field caused changes in diffraction peak intensities and positions. It was found that X-ray diffraction can be used to study the amplitude of acoustic vibrations in Permalloy foils.     

Time modulation of recoilless nuclear resonance fluorescence

The time dependence of the resonance fluorescence of nuclei excited by the spontaneous radiation of identical nuclei is studied. Particular attention is paid to the influence of the periodic overlap of the source on the form of the scattered radiation line and it is shown that the line may even split. A mechanical filter permitting measurement of pure radiation scattering is calculated.     

Quantum optics with nuclear gamma radiation

Some features of quantum optics related to inversionless amplification are translated to nuclear systems. Nuclei and nuclear transitions differ in several ways from atomic systems: gamma radiation has a much shorter wavelength (of the order of lattice-distances), nuclear transitions are many orders of magnitude weaker than atomic ones (making nuclear pumping extremely hard), no coherent gamma-ray sources are available to produce bichromatic gamma radiation. All this makes it very hard to merely translate quantum optical results to nuclear systems. We show that under very specific conditions destructive quantum interferences can occur in the nuclear absorption probability, while the stimulated emission probability is not affected. Nuclear level mixing plays a crucial role in this. This revised version was published online in August 2006 with corrections to the Cover Date.     

Vector model of electron spin echo envelope modulation due to nuclear hyperfine and zeeman interactions

The transverse electron spin magnetization of a paramagnetic center with effective spinS=1/2 interacting with nonquadrupolar nuclei may be presented as a function of pairs of nuclei magnetization vectors which precess around the effective magnetic field directions. Each vector of the pair starts its precession perpendicular to both effective fields. The free induction decay (FID) signal is proportional to the scalar product of the vectors for nuclear spinI=1/2. The electron spin echo (ESE) signal can be described with two pairs of magnetization vectors. The ESE shape is not equal to two back-to-back FID signals except in the absence of ESE envelope modulation. A recursion relation is obtained which allows calculation of ESE signals for larger nuclear spins in the absence of nuclear quadrupole interaction. This relation can be used to calculate the time course of the ESE signal for arbitrary nuclear spins as a function of the nuclear magnetization vectors. While this formalism allows quantitative calculation of modulation from nuclei, it also provides a qualitative means of visualizing the modulation based on simple magnetization vectors.     

Controlling absorption of gamma radiation via nuclear level anticrossing

A significant reduction of absorption for single gamma photons has been experimentally observed by studying M?ssbauer spectra of 57Fe in a FeCO3 crystal. The experimental results have been explained in terms of a quantum interference effect involving nuclear level anticrossing due to the presence of a combined magnetic dipole and electric quadrupole interaction.     

Polydimethylsiloxane rubber gamma radiation effect studies by positron annihilation lifetime spectroscopy

Polydimethylsiloxane rubber was irradiated at various radiation doses up to 800 kGy in air. The lifetime and intensity of the long component τ₃ were obtained by positron annihilation lifetime spectroscopy (PALS). The crystallization property and the molecular flexibility were estimated using the differential scanning calorimetry and dynamic thermomechanic analysis. Thermal volatile property was determined by thermogravimetry analysis. It was proved that the cross-linking reaction made the chain flexibility of the rubber to reduce gradually during gamma radiation, which resulted in the reduction of the o-Ps intensity observed by PALS. Although the degradation effect existed during gamma radiation, it was still less significant than the cross-linking effect when the radiation dose was up to 800 kGy.     

Phase modulation of propagation effect with Doppler broadening

This paper studies the propagation effect in a closed lambda-type three-level atomic system with Doppler broadening. It is shown that, Doppler broadening due to atomic motion and propagation effect associated with driving field depletion along the active medium decreases obviously the gain and output of the lasing without inversion （LWI）; the relative phase between the probe and driving fields has a remarkable modulation role to the propagation effect on LWI when Doppler broadening presents; by choosing suitable value of the relative phase, we can get the largest gain and output of LWI.     

Narrow spectral lines of modulation harmonics of gamma radiation in unordered magnetic materials

The spectra of gamma-resonance lines excited using the amplitude modulation of the pumping field of the Mössbauer effect were studied in unordered magnetic materials with a strong spread of magnetic hyperfine fields at nuclei of Mössbauer isotopes. The analysis demonstrates that the spectra of modulation harmonics consist of narrow lines, and their form and intensity are determined by the contribution of magnetic local hyperfine fields, which are excited at a pumping frequency. The inversion of intensities for odd harmonics with the change in sign of detuning of the pumping frequency relative to the average Larmor frequency of the Mössbauer nucleus was noted. The application of this method to the spectral analysis of inhomogeneous magnetic materials is discussed.     

Phase modulation of charge density wave around a short-range potential by the Aharonov-Bohm effect

The analytic result of the Aharonov-Bohm effect for its influence on the oscillation of a two-dimensional charge density around a short range potential is given. Without losing generality, the cases of δ-function and hard disc potentials were examined. Numerical calculations show that the interferences among quantum particles are greatly influenced by the nonlocal effect, which leads to the modulation of phase and amplitude of the oscillation of charge density. Since the presence of a nonlocal influence of the Aharonov-Bohm effect on charged particles is universal, the results in the specific potentials examined are expected to appear also in other general systems which may be beneficial to the study of nanotechnology.     

大芯径紫外石英光纤γ射线辐照效应研究

阐述了三种不同芯径的紫外石英光纤的稳态γ射线辐照效应,对比研究了其发光特性、光谱衰减以及光谱展宽。设计了基于钴-60源的大芯径紫外石英光纤稳态γ射线辐照效应实验,对三种芯径(200μm,400μm和600μm)的光纤进行了研究。实验表明,大芯径紫外石英光纤在稳态γ射线辐照下存在稳定的发光现象,并对其光谱衰减有补偿作用,其光谱展宽效应不明显。     

Dynamic polarization of a nuclear zeeman subsystem within the framework of the EPR spin-temperature concept

In a high-temperature approximation, theoretical consideration is given to dynamic polarization of nuclei within the framework of the EPR spin-temperature concept. We show that the maximum polarization of nuclei can be attained at a certain value of the detuning of an SHF-field if the intensity of the latter is fixed. The possibility of determining some relaxation parameters of the system by the value of this detuning at a high value of the saturating field is shown. In the presence of a trial field, the effect of a nuclear Zeeman subsystem on the time of transverse relaxation T₂ is evaluated. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 404–406, May–June, 2000.     

Quantum-interference effects for gamma radiation under crossing-anticrossing conditions for nuclear levels in an RF field

A new approach to observing the effect of electromagnetically induced transparency in gamma optics is proposed. The propagation of a resonant photon in a ⁵⁷Fe magnetic medium in an applied rf field is considered for this purpose. It is shown that, under crossing-anticrossing conditions, a resonant rf field substantially changes the gamma-optical properties of the medium, which become dependent on the parameters of the field. This opens the possibility for exercising a coherent control of the photon group velocity and a controllable filtration of unpolarized gamma radiation in a sample.     

Phase relations in the modulation of light through the linear electro-optical effect

General expressions for the phases of the two light waves passing through a crystal plate in the normal direction are developed for arbitrary directions of the optic axis of a monoaxial crystal and of the electric vector of the modulating, linearly polarized superhigh frequency wave. The expressions obtained permit one to describe in general form the amplitude, polarization, and phase modulations of light by electrooptical modulators.