Energy dependence of the response of an electromagnetic spectrometer with oriented crystal converter

The experimental results of the study of the dependence of the response of a composite Cherenkov shower spectrometer with a converter made of 〈111〉 tungsten crystal 1 mm thick on the electron energy of 26, 28, and 31 GeV are presented. It is found that the cascade curve maximum position and the energy release at the maximum of the cascade curve of shower development in the spectrometer with both oriented or misoriented converters have the logarithmic and proportional dependences on electron energy.     

Effect of an oriented crystalline converter on the electromagnetic spectrometer response

The results of the experimental studies of the response of an electromagnetic spectrometer with a converter made of 〈111〉 tungsten crystal at electron energies of 26, 28, and 31 GeV are presented. It is found that the ratio of the difference between positions of the cascade curve maximum for misoriented and oriented converter to the difference between energy releases at the cascade curve maximumis a constant value at a given electron energy, converter type and thickness, and is independent of the converter temperature.     

Estimation of the parameters of the cascade curve of electromagnetic shower development in a spectrometer with oriented crystal converter

Based on the experimental results on the development of electromagnetic showers from 26-GeV electrons in misoriented and oriented along the 〈111〉 axis tungsten crystals 2.7, 5.8, 8.4mm thick and then in a composite Cherenkov shower spectrometer, the parameters of the cascade curve of shower development in a spectrometer with 1-mm tungsten crystal converter were estimated.     

Effect of oriented crystalline converter temperature on spectrometer response

Cooling of a 1-mm crystalline tungsten converter oriented along the ??111?? axis situated in front of an electromagnetic spectrometer of thickness 25X ₀, recording showers of 28-GeV electrons, to a temperature of 77 K results in a decrease of the crystal radiation length by ??30%, shifts the cascade curve of the shower development in the spectrometer by ??7%, and improves the spectrometer energy resolution by ??5% in comparison with similar parameters of the spectrometer at a crystal temperature of 293 K.     

A positron source using an axially oriented crystal associated to a granular amorphous converter

A non-conventional positron source using the intense γ radiation from an axially oriented monocrystal which materializes into e⁺e^- pairs in a granular amorphous converter is described. The enhancement of photon radiation by multi-GeV electrons crossing a tungsten crystal along its <111> axis is reported. The resulting enhancement of pair production in an amorphous converter placed 2 meters downstream, is also reported. Sweeping off the charged particles from the crystal by a bending magnet upstream of the converter allows a significant reduction of the deposited energy density. Substituting a granular target made of small spheres for the usual compact one, makes the energy dissipation easier. The deposited energy and corresponding heating are analyzed and solutions for cooling are proposed. The configurations studied here for this kind of positron source allow its consideration for unpolarized positrons for the ILC.     

Structure of electromagnetic fields near the surface of an ionic crystal

A NaCl ionic crystal whose (100) face is in contact with vacuum is used as an example to consider static and dynamic contributions to an electromagnetic field in close proximity to its surface. The expression for the potential of the electric field produced by a system of point charges in vacuum (derived by Lennard-Jones and Dent) is taken as the basis. The dynamic correction to the static field has been found. It appears as a result of thermal fluctuations of ions near equilibrium positions in the ionic lattice. Various contributions of the electrostatic field of the ionic lattice, the field of fluctuating ions of this lattice near their equilibrium positions, and of the dipole-type fluctuation field produced by spontaneous deformations of the crystal??s elementary cells to the energy density of the electromagnetic field near the surface of the ionic crystal have been calculated and compared. The periodic structuring of the electromagnetic field??s energy density caused by the presence of static and dynamic ionic lattices of the crystal at small distances from its surface is illustrated graphically. Fields generated by a film with a finite thickness containing an arbitrary number of ion monolayers have also been considered.     

Mössbauer spectrometer providing measurement of spectral dependences on external parameters

A method of simultaneous measurement of Mössbauer spectra for a set of discrete values of an external parameter is proposed. The method proposed makes it possible to simplify series measurements and replaces a number of specialized techniques. The possibilities of the spectrometer have been experimentally demonstrated by the example of observation of the dependences of the Mössbauer spectra of an α-Fe foil on the external magnetic field strength.     

Simulation of incoherent radiation of fast particles in an oriented crystal

Incoherent bremsstrahlung of high-energy electrons in a crystal is due to the thermal spread of atoms with respect to their equilibrium positions in the lattice. In this paper, an incoherent-radiation simulation procedure based on semiclassical formulas of bremsstrahlung theory is developed. A significant orientation dependence of the intensity of hard incoherent radiation is demonstrated for angles of electron incidence on a densely packed crystallographic axis (plane) that are close to the critical axial (plane) channeling angle. The simulation results are in good agreement with the experimental data.     

Exclusive nuclear response to an electromagnetic probe

The nuclear response is studied in exclusive processes such as one- and two-nucleon knockout by an electromagnetic probe. The theoretical framework is the one-photon exchange approximation. The special role of the different theoretical ingredients is discussed with particular reference to nucleon-nucleon correlations, final-state interactions and reaction mechanism. An extension to high energy and momentum transfer is also considered where precursor phenomena connected with colour transparency may occur.Lectures given at the Indian-Summer School on Electron Scattering from Nucleons and Nuclei, Prague (The Czech Republic), September 1994.     

平面晶体谱仪弯曲谱线波长定标方法

为了满足激光等离子体X射线光谱测量的需要,提出了一种利用平面晶体谱仪记录得到的弯曲谱线来进行波长标定的新方法。传统的参考谱线法需要已知两条以上谱线的确切波长才能进行波长标定,而利用弯曲谱线可以在不知道任何谱线信息的情况下进行波长标定。通过对实验中所获得的铝等离子体He自发射谱线弯曲图像的分析,得到在目前所使用的谱仪条件下,该方法的波长定标精度可以达到210-4 nm。     

Theory of channel-cut double crystal X-ray spectrometer with vertical dispersion

The formula for diffracted power for any X-ray beam which may be diffracted from two crystals in antiparallel position is derived. The distortion of X-ray spectrum measured by the method of vertical dispersion is estimated. The function and adjustment of the spectrometer is discussed.     

平面晶体谱仪弯曲谱线波长定标方法

为了满足激光等离子体X射线光谱测量的需要,提出了一种利用平面晶体谱仪记录得到的弯曲谱线来进行波长标定的新方法。传统的参考谱线法需要已知两条以上谱线的确切波长才能进行波长标定,而利用弯曲谱线可以在不知道任何谱线信息的情况下进行波长标定。通过对实验中所获得的铝等离子体Heα自发射谱线弯曲图像的分析,得到在目前所使用的谱仪条件下,该方法的波长定标精度可以达到2×10-4 nm。     

Optical bistability polarization dependences with an interference modulator

Polarization-dependent hysteresis of a bistable device on the base of an electrooptical modulator at oblique incidence of light is observed. The device switching is performed by variation of the incident light polarization. The multistable character of the transmitted light polarization is discussed.     

Longitudinal development of electromagnetic showers in directional spectrometer

The length of the longitudinal development of the electromagnetic shower induced by electrons with an energy of 26 GeV in a directional spectrometer consisting of a crystalline tungsten converter oriented along the ??111?? axis and a composite Cherenkov shower spectrometer is shorter in comparison with the length of the standard shower development by 20?C30% at a converter thickness from 2.7 to 8.4 mm.     

Orientation of stereoisomers by electromagnetic field

A magnetic orientation is shown to appear during light-induced drift of stereoisomers relative to a buffer gas. The magnetic orientation can be initiated even by linearly polarized or nonpolarized radiation.