H. Nitta

Kinematical theory of parametric X-ray radiation

Abstract Based on a perturbative solution of Maxwells equations in crystal, an analytic expression for the coherent radiation from relativistic electrons in a crystal observed recently (called “parametric X-ray radiation”) has been derived. The mechanism of the radiation process is clearly shown by using dispersion surfaces.

Observation of monochromatic and tunable hard X radiation from stratified Si single crystals

Abstract X radiation by 900 MeV electrons in accurately aligned 1–100 layers of 16 μm thick monocrystalline foils of Si was measured. We found intense and well collimated monochromatic photons, i.e. self-diffracted X rays (SDX), emitted to the “Bragg angle”. The intensity of SDX was much greater than the parametric X rays from a Si plate of equivalent thickness. For 35.5 keV X rays with 100 layered Si target, absolute brightness of SDX was comparable to the synchrotron radiation from a 1.7 GeV storage ring.

Electron–phonon coupling effect on wakefields in piezoelectric semiconductors

Using an appropriate dielectric constant for an n-type piezoelectric semiconductor plasma and a moving test particle approach, it is shown that, besides the usual screened potential, there exists a non-Coulombian oscillatory potential or a wakefield behind a moving charged particle due to a strong resonant interaction between the charged particle and the electro-acoustic mode of the host semiconductor. With the concept of the wakefield, a possible lattice formation of colloids resulting from ion implantation in a current-carrying piezoelectric semiconductor has been examined.

X-ray generation produced by relativistic electrons in compound “multifoil structure + crystal” targets

Abstract Novel concepts of X-ray production by relativistic electrons in stratified targets are developed. It is shown that by transmitting an electron beam through a compound target, consisting of a periodic multifoil structure and a crystal, it is possible to obtain the intense, tunable, quasi-monochromatic X-rays, emitting at large (Bragg) angles with respect to the electron beam axis due to the diffraction on the crystal of resonance transition radiation, previously generated in the multilayered structure. The first results of experimental investigation of this effect for 900 MeV electrons, transmitting through the periodic stack of 10 Mylar foils and pyrolytic graphite crystal, are presented. The obtained results show that, by using of the combined radiator, it is possible to produce much more intense X-rays than parametric X-ray radiation, emitting by relativistic electrons due to the diffraction of virtual photons of electron eigenfield during the electron passage through the crystal.

PARAMETRIC X-RAY RADIATION BY RELATIVISTIC CHANNELED PARTICLES

Abstract In this paper, the radiation intensity around the Bragg angle (with respect to a target crystal plane) by relativistic channeled particles is calculated based on the kinematical theory of parametric X-ray radiation (PXR). It is predicted that, in consequence, not only PXR but also Bragg diffraction of channeling radiation will be observed. The latter process is divided into two types by the incident energy. Ordinary photon diffraction occurs in the high energy region and virtual photon diffraction in the low energy region.

NUMERICAL CALCULATION OF PARAMETRIC X-RAY RADIATION BY RELATIVISTIC ELECTRONS CHANNELED IN A SI CRYSTAL

Abstract Recently, a new type of radiation called “parametric X-ray radiation”, is of special interest and several experimental studies have been reported. By using the kinematical theory, we calculate differential scattering cross section of parametric X-ray radiation (PXR) and diffracted channeling radiation (CR) by (111) planes in silicon for 15–50 MeV electron beams channeled along (110) planes.

Modification of the shielding and wake potentials in a streaming dusty magnetoplasma

The effect of an external magnetic field on the Debye shielding and dynamical wake potentials has been examined analytically in a uniform dusty plasma containing equilibrium ion and dust flows. The effects of the ion polarization drift and dust particle dynamics on the strength and the effective length of the new static Debye shielding potential and the dynamical oscillatory potential are studied. It is found that for the supersonic ion flow, the modified Debye–Huckel screening length, and the effective length, L∥, of the oscillatory wake potential due to the modified dust acoustic modes [cf. Eqs. (7) and (17)] become larger by a factor of ωpi/ωci than those due to the usual dust-acoustic wave, where ωpi and ωci are the ion plasma and ion gyrofrequencies, respectively.

Theoretical notes on parametric X-ray radiation

Abstract Some problems in the theory of parametric X-ray radiation or coherent polarization radiation are considered. (1) A diffusion model for multiple scattering of electrons is developed. (2) A new dynamical expression for the radiation intensity is obtained which is reduced to the kinematical expression at low energies. (3) Theory is extended for taking into account the effect of the absorption edge.

On the Shukla–Nambu–Salimullah potential in magnetized plasmas

Abstract In magnetized plasmas, there are two electrostatic potentials, i.e., the almost spherical Debye–Huckel and the strongly anisotropic Shukla–Nambu–Salimullah potentials. The physics of the latter potential due to ion polarization drift is clarified. The exact solution for the Shukla–Nambu–Salimullah potential introduces a new shielding length across the external magnetic field which is much larger than that of the Debye–Huckel potential. There is no exponential decay of the potential for v t = C s , where v t is the test particle velocity and C s is the ion sound velocity.

Computer studies of channeling of antiprotons

Abstract The channeling yield of MeV antiprotons as a function of crystal depth is studied by computer simulation. It is found that a small fraction of channeled antiprotons penetrates anomalously into crystals.