Secondary Radiation Spectra Research Articles

Charged-particle induced background expected in X-ray detecting CCDs in highly eccentric earth orbits

Charged particle fluxes on satellites in highly eccentric Earth orbits are studied, using data from ISEE1 and EXOSAT missions. The effects of minimum-ionizing particles, low-energy electrons and secondary radiation produced by these particles on CCDs used as X-ray detectors are identified. A technique to discriminate events caused by minimum-ionizing particles from X-ray events is proposed. The need for a deflecting system against low-energy electrons with focusing X-ray optics is demonstrated. An expected secondary radiation spectrum behind a typical detector shielding based on Monte-Carlo-simulations is presented. For the EPIC detectors on XMM, detection rates due to this radiation environment are estimated.

Resonant Secondary Radiation in Strongly Coupled Localized Electron-Phonon System

Numerical calculations of the resonant secondary radiation spectrum of the strongly coupled localized electron-phonon system are presented both for the stationary and transient responses. The time evolution of the transient response makes it clear how the line shape of the stationary radiation spectrum is formed in accordance with the three characteristic time-scale, namely, the phase relaxation time, the energy relaxation time and the population decay time.

Anomalied in the intensity of the resonant secondary radiation of F-centers in KCl

The resonant secondary radiation spectrum for a two-level system with strong electron-phonon coupling is calculated and compared with that observed in F-centers of KCl. It is shown that the effective transition probability from the excited to the ground state of the F-center decreases dramatically as the lattice relaxation goes on.

Resonant secondary emission and spectral diffusion in isotopically mixed naphthalene crystals

Resonant secondary radiation (zero-phonon lines) flourescence spectra of isotopic 3D aggregates of traps (NH 8) in a host crystal (ND 8), as well as transfer-induced fluorescence at trap concentrations between 0.01 and 10% and at temperatures between 1.6 and 10 K, are presented. Laser-excited (0–1) resonant secondary (zero-phonon) emission is used to resolve close-lying electronic resonances, corresponding to monomers, aggregates and to their host and trap satellite lines, in a quasi-continuum of 3D trap states. Such states are also calculated by numerically diagonalizing a mixed-crystal 3D hamiltonian. Measured and calculated delocalization indices are given for all trap species. In addition, low-temperature spectral diffusion of photoselected trap species is measured by plotting the attenuation of the zero-phonon lines. We give a simple discussion on the modulation of the resonant secondary radiation spectra by concentration, excitation wavelength and temperature. We show that low-temperature exciton diffusion, assited by acoustical phonon creation, occurs above a very low concentration threshold ( C > 0.05% for monomers at T = 1.6 K). Thermally activated transfer of the photoselected excitons is also plotted for temperatures up to 10 K above which the zero-phonon lines are quenched.

Recombination radiation and electroreflection of excitons in ZnxCd1−xSe solid solutions

AbstractThe simultaneous investigation of electroreflection (ER) and secondary radiation (SR) spectra of ZnxCd1−xSe solid solutions under off‐resonance (resonance) laser excitation at 5 to 300 K reveals the fine structure of the fundamental absorption edge which arises from the direct and indirect creation and annihilation of excitons of series Γ6–Γ8 or Γ7–Γ9 und Γ7–Γ7. The shape of the SR exciton line at low temperatures is determined by the exciton trapping processes at random potential fluctuations of composition. This statistic random potential manifests itself in a blue shift of the SR exciton line with the N2‐laser excitation. The behaviour of the SR exciton line at 77 K is strongly governed by the exciton annihilation processes with the simultaneous emission or absorption of LO phonons. A possible effect of extended and self‐trapped exciton states in SR spectra at high temperature is considered.

Vibronic and resonance Raman spectra of NO2−impurity ions in the body-centered alkali halide crystals

The low-temperature resonance secondary radiation spectrum as well as the absorption and luminescence excitation spectra of NO2− impurity ions in cesium halides have been studied. The energy relaxation processes and NO2− equilibrium orientation and reorientation problems have also been discussed. It was shown that the systems under study were characterized by average Stokes' losses and strong lattice distortions, exemplified by the Generation of a number of low-frequency local and pseudolocal vibrations. The inhomogeneous broadening in CsCl-NO2− and CsI-NO2− spectra was extremely large for the simple molecular impurity systems, leading to the interesting peculiarities of energy relaxation processes. Unlike some alkali halide crystals with NaCl structure the impurity NO2− does not rotate in the lattices with CsCl structure. The NO2− equilibrium orientation in cesium halides was fixed: both the molecular axis and the axis perpendicular to the molecular plane were directed in (100) directions of the crystal.

Two‐Photon Resonance Raman Scattering by Excitons via an Intermediate Excitonic Molecule. I. Bare‐Exciton Approach

AbstractTwo‐photon resonance Raman scattering from excitons via an intermediate excitonic molecule is studied theoretically. The line shape and dispersion of the scattering spectrum is calculated in terms of damping theory for excitation near the resonance energy of the two‐photon absorption for the molecule. By taking into account a finite band width of the exciting laser light the secondary radiation spectrum is decomposed into a Raman‐ and a luminescence‐like part. The relation between these parts is discussed in dependence on the dampings acting on the electronic intermediate and final states of the scattering process as well as the laser band width. Qualitative agreement is found with the experimental results for CuCl and CdS.

On the Theory of Hot Luminescence and Resonant Raman Effect of Impurity Centres

AbstractFor an impurity centre the resonant secondary radiation spectrum, consisting of luminescence, Raman scattering, hot luminescence, and interference terms, is studied at low temperatures using the model of one local or pseudolocal mode, active in the electronic transition and taking into account the change of the equilibrium position and frequency of this mode. It is shown that the latter plays an essential role in the problem of the classification of the resonant Raman scattering and hot luminescence. The anti‐Stokes region of the spectrum is analysed in detail for three cases of excitation: monochromatic, “white”, and intermediate excitation. The influence of the interference of different relaxation channels on the intensity, width, and shape of the lines is considered.

Hot luminescence lines in the secondary radiation spectrum of KClNO 2− and KBrNO 2− crystals

In the secondary radiation spectra of KClNO 2 − and KBrNO 2 − weak additional lines were observed and investigated by means of a phonon-counting system. The lines were interpreted as hot luminescence, i.e. the radiation emitted by the impurity during vibrational relaxation before the establishment of thermal equilibrium with lattice modes.

Density Matrix Method in the Theory of Optical Spectra of Impurities in Solids

AbstractThe results of a previous paper describing the vibrational structure in the secondary radiation spectrum of impurities in solids are extended to the general case of finite temperature. The impurity centres are treated as two‐level electronic systems interacting with a localized mode of vibration. The anharmonic interaction of the localized mode with the crystal modes is taken into account. Expressions are derived describing the Raman‐type and luminescence parts of the spectrum. The relation between the integral intensities of these spectral components are examined as a function of the frequency of the incident light.

Theory of Resonant Secondary Radiation due to Impurity Centres in Crystals

AbstractThe resonant secondary radiation spectrum of impurity centres in crystals is studied on the basis of a second‐order approximation for the interaction between the electromagnetic field and the material. It is shown that for the case of excitation in the phonon wing of the absorption band, the main part of the secondary radiation represents the ordinary luminescence. The spectrum also contains Rayleigh and Raman scattering which is considerably weaker (by about four orders of magnitude). Formulas are obtained for the intensities of Rayleigh‐ and Raman scattering; particular consideration is made for the case of large Stokes' losses. It is also shown that excitation in the region of the pure‐electronic line yields a spectrum consisting of the Rayleigh and the pure‐electronic line, and the phonon wing of the luminescence.

The average multiplicity and inelasticity in π-meson production in the atmosphere

The energy spectra of primary and secondary cosmic radiation are analysed to find the multiplicity-energy relation in the π-meson production in the atmosphere at the energy region from several GeV to some thousands GeV with the help of simplified considerations on the meson production by nucleus-nucleus collisions. The results being subjected to the assumed values of inelasticity suggest that the multiplicity-energy relation agrees with the formula of the type given by Fermi and Landau under the condition of a practically constant small inelasticity.