Search results for "Excitation"
showing 10 items of 1290 documents
Determination of ion-induced K-shell ionization cross sections by comparison with nuclear Coulomb excitation
1979
Abstract A new method for the determination of cross sections for K-shell ionization of heavy atoms by charged particles is proposed. The method is based on a comparison of photon lines due to K X-rays and low-energy γ-rays, the latter ones being produced in nuclear Coulomb excitation with accurately known cross sections. This procedure applies within a limited energy range to the study of targets comprising deformed even nuclei, but can also be extended to other targets having Z≳30. A test of the new technique has been carried out for Gd, W, Th and U natural targets irradiated by 4.75 MeV protons. For Th, also energies of 6.80–10.10 MeV were used. The results are briefly discussed with ref…
Energy transfer reaction K(4s) + K(7s) → K(4s) + K(5f), theory compared with experiment
2019
Abstract A comparison between theory and experiment, concerning the K(4 s) + K(7s)→K(4 s) + K(5f) reaction of excitation energy transfer in thermal collisions, is presented. The cross sections for this process are calculated for the potassium vapour temperatures in the range of 310–1000 K. The calculations are based on the theoretical adiabatic K2 potential energy curves and on the use of the multicrossing Landau-Zener model. The experiment was carried out using the method of spectroscopy with resolution in time. The signals of the direct-fluorescence decay from pulsed-laser-excited 7s state, and of the sensitized-fluorescence from 5f state, were registered and analysed. In the temperature …
High Cyclotron Harmonics Excitation in Multi-beam Terahertz Range Gyrotrons
2019
The paper presents recent results on the multi-beam gyrotrons operating at cyclotron harmonics in terahertz frequency range. The theoretical and experimental investigation of second harmonic 0.78 THz gyrotron includes comparison of generating and absorbing beam schemes, research on the effect of velocity spread and mode competition process, along with development of third harmonic 1.2 THz tube based on verified numerical codes and latest experimental results.
Nonlinear plasmonic amplification via dissipative soliton-plasmon resonances
2017
In this contribution we introduce a new strategy for the compensation of plasmonic losses based on a recently proposed nonlinear mechanism: the resonant interaction between surface plasmon polaritons and spatial solitons propagating in parallel along a metal/dielectric/Kerr structure. This mechanism naturally leads to the generation of a quasi-particle excitation, the so-called soliplasmon resonance. We analyze the role played by the effective nonlinear coupling inherent to this system and how this can be used to provide a new mechanism of quasi-resonant nonlinear excitation of surface plasmon polaritons. We will pay particular attention to the introduction of asymmetric linear gain in the …
PRODUCTION OF Θ+ HYPERNUCLEI WITH THE (K+, π+) REACTION
2005
Abstract We present results on the production of bound states of Θ + in nuclei using the ( K + , π + ) reaction. By taking into account the states obtained within a wide range of strength of the Θ + nucleus optical potential, plus the possibility to replace different nucleons of the nucleus, we obtain an excitation spectra with clearly differentiated peaks. The magnitude of the calculated cross sections is well within reachable range.
Model-independent determination of dissociation energies: method and applications
2003
A number of methods are available for the purpose of extracting dissociation energies of polyatomic particles. Many of these techniques relate the rate of disintegration at a known excitation energy to the value of the dissociation energy. However, such a determination is susceptible to systematic uncertainties, mainly due to the unknown thermal properties of the particles and the potential existence of 'dark' channels, such as radiative cooling. These problems can be avoided with a recently developed procedure, which applies energy-dependent reactions of the decay products as an uncalibrated thermometer. Thus, it allows a direct measurement of dissociation energies, without any assumption …
Conversion of bright magneto-optical resonances into dark resonances at fixed laser frequency forD2excitation of atomic rubidium
2012
Nonlinear magneto-optical resonances on the hyperfine transitions belonging to the ${D}_{2}$ line of rubidium were changed from bright to dark resonances by changing the laser power density of the single exciting laser field or by changing the vapor temperature in the cell. In one set of experiments atoms were excited by linearly polarized light from an extended cavity diode laser with polarization vector perpendicular to the light's propagation direction and magnetic field, and laser-induced fluorescence was observed along the direction of the magnetic field, which was scanned. A low-contrast bright resonance was observed at low laser power densities when the laser was tuned to the ${F}_{g…
Nonlinear magneto-optical resonances atD1excitation ofR85bandR87bfor partially resolved hyperfineFlevels
2009
Experimental signals of nonlinear magneto-optical resonances at ${D}_{1}$ excitation of natural rubidium in a vapor cell have been obtained and described with experimental accuracy by a detailed theoretical model based on the optical Bloch equations. The ${D}_{1}$ transition of rubidium is a challenging system to analyze theoretically because it contains transitions that are only partially resolved under Doppler broadening. The theoretical model took into account all nearby transitions, the coherence properties of the exciting laser radiation, and the mixing of magnetic sublevels in an external magnetic field and also included averaging over the Doppler profile. The experimental signals wer…
Light Ion Induced Reactions at Intermediate Energies
1995
We study the light ion induced reactions at intermediate energies theoretically. We show that (3He, t) reactions on unstable nuclei are useful tool to investigate the surface of the unstable nuclei and isospin dependence of the ∆ excitation mechanism in nuclei. We also show that (α, α′) reactions on proton target are interesting since we can observe Roper resonance excited by σ-meson exchange. In both cases we can get interesting results by making use of properties of the light ions.
Parametric excitation of bending deformations of a rod by periodic twist
2013
A model of a semiflexible magnetic filament with magnetization frozen in the direction perpendicular to the tangent of its center line is formulated. It is shown that if the rod is magnetized at its ends in opposite directions, an AC magnetic field causes parametric excitation of bending deformations. Neutral curves of parametric excitation are calculated both analytically and numerically. The shapes arising upon parametric excitation of bending deformations are chiral. Periodic rotation of the chiral filament due to nonhomogeneous twist in a nonhomogeneous AC field causes its unidirectional motion.