L-shell ionization of atoms and their subsequent decay by radiative and non-radiative transitions

The study of the ionization of atoms resulting in vacancies in their inner shells and the subsequent decay of the atomic-vacancy states by x-ray and Auger transitions continue to be an active area of interest. A rapid survey of the theoretical efforts to calculate the transition probabilities involvingL-subshells in the high-Z atoms is presented. A complete review of theL ₁-subshell yields for single-vacancy atomic states obtained by various experimental techniques is included. The production of multiple vacancies in theL shell and the role of the spectator vacancies in the decay process is discussed. A detailed case study of determining experimentally the number of multiple vacancies produced, and the x-ray fluorescence yields during ionization by heavy-ion bombardment is presented. It is established that the effect of spectator vacancies is to increase the x-ray fluorescence yields substantially.     

Pair excitation of atoms in radiative collisions

The kind of radiative collision in which two atoms are simultaneously excited by one photon is considered. The experiment on observation of this effect is proposed.     

Examining coupled-channel effects in radiative charmonium transitions

Coupled-channel effects due to coupling of charmonia to the charmed and anticharmed mesons are of current interest in heavy quarkonium physics. However, the effects have not been unambiguously established. In this Letter, a clean method is proposed in order to examine the coupled-channel effects in charmonium transitions. We show that the hindered M1 radiative transitions from the 2P to 1P charmonia are suitable for this purpose. We suggest to measure one or more of the ratios Γ(h(c)'→χ(cJ)γ)/Γ(χ(cJ)'→χ(cJ)π(0)) and Γ(χ(cJ)'→h(c)γ)/Γ(χ(cJ)'→χ(cJ)π(0)), for which highly nontrivial and parameter-free predictions are given. The picture can also be tested using both unquenched and quenched lattice calculations.     

Field-theoretical treatment of the liquid-vapor phase transition in nuclear systems

The liquid-vapor phase transition in hot nuclear matter is investigated in a field-theoretical approach employing euclidean-space (imaginary time) path-integral techniques. This approach allows us to study the nucleation due to both quantum and thermodynamic fluctuations. The bubbles of the new phase appear as instanton solutions of the euclidean-space field equations. The critical bubble sizes and associated transition probabilities are calculated. We examine the temperature and density values for which a phase transition may develop in hot nuclear matter produced in the course of a heavy-ion reaction.     

The spin-orbit term in radiative transitions of hadrons

We point out that one finds in the literature two different results for the spin-orbit term in radiative transitions of hadrons. We analyze the problem and find that, besides the term usually quoted $$ - ie\omega (\sigma \times p) \cdot \varepsilon _\gamma /4m^2 \cong e[\nabla (V_v + V_s ) \times \sigma ] \cdot \varepsilon _\gamma /4m^2 $$ (V _v ,V _s are the Lorentz vector and scalar pieces of the binding potential and ω the photon energy), there is another term that gives as final resulte(?V _v ×σ)·ε ^γ/2m ². We use for our proof two different approaches: the Foldy-Wouthuysen transformation, and the method of Brodsky and Primack based on a dipole formula. In hadrons, the electric field has two pieces, the photon radiation field, and a strong interaction piece, of order 1/e relative to the former. These two pieces are at the origin of the two spin-orbit terms at the order (v/c)³.     

TheE1 transitions in kaonic atoms

The electric dipole transition rates in kaonic atoms are calculated by using distorted relativistic wave functions. The kaon-nucleus strong interaction which is responsible for the distortion of atomic states is considered to be proportional to the nuclear density and the effective isospin-averaged kaon-nucleon scattering length. Six atoms have been studied for which the last observed X-rays correspond to 3d-2p, 4f-3d, 5g-4f, 6h-5g, 7i-6h and 8j-7i transitions. It is found that the electric dipole transition rate is enhanced by an amount (0.3–7.6)×10¹³s^?1     

Spectral radiative transfer approximations for multicomponent gas mixtures

Expressions for the radiative flux and flux divergence for a hot gas are multiple integrals over spectral frequency and gas volume. The integrals are often replaced by the transparent or strongly absorbed approximations which employ Planck or Rosseland absorption coefficients, respectively. These coefficients smear out all spectral details. This note presents simple flux and flux divergence expressions that retain the advantage of the transparent and strongly absorbed approximations but preserve the important features of the spectral variation.     

Muon-electron transitions in models of radiative lepton masses

In models where both the electron and muon acquire radiative masses, the same mechanism often allows μ-e transitions as well at a certain level. We discuss the phenomenological constraints on some recently proposed models of this type and show that they are incompatible with present experimental limits on μ→eγ, and in one case also μ→eee, without the fine tuning of parameters which these models are supposed to avoid.     

On intensity perturbations in vibronically induced radiative transitions

Intensity perturbations in forbidden radiative transitions due to cubic anharmonic mixing involving the inducing mode and a totally symmetric progression-forming mode are discussed. It is shown that such mixing will lead to deviations from mirror symmetry of the absorption and fluorescence structure because the destructive-constructive interference pattern which prevails in absorption is different to that in emission. This analysis is applied to intensities in the 2600 Å system of benzene. Moderate cubic coupling energies (ca. 10 cm^-1) have marked effects on intensity distributions even when the interacting levels are 200 cm^-1 apart. The splitting of the progressions 1₀ ⁿ 6₁ ² and 1 _n ⁰6₂ ¹ into two sub-progressions (l=0, 2) is linearly dependent on the extent of vibronic excitation in the a _1g mode v ₁. These effects are amenable to experimental detection.     

Cascade transitions in heavy hadronic hydrogen atoms

The majority of deexcited hadronic atoms (hX) (h=K ^?, $\bar p$ , ... and X=p, d, t) are accelerated up to energies of about 100 eV due to Coulomb transitions. The diffusion model of Stark transitions is developed. The resulting nuclear capture rate is higher than that in Bethe-Leon theory by a factor not less than five. Thus, only nonaccelerated atoms can survive. Therefore, the yield Y of Kα x rays is significantly less (by a factor of about ten) than that calculated in standard cascade models and is approximately equal to 0.2% and 1.0% for (K ^?p) atoms at hydrogen densities of N=2 × 10²¹ and 5 × 10²⁰ atom/cm³, respectively. The scheme of a more accurate calculation of Y is also presented.     

Probabilities of radiative transitions between Stark states in orthohelium

The wavefunctions, matrix elements, and probabilities of radiative transitions between Stark sub-levels of atomic multiplets are calculated as a function of the strength of a dc electric field. The general expressions for the wavefunction of a multiplet state in a field obtained by perturbation theory for close-lying levels with the use of completely reduced Green’s function allow one to determine the field dependence of both the dipole-allowed and dipole-forbidden radiation amplitudes. A decomposition of the second-order amplitude for the transition between fine-structure sublevels of two levels of equal parity into irreducible components is obtained. Numerical calculations of the probabilities of radiative transitions between triplet states of helium show the possibility of experimental observation of the emergence and vanishing of Stark lines of radiative transitions in the vicinity of anticrossing fields.     

Interference between multi-step transitions in exotic atoms

We discuss the interference effects due to coherent transitions involving more than one photon in exotic atoms. It is found that the populations are not influenced by this interference. In the case of muonic atoms there is an influence on the polarizations under specific conditions.     

Difference between radiative transition rates in atoms and antiatoms

We demonstrate that CP violation results in a difference of the partial decay rates of atoms and antiatoms. The magnitude of this difference is estimated.