Yu.L. Pivovarov

On the resonant coherent excitation of relativistic heavy ions

Abstract New accelerator facilities open up an interesting new field of experiments on basic channeling as well as on atomic and nuclear resonant coherent excitation (RCE) of heavy ions penetrating through aligned crystals at relativistic energies. Results of computer simulations are presented to characterize the resonant coherent excitation of atomic levels of relativistic hydrogen-like heavy ions. Nuclear resonant coherent excitation reveals interesting different characteristics compared to the corresponding atomic excitation inside crystals. An important results of our model calculations is that poorly-channeled ions have a higher nuclear excitation probability than well-channeled ions.

Basic channeling with Mathematica©: A new computer code

The Mathematica© software is a powerful tool to solve numerous problems in physics, essentially when the analytical solution is not possible. The channeling and related phenomena is just that case. Here we suggest to introduce a standard in calculations of channeling and related phenomena using Mathematica© software. The new computer code Basic Channeling with Mathematica© BCM-1.0, at the first stage, will include a set of packages to make symbolic calculation of the planar channeling phenomena.

Angular Distribution of Diffracted X Rays from (111) Channeled Electrons in Si: The Effect of the Band Structure of Energy Levels

It has been shown that the inclusion of the band structure of the energy levels of channeled electrons qualitatively changes the angular distributions of x rays at the Bragg angles, which can be useful for the experimental detection of the effect.

Coherent X-ray radiation of 5.7 MeV electrons from a (002) mosaic pyrolytic graphite crystal

Abstract Coherent X-ray radiation associated with so-called Parametric X-ray Radiation (PXR) has been observed from a mosaic pyrolytic graphite crystal using an electron beam energy of 5.7 MeV. The 1st order (002) PXR reflection under Bragg geometry results in emission of photons with energies peaked near 7 keV, at a large angle θD = 28° with respect to the electron beam.

Angular distribution of Cherenkov radiation from relativistic heavy ions taking into account deceleration in the radiator

Numerical methods are used to study the dependence of the structure and the width of the angular distribution of Vavilov-Cherenkov radiation with a fixed wavelength in the vicinity of the Cherenkov cone on the radiator parameters (thickness and refractive index), as well as on the parameters of the relativistic heavy ion beam (charge and initial energy). The deceleration of relativistic heavy ions in the radiator, which decreases the velocity of ions, modifies the condition of structural interference of the waves emitted from various segments of the trajectory; as a result, a complex distribution of Vavilov-Cherenkov radiation appears. The main quantity is the stopping power of a thin layer of the radiator (average loss of the ion energy), which is calculated by the Bethe-Bloch formula and using the SRIM code package. A simple formula is obtained to estimate the angular distribution width of Cherenkov radiation (with a fixed wavelength) from relativistic heavy ions taking into account the deceleration in the radiator. The measurement of this width can provide direct information on the charge of the ion that passes through the radiator, which extends the potentialities of Cherenkov detectors. The isotopic effect (dependence of the angular distribution of Vavilov-Cherenkov radiation on the ion mass) is also considered.

Brilliance of coherent peaks for type-B photoproduction of electron-positron pairs in a crystal

Abstract The shape and magnitude of coherent peaks are studied for the type-B coherent photoproduction of electron-positron pairs in a crystal, in the energy range of photons ω = 102–103 MeV. It is shown that under detection of pairs with restricted emission angles the coherent peaks (as a function of photon energy ω) become more brilliant, with larger value of relation of peak height to background, and lower width. The influence of channeling effect on the position of coherent maxima is estimated.

Quantum effects for parametric X-ray radiation during channeling: Theory and first experimental observation

The theory of X-ray radiation from relativistic channeled electrons at the Bragg angles—parametric X-ray radiation (PXR) during channeling (PXRC)—is developed while accounting for two quantum effects: the initial population of bound states of transverse motion and the transverse “form-factor” of channeled electrons. An experiment was conducted using a 255 MeV electron beam from a linac at the SAGA Light Source. We have identified a difference in the angular distributions of PXR and PXRC and obtained a fairly good agreement between the theoretical and experimental results.

Detection of parametric X-ray radiation from moderately relativistic protons in crystals

The spectral maxima of parametric x-ray radiation that are emitted by moderately relativistic protons interacting with various crystals have been detected. The spectral positions of these maxima depend on the crystal orientation angle and they are consistent with the theoretical values. The measurements were carried out with silicon and graphite crystals on the 5-GeV proton beam extracted from the Nuclotron at the Laboratory of High Energies, JINR.

Coherent excitation of hydrogen-like relativistic heavy ions in a crystal: Structure of electronic levels of an ion and resonance width

Abstract The width of the resonance arising due to coherent excitation of electronic levels of relativistic hydrogen-like heavy ions penetrating through aligned crystal is estimated. The influence of Stark- and Zeeman effects, wake potential and eigen structure of electronic levels of heavy ion is considered. It is shown that the fine structure of electronic levels of heavy ions will play the key role in forming of the shape and width of resonances, at the ion energy greater than few GeV/nucleon.

Enhanced type-B coherent effect in collimated electron-positron photoproduction from Si crystal

Abstract The relative cross section of pair creation from a silicon single crystal has been measured with a bremsstrahlung beam from 350 MeV electrons. A clear enhancement was observed above 230 MeV as expected from the theory based on the type-B coherent effect.