Photoelectron Circular Dichroism as a Probe of Chiral Hydrocarbons

The sensitivity of Photoelectron Circular Dichroism (PECD) in the angular distribution of photoelectrons, a recent chiral technique, to detect chirality in pure hydrocarbons is investigated in a number of benchmark molecules. It is found that a very large chiral signal is expected, surpassing most current examples, giving a sure fingerprint of absolute configuration. On the other hand, the sensitivity to specific isomers or closely related molecules is relatively modest.

Mechanisms of 1s Double-Core-Hole Excitation and Decay in Neon

The formation and decay of double-core-hole (DCH) states of the neon ion irradiated by an intense electromagnetic x-ray field are studied theoretically. In the present research DCH formation is the result of sequential absorption of two photons with the creation of an intermediate ion. Detailed calculations of the partial decays and probabilities of shake-ups at the atomic and ionic ionization stages are presented. The angular distribution of photoelectrons corresponding to various residual ionic states are calculated. Specifically, we predict the lack of any photoelectrons corresponding to the residual ionic state 1s12s22pnmpn′2Sf+1D in the direction of the electric field polarization. Dynamical competition between single-core-hole state decay and excitation is analyzed and pulse parameters corresponding to various dynamical regimes are found.

Assessment of secondary neutrons in particle therapy by Monte Carlo simulations

Objective: The purpose of this study is to estimate the energy and angular distribution of secondary neutrons inside a phantom in hadron therapy, which will support decisions on detector choice and experimental setup design for in-phantom secondary neutron measurements. Approach: Dedicated Monte Carlo simulations were implemented, considering clinically relevant energies of protons, helium and carbon ions. Since scored quantities can vary from different radiation transport models, the codes FLUKA, TOPAS and MCNP were used. The geometry of an active scanning beam delivery system for heavy ion treatment was implemented, and simulations of pristine and spread-out Bragg peaks were carried out. Previous studies, focused on specific ion types or single energies, are qualitatively in agreement with the obtained results. Main results: The secondary neutrons energy distributions present a continuous spectrum with two peaks, one centred on the thermal/epithermal region, and one on the high-energy region, with the most probable energy ranging from 19 MeV up to 240 MeV, depending on the ion type and its initial energy. The simulations show that the secondary neutron energies may exceed 400 MeV and, therefore, suitable neutron detectors for this energy range shall be needed. Additionally, the angular distribution of the low energy neutrons is quite isotropic, whereas the fast/relativistic neutrons are mainly scattered in the down-stream direction. Significance: It would be possible to minimize the influence of the heavy ions when measuring the neutron-generated recoil protons by selecting appropriate measurement positions within the phantom. Although there are discrepancies among the three Monte Carlo codes, the results agree qualitatively and in order of magnitude, being sufficient to support further investigations with the ultimate goal of mapping the secondary neutron doses both in- and out-of-field in hadrontherapy. The obtained secondary neutron spectra are available as supplementary material.

SCALING OF SENSATIONS DURING THE PERFORMANCE OF VISUAL TASKS IN RELATION TO HUMAN CENTRIC LIGHTING

Currently, programs for lighting calculation based on computer graphics (CG) allows us to move to a fundamentally new approach to a assessing the quality of lighting. A designing based on illuminance can be complement with designing based on synthetic images or on lighting design. Modern CG programs can calculate the spatial-angular distribution of luminance (SADL). However, to make the assessment of the quality of lighting using SADL a new criterion is needed. This paper considers constructing a physiological model of the visual perception scale based on experimental data and on neural network for simple scene as light source viewed on a uniform background with different luminance levels. Scale based on threshold contrasts of luminance for each sensation can be a fundament of new criterion. The article offers the method of construction the map for each sensation using the example of «discomfort» and «unpleasant» maps that can easily applied in programs.

IMAGE CONVERSION OF ϭ- AND π-COMPONENTS OF RADIATION OF RELATIVISTIC ELECTRON AND METROLOGICAL CHARACTERISTICS OF THE PHOTON FLUX IN THE SYNCHROTRON RADIATION OUTLET

The paper deals with the efficiency of the capture of a photon flux of the synchrotron radiation (SR) σ- and π-components by the optical window in the SR quantum extraction channel of the NESTOR generator. It also anal-yses the dependence between the capture quality and different radiation wavelengths. Consideration has been giv-en to the beam size effect on the shape and dimensions of the angular distribution of the photon flux. A model has been constructed to describe the optical imaging in the registration plane. Expressions are given for estimating the efficiency of the capture of SR quanta into the optical window of the extraction channel. The factors that exert influence on the efficiency of capturing through the window are analyzed. Examples of numerical calculations are provided for formation of the final SR spectral density of the 225 MeV relativistic electrons at the output of the optical channel. The dimensions of the optical window have been determined, which ensure the reliable registration of the total flux of SR quanta for the chosen spectral range of SR quanta wavelengths.