Polarization experiments with the SPIN setup at the ITEP synchrotron

New experimental data on the spin-rotation parameters A and R measured for elastic π ^± p scattering in the resonance region and on the asymmetry in pC scattering at primary momenta in the range 1.35–2.02 GeV/c, as well as in quasielastic proton scattering on nuclei in the same momentum range, are summarized. All these data were recently obtained by using the proton synchrotron installed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The spectrum and features of seven isospin-3/2 baryon resonances that form a peak in the total cross section at a c.m. energy of 1.9 GeV are analyzed on the basis of new data on the parameters A and R, and the results of this analysis are presented. The experiments surveyed in this article were performed by a collaboration of researchers from ITEP and the Petersburg Nuclear Physics Institute (PNPI, Gatchina), the ITEP-PNPI collaboration.     

A Water Molecule Triggers Guest Exchange at a Mono-Zinc Centre Confined in a Biomimetic Calixarene Pocket: a Model for Understanding Ligand Stability in Zn Proteins

In this study, the ligand exchange mechanism at a biomimetic Zn^II centre, embedded in a pocket mimicking the possible constrains induced by a proteic structure, is explored. The residence time of different guest ligands (dimethylformamide, acetonitrile and ethanol) inside the cavity of a calix[6]arene-based tris(imidazole) tetrahedral zinc complex was probed using 1D EXchange SpectroscopY NMR experiments. A strong dependence of residence time on water content was observed with no exchange occurring under anhydrous conditions, even in the presence of a large excess of guest ligand. These results advocate for an associative exchange mechanism involving the transient exo-coordination of a water molecule, giving rise to 5-coordinate Zn^II intermediates, and inversion of the pyramid at the Zn^II centre. Theoretical modelling by DFT confirmed that the associative mechanism is at stake. These results are particularly relevant in the context of the understanding of kinetic stability/lability in Zn proteins and highlight the key role that a single water molecule can play in catalysing ligand exchange and controlling the lability of Zn^II in proteins.     

Classical molecular dynamic simulation of (111) Si and Al surface sputtering under bombardment by polyatomic clusters

The self-sputtering processes of (111) Si and Al surfaces under bombardment by Si _N and Al _N ions and clusters (N = 1−60) with the same energy per particle-projectile atom (1 keV/atom) are studied in this paper. The nonlinear effects produced in the target during the development stage of an atomic-collision cascade and during the postcascade stage are analyzed, and a correlation between these effects and secondary emission characteristics is found. The study has been carried out in the framework of classical molecular dynamics. As a result, a number of features of (111) Si and Al surface sputtering and erosion have been revealed. Thus, it has been established that the sputtering yield increases nonadditively as the size N of the implanted cluster increases at N > 10, which is related to the appearance of nonlinear cascades and the postcascade heat spike, and is accompanied by microcrater formation. It is shown that the implantation of clusters into the Si target leads to the formation of amorphous regions.     

Ranges of implanted atoms under polyatomic cluster bombardment of the Cu (111) surface

A computer simulation of the bombardment of the Cu (111) surface with Cu_N and Au_N polyatomic clusters differing in size (N = 1, 6, and 13) with energies of 0.5 and 5 keV/atom has been performed in the framework of classical molecular dynamics. The spatial distribution of the implanted atoms, their ranges, and range fluctuations (straggling) depending on the size N and energy E/N of the incident cluster has been investigated. It has been shown that an increase in the mean range and range straggling is observed at a fixed energy per incident atom as the cluster size N increases. At the same time, the effect of an increase in the range (at a specified value of E/N) gradually disappears with increasing cluster energy, whereas the effect of an increase in straggling is retained. These tendencies qualitatively agree with the available experimental observations. It has been shown that the dominating contribution to the increase in the atom range of the implanted cluster is made by the so-called clearing-the-way effect, which is weakened with increasing the incident cluster energy. The effect of the range straggling increasing is significantly due to the presence of nonlinear “spike” effects at the bombarded target.     

Program of measurement of the asymmetry P at the minima of the differential cross section for elastic π + p scattering

A program of measurement of the polarization parameter P in elastic π ⁺ p interaction in the resonance region of backward pion scattering is presented. This program is aimed at determining the bifurcation points of the trajectory of zeros of the pion-nucleon amplitude and, hence, at unambiguously reconstructing the amplitude of πN scattering in the second resonance region. It is planned to perform a relevant experiment in a pion beam from the accelerator of the Institute of Experimental and Theoretical Physics (ITEP, Moscow).     

Measurement of the spin rotation parameter Ain the elastic pion-proton scattering at 1.43 GeV/c

The ITEP-PNPI collaboration presents new results of the measurements of the spin rotation parameter A in the elastic scattering of negative pions on protons at P_beam = 1.43 GeV/c. The results are compared to the predictions of several partial wave analyses. The experiment was performed at the ITEP proton synchrotron, Moscow.     

Bound exciton diffusion in Si : B

Photoluminescence measurements as a function of excitation intensity and temperature are presented for moderately doped Si : B. Some evidence is obtained for hopping motion of the bound excitons around the impurity centers with trapping at the clusters of impurities. Kinetic parameters of the excitation transfer are estimated.     

Investigation of the passage of 100–1000-MeV/nucleon superheavy ions through homogeneous media

This work is a continuation of the experimental and theoretical investigations of the effect of the Z ₁ ³ correction to the stopping power of ions on the passage of heavy ions ⁴⁰Ar, ⁵⁶Fe, ¹⁹⁷Au, ¹³¹Xe, and ²³⁸U with energies of about 1 GeV/nucleon through a homogeneous medium. The previously observed systematic deviations of the calculations based on the first Born approximation to the scattering of a particle by the atomic electrons in the medium from the experimental values of the total ionization ranges of the nuclei and their stopping powers is confirmed. The discrepancy increases with the atomic number of the projectile nucleus. It is shown that the Z ₁ ³ correction in the form proposed by Jackson and McCarthy eliminates, especially for ions with Z ₁>50, the systematic discrepancy between the computed and experimental values. For the experimental energy range relativistic Mott scattering of a particle by the atomic electrons in the target makes the dominant contribution to the observed Z ₁ ³ effect. Zh. éksp. Teor. Fiz. 115, 404–415 (February 1999)     

Intercalation ofn-alkylamines into α-titanium phosphate from aqueous solutions

Journal of Inclusion Phenomena and Macrocyclic Chemistry - The intercalation reactions betweenn-alkylamines and α-titanium phosphate in aqueous media have been investigated. The compounds with...