Ce:LaB3O6 glass for high-resolution radiation dosimetry

Ce:LaB3O6 (LBO) glass, whose constituents are abundant elements and fabrication is easy and cheap, is found to be a promising thermoluminescence (TL) dosimeter. This is originally achieved by CeF3 doping and melting under a reducing atmosphere, with the optimum concentration of 0.1% (quantum efficiency = 66%). The corresponding Ce interatomic distance is ~ 4 nm, below which concentration quenching occurs via Ce dipole-dipole interaction, as elucidated experimentally by Dexter’s theory. Ce:LBO exhibits a good dose resolution, with a linear dependence covering five orders of magnitude on both irradiation-dose and TL-response. Furthermore, it can be cyclically irradiated and read without degradation.

UV-induced dissociation of CH2BrI probed by intense femtosecond XUV pulses

The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH2BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump — XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH2Br radicals produced by C—I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH2BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way.

Long-Range Interactions for Hydrogen Atoms in Excited D States

Pressure shifts inside an atomic beam are among the more theoretically challenging effects in high-precision measurements of atomic transitions. A crucial element in their theoretical analysis is the understanding of long-range interatomic interactions inside the beam. For excited reference states, the presence of quasi-degenerate states leads to additional challenges, due to the necessity to diagonalize large matrices in the quasi-degenerate hyperfine manifolds. Here, we focus on the interactions of hydrogen atoms in reference states composed of an excited nD state (atom A), and in the metastable 2S state (atom B). We devote special attention to the cases n=3 and n=8. For n=3, the main effect is generated by quasi-degenerate virtual P states from both atoms A and B and leads to experimentally relevant second-order long-range (van-der-Waals) interactions proportional to the sixth inverse power of the interatomic distance. For n=8, in addition to virtual states with two states of P symmetry, one needs to take into account combined virtual P and F states from atoms A and B. The numerical value of the so-called C6 coefficients multiplying the interaction energy was found to grow with the principal quantum number of the reference D state; it was found to be of the order of 1011 in atomic units. The result allows for the calculation of the pressure shift inside atomic beams while driving transitions to nD states.

Long range and highly tunable interaction between local spins coupled to a superconducting condensate

Interfacing magnetism with superconducting condensates is rapidly emerging as a viable route for the development of innovative quantum technologies. In this context, the development of rational design strategies to controllably tune the interaction between magnetic moments is crucial. Here we address this problem demonstrating the possibility of tuning the interaction between local spins coupled through a superconducting condensate with atomic scale precision. By using Cr atoms coupled to superconducting Nb, we use atomic manipulation techniques to precisely control the relative distance between local spins along distinct crystallographic directions while simultaneously sensing their coupling by scanning tunneling spectroscopy. Our results reveal the existence of highly anisotropic interactions, lasting up to very long distances, demonstrating the possibility of crossing a quantum phase transition by acting on the direction and interatomic distance between spins. The high tunability provides novel opportunities for the realization of topological superconductivity and the rational design of magneto-superconducting interfaces.

Decline of protein structure rigidity with interatomic distance

Background Protein structural rigidity was analyzed in a non-redundant ensemble of high-resolution protein crystal structures by means of the Hirshfeld test, according to which the components (uX and uY) of the B-factors of two atoms (X and Y) along the interatomic direction is related to their degree of rigidity: the atoms may move as a rigid body if uX = uY and they cannot if uX ≠ uY. Results It was observed that the rigidity degree diminishes if the number of covalent bonds intercalated between the two atoms (d_seq) increases, while it is rather independent on the Euclidean distance between the two atoms (d): for a given value of d_seq, the difference between uX and uY does not depend on d. No additional rigidity decline is observed when d_seq ≥ ~ 30 and this upper limit is very modest, close to 0.015 Å. Conclusions This suggests that protein flexibility is not fully described by B-factors that capture only partially the wide range of distortions that proteins can afford.

Memory Effect in the Spatial Series Based on Diamond and Graphite Crystals

To study the relation between the structure of a compound and its properties is one of the fundamental trends in chemistry and materials science. A classic example is the well-known influence of the structures of diamond and graphite on their physicochemical properties, in particular, hardness. However, some other properties of these allotropic modifications of carbon, e.g., fractal properties, are poorly understood. In this work, the spatial series (interatomic distance histograms) calculated using the crystal structures of diamond and graphite are investigated. Hurst exponents H are estimated using detrended fluctuation analysis and power spectral density. The values of H are found to be 0.27–0.32 and 0.37–0.42 for diamond and graphite, respectively. The calculated data suggest that the spatial series have long memory with a negative correlation between the terms of the series; that is, they are antipersistent.

Partial spectral flow and the Aharonov–Bohm effect in graphene

We study the Aharonov–Bohm effect in an open-ended tube made of a graphene sheet whose dimensions are much larger than the interatomic distance in graphene. An external magnetic field vanishes on and in the vicinity of the graphene sheet and its flux through the tube is adiabatically switched on. It is shown that, in the process, the energy levels of the tight-binding Hamiltonian of $$\pi $$ π -electrons unavoidably cross the Fermi level, which results in the creation of electron–hole pairs. The number of pairs is proven to be equal to the number of magnetic flux quanta of the external field. The proof is based on the new notion of partial spectral flow, which generalizes the ordinary spectral flow already having well-known applications (such as the Kopnin forces in superconductors and superfluids) in condensed matter physics.

The Birth and Initial Exploitation of X-ray Diffraction

A non-mathematical account of the discovery of X-ray diffraction by von Laue and its use as a new kind of high-resolution microscopy by W. L. Bragg is given. There follows a simple explanation of how the electron densities in various regions of any molecule that can be crystallized can be retrieved from its X-ray diffraction pattern. Also, it is explained how the molecular weight of the molecule can be determined from straightforward measurements of the diffraction and the density of the crystal. The identity of the elements in a crystal, as well as the nature of the chemical bonding between them, may also be derived from measurement of the electron density distribution within it. The importance of Bragg’s Law, relating X-ray pattern to interatomic distance, is demonstrated, and initial applications of it by Bragg and Pauling are given.