LXI. The laws of deflexion of a particles through large angles

Resolving the Scales of the Quark-Gluon Plasma with Energy Correlators

Jets provide us with ideal probes of the quark-gluon plasma (QGP) produced in heavy-ion collisions, since its dynamics at its different scales is imprinted into the multiscale substructure of the final state jets. We present a new approach to jet substructure in heavy-ion collisions based on the study of correlation functions of energy flow operators. By analyzing the two-point correlator of an in-medium quark jet, we demonstrate that the spectra of correlation functions robustly identify the scales defined by the properties of the QGP, particularly those associated with the onset of color coherence.

Elemental Depth Profiling of Intact Metal-Organic Framework Single Crystals by Scanning Nuclear Microprobe

The growing field of MOF–catalyst composites often relies on postsynthetic modifications for the installation of active sites. In the resulting MOFs, the spatial distribution of the inserted catalysts has far-reaching ramifications for the performance of the system and thus needs to be precisely determined. Herein, we report the application of a scanning nuclear microprobe for accurate and nondestructive depth profiling of individual UiO-66 and UiO-67 (UiO = Universitetet i Oslo) single crystals. Initial optimization work using native UiO-66 crystals yielded a microbeam method which avoided beam damage, while subsequent analysis of Zr/Hf mixed-metal UiO-66 crystals demonstrated the potential of the method to obtain high-resolution depth profiles. The microbeam method was further used to analyze the depth distribution of postsynthetically introduced organic moieties, revealing either core–shell or uniform incorporation can be obtained depending on the size of the introduced molecule, as well as the number of carboxylate binding groups. Finally, the spatial distribution of platinum centers that were postsynthetically installed in the bpy binding pockets of UiO-67-bpy (bpy = 5,5′-dicarboxyy-2,2′-bipyridine) was analyzed by microbeam and contextualized. We expect that the method presented herein will be applicable for characterizing a wide variety of MOFs subjected to postsynthetic modifications and provide information crucial for their optimization as functional materials.

Atomic Concealment Due to Loss of Coherence of the Incident Beam of Projectiles in Collision Processes

In the study of collision processes, a series of conditions is usually assumed. One of them is that the beam of projectiles is coherent in lengths greater than those of the targets against which it strikes. However, recent experimental results and theoretical analyzes have shown that this assumption can not only fail, but that it is possible to manipulate the coherence length experimentally to go from a coherent situation to an incoherent one. The most conspicuous and studied manifestation of such loss of coherence is the disappearance of interference effects. However, in the present work we show that a strong decrease can also occur in the magnitude of the cross section, not only differential but also total, due to an atomic concealment effect.

Henry Moseley, X-ray spectroscopy and the periodic table

Just over 100 years ago, Henry Moseley carried out a systematic series of experiments which showed that the frequencies of the X-rays emitted from an elemental target under bombardment by cathode rays were characteristic of that element and could be used to identify the charge on its atomic nucleus. This led to a reorganization of the periodic table, with chemical elements now arranged on the basis of atomic number Z rather than atomic weight A, as had been the case in previous tables, including those developed by Mendeleev. Moseley also showed that there were four 'missing elements' before gold. With further measurements up to uranium Z = 92, the Swedish physicist Manne Siegbahn identified two more missing elements. This paper provides an introduction to Moseley and his experiments and then traces attempts to 'discover' missing elements by X-ray spectroscopy. There were two successes with hafnium (Z = 72) and rhenium (Z = 75), but many blind alleys and episodes of self-deception when dealing with elements 43, 61, 85 and 87. These all turned out to be radioactive, with extremely small natural abundances: all required synthesis by a nuclear reaction, with radiological characterization in the first instance. Finally, the paper moves on to consider the role of X-ray spectroscopy in exploring the periodic table beyond uranium. Although the discovery of artificial radioactive elements with Z > 92 again depended on nucleosynthesis and radiological characterization, measurement of the frequencies or energies of characteristic X-rays remains the ultimate goal in proving the existence of an element. This article is part of the theme issue 'Mendeleev and the periodic table'.

The multi-scale nature of the solar wind

The solar wind is a magnetized plasma and as such exhibits collective plasma behavior associated with its characteristic spatial and temporal scales. The characteristic length scales include the size of the heliosphere, the collisional mean free paths of all species, their inertial lengths, their gyration radii, and their Debye lengths. The characteristic timescales include the expansion time, the collision times, and the periods associated with gyration, waves, and oscillations. We review the past and present research into the multi-scale nature of the solar wind based on in-situ spacecraft measurements and plasma theory. We emphasize that couplings of processes across scales are important for the global dynamics and thermodynamics of the solar wind. We describe methods to measure in-situ properties of particles and fields. We then discuss the role of expansion effects, non-equilibrium distribution functions, collisions, waves, turbulence, and kinetic microinstabilities for the multi-scale plasma evolution.

100th anniversary of Bohr's model of the atom

In the fall of 1913 Niels Bohr formulated his atomic models at the age of 27. This Essay traces Bohr's fundamental reasoning regarding atomic structure and spectra, the periodic table of the elements, and chemical bonding. His enduring insights and superseded suppositions are also discussed.

Artificial neural network algorithm for analysis of rutherford backscattering data

Rutherford backscattering (RBS) is a nondestructive, fully quantitative technique for accurately determining the compositional depth profile of thin films. The inverse RBS problem, which is to determine from the data the corresponding sample structure, is, however, in general ill posed. Skilled analysts use their knowledge and experience to recognize recurring features in the data and relate them to features in the sample structure. This is then followed by a detailed quantitative analysis. We have developed an artificial neural network (ANN) for the same purpose, applied to the specific case of Ge-implanted Si. The ANN was trained with thousands of constructed spectra of samples for which the structure is known. It thus learns how to interpret the spectrum of a given sample, without any knowledge of the physics involved. The ANN was then applied to experimental data from samples of unknown structure. The quantitative results obtained were compared with those given by traditional analysis methods and are excellent. The major advantage of ANNs over those other methods is that, after the time-consuming training phase, the analysis is instantaneous, which opens the door to automated on-line data analysis. Furthermore, the ANN was able to distinguish two different classes of data which are experimentally difficult to analyze. This opens the door to automated on-line optimization of the experimental conditions.

The application of ion beam analysis to calcium phosphate-based biomaterials

Ion beam technology may be applied in a straightforward fashion to the analysis and modification of biomaterials. For analytical purposes, characterization using megaelectron-volt He2+ ions provides a standardless, nondestructive means for accurately quantifying the composition of material surfaces and the thickness of thin films. In this study, three complementary ion backscattering techniques were utilized to characterize hydroxyapatite (HA) films: Rutherford backscattering spectrometry (RBS) can determine composition and amounts of elements heavier than He; forward recoil elastic spectrometry (FRES) can determine hydrogen content; resonance-enhanced RBS can quantify small amounts of light elements, e.g. carbon, by choosing a particular incident beam energy resulting in excitation of the light element nucleus. At this resonance energy, the scattering cross section greatly increases, improving elemental sensitivity. Sol-gel chemistry was used to synthesize HA films by spin coating and annealing in a rapid thermal processor. Using these techniques, the chemical composition of unfired films was Ca1.63O5.4H1.8C0.24P with a thickness of 3.01 x 10(18) atoms/cm2 and after firing at 800 degrees C as Ca1.66O4.0H0.26C0.09P with a thickness of 2.11 x 10(18) atoms/cm2. This compares favorably to stoichiometric HA, which has a composition of Ca1.67O4.33H0.33P.