Ionization is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected.
A Rydberg atom is an excited atom with one or more electrons that have a very high principal quantum number, n. The higher the value of n, the farther the electron is from the nucleus, on average. Rydberg atoms have a number of peculiar properties including an exaggerated response to electric and magnetic fields, long decay periods and electron wavefunctions that approximate, under some conditions, classical orbits of electrons about the nuclei. The core electrons shield the outer electron from the electric field of the nucleus such that, from a distance, the electric potential looks identical to that experienced by the electron in a hydrogen atom.
Plasma acceleration is a technique for accelerating charged particles, such as electrons, positrons, and ions, using the electric field associated with electron plasma wave or other high-gradient plasma structures. The plasma acceleration structures are created either using ultra-short laser pulses or energetic particle beams that are matched to the plasma parameters. These techniques offer a way to build high performance particle accelerators of much smaller size than conventional devices. The basic concepts of plasma acceleration and its possibilities were originally conceived by Toshiki Tajima and John M. Dawson of UCLA in 1979. The initial experimental designs for a "wakefield" accelerator were conceived at UCLA by Chandrashekhar J. Joshi et al. Current experimental devices show accelerating gradients several orders of magnitude better than current particle accelerators over very short distances, and about one order of magnitude better at the one meter scale.
Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. Normally, beams of light pass through each other unperturbed. Inside an optical material, and if the intensity of the beams is high enough, the beams may affect each other through a variety of non-linear effects. In pure vacuum, some weak scattering of light by light exists as well. Also, above some threshold of this center-of-mass energy of the system of the two photons, matter can be created.
A shape resonance is a metastable state in which an electron is trapped due to the shape of a potential barrier. Altunata describes a state as being a shape resonance if, "the internal state of the system remains unchanged upon disintegration of the quasi-bound level." A more general discussion of resonances and their taxonomies in molecular system can be found in the review article by Schulz,; for the discovery of the Fano resonance line-shape and for the Majorana pioneering work in this field by Antonio Bianconi; and for a mathematical review by Combes et al.
Elastic recoil detection analysis (ERDA), also referred to as forward recoil scattering, is an ion beam analysis technique in materials science to obtain elemental concentration depth profiles in thin films. This technique is known by several different names. These names are listed below. In the technique of ERDA, an energetic ion beam is directed at a sample to be characterized and there is an elastic nuclear interaction between the ions of beam and the atoms of the target sample. Such interactions are commonly of Coulomb nature. Depending on the kinetics of the ions, cross section area, and the loss of energy of the ions in the matter, ERDA helps determine the quantification of the elemental analysis. It also provides information about the depth profile of the sample.
Electron beam ion trap (EBIT) is an electromagnetic bottle that produces and confines highly charged ions. An EBIT uses an electron beam focused with a powerful magnetic field to ionize atoms to high charge states by successive electron impact.
Di-positronium, or dipositronium, is an exotic molecule consisting of two atoms of positronium. It was predicted to exist in 1946 by John Archibald Wheeler, and subsequently studied theoretically, but was not observed until 2007 in an experiment performed by David Cassidy and Allen Mills at the University of California, Riverside. The researchers made the positronium molecules by firing intense bursts of positrons into a thin film of porous silicon dioxide. Upon slowing down in the silica, the positrons captured ordinary electrons to form positronium atoms. Within the silica, these were long lived enough to interact, forming molecular di-positronium. Advances in trapping and manipulating positrons, and spectroscopy techniques have enabled studies of Ps–Ps interactions. In 2012, Cassidy et al. were able to produce the excited molecular positronium angular momentum state.
David Matthew Ceperley is a theoretical physicist in the physics department at the University of Illinois Urbana-Champaign or UIUC. He is a world expert in the area of Quantum Monte Carlo computations, a method of calculation that is generally recognised to provide accurate quantitative results for many-body problems described by quantum mechanics.
Hot spots in subatomic physics are regions of high energy density or temperature in hadronic or nuclear matter.
Swift heavy ions are the components of a type of particle beam with high enough energy that electronic stopping dominates over nuclear stopping. They are accelerated in particle accelerators to very high energies, typically in the MeV or GeV range and have sufficient energy and mass to penetrate solids on a straight line. In many solids swift heavy ions release sufficient energy to induce permanently modified cylindrical zones, so-called ion tracks. If the irradiation is carried out in an initially crystalline material, ion tracks consist of an amorphous cylinder. Ion tracks can be produced in many amorphizing materials, but not in pure metals, where the high electronic heat conductivity dissipates away the electronic heating before the ion track has time to form.
High-precision experiments could reveal small previously unseen differences between the behavior of matter and antimatter. This prospect is appealing to physicists because it may show that nature is not Lorentz symmetric.
The helical orbit spectrometer (HELIOS) is a measurement device for studying nuclear reactions in inverse kinematics. It is installed at the ATLAS facility at Argonne National Laboratory.
Erwin Gabathuler was a particle physicist from Northern Ireland.
Double ionization is a process of formation of doubly charged ions when laser radiation is exerted on neutral atoms or molecules. Double ionization is usually less probable than single-electron ionization. Two types of double ionization are distinguished: sequential and non-sequential.
A non-neutral plasma is a plasma whose net charge creates an electric field large enough to play an important or even dominant role in the plasma dynamics. The simplest non-neutral plasmas are plasmas consisting of a single charge species. Examples of single species non-neutral plasmas that have been created in laboratory experiments are plasmas consisting entirely of electrons, pure ion plasmas, positron plasmas, and antiproton plasmas.
Carlos O. Lousto is a Distinguished Professor in the School of Mathematical Sciences in Rochester Institute of Technology, known for his work on black hole collisions.
Louis Franklin DiMauro is an American atomic physicist, the Edward and Sylvia Hagenlocker Professor In the Department of Physics at The Ohio State University, Columbus, Ohio, USA. His interests are atomic, molecular and optical physics. He has been elected a Fellow of the American Association for the Advancement of Science, American Physical Society and Optical Society.
Frans Pretorius is a South African and Canadian physicist, specializing in computer simulations in astrophysics and numerical solutions of Einstein's field equations. He is professor of physics at Princeton University and director of the Princeton Gravity Initiative.
Toshiki Tajima is a Japanese theoretical plasma physicist known for pioneering the laser wakefield acceleration technique with John M. Dawson in 1979. The technique is used to accelerate particles in a plasma and was experimentally realized in 1994, for which Tajima received several awards such as the Nishina Memorial Prize (2006), the Enrico Fermi Prize (2015), the Robert R. Wilson Prize (2019), the Hannes Alfvén Prize (2019) and the Charles Hard Townes Award (2020).
