Atomic Physics

Atomic physics is the study of the composition of the atom, its interactions with other particles and subatomic energy states. This branch of physics has been proved to be a brilliant application of quantum mechanics. It is one of the essential pillars of modern physics.

Ernest Rutherford laid down the foundations of modern atomic physics through a set of experiments. With the help of alpha particles, he detected the variations in the atomic composition by visually observing results on a phosphorescent screen. He bombarded alpha particles as projectiles on a variety of targets. Through the analysis of scattered particle distribution, he demonstrated that the interaction of atoms with the alpha particles followed Coulomb’s inverse-square law, up to the lengths of 100 fm (femtometre).

Evolution of Atomic Physics

The image produced from Rutherford’s tests was of a body consisting of a massive and concentrated positively charged core. A negatively charged gas envelops the dense core. Previous atomic models were filled with some glaring drawbacks. J.J Thomson’s atomic model lacked a solid explanation of positive and negative entities. The finding of the neutron by James Chadwick solved the issue of isotopic composition. It also clarified the connection between nuclear spin and atomic weight. With the discovery of the building blocks of atoms like neutrons and protons, modern atomic physics was launched.

In 1913, Niels Bohr proposed his atomic model in which electrons circle around the dense nucleus in quantised planetary orbits. Studies of subatomic interactions by physicists like Werner Heisenberg and Erwin Schrödinger led to the formation of quantum mechanics. The uncertainty principle and Schrödinger’s equation fundamentally define the characteristics of subatomic particles and interactions.

Hideki Yukawa proposed the existence of an exclusive intermediate elementary particle to act as an agent to glue protons and neutrons together in the nucleus. In 1938, Seth Neddermeyer and Carl Anderson discovered a probable particle that did not look to interact strongly with the nuclei. The issue was solved by Cecil Powell, who discovered two particles, the pi and mu mesons. The pi mesons are the hypothetical Yukawa particle. The muon or mu meson is also known as the Anderson–Neddermeyer particle. These discoveries solidified the relevance of speculative theoretical induction. It helped to finish the first phase of microscopic representation of the nuclear structure. Subsequently, a plethora of elementary particles has been discovered. Each has its own unique role in the quantum world.

The detection of the fission process by Otto Hahn and Fritz Strassmann paved the way for developing the atomic bomb and fission reactors for power generation. The fusion reaction is the process by which the stars generate their energy. This was the primary inspiration for the design of the hydrogen bomb in the 1950s. There has been heavy research during the adjacent decades to exploit thermonuclear fusion as a consumable power source. Many new stable isotopes and radioactive isotopes have been discovered since. Isotope identification techniques and nuclear magnetic resonance have been developed from this science. These are very helpful for archaeological and geological dating, planetary histories, atmospheric flow patterns, tracing of water, medical diagnosis, and many other applications.

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Modern Atomic Physics

Recently, the power lasers have dramatically rejuvenated the field of atomic physics. Lasers have exponentially increased the precision of measurement of an atom’s characteristic wavelengths. Modern standards of frequency and time are based on the calculations of transition frequencies in atomic caesium clocks. The definition of unit ‘metre’ is connected to the measurement of frequency through the light’s velocity. Apart from these examples, lasers have been utilised in techniques for separating individual atoms and cooling them close to absolute zero. When atoms are made to rest in the electromagnetic trap, they can indulge in a quantum mechanical phase change to form a unique superfluid called Bose-Einstein condensation, while continuing to be in the form of a dilute gas. In this matter state, every atom is in the identical coherent quantum state. As a result, the atoms drop their individual characteristics. The quantum mechanical wave characteristics become more prominent. The whole condensate then reacts to external influences as a lone coherent entity instead of a set of individual atoms. Recent research has revealed that a coherent beam of atoms can be taken from the trap to make an “atom laser” similar to the coherent photon beam in a conventional laser. This form of laser is still being developed. It has a huge potential to be a key tool in the development of cutting edge technologies for the creation of microelectronic and nanoscale apparatuses.

Atomic Structure – Electronic Configuration

The electronic configuration of atoms is the depiction of the order of electrons placed among the subatomic shells and subshells. Generally, the electron configuration is used for the above purpose, but it is also helpful to depict atoms that have ionised into an anion or action by compensation for the gain or loss of electrons in their adjacent orbitals. Various chemical and physical characteristics of elements are connected to their distinct electronic configurations. The electrons in the farthest shell are the critical factor for the distinct chemistry of the elements.

Electrons make up the subatomic shells around the proton-neutron core. These are usually in a ground state. However, they can be excited by the intake of energy from light, interaction with colliding particles, or magnetic fields. Electrons that make up the shell are considered to be in a bound state. The energy required to eliminate an electron from the corresponding shell is known as the binding energy. Any amount of energy absorbed by the electrons greater than this amount is transformed into kinetic energy (as per conservation of energy). The atom is considered to have gone through ionisation. If the electrons absorb an amount of energy greater than the fixed binding energy, it will be displaced to an excited state. After a fixed period of time, the electrons in excited states will jump to a lower energy state. In the case of a neutral atom, it will release a photon of the variation in energy since energy is always conserved.

When an electron has consumed much more than the binding energy, a more exterior electron may go through a transition to occupy the inner orbital. In this scenario, a characteristic x-ray or a visible photon is released. In another case, a process called the Auger effect could occur, where the emitted energy is transmitted to another bounded electron. There are strict conditions for achieving different types of electronic configurations that can be achieved by excitation by light. In the case of collision processes, there are no such rules.

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