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Atomic and Nuclear Physics

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[Palo Verde Nuclear Power Plant, Arizona - US Department of Energy]


- Overview

Knowledge of nuclear physics is essential in many areas of our lives. The most common application of nuclear physics is nuclear power generation. Modern nuclear physics also includes particle physics, which is closely related to nuclear physics. Many of today's most important advances in medicine, materials, energy, security, climatology, and many other scientific fields stem from the wellspring of fundamental research and development in nuclear physics. 

Knowledge of atomic and nuclear physics is essential for nuclear engineers dealing with nuclear reactors. It should be noted that atomic and nuclear physics is a very broad branch of science. Nuclear reactor physics belongs to applied physics. Reactor physics, particle physics or other branches of modern physics share common ground. Atomic and nuclear physics describe elementary particles (i.e. electrons, protons, neutrons), structure, properties and behavior.

Atomic physics is not the same as nuclear physics. Due to the synonymous use of atom and nucleus in Standard English, the term atomic physics is often associated with nuclear energy. However, physicists distinguish between atomic physics and nuclear physics. Atomic physics treats atoms as systems composed of nuclei and electrons. Nuclear physics treats the nucleus as a system of nucleons (protons and neutrons). The main difference is scale. While the term atom refers to 1Å = 10-10m, where Å is an ångström (according to Anders Jonas Ångström), the term nucleus refers to 1femtometre = 1fermi = 10-15m.


- Nuclear Physics

Nuclear physics is the field of physics that studies the composition (protons and neutrons) and interactions of atomic nuclei. The most well-known application of nuclear physics is nuclear power generation, but modern nuclear physics also includes particle physics, which is closely related to nuclear physics. Nuclear physics has provided applications in many fields, including nuclear medicine (positron emission tomography, isotope production, etc.) and magnetic resonance imaging, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology.

The physical world consists of various combinations of subatomic or elementary particles. These are the smallest components of matter.  Elementary particles and interactions are summarized in a theoretical model called the Standard Model. An atom consists of two parts. An atomic nucleus and an electron cloud.

The nuclear properties of an element (atomic mass, nuclear cross section) are determined by the number of protons (atomic number) and the number of neutrons (number of neutrons).

Nuclear stability is a concept that helps determine isotopic stability. The ratio of neutrons to protons needs to be found to determine the stability of an isotope. To determine the stability of an isotope, you can use the neutron/proton ratio (N/Z).

Nuclear decay (radioactive decay) occurs when unstable atoms lose energy by emitting ionizing radiation.

Each type of particle interacts differently. Therefore, we have to describe the interactions of the particles separately (radiation as the flow of these particles).

A nuclear reaction is considered a process by which two nuclear particles (two nuclei or a nucleus and a nucleus) interact to produce two or more nuclear particles or ˠ rays (gamma rays).


- Atomic Physics

Atomic physics is the field of physics that studies atoms as isolated systems of electrons and nuclei. It focuses on the arrangement of electrons around the nucleus and the processes by which these arrangements change. This includes ions and neutral atoms, unless otherwise stated, the term atom should be assumed to include ions as used in this discussion. Atomic physics also helps to understand the physics of molecules, but molecular physics also describes the physical properties of molecules.


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- Nuclear Reactor Physics

Nuclear reactor physics is the field of physics that studies and deals with the applied research and engineering applications of neutron diffusion and fission chain reactions to induce controlled fission rates in nuclear reactors to produce energy. Nuclear reactor theory is based on diffusion theory and reactor dynamics, which define the "criticality" of a reactor. 

In general, the study of neutron nuclear reactions and nuclear reactions is crucial in the physics of nuclear reactors. Nuclear fission is a nuclear reaction or decay process in which heavy nuclei split into smaller parts (lighter nuclei). In nuclear physics, the nuclear cross-section of an atomic nucleus is often used to characterize the probability of a nuclear reaction occurring.

The Doppler broadening of the resonant capture cross section of fertile materials (eg, 238U or 240Pu) caused by the thermal motion of the target nucleus in the nuclear fuel is critical for reactor stability.

If the multiplication factor of the multiplication system is equal to 1.0, the chain reaction will be self-sustaining.

Neutron diffusion theory deals with the spatial migration of neutrons and helps to understand the relationship between reactor size, shape and criticality. It is also used to determine the spatial flux distribution within the power reactor.

Nuclear reactor dynamics deal with transient neutron flux changes due to deviations from criticality. Reactor dynamics is also known as reactor dynamics with feedback and steric effects.

Basic Reactor Operating Physics includes the following topics: Reactor Startup ("Critical Approach"), Reactor Control and Power Handling, and Xenon Oscillation.


- Nuclear Energy, Nuclear Fusion and Nuclear Fission

Nuclear technology uses the energy released by splitting the atoms of certain elements. It was first developed in the 1940s, and during the Second World War research initially focused on producing bombs. In the 1950s attention turned to the peaceful use of nuclear fission, controlling it for power generation. Nuclear energy is harnessed by either splitting (fission) or merging (fusion) the nuclei of two or more atoms. 

Nuclear fission usually uses uranium in the process of harnessing energy. At our current rates of consumption, the uranium found in the Earth’s crust can last us about a century. However researchers predict that the energy consumption will triple in the next decades, which means that the available uranium resources will only last us for approximately 30 years. One option is the reprocessing of the spent fuel. This spent fuel is rich in plutonium and when combined with the leftover uranium, it can be reprocessed into a mixture known as MOX, which can be used as fuel. This may help to stretch the available uranium resources by a few more decades. The biggest drawback to this source of energy is the disposal of radioactive waste and the high cost of building nuclear power plants. 

Nuclear fission, on the other hand, could be the answer to our energy problems. Fission utilizes hydrogen isotopes, lithium, and boron. The lithium reserves from the earth, combined with those from the sea, can last us for more than 60 million years. Deuterium, an isotope of hydrogen, can last another 250 million years. However, the process of harnessing energy from this isotope is fairly complicated and is still in its infancy. If we can successfully learn how to utilize nuclear fusion for the generation of energy in a viable manner, it could well be the new king of the energy world. Nuclear fusion is a clean process, with low carbon dioxide emissions, and the radioactive waste products also have a relatively short half-life.



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