The combined results of various scientific experiments, technological efforts, and commercial applications have shaped the nuclear physics we know today. Over the past few centuries, the foundational principles of nuclear physics have emerged from the integration of knowledge gained in chemistry and physics, evolving through various experiments in the last 100 years to achieve its modern form.
The origins of nuclear physics can be traced back to the latter half of the 19th century through the quest to unravel the mysteries of the atom. In 1808, Dalton provided a scientifically valid explanation of atomic theory. According to his theory, the atom is the smallest indivisible part of an element. Although the notion of the atom being indivisible persisted for a long time, it failed to satisfy the curiosity of knowledge-seeking individuals.
In 1879, Crookes ionized gas with the help of electric discharge, adding a new dimension to the history of physics and marking the start of the modern era of nuclear physics. In 1895, Röntgen discovered highly penetrating rays (X-rays) from an electric discharge tube, and in 1896, Becquerel observed a similar type of ray (γ ray), which is spontaneously emitted from uranium. These discoveries enriched the field’s body of knowledge and also provided proof that particles smaller than atoms exist in nature, residing within the atom itself. In 1897, Sir J.J. Thomson discovered such a particle. Known as the electron, this tiny, negatively charged particle has a mass of 9×10^-31 kg and determines the atom’s chemical properties.
Although the presence of electrons and positive particles inside an atom had been discovered, the true structure of the atom still remained unknown. Later, through various experiments by Rutherford and Bohr, it was established that within the atom, electrons revolve around a positively charged nucleus.
Subsequently, scientists became determined to explore the mysteries of the nucleus. In 1919, Rutherford used alpha particles to bombard nitrogen and observed the first nuclear transformation. It was during this time that the proton was discovered. In 1932, James Chadwick bombarded beryllium with alpha particles emitted from polonium and discovered the neutron. For the first time, scientists realized that the nucleus is made of neutrons and protons. To answer how neutrons and protons stay bound so strongly together, Japanese scientist Yukawa proposed the meson theory in 1935. Later, with the discovery of the meson during cosmic ray research in 1947, a revolutionary chapter was added to nuclear physics. The invention of particle accelerators also ushered in a new era. These devices hurl powerful particles at great speeds toward various nuclei, causing numerous reactions that reveal new information about the structure of the target nucleus. Additionally, because neutrons are electrically neutral, slow neutrons can easily react with nuclei. For this reason, neutron reactions have become particularly significant in the study of nuclear properties and characteristics.
In general, these reactions require some energy to occur, and in the process, a significant amount of energy is released—far greater than that of chemical reactions. It is believed that, with the right reaction, tremendous amounts of energy can be generated. In 1938, such a process—the ‘fission process’ (the splitting of a nucleus)—was discovered, releasing vast quantities of energy. The uncontrolled release of this energy is what powers atomic bomb explosions, a dark chapter in the history of nuclear physics.
Over time, the knowledge of nuclear physics has extended beyond fundamental research to serve humanity’s needs. The discovery of radioactive isotopes and the invention of certain nuclear techniques have greatly benefited humankind. Nuclear physics is now used in various fields of science, such as medicine, agricultural science, food preservation, industry, geology, archaeology—even in seemingly unrelated areas like anti-corruption efforts.
Today, a significant portion of the world’s energy needs is met by nuclear (fission) reactors. It is believed that the necessary uranium can be harvested for a very long time in the future. Furthermore, a special kind of fission reactor known as a breeder reactor has been developed, which produces more fuel than it consumes. The construction and use of these reactors remain at an early stage, but the development and effectiveness of this technology will determine the future supply of energy for humanity.
We may have noticed that the sun has been shining for billions of years. If it used conventional fuels like oil or coal, it would certainly have gone out by now. After much research, it was discovered that within the sun, energy is being generated through a remarkable nuclear reaction. This reaction is the complete opposite of the fission process. In fission, a heavy nucleus splits to form lighter nuclei; in the sun, light nuclei fuse together to form a heavy nucleus. In this way, humans came to know about the fusion process, or ‘thermonuclear reaction.’ Though fission and fusion are opposite processes, the fundamental secret of energy production lies in the same realm. For the first time in 1951, humanity managed to trigger this reaction in an uncontrolled manner in the explosion of the hydrogen bomb. Today, tremendous efforts are being made to harness energy through controlled fusion reactions. If ‘fusion reactors’ can be built, humanity will never have to worry about fuel again, because the fuel for these reactors will be deuterium or heavy hydrogen, which is abundantly available in seawater. However, no one knows yet when this inexhaustible energy source will become available to humanity. Thus, the realization of future fusion reactors remains a significant challenge for humankind. To achieve their successful use, we must advance our technical capabilities to the highest possible standards—requiring continuous, accelerated experimentation.
Inside the nucleus, neutrons and protons are arranged in different energy levels, much like electrons in the atom. Currently, attempts are being made to explain the wide range of nuclear properties through a combination of two contrasting models: nucleons moving in ‘shells’ and being bound together by the strong nuclear force. However, much remains to be understood, as the nature of this force has not yet been fully elucidated. Moreover, the strong interactions among the nucleons in the nucleus add to the complexity. Overcoming the theoretical challenges associated with these two problems is extremely difficult.
Nuclear reactions between two large nuclei (heavy ion collisions) occur at very high energies, and this branch of nuclear physics has recently become an area of extensive research. Scientists believe that these reactions may lead to the discovery of ‘super heavy’ elements.
Electron, proton, neutron, the meson (carrier of the nuclear force), neutrino produced in beta decay, the photon—and all their corresponding antiparticles—made up the known world of fundamental particles. From the early 1950s, new types of fundamental particles began to be discovered in large numbers. Scientists have been busy trying to understand the properties and characteristics of these particles and classify them in various ways. As a result, many mysteries of the particle world have been revealed and continue to be so even today. Currently, the number of all recognized fundamental particles exceeds two hundred. Now, the very fundamentality of many particles has come into question, as it has been found that almost all of them are actually made up of a few even smaller, truly ‘elementary’ particles called ‘quarks.’
Quantum mechanics, developed in the 20th century, has provided the theoretical foundation for modern physics. Around the same time, the discovery of nuclear accelerators and particle detectors greatly expanded the field of experimentation. Since World War II, ever more powerful and versatile accelerators have been built, along with advanced detectors and computer technology. These advancements have accelerated the progress of nuclear physics and opened doors to the previously unknown world of particle physics. Likewise, the advent of quantum electrodynamics and quantum chromodynamics has revolutionized the world of theory. Today, nuclear physics is mainly divided into two areas: ‘low energy nuclear physics,’ which focuses on nuclear forces and structure, and ‘high energy nuclear physics,’ which covers particle physics topics.
An inseparable part of fundamental particle physics is the four fundamental forces of nature: gravitational, weak, electromagnetic, and strong. Whether it is galaxies, stars, the earth, molecules, atoms, nuclei, or fundamental particles, all forms of energy interactions are governed by the individual or combined effects of these four forces. Through theoretical and experimental research in particle physics, the properties and mysteries of these forces have been revealed in revolutionary ways. Although these forces may appear different in nature, deep relationships and harmonies have been observed among them. Continuous efforts are underway to unify all four forces, either individually or collectively. In 1967, American scientist Steven Weinberg and Pakistani scientist Abdus Salam first unified the weak and electromagnetic forces through the ‘gauge theory.’ Later, the discovery of experimental results that matched the predictions of this theory advanced the process of unification significantly. Scientists hope that in the future, it will be possible to unify all four forces. The immense order and breathtaking beauty we believe exists in nature will be justified with the much-anticipated discovery of the ‘grand unification.’
References: Introductory Nuclear Physics- Krane
An Introduction to Nuclear Physics- Cottingham & Greenwood
Nuclear Physics- Islam & Islam
Nuclear Energy- Raymond L. Murray
The Harnessed Atom- U.S. Department of Energy
Addendum
This is my first article on any technology forum. Besides, writing is not exactly my strong suit. I have gathered information from various references and refined, edited, and presented them to readers. Nevertheless, knowing that readers appreciate this ‘refinement and editing’ makes me very happy and inspired.
Everything in the created universe moves forward along a defined path. To know where this ‘forward’ journey is heading, one must first understand the entire path—which compels us to look back. Perhaps that is why scientific articles often begin with the ‘burden of history’ (which is, most of the time, unnecessary!).
The first 92 elements of the periodic table are naturally occurring. The rest are artificial—each is radioactive and extremely short-lived, with half-lives ranging from a few milliseconds to a few seconds! The elements above atomic number 104 (Rutherfordium) in the periodic table are known as ‘Super Heavy Elements’ (SHE). Currently, scientists aim to achieve stable SHEs, which could be possible if the ‘Island of Stability’ is reached through some nuclear reaction. The Island of Stability refers to the position of elements with ‘magic numbers’1 of neutrons and protons in the periodic table—a position associated with stability for a particular element, while those nearby are unstable. This element must be a transition metal isotope with much higher endurance. Thus, the desired SHE will be a very stable element.
Gauge Theory refers to a special type of ‘symmetry transformation’ of a field, where the field can transform either locally or globally, while maintaining ‘invariance.’ Gravity is the simplest example of a gauge theory since gravity remains the same ‘event’ under transformations across different ‘frameworks.’
The gauge theory can successfully explain the interactions between ‘quarks’ and ‘gluons’ if they are in a state of very high energy. However, gauge theory cannot explain the behavior of low-energy particles.
##1:
In nuclear physics, a magic number refers to the specific numbers of protons or neutrons (or both) in a nucleus that result in particularly strong binding energy, making the nucleus very stable. So far, seven magic numbers—2, 8, 20, 28, 50, 82, and 126—have been identified. There is also a potential magic number, 184, which may be the possible neutron count for the Island of Stability.
This article was first published on our technology forum on January 14, 2008.
With the author’s permission, it is republished on Scientist.org.
The author is currently serving as a Research Assistant at the Solar Energy Research Centre of Jagannath University.
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