The discovery of radioactivity opened up the way for the creation and development of nuclear chemistry in the early twentieth century. In the mid-twentieth century, novel findings and the Second World War ushered in the Nuclear Age. From nuclear power generation to war damage, nuclear chemistry has shown tremendous potential. The wide proliferation of the area has brought about a wide variety of nuclear chemistry topics - what is nuclear chemistry, nuclear radiations, artificially simulated nuclear reactions (fission and fusion), and the uses of nuclear chemistry.
Nuclear chemistry is a sub-discipline of chemistry dealing with the study of changes in the nucleus of atoms of elements. These nuclear changes are a source of nuclear power and radioactivity, and the energy released from the nuclear reactions have far-reaching applications. Nuclear chemistry is also termed as radiochemistry, which involves the study of the elements composing the universe, design, and development of radioactive drugs for medicinal uses, and several other scientific applications.
Nuclear radiation refers to the photons and particles that are emitted during nuclear reactions. The particles emitted in nuclear reactions possess an energy that is tremendous enough to knock electrons from atoms and molecules, thereby ionizing them. For this reason, nuclear radiations are also known as ionizing radiation.
Nuclear radiations include alpha rays, beta rays, and gamma rays. Nuclear reactions release ionizing subatomic particles, including alpha particles, neutrons, beta particles, mesons, muons, positrons, and cosmic rays. Example: during Uranium-235 fission, the nuclear radiation that is emitted contains gamma-ray photons and neutrons.
Types of Radiations
Alpha Radiation: Alpha radiation is the emission of alpha particles when an atom goes through radioactive decay. An alpha particle consists of two protons and two neutrons and is similar to a Helium-4 atom. Thus, the resulting element has an atomic number less by two units and an atomic mass less by four units than that of the originating element. Example: Uranium-238 undergoes alpha decay in the following manner:
23892U → 23490Th + 42He
Beta Radiation: Consists of a stream of high-speed electrons. Beta-decay is of two types –beta plus and beta minus. In beta plus decay, the nucleus emits a positively charged electron (positron) and a proton that is converted into a neutron (neutrino). In beta minus decay, the nucleus emits a neutron that is transformed into a proton (antineutrino) and an electron.
Beta minus decay: 1n → 1p+ + 0-1β- + v̅
Beta plus decay: 11p+ → 10n + 01β + v
127N ⟶ 612C + 01β+
146C ⟶ 147N + 0-1β
Gamma Radiation: Gamma radiation (γ) does not consist of any particles. Instead, it involves photons of energy being emitted from an unstable radioactive nucleus. Gamma rays are electromagnetic radiations of short wavelength and have no charge or mass. These rays represent the loss in energy when the remaining nucleons undergo stable rearrangements, and thus, gamma rays accompany other radioactive emissions. Example:
23892U → 23490Th + 42He + 200γ
Nuclear Fission is an artificially simulated nuclear reaction where a heavy nucleus splits into two lighter nuclei. Fission was discovered by bombarding a sample of Uranium-235 with neutrons, which resulted in the production of lighter elements like Barium. In a typical nuclear chain reaction, each dividing nucleus releases more than one neutron, which, in turn, collides with neighboring nuclei and induces a succession of self-sustaining nuclear fission reactions. The fission rate increases geometrically with each generation of events.
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Nuclear Fusion is also an artificially simulated nuclear reaction in which two or more nuclei of elements combine to produce a heavier and more stable nucleus. The initiation of the fusion process requires very high temperatures, which are obtained from nuclear fission reactions. Nuclear Fusion generates explosive amounts of energy, which is the source of power for the sun and all the stars. Examples: deuterium-deuterium (D-D) fusion, deuterium-tritium (D-T) fusion.
2 21H → 32He + 10n
21H + 31H → 42He + 10n
Plant mutation breeding to achieve improved nutrition and food security.
Management of fertilizer use through Radiolabelling.
Controlling insect populations.
Smoke detectors, non-stick materials, clocks, and watches utilize radioisotopes.
Food irradiation with gamma rays to prevent spoilage and enhance shelf-life.
Radioactive tracers find use in industrial processes.
Inspection of instruments.
Nuclear desalination of water.
MRI scans, CT scans, and X-rays for diagnosis.
Radioactive Iodine is used for the treatment of cancers.
Sterilization of medical instruments.
Nuclear-powered submarines and ships.
Radioisotope thermal generators for electricity production in space missions.
1. How are Nuclear Reactions Different from Chemical Reactions?
In chemical reactions, bonds are broken and formed between two different atoms, whereas in nuclear reactions, the nuclei of a single atom emit particles or rays.
Atoms themselves remain unchanged but undergo rearrangements in chemical reactions. On the other hand, nuclear reactions involve a change in the nuclear composition and hence, a transformation of one atom to another type.
While chemical reactions involve valence electrons, nuclear reactions include electrons, protons, and neutrons.
Chemical reactions entail small energy changes. But nuclear reactions are accompanied by substantial changes in energy.
The factors influencing the rate of a chemical reaction include temperature, reactant, and product concentration, pressure, and the presence of catalysts. However, nuclear reactions are unaffected by any of these factors, and their rate can vary between a few milliseconds or millions of years.
2. What is Transmutation in Nuclear Chemistry?
Nuclear transmutation is the conversion of an atom of one element into an atom of another element through nuclear reactions. Transmutation can occur in two ways – when the nucleus of an atom decays radioactively, or when the nucleus reacts with another particle. In induced nuclear transmutation, the nuclei are bombarded with high volume particles to induce transmutation. In 1919, Ernest Rutherford carried out the first nuclear transmutation. He used high-speed α particles from a natural isotope of radioactive radium to bombard nitrogen atoms. The reaction is:
147N + 42He →178O + 11H
The reaction resulted in the formation of protons and oxygen nuclei, which were stable, and thus, no further nuclear changes took place.
Particle accelerators are used to achieve the kinetic energy necessary for transmutation reactions. These devices utilize electric and magnetic fields to accelerate nuclear particles; the latter move in vacuum to avoid smashing with gas molecules.