Radioactivity, Atomic Nucleus, and Nuclear Reactions
Classified in Chemistry
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Radioactivity
Radioactive substances are characterized by emitting radiation capable of penetrating bodies that are opaque, ionizing the air, impressing photographic plates, and exciting the fluorescence of certain substances.
Alpha, Beta, and Gamma Radiation
Radioactive nuclei emit α radiation (helium nuclei), β (fast electrons), or γ (electromagnetic waves more energetic than X-rays). These radiations are ordered by their penetrating power in this way: α, β, and γ (from least to most penetrating).
Radioactive Decay
Radioactive decay is a random process. The number of nuclei, N, which have not yet disintegrated at an instant of time t is given by:
N = N0e-λt
The half-life, T, is the time required to disintegrate half of the initial nuclei.
T = ln2 / λ
Biological Effects and Applications of Radioactivity
Exposure to high doses of radiation can increase the risk of cancer and other genetic disorders. The most dangerous radiation to humans when the source is external to the body is γ (gamma) radiation, and when the source is internal to the body, it is α (alpha) radiation.
Radioactivity also has many uses in different fields: medicine, industry, chemistry, agriculture, engineering, etc.
The Atomic Nucleus
It is characterized by its atomic number Z (number of protons in the nucleus) and its mass number, A, (number of nucleons in the nucleus). That is, the atomic nucleus consists of Z protons and (A-Z) neutrons.
Nuclear Forces
The strong nuclear force holds the nucleus together. The weak nuclear force is responsible for β (beta) decay. Both forces are very short-range, but very intense.
Binding Energy
It is the energy released when several isolated nucleons come together to form the nucleus. In this process, the nucleons lose some of their mass. The mass defect is:
Δm = (Z mp + (A-Z) mn) - Mn
- mp = mass of the proton
- mn = mass of the neutron
- Mn = mass of the nucleus
The binding energy is related to the mass defect:
ΔE = Δm c2
Nuclear Reactions
These are processes in which atomic nuclei are converted into other, different nuclei.
Nuclear Reactions and Radioactivity
Radioactive nuclei disintegrate spontaneously, emitting α (alpha) and β (beta) radiation. The set of all the isotopes that occur until a stable nucleus is reached is called a radioactive series or family.
Nuclear Fission
It is a nuclear reaction in which a heavy nucleus is divided into two lighter nuclei when bombarded with neutrons. In the process, more neutrons and large amounts of energy are released.
Nuclear Fusion
It is a nuclear reaction in which two light nuclei combine to form a heavier nucleus. The process releases large amounts of energy.
Subatomic Particles and Fundamental Forces
Most subatomic particles are formed by other, simpler, known elementary particles.
All subatomic particles fall into two groups: leptons (not subject to the strong nuclear force) and hadrons (subject to the strong nuclear force). The latter, in turn, are formed by elementary particles called quarks.
There are four fundamental forces in nature: gravitational, electromagnetic, strong nuclear, and weak nuclear. Research is underway to unify all of them in the same mathematical theory. To date, the electromagnetic and weak nuclear forces have been unified.