Glossary
Conservation Laws in Nuclear Reactions
Principles stating that fundamental quantities such as energy, linear momentum, and angular momentum are conserved (remain constant) before and after a nuclear reaction.
Example:
When a nucleus undergoes decay, the total conservation laws in nuclear reactions dictate that the momentum of the emitted particles must balance the recoil of the remaining nucleus.
Conservation of Nucleon Number
A fundamental principle stating that the total number of protons and neutrons (nucleons) remains constant in any nuclear reaction.
Example:
In alpha decay, while the element changes, the total conservation of nucleon number ensures the sum of protons and neutrons before and after the decay remains the same.
Decay Constant ($\lambda$)
A proportionality constant that represents the probability per unit time that a single nucleus will undergo radioactive decay. It is inversely related to the half-life.
Example:
A high decay constant indicates that a radioactive isotope decays very quickly, meaning it has a short half-life.
Energy Release in Nuclear Processes
The phenomenon where nuclear reactions, like fission or fusion, result in a net decrease in mass, which is converted into kinetic energy of products or high-energy photons (gamma rays).
Example:
The heat generated in a nuclear reactor is a result of energy release in nuclear processes, primarily as kinetic energy of fission fragments.
Fission
The process where a heavy atomic nucleus splits into two or more lighter nuclei, often initiated by a neutron, releasing a large amount of energy.
Example:
Nuclear power plants generate electricity by controlling the fission of uranium atoms.
Fusion
The process where two or more light atomic nuclei combine to form a single, heavier nucleus, releasing a tremendous amount of energy.
Example:
The Sun's energy is produced through continuous fusion reactions of hydrogen isotopes.
Half-Life ($t_{1/2}$)
The characteristic time required for half of the radioactive nuclei in a given sample to undergo radioactive decay.
Example:
If a radioactive sample has a half-life of 10 years, after 20 years, only one-quarter of the original radioactive material will remain.
Induced Fission
The process where a heavy atomic nucleus is forced to split into lighter nuclei by absorbing an external particle, typically a neutron.
Example:
Nuclear reactors rely on induced fission by bombarding uranium-235 with neutrons to sustain a chain reaction.
Mass Defect
The difference between the mass of an atomic nucleus and the sum of the individual masses of its constituent protons and neutrons. This 'missing' mass is converted into the binding energy that holds the nucleus together.
Example:
The mass defect explains why the combined mass of two hydrogen nuclei is slightly greater than the mass of the helium nucleus they form in fusion, with the difference released as energy.
Mass-Energy Equivalence ($E=mc^2$)
Albert Einstein's principle stating that mass and energy are interchangeable and directly proportional, with a small change in mass corresponding to a large change in energy.
Example:
The immense energy released in nuclear bombs is a direct demonstration of mass-energy equivalence, where a tiny amount of mass is converted into pure energy.
Neutrons
Electrically neutral subatomic particles found in the nucleus of an atom, contributing to the atom's mass but not its charge.
Example:
Isotopes of an element, like carbon-12 and carbon-14, differ only in their number of neutrons.
Nuclear Physics
The study of the atomic nucleus, including its structure, forces, and transformations like fission, fusion, and radioactive decay.
Example:
Understanding nuclear physics is essential for designing safe and efficient nuclear power plants.
Nucleons
A collective term for the particles found in an atomic nucleus, specifically protons and neutrons.
Example:
The mass number of an atom represents the total count of nucleons within its nucleus.
Protons
Positively charged subatomic particles found in the nucleus of an atom, determining the element's atomic number.
Example:
The number of protons in an atom defines its identity; for instance, all carbon atoms have six protons.
Radioactive Decay
The spontaneous process by which an unstable atomic nucleus transforms into a more stable configuration by emitting particles or energy.
Example:
Scientists use radioactive decay of carbon-14 to determine the age of ancient artifacts.
Spontaneous Fission
A type of radioactive decay where a heavy, unstable atomic nucleus splits into two or more smaller nuclei without any external trigger.
Example:
Some very heavy isotopes, like Californium-252, undergo spontaneous fission at a measurable rate, emitting neutrons.
Spontaneous Nuclear Transformation
The natural process by which an unstable atomic nucleus changes its composition to become more stable, often by emitting radiation. This is synonymous with radioactive decay.
Example:
The spontaneous nuclear transformation of an unstable isotope like Iodine-131 makes it useful in medical imaging as it decays into a more stable form.
Strong Force
The fundamental force that binds protons and neutrons together within the atomic nucleus, overcoming the electromagnetic repulsion between protons.
Example:
Without the strong force, atomic nuclei would fly apart due to the repulsion between positively charged protons.