放射能と核方程式

A nuclide is an atom with a specific number of protons and neutrons in a specific nuclear energy state. Isotopes are nuclides of the same element with identical atomic numbers but different mass numbers. For example, carbon has three isotopes that differ in neutron count but share the same number of protons.

Alpha decay emits an alpha particle, which is a helium-4 nucleus. This emission reduces the atomic number by 2 and the mass number by 4. For instance, uranium-238 undergoes alpha decay to produce thorium-234, demonstrating how both nuclear parameters decrease simultaneously.

A metastable state is a long-lived excited energy state of a nuclide, denoted by adding 'm' to the mass number. Technetium-99 exists in both a lower-energy ground state and a metastable state. Although these species have identical protons and neutrons, they are considered different nuclides due to their distinct energy states.

Beta-minus emission releases an electron, increasing the daughter nuclide's atomic number by 1. Beta-plus emission releases a positron with opposite charge, decreasing the atomic number by 1. Both processes change atomic number but leave mass number unchanged, representing distinct decay pathways.

Nuclear equations obey conservation of mass and charge. The sum of mass numbers must be equal on both sides of the equation, as must the sum of atomic numbers. This balancing principle ensures that nuclear reactions account for all particles and energy transformations during radioactive decay and radiometric dating applications.

Stable nuclides remain intact indefinitely without spontaneous transformation. Radionuclides are unstable and spontaneously undergo radioactive decay, transforming into daughter nuclides through emission of particles or electromagnetic radiation. Some elements contain only radionuclides, while others have stable isotopes that persist unchanged.

Gamma rays are high-energy electromagnetic radiation emitted during radioactive decay. Unlike alpha and beta particles, gamma ray emission changes neither the atomic number nor the mass number of the nucleus. Gamma radiation often accompanies other decay types, representing energy release without altering nuclear composition.