Nuclear Science and Radioactivity

Nuclear science studies the atomic nucleus, the tiny dense core that contains nearly all of an atom's mass. The nucleus is made of protons and neutrons held together by the strong nuclear force, which overcomes the electrical repulsion between the positively charged protons. The number of protons defines the chemical element, while atoms of the same element with different numbers of neutrons are called isotopes.

Many isotopes are unstable and undergo radioactive decay, emitting particles or energy to reach a more stable configuration. The main types are alpha decay, which releases a helium nucleus; beta decay, which involves an electron or positron; and gamma emission of high-energy electromagnetic radiation. The time for half of a sample to decay is the half-life, a fixed property of each radioactive isotope that ranges from fractions of a second to billions of years and underlies techniques such as radiometric dating.

Energy can be released from the nucleus in two ways. Fission splits a heavy nucleus into lighter ones, while fusion joins light nuclei into a heavier one; both convert a small amount of mass into a large amount of energy. The behaviour of particles at this scale is governed by quantum physics, developed in the early twentieth century by figures such as Erwin Schroedinger and Werner Heisenberg, whose uncertainty principle limits how precisely position and momentum can be known together.

Frequently asked questions

What is radioactivity?

Radioactivity is the spontaneous emission of particles or energy by unstable atomic nuclei as they decay toward a more stable state, producing alpha, beta or gamma radiation.

What does half-life mean?

Half-life is the time required for half of the atoms in a radioactive sample to decay. It is constant for a given isotope and is used to date materials and gauge decay rates.

What holds the nucleus together?

The strong nuclear force binds protons and neutrons together over very short distances, overcoming the electrical repulsion between the positively charged protons.