IB Physics E.3 Radioactive Decay Key Definitions

The activity of a radioactive sample is the number of decays per unit time.

Alpha decay occurs when an unstable nucleus emits an alpha particle, which is essentially a helium nucleus made up of two protons and two neutrons ($^4_2 \text{He}$).

In beta minus decay, a neutron in the nucleus is converted into a proton, emitting an electron ($\beta^-$) and an antineutrino ($\bar{\nu}$):

$$
n \rightarrow p + e^- + \bar{\nu}
$$

In beta plus decay, a proton is converted into a neutron, emitting a positron ($\beta^+$) and a neutrino($\nu$):

$$
p \rightarrow n + e^+ + \nu
$$

Binding energy is the energy required to hold the nucleus together.

The decay constant, $\lambda$, measures how quickly a radioactive substance decays. It is defined as the probability of decay per unit time for a single nucleus.

Gamma decay occurs when an excited nucleus releases excess energy by emitting a gamma ray, a high-energy photon.

An electrically neutral particle with negligible mass that interacts only weakly with matter. It is emitted in beta decay and carries away part of the energy and momentum released.

Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation.

The half-life $T_{1/2}$ is the time it takes for half of the radioactive nuclei in a sample to decay.

The strong nuclear force is one of the four fundamental forces of nature and is responsible for holding the nucleus together. It acts between all nucleons (protons and neutrons).