Nuclear Decay

Parent nucleus

any unstable nuclei will spontaneously decay into lighter nuclei. The nucleus that is unstable is called the

Daughter nucleus

the decaying nucleus then leaves behind a

Transmutation

if the decay occurs naturally then it is called a

Artificial transmutation

we can force nuclei to decay and this is called

Types of Decay

alpha decay, beta decay, gamma decay

Alpha Decay - α

occurs when an alpha particle (a Helium nucleus which contains two protons and two neutrons) is emitted from a radioactive nuclei. The alpha particle is the largest of the decay particles and therefore is also relatively slow moving. It has a charge of 2+. When emitting an alpha particle, it carries away with it excess energy

Beta Decay - β

beta decay has two modes which both require the spontaneous change of a nucleon.
• betanegative radiation (an electron) a neutron changes into a proton
• betapositive radiation (a positron) a proton changes into a neutron

In addition to the beta particles released, there are also additional particles that are released to help remove energy from the system. These particles are tiny, neutral and almost massless. They are the neutrino (for β+ decay) and the antineutrino (for β decay)

Gamma Decay - γ

in this decay, rather than reduce the number of nucleons, gamma decay reduces the amount of energy an unstable nucleus has. The gamma ray is a very energetic part of the electromagnetic spectrum that travels at the speed of light. A gamma ray has no charge and no mass. The star on the parent nuclide indicates that the atom is unstable and in an excited state. It needs to lose energy to become more stable

Ionising radiation

Ionising radiation is energy or particles that can remove electrons from atoms. Alpha particles (helium nuclei) are highly positive and ionise air as they pass through. Other examples include beta particles, neutrons, and high-energy electromagnetic radiation like UV rays, X-rays, and gamma rays. Ionising radiation is harmful to living tissue because ionised atoms are highly reactive, leading to unwanted chemical reactions and potentially causing cancer. In contrast, low-energy radiation, such as radio waves, microwaves, and visible light, is non-ionising and poses no significant risk.

Penetrating ability

Alpha particles will travel a few cm in air, can be stopped by a sheet of paper or skin.

Beta particles will travel a few m in air, can be stopped by 3mm of aluminium.

Gamma rays - will travel a few km in air, can be stopped by thick lead.

Decay series

is a sequence of various radioactive decays by successive daughter nuclei that eventually forms a stable nucleus.

Reason for decay series

Every radioactive nucleus has an excess of energy. In the process of decay, some of the energy is lost in order to obtain a more stable nucleus. Often the daughter nucleus is radioactive, so the process continues.