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the unit of activity

1 Bq

1 decay per second


positively charged sub-atomic particle found in the nucleus


a subatomic particle that has no charge and that is found in the nucleus of an atom


negatively charged particle; located outside the atomic nucleus

atomic (proton) number

The number of protons present in the nucleus of all atoms of one particular element.

mass (nucleon) number

The combined total of neutrons and protons in the nucleus of one particular isotope of an element.


atoms of the same element that have different numbers of neutrons


the process by which an unstable nucleus gives off nuclear radiation

alpha decay

radioactive decay that results in an alpha particle (a helium nucleus) being emitted from the nucleus of a radioactive element.

beta minus decay

A neutron is converted into a proton, an electron. The electron is released as a beta particle.

gamma decay

the release of gamma rays from a nucleus.

alpha particles

Made up of 2 protons and 2 neutrons.

beta particle

an electron emitted by an unstable nucleus.

alpha particles

are stopped by paper or skin.

beta particles

are stopped by a thin sheet of aluminium foil.

gamma rays

are stopped by lead or thick layer of concrete.

alpha decay

is the most ionizing but the least penetrating.

gamma decay

is the least ionizing but the most penetrating.

half life

length of time required for half of the radioactive atoms in a sample to decay.

carbon 14

element used in dating organic material.

medical tracers

Radioactive material (γ-emitters) which are ingested into the body. Must have a long enough half-life to carry out investigation but no longer.

paper thickness

is monitored by passing beta particles through the paper when it is manufactured.

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