RADIOACTIVITYTHE IDEAS THAT HAVE LIGHTED MY WAY HAVE BEEN KINDNESS, BEAUTY AND TRUTH.ALBERT EINSTEIN

Ch3. J.C. Rowe

Windsor University School of Medicine

Concept Map

radioactivity

Type of radiation emitted

Penetrating powers

Used of radioactiv

e substance

s

Half-life

Radioactive decay

An unstable nucleus changes by ejecting small fragments. This process is called radioactivity.

The changing radioactive atoms are said to decay.

Fragments which can be thrown out include:1. Neutron2. Alpha particles (bundles of 2 neutrons &

2protons)3. Beta particles (which are electrons)4. Gamma rays (which are electromagnetic rays

like X-rays.

Cont’d

The number of protons in the nucleus changes when an atom emits alpha or beta particles.

Losing gamma-rays only reduces the energy of the nucleus.

Half-life

Each radioactive isotope decays at its own fixed rate

The time taken by one-half of the atoms to decay is constant

Half-lives can vary from tiny fractions of a second to hundreds or thousands of years

Penetrating power

Alpha & beta particles & gamma rays have different powers of penetration.

1. Alpha particles are stopped by a sheet of paper or human skin.

2. Beta particles will penetrate a thin sheet of metal

3. Gamma-rays may penetrate several inches of lead.

Cont’d

alpha

beta

gama

tissue

aluminium lead

Uses of radioactivity

Chemical tracer To date ancient objects To produce electricity on a large scale &

small scale In radiotherapy In smoke alarms To sterilize materials

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