RADIOACTIVE DECAY

RADIOACTIVE DECAY

Yesterday we learned that all elements have different isotopes. Example:

1H (1 proton, 0 neutrons) 2H (1 proton, 1 neutron) 3H (1 proton, 2 neutrons)

Some isotopes are stable and will last essentially forever.

Some aren’t stable.

RADIOACTIVE DECAY

An unstable isotope is said to be radioactive. Radioactive (unstable) isotopes =

radioisotopes Radioisotopes eventually decay into more

stable forms. A radioisotope releases energy by emitting

radiation during the process of radioactive decay.

RADIOACTIVE DECAY

Carbon-12 and carbon-13 are stable, but carbon-14 is radioactive.

6 p+ and 6 n0 6 p+ and 7 n0 6 p+ and 8 n0

WHAT MAKES A RADIOISOTOPE UNSTABLE?

An isotope can be unstable if: it is too heavy (more than 83 protons). its n0 to p+ ratio is too high. its n0 to p+ ratio is too low.

TYPES OF RADIATION

Alpha radiation Composition: Alpha particle (helium nucleus) Symbol: or 4He Charge: +2 Mass: 4 amu Penetrating power: Low (0.05 mm body tissue) Shielding: Paper, clothing Effect on nucleus: Z – 2, A – 4

ALPHA DECAY

U23592

alpha

Th23190

TYPES OF RADIATION

Beta radiation Composition: Beta particle (electron) Symbol: or e-

Charge: -1 Mass: 1/1837 amu Penetrating Power: Moderate (4 mm body

tissue) Shielding: Metal foil Effect on nucleus: Z + 1; A unchanged.

BETA DECAY

C146

e-

N147

TYPES OF RADIATION

Gamma radiation Composition: High-energy EM radiation Symbol: Charge: 0 Mass: 0 Penetrating power: Very high Shielding: Lead, concrete Effect on nucleus: decreases energy

USES OF RADIATION

Radioisotopic labelling – can be used to track the movement of a particular substance through a living organism.

Radiometric dating – used to determine the age of ancient objects.

Many uses in medicine, from imaging to cancer therapy.