Post on 26-May-2015
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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.