Radioactive DecayRadioactive Decay

Radioactive DecayRadioactive 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.

A Lesson on PronunciationA Lesson on Pronunciation

Nuclear = NU – clearNuclear NUK-you-lar

Radioactive DecayRadioactive 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 DecayRadioactive 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?

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.

Band of StabilityBand of Stability

Types of RadiationTypes of Radiation

Alpha radiationComposition: Alpha particle (helium nucleus)Symbol: or 4HeCharge: +2Mass: 4 amuPenetrating power: Low (0.05 mm body tissue)Shielding: Paper, clothingEffect on nucleus: Z – 2, A – 4

Alpha DecayAlpha Decay

U23592

alpha

Th23190

Types of RadiationTypes of Radiation

Beta radiationComposition: Beta particle (electron)Symbol: or e-

Charge: -1Mass: 1/1837 amuPenetrating Power: Moderate (4 mm body tissue)Shielding: Metal foilEffect on nucleus: Z + 1; A unchanged.

Beta DecayBeta Decay

C146

e-

N147

Types of RadiationTypes of Radiation

Gamma radiationComposition: High-energy EM radiationSymbol: Charge: 0Mass: 0Penetrating power: Very highShielding: Lead, concreteEffect on nucleus: decreases energy

Ionizing Radiation Warning Symbol

Ionizing Radiation Warning Symbol

Hazards of Ionizing Radiation

Hazards of Ionizing Radiation

At low levels of exposure, radiation danger is minimal.Radiation may damage cells, but cells can repair themselves.Severely damaged cells can self-destruct and limit damage to

tissue.Serious trouble happens when radiation causes a non-

lethal (to the cell) mutation that is passed to daughter cells.

If the mutation happens in a gene that controls cell division, the cell could give rise to cancer.

Large radiation exposures can cause death much more quickly from severe tissue damage.

Radiation ExposureRadiation ExposureMeasured in milliSieverts (mSv).

0.001 to 0.01 mSv = hourly dose from cosmic rays on a commercial airliner.

0.27 mSv = average yearly exposure to cosmic radiation in USA (slightly higher at high altitudes)

0.66 mSv = average yearly exposure to radiation from manmade sources in USA

50 mSv = yearly limit for adults set by NRC500 to 1000 mSv = victims of Hiroshima and Nagasaki nuclear bombs500 to 1000 mSv = dose that will cause most people to get sick from

short-term exposure4500 to 5000 mSv = dose that will kill 50% of people after brief

exposure

Uses of RadiationUses 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.