Isotopes Atoms of the same element (same Z) but different mass number (A)

• Review Session:

• Tuesday C-106 6-8pm

Isotopes

• Atoms of the same element (same Z) but different mass number (A).

• Boron-10 (10B) has 5 p and 5 n: 105B

• Boron-11 (11B) has 5 p and 6 n: 115B

Radioactivity

• One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934).

• She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

Types of Radiation

Penetrating Ability

Nuclear Reactions

• Alpha emission

Nuclear Reactions

• Beta emission

Nuclear Reactions

• Gamma rays – very high energy waves!

Origin of the Elements

Element Abundance

Stability of Nuclei Screens 23.3 and 23.4

• H is most abundant element in the universe.

• 88.6% of all atoms
• He is 11.3% of all atoms
• H + He = 99.9% of all atom & 99% of mass of the universe.

• This tells us about the origin of the elements, and so does the existence of isotopes.

Half-Life Section 15.4 & Screen 23.6

• HALF-LIFE is the time it takes for 1/2 a sample is disappear.

• The rate of a nuclear transformation depends only on the “reactant” concentration.

• Concept of HALF-LIFE is especially useful for 1st order reactions.

Half-Life

Kinetics of Radioactive Decay

• Activity (A) = Disintegrations/time = (k)(N)

• where N is the number of atoms

• Decay is first order, and so

• ln (A/Ao) = -kt

• The half-life of radioactive decay is

• t1/2 = 0.693/k

Nuclear Fission

Nuclear Fission & Lise Meitner

Nuclear Fission & POWER

• Currently about 103 nuclear power plants in the U.S. and about 435 worldwide.

• 17% of the world’s energy comes from nuclear.

Radon – a deadly gas?

Units for Measuring Radiation

• Curie: 1 Ci = 3.7 x 1010 distintegrations/s

• SI unit is the becquerel: 1 Bq = 1 dps

• Rad: measures amount of energy absorbed

• 1 rad = 0.01 J absorbed/kg tissue

• Rem: based on rad and type of radiation. Quantifies biological tissue damage

• Usually use “millirem”

Effects of Radiation

Nuclear Medicine: Imaging

Nuclear Medicine: Imaging

Nuclear Medicine: Imaging

Food Irradiation