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Intro to Nuclear Chemistry
How does a nuclear reactor work?
How does a small mass contained in this bomb cause……
• Nuclear Bomb of 1945 known as “fat man”
…this huge nuclear explosion?
Is there radon in your basement?
Notation
Nucleons
• Protons and Neutrons
• The nucleons are bound together by the strong force.
Isotopes
• Atoms of a given element with: same #protons
but different # neutrons
H H H
http://education.jlab.org/glossary/isotope.html
Isotopes of Carbon
• Isotopes of certain unstable elements that spontaneously emit particles and energy from the nucleus.
• Henri Beckerel 1896 accidentally observed radioactivity of uranium salts that were fogging photographic film.
• His associates were Marie and Pierre Curie.
Radioactive Isotopes
Marie Curie: born 1867, in Poland as Maria Sklodowska
• Lived in France• 1898 discovered the
elements polonium and radium.
Marie Curie a Pioneer of Radioactivity
• Winner of 1903 Nobel Prize for Physics with Henri Becquerel and her husband, Pierre Curie.
• Winner of the sole 1911 Nobel Prize for Chemistry.
3 Main Types of Radioactive Decay
• Alpha
• Beta
• Gamma
Emission of alpha particles :
• helium nuclei • two protons and two neutrons • charge +2e • can travel a few inches through air• can be stopped by a sheet of
paper, clothing.
Alpha Decay
Alpha Decay
Uranium Thorium
Alpha Decay
Beta Decay
• Beta particles : electrons ejected from the nucleus when neutrons decay
( n -> p+ +- ) • Beta particles have the same charge and
mass as "normal" electrons.
Beta Decay
• Beta particles : electrons ejected from the nucleus when neutrons decay
n -> p+ +-
• Beta particles have the same charge and
mass as "normal" electrons.
• Can be stopped by aluminum foil or a block of wood.
Beta Decay
Beta Decay
Thorium Protactinium
• Gamma radiation electromagnetic energy that is released.
• Gamma rays are electromagnetic waves.• They have no mass.• Gamma radiation has no charge.
– Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead.
Gamma Decay
Examples of Radioactive DecayAlpha Decay
Po Pb + He
Beta Decay p n + en p + e
C N + eGamma Decay
Ni Ni + (excited nucleus)
Which is more penetrating? Why?
Part II
•Nuclear Stability •Half-Life
Nuclear Stability
• Depends on the neutron to proton ratio.
Band of Stability
Number of Neutrons, (N)
Number of Protons (Z)
What happens to an unstable nucleus?
• They will undergo decay
• The type of decay depends on the reason for the instability
What type of decay will happen if the nucleus contains too many
neutrons?
• Beta Decay
Example:C N + e
In N-14 the ratio of neutrons to protons is 1:1
14
7 -1
014
6
• Nuclei with atomic number > 83 are radioactive
Radioactive Half-Life (t1/2 ):
• The time for half of the radioactive nuclei in a given sample to undergo decay.
Common Radioactive Isotopes
Isotope Half-Life Radiation Emitted
Carbon-14 5,730 years
Radon-222 3.8 days
Uranium-235 7.0 x 108 years
Uranium-238 4.46 x 109 years
Radioactive Half-Life
• After one half life there is 1/2 of original sample left.
• After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.
Graph of Amount of Remaining Nuclei vs Time
A=Aoe-t
A
Example
You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years.
• How many grams are left after one half-life? Answer:50 g
• How many grams are left after two half-lives?
Problem
A sample of 3x107 Radon atoms are trappedin a basement that is sealed. The half-life ofRadon is 3.83 days. How many radon atoms are left after 31 days?
answer:1.2x105 atoms