Nuclear Chemistry
Ch. 28
Nuclear Radiation
28-1
Radioactivity
• Radioactivity = spontaneous emission of radiation by an unstable atomic nucleus.– Some elements give off radiation naturally,
without an input of energy!!– In chemical reactions the number of electrons
changes, in nuclear reactions the number of protons + neutrons changes!
– If the proton number changes a new element is made!
6
Nuclear Notation• Nuclear Notation – Indicates mass number
and atomic number, allowing isotopes to be differentiated
• 23892U – can also be written as Uranium-238
• Superscript: Mass # = # of protons plus neutrons
• Subscript: Atomic # = # of protons• Isotopes have same # of protons but different
# of neutrons
Ex: Isotopes of Hydrogen
Radioactive Decay• Radioactive Decay = release of radiation by
radioactive isotopes, or radioisotopes, to become more stable.
• Nuclei of radioisotopes are unstable, give off varying degrees and different types of nuclear radiation.
• Three types of nuclear radiation:1) Alpha particles
2) Beta particles
3) Gamma rays
Alpha Decay• Alpha particle: helium nuclei consisting of 2
protons and 2 neutrons (+2 charge!)– Symbol: 4
2He or α– Affect: large in size, do not penetrate into
matter easily, stopped by thin layer of material (paper, skin)
• Alpha decay: nucleus releases an alpha particle, becoming a different element– Decreases mass of original nucleus by 4 and
the new element has an atomic number 2 less than original
• As uranium decays it becomes multiple elements releasing multiple types of radiation!
• Transmutation = when a nucleus releases either an alpha or beta particle the atomic # changes becoming a different element!
Beta Decay• Beta particle = a high energy electron with a charge of -1.
– Symbol: 0-1e or ß-
– Affect: smaller, lighter, can be stopped only by thicker materials (aluminum foil or wood).
• Beta decay = decaying nucleus turns into new element with atomic number + 1 but with same mass.
Gamma Decay• Gamma ray = high energy form of
electromagnetic radiation without mass or charge.
– Symbol: γ or 00γ
– Affect: Very hard to stop, only thick layers of lead or thick concrete. Causes great harm to living cells
• Gamma Decay = only energy is given off, usually occurs simultaneously with other types of decay, often omitted from equations.
Overview
• Draw!
Type of Radiation
Symbol Atomic mass
Atomic #
Affect
Alpha
Beta
Gamma
Type of Radiation
Symbol Atomic mass
Atomic # Affect
Alpha
42He
α Decrease by 4
Decrease by 2
Stopped by thin layer
Beta
0-1e
ß- same Add 1
Stopped by thick material
Gamma
γ0
0γ same same
Only stopped by thick
concrete, or lead
Explain why the 3 types of radiation moved in the following directions!
Nuclear Transformations
28-2
Radioactive Dating
• Unlike chemical reactions affected by temperature, pressure, and concentration, the rate of nuclear decay cannot be changed!
• Able to predict amount of decay that has occurred.
• Half-life = time it takes for half the given amount of a radioisotope to decay.
“Is that what atoms do when they’re single?!”
• Half-life Calculation:– MO = 2xMr
– Where MO = original mass, x = # of half-lives,
Mr = mass remaining• Example: 2.00 g of nitrogen-13 emits beta radiation with a
half-life of 10 minutes. – Write a nuclear equation.
• 137N 13
8O + 0-1e
– How long is 3 half-lives?• 10 minutes x 3 half-lives = 30 minutes
– How many grams of oxygen-13 will be present at the end of 3 half-lives?• MO = 2xMr 2.00g = 23Mr
Mr = 0.250g of oxygen-13
What is the half-life (time) of this radioactive sample?
Commonly used Radioisotopes for Radioactive Dating
• Carbon-14 used to date artifacts made of organic material
• Uranium-238 used to date rocks as old as solar system
• Radon-222 and Thorium-234 used in nuclear medicine
Isotope Half-life Radiation emitted
Carbon-14 5.73 x 103 years β
Uranium-238 4.46 x 109 years α
Radon-222 3.8 days α
Nuclear Reactions and Energy
28-3
Nuclear Fission
• Nuclear Fission = an atomic nucleus is split into two or more large fragments
• Ex: Uranium is bombarded with a neutron forming two lighter elements: krypton and barium, 3 neutrons, and a large amount of energy!235
92U + 10n 140
56Ba + 9336Kr + 31
0n
• If the reaction takes place too quickly an explosion will occur (atom bomb), if it is controlled to release heat slowly it can be used to heat water and do other useful work! = nuclear reactor
San Onofre Nuclear Power Plant(Fission of Uranium!)
Nuclear Fission as a source of energy!
• Pros: – >100 nuclear reactors
in U.S.– Provide ~20% of
electricity used– Do not release
pollutants to air
• Cons:– Form highly
radioactive waste– Can cause serious
accidents– Limited supply of
fissionable material– Higher cost than fossil
fuels
Nuclear AccidentsChernobyl, Ukraine, 1986 Fukushima, Japan, 2011
Nuclear Fusion
• Nuclear Fusion = two or more nuclei combine to form a larger nucleus.
• Fusion is the process that produces energy in stars, sun (2 H nuclei form He)2
1H + 31H 4
2He + 10n
deuterium + tritium helium + neutron• The fusion of hydrogen produces 20 times
the energy produced by fission of uranium but can only take place at very high temperatures! (40 million °C)
Nuclear Fusion as a source of energy!
• Pros:– Fusion done successfully
in laboratories– Deuterium, a fuel in
fusion, abundant on Earth– No radioactive products
produced– Easier to control than
fission
• Cons:– Requires large input of
energy, 200 million K heat required!!!
– Only known source of this amount of thermal energy is an atom bomb, thus must be used to start reaction!
– Material to contain reaction melts
– Tokamak = uses electromagnets to contain nuclei, radio waves initiate fusion, but no net energy produced
The Large Hadron Colliderat CERN, Switzerland
17 mile circumference, 574 ft below the surface.World’s largest particle accelerator
Artificial Transmutation: can occur by applying an outside force.Requires lots of energy!! High speed neutrons act as “bullets” to hit nuclei = Particle accelerators Neptunium and Plutonium were discovered in lab (synthetic elements), as were all elements with atomic #’s greater than 92 on periodic table = transuranium elements.
Fermilab, Illinois
Shutdown in 2011
Comparison (DRAW!)
