Nuclear Chemistry (Notes)

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Discovery of Radiation
Henri Becquerel 1896
– wrapped photographic film in black paper, put uranium on top and left it in the sun
– the photograph was “exposed” so he figured the uranium had absorbed and emitted sunlight
– did same experiment on cloudy day…film was still exposed
– concluded that uranium was emitting energy from within itself
– was considered worthless (pitchblende)
– unstable nucleus: 92 protons, 146 neutrons
-releases a helium nucleus
– changes into thorium when it loses protons
Band of Stability
Ratio of neutrons to protons that produces the most stable nucleus
– 1:1 ratio for atoms with low atomic numbers
– 1.5:1 ratio for atoms with higher atomic numbers
– all nuclides after 83 are unstable and radioactive
-unstable nuclei undergo spontaneous decay to make the nucleus more stable
Radioactive Decay
the process by which an unstable nucleus becomes more stable
the particles or energy that are emitted during decay (more energy than regular chemical reactions)
Decay series
a series of radioactive nuclides produced by successive decays until a stable nuclide is produced
Alpha Decay
-alpha particle released
-helium nucleus (2p, 2n)
-emitted by heavy nuclei
-heaviest and largest particles
-travel the least
-least penetrating power –> stopped by skin or paper
-mass # down 4, atomic # down 2
-ex: radon in homes
Beta Decay
-nucleus decays in order to reduce the number of neutrons
-neutron converted into a proton and electron
– proton stays in nucleus (mass # doesn’t change but atomic number up by 1)
-electron is emitted as a beta particle
-negatively charged, fast moving electron
-lightest, smallest particle
-travel farther than alpha, more penetrating power than alpha (can be stopped by aluminum)
Gamma emission
-high energy waves emitted from nucleus as it changes from excited to ground energy state
-usually occurs immediately following other types of decay as the alpha or beta particles leave the nucleus in an excited, unstable condition
-travel farthest, most penetrating (stopped by lead)
– no change to mass or atomic #
Fission reaction
larger nucleus splits into 2 or more stable daughter nuclei
E = mc^2
Einstein determined that a little bit of mass is converted to a LOT of energy
c = speed of light (300,000,000m/s ^2)
Nuclear Chain reaction
a reaction in which the material that starts the reaction is also one of the products and can start another reaction
Manhattan Project 1942-1946
-secret project to build the atomic bomb
-built a secret city in Los Alamos in New Mexico desert
-best scientists, lots of money
Enriching Uranium
most uranium mined from ground is U-238, not U-235 –> U-235 isotope needed to keep the chain reaction going
Critical mass
the amount needed to sustain a runaway chain reaction
Trinity bomb test July 16, 1945
little boy – dropped on Hiroshima Aug 6, 1945
fat man – dropped on nagasaki Aug 9, 1945
Nuclear power plant
heat produced via fission is used to heat water to produce steam to turn a turbine to generate electricity
Controlled fission reaction
controlled by
1. using water to absorb and remove heat produced during the reaction
2. using control rods in the fuel assembly to absorb excess neutrons
Control rods
used to absorb neutrons to decrease the number of neutrons that collide with nuclei. If control rods malfunction, the reactor core could overheat, cause a mechanical failure and radioactive materials could be released “meltdown”
Nuclear Waste
-fuel rods made from fissionable material
– over time amount of fissionable material decreases and the rods are considered “spent”, must be removed, replaced, and stored
-stored in holding tanks filled with water which absorbs heat and acts as a radiation shield
-Dry cask: moved into canisters on land after spending years in water
Geiger Counter
measures nuclear radiation, tiny particles being emitted. units = rem or microsieverts
Film badges
personal device worn that contains photographic film to measure and record radiation exposure
Risks of radiation
1. type of radiation
2. dose
3. dose rate (length of time of exposure)
Background radiation
.2 microsieverts/hr
in air, food, soil, space
Acute Radiation Syndrome
high dose of radiation in a short period of time; health effects including DNA damage
Half Life
t1/2 –> time required for half of the radioactive atoms to undergo decay. unique to a particular nuclide
-half-life of Ce is 30 years, so it’s uninhabitable for hundreds of years
-enclosed by a concrete sarcophagus
-half life of U-238 is 4.5 billion years
Carbon dating
-use half life of C-14 to determine how old something is
-C-12 and C-14 found in plants and animals
-C-14 decays but living organism takes in new C-14 so the level remains constant while it’s alive
-plants and animals stop taking in carbon when they die
-C-14 decays into N-14 at a half life of 5730 years
-C-12 doesn’t change bc it’s stable
-Scientists measure the amount of C-14 left to determine age
Space exploration
Voyager 1 spacecraft – 1977, lifted off and left our solar system still powered by nuclear radiation
Nuclear Medicine
Radioactive tracers used to detect cancer, gathers at site of tumors, half-life of 6 hours
Smaller nuclei combine to produce a nucleus with a greater mass (ex: sun –> hydrogen nuclei fuse to make helium nuclei)
E = mc^2 fusion
more change in mass, so fusion releases much more E than fission reactions. would be used as an energy source if we could achieve the high temperatures necessary to start and continue the reaction
Categories: Nuclear Chemistry