nuclear energy. review: elements and isotopes what are elements defined by? what are isotopes? ...
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Nuclear energy
Review: Elements and Isotopes What are elements defined by?
What are isotopes?
What is the difference between a stable and a radioactive isotope?
Radioisotopes
experience radioactive decay (the loss of alpha or beta particles over time)
Result: atoms of one element physically change into another element.– Eg Carbon-14 decays to Nitrogen-14 by loss of
negative beta particles
Radioactive half life= the amount of time it takes for 50% of the radioactive isotope in a substance to decay.
Practice:
Plutonium-239 has a half-life of 24,000 years. How much of a 4 gram sample will remain after 96,000 years?
a. 1gb. 0.5gc. 0.25gd. 0.125ge. 0.625g
Dating with radioactive isotopes
Carbon-14 can be used to estimate the age of plant and animal remains
Geological dating with Uranium
Uranium-238 is a very common radioisotope that decays to a stable isotope of lead
It has a half life of 4.5 billion years
The discovery of radioactive atoms 1896 uranium radiation observed
1898 radiation consists of high energy particles
1919 N nuclei hit with alpha particles turned into O
1938 First fission reaction
Nuclear rxns vs combustion
Combustion Atoms do not change;
are rearranged Mass of reactants =
mass of products Energy is released as
heat when bonds break
Nuclear Nucleic changes result
in element transformations
Small of amount of matter releases large amounts of energy…less mass in products
Types of nuclear reactionsFission
Fusion
NUCLEAR ENERGY Nuclear power plants use U-235, a
radioactive isotope of uranium.– Mining– Enrichment
Fuel assembly
Nuclear power plant
NUCLEAR WASTE
NUCLEAR WASTE
Math Practice1. After 100 million years, only 1/32 of the original amount of
a particular radioactive waste will remain. The half-life of this radioactive waste is how many million years?
a. 10 b. 20 c. 30 d. 40 e. 50
2. You have 180g of a radioactive substance. It has a half-life of 265 yrs. After 1,325 yrs, what mass remains?
Nuclear waste Low level
– Radioactive solids, liquids, or gases that give off small amounts of ionizing radiation
– Sources include power plants, hospitals, research labs, and industries
– Low Level Radioactive Waste Policy Act 1980 & 1985 All states must be responsible for disposal of non-defense
related waste produced w/in their borders.
High level– Radioactive solids, liquids, or gases that initially give
off large amounts of ionizing radiation– Sources include anything that was inside the reactor
core (metals, water, gases, spent fuel)
Nuclear Waste Policy Act 1982 Stated that there must be a permanent site for
storing high level waste by 1998– That was not met; postponed to 2010 at earliest
1987 Congress identified Yucca Mountain in Nevada as the best potential site
In 2002 it was officially approved by Congress Rescinded by Obama in 2009
NUCLEAR ENERGY Scientists disagree about the best
methods for long-term storage of high-level radioactive waste:– Bury it deep underground.– Shoot it into space.– Bury it in the Antarctic ice sheet.– Bury it in the deep-ocean floor that is
geologically stable.– Change it into harmless or less harmful
isotopes.
The risks of nuclear energy Meltdown Acute radiation syndrome Daily radiation for workers (carcinogenic over
time) Radiation into groundwater from stored waste Small scale persistent radiation to nearby
communities
Radiation and health We are exposed to natural (background
radiation) and artificial radiation every day
– 300 millirems per year from space/the atmosphere, the soil (radon), foods we eat (radioactive potassium)
– 60 millirems from manmade radiation (radiowaves, hospitals, industries, housing materials, microwaves, cell phones, tobacco, television, smoke detectors, etc.)
Figure 16-19Figure 16-19