The next unit in our exploration of matter and energy applies our understanding of matter’s atomic structure--nuclear reactions. This corresponds to pages 233 - 251 in the textbook. It is a short unit.
Nuclear reactions are what happens inside the nucleus of atoms when they change into other atoms (gain or lose protons). There are two types of nuclear reaction: gaining proton(s) and losing proton(s). These are called fusion and fission.
Fusion - 2 or more nuclei combine to form one larger nuclei (they fuse into one)
The proton repulsion must be overcome meaning that very high temperatures are required (around 100,000,000 Celsius). At this temperature, everything is plasma.
The sun has Hydrogen fusing into Helium as its fuel source.
The required high temperatures have meant that it takes more energy to do fusion than we have been able to get back from it. Cold fusion has long been sought after, yet never attained.
Advantages of fusion for energy:
There is a much smaller chance of an accident, the waste products are not harmful, there is tons of fuel for it, and more energy is released per mass.
Fission - 1 nucleus breaks down into 2 smaller nuclei while spitting out 3 neutrons.
Fission will occur naturally with any atom that doesn’t have enough “peacekeeping” neutrons or may be accelerated by neutron bombardment.
A small amount of the atomic mass is converted to energy. The energy is small, but
the atoms are tiny, so a fuel cell the size of this “O” has the equivalent energy of
burning 1000 kg of coal!
A nuclear chain reaction progresses because the neutrons shot out by the decay bombard the other atoms and cause their decay. They can either be controlled or not.
Uncontrolled chain reaction - huge amount of energy in a very short time = BOMB!
Controlled chain reaction - many of the emitted neutrons are absorbed away to slow the decay down. This is what occurs inside a nuclear power plant. They have rods of U235 with control rods to absorb the extra neutrons. This heats up some water which in turn turns a turbine.
Concerns with nuclear power are:
Accidents like Chernobyl and wastes that will be highly radioactive for the thousands of years.
Benefits of it are:
Cheaper to run and it does not release harmful gases into the atmosphere.
Radioactive particles that fly out during nuclear reactions:
Alpha particle - 2 protons and 2 neutrons. Has a +2 charge and weighs 4 (huge, atomically speaking). Most dangerous, but blocked by paper.
Beta particle - negatively charged electron or positively charged positron weighing virtually nothing. Next most dangerous, but blocked by aluminum foil.
Gamma rays - No mass or charge. Least powerful, but cinder block or lead to block.
These energies can break bonds.
If living this causes: fatigue, loss of appetite and hair, mutations, cancer, and death.
If not living, just weakens the structure.
Radioactive substances decay (undergo fission) at a set rate called a half life. One half life is the time it takes one half of the substance to decay into daughter atoms and it is constant for a specific material.
There are many uses for radioactive substances:
Dating objects - knowing the rate of decay, we can determine the age of many objects based on the ratio of parent to daughter atoms.
Many smoke detectors use radioactive substances to detect smoke particles.
Radioactive tracers are used in medicine to follow specific pathways inside of you and get a better look at your organs.
Food is often sterilized by irradiation. This kills off the bacteria which cause spoilage.
Radioactivity is used to find weak spots in many structures and pipes.
Radioactivity is also used for nuclear power (bombs too).
What are the two types of nuclear reactions?
Contrast fusion and fission.
How would you know if an atom was likely to undergo fission?
Name the three radioactive particles / energy that are emitted during nuclear reactions.
What is a half life?
Calculate the age of something based on its half life rate and proportion of parent / daughter
What are the advantages and disadvantages of the two types of nuclear reactions for
What are the many uses for nuclear reactions?
Hypothesize how to create that “Holy Grail” of nuclear physics--cold fusion.
If you have enjoyed the topics in this unit, feel free to investigate further. Here are some ideas. These are NOT required, but I hope you have fun and delve into some of them:
How does a nuclear power plant really work? What happened at Chernobyl? Three Mile Island?
Find out more about half lives. Which ones do we use to date the age of the Earth? A dinosaur fossil? The first human artifacts?
Do you have any ideas on how to “clean up” the nuclear wastes?
Which is better: nuclear power that produces radioactive byproducts that take thousands of years to decay, or fossil fuels that produce carbon dioxide (causing global warming)? Why?