Half-Life and Radioactivity (7.2 and 7.3)

By Kira Nishi-Beckingham

What is Half-Life?

A half-life is the amount of time it takes for half the nuclei in a sample to decay.

A half-life is constant for any radioactive isotope ( isotope - an atom of the same element with a different number of neutrons)

Number of Half Lives Percentage Decayed Percentage Left

0 0% 100%

1 50% 50%

2 75% 25%

3 87.5% 12.5%

4 93.75% 6.25%

Video!

http://youtu.be/tzM6aK5QbSU

Decay Curve

A decay curve is a curved line on a graph that shows the rate of decay of a radioisotope (an isotope that is radioactive)

It will look the same no matter what radioisotope you graph, the only difference will be the length of the half-life

Common Isotope Pairs and Dating

There are many pairs of isotopes that can be used for dating fossils

The parent isotope is the one undergoing radioactive decay and the daughter isotope is the result or product of the radioactive decay.

Dating Fossils

Historians and scientists use radioactive isotopes to date fossils

The most commonly known is Carbon-14Every living thing contains Carbon-14, but when they die it

starts to decay into Nitrogen-14. To be able to tell when the plant or animal died, you just have to compare the amount of Carbon-14 to the amount of Nitrogen-14

Lets say a sample contained 20g of Carbon-14 and 20g of Nitrogen-14. This means that one half-life has occurred (5730 years).

If there is more of the parent isotope then less than one half-life has occurred and if there is more of the daughter isotope then more than one half-life has occurred.

Another Video

http://youtu.be/phZeE7Att_s

Quiz #1

Answer the following questions correctly or Radioactive Man will take over the world!

1. Define the following Half-Life Isotope Decay Curve Parent Isotope Daughter Isotope2. What is the daughter isotope of Carbon-14?3. a) If there is more of the parent isotope this means..b) If there is more of the daughter isotope?c) If there is the same amount of the parent and daughter

isotopes?

Nuclear Fission

Nuclear fission is the splitting of a heavy atom into two smaller ones, subatomic particles, and energy

Nuclear fission is accompanied by a huge release of energy. We use this energy to generate power in nuclear reactors

While nuclear reactors reduce the amount of burning fossil fuels, they produce dangerous waste that needs to be stored for hundreds of thousands of years, the physical deterioration is a large problem, and the concern that the nuclear material could be used to make dangerous weapons

Chemical Reaction Vs. Nuclear Reaction

Chemical reactions involve electrons and change the way atoms are arranged

Nuclear reactions change the atom’s nucleusIn nuclear reactions, a small change creates a large

amount of energy.Natural nuclear reactions are Alpha, Beta, and

Gamma decayNon-Natural nuclear reactions are called induced

nuclear reactions. These occur when scientists bombard a nucleus with an alpha particle, beta particle, or gamma rays

Rules and Symbols

The rules for writing nuclear equations are:1. The sum of the mass numbers on each side of the

equation stays the same2. The sum of the charges on each side of the equation

stays the same

This table shows the symbols for each subatomic particle

Chain Reaction

When Uranium-235 is bombarded with a neutron, it absorbs it making it Uranium-236 which is highly unstable causing it to split immediately.

When it splits, it also releases energy and more neutrons

This is important because if there is more atoms of Uranium-235 around, these neutrons hit the atoms causing them to split and release more neutrons which hit more atoms and so on

This is called a chain reaction

Video

http://youtu.be/0v8i4v1mieU

Another Video

http://youtu.be/1U6Nzcv9Vws

Nuclear Fusion

Nuclear fusion is when two smaller, light weight atoms fuse together to create one large one.

This happens at the core of our sun and other stars where there is enough heat and pressure to force the atoms together

This creates a large amount of energy that eventually brings light and heat to us

Scientists have been searching for ways to use nuclear fusion to create energy however it is extremely difficult to reach the temperature and amount of pressure needed as well as finding a way to contain the heat and pressure

Quiz #2

Answer the following questions correctly or Radioactive Man will take over the world!

1. Define the following Nuclear Fission Nuclear Fusion Nuclear Reaction Chain Reaction2. What are the rules for writing a Nuclear Equation?3. What is the name of an isotope that can create a chain

reaction?4. Where does nuclear fusion occur naturally?

Sources

http://wps.prenhall.com/wps/media/objects/3084/3158429/blb2101.html http://wwwchem.csustan.edu/chem3070/3070m04.htm http://www2.estrellamountain.edu/faculty/farabee/BIOBK/

biobookpaleo1.html http://ohhs.ohsd.net/~brick/ear/eara_measuring_geotime_es3b.htm http://science.howstuffworks.com/environmental/earth/geology/carbon-

141.htm http://wps.prenhall.com/wps/media/objects/3084/3158429/blb2101.html https://www.youtube.com/watch?v=1U6Nzcv9Vws http://www2.estrellamountain.edu/faculty/farabee/BIOBK/

biobookpaleo1.html https://www.youtube.com/watch?v=0v8i4v1mieU https://www.youtube.com/watch?v=phZeE7Att_s https://www.youtube.com/watch?v=tzM6aK5QbSU http://marvel.com/universe/Radioactive_Man_%28Chen_Lu%29

Answers to Quiz #1

1. Half-Life – the amount of time it takes for half of a sample of radioactive nuclei to decay

Isotope – an atom of the same element with a different number of neutrons

Decay Curve – a curved line on a graph that shows the decay rate of a radioisotope

Parent Isotope – The isotope that is undergoing the radioactive decay

Daughter Isotope – The isotope that is the stable product of the radioactive decay

2. Nitrogen- 143. a) Less than one half-life has occurredb) More than one half-life has occurredc) Exactly one half-life has occurred

Answers to Quiz #2

1. Nuclear Fission – One heavy and large atom splits into two smaller ones releasing a large amount of energy

Nuclear Fusion – Two small, light weight atoms fuse together to create one large one releasing a large amount of energy

Nuclear Reaction – When the nucleus of an atom is changedChain Reaction – One thing that causes another thing that

causes another thing and so on2. The sum of the mass numbers on each side of the equation

stays the sameThe sum of the charges on each side of the equation stays the

same3. Uranium-2354. The sun