Nuclear Fission and Fusion Notes

November 3, 2008 What part of the atom is affected by Nuclear Chemistry? Do you think the benefits of nuclear energy outweigh the dangers? Why or why not?

Goals To explain the difference between fusion and fission To describe half life and solve problems using half life

An element can have both stable and unstable isotopes Ex: –C-12 is stable so there is no nuclear decay –C-14 is unstable and radioactive

 A special force called the strong nuclear force holds the p and the n in the nucleus together. This force occurs over a very short distance.

Because of the strong nuclear force, the n and p attract other n and p. *n have no charge and they do not repel each other or the protons. *p repel each other with the electric force and attract each other with the strong nuclear force.

In stable nuclei, the attractive forces (strong nuclear) are stronger than the repulsive forces (electric).

Nuclear Fission Fission- The process by which a nucleus splits into two or more smaller fragments, releasing neutrons and energy. (The production of lighter nuclei from heavy nuclei)

When U-235 is bombarded by neutrons, the products of the reaction include 2 lighter nuclei that include Ba and Kr together with neutrons and energy Each dividing nucleus releases about 3.2 x 10^-11 joules of energy.

Some of the mass of the particles before the fission reaction is turned into energy after the reaction.

matter  energy mass-energy equation –E=mc 2 Einstein A small loss of mass results in a great amount of energy that is given off.

Nuclear Fusion Fusion – The process in which light nuclei combine at extremely high temperatures, forming heavier nuclei and releasing energy. Energy is also obtained during the fusion process

*Stars and Sun: Energy is produced when H nuclei combine *We need a large amount of energy to start a fusion reaction so that the H nuclei can be brought together and overcome the electric forces

This energy is provided by the high temperature

Radioactive Decay Rates Half life- The time required for half of the sample of radioactive nuclei to decay. 1st half life  ½ sample remains unchanged 2nd half life-> ¼ sample remains unchanged

3rd half life -> 1/8 sample remains 4th half life - > 1/16 sample remains 1. Eventually the entire sample will decay

2. With each successive half life, half of the remaining sample decays to form another element. –Different radioactive isotopes have different half lives. –Half lives can last from nanoseconds  billions of years

3. If we know how much of the isotope is present at the beginning, we can predict how old the object is. a.Rocks 40K decays to 40Ar. b.The ratio of 40K to 40Ar is smaller in older rocks ( We have more 40Ar than 40K) ( We have more 40Ar than 40K)

c. We can look at the ratios between 14C and 12C to determine the age of animal remains or plant remains.

Agenda Items Chernobyl Article w/ Questions Half Life problems –BOTH DUE TOMORROW  Review for BIG TEST (Due Friday)

4. Calculations with half life a.226Ra has a half life of 1599yrs. How long would it take 7/8 of 226Ra to decay? b.131I half life= 8.1days. How long will it take for ¾ of the sample to decay? c.Ra 222 has a half life of 3.82days. How long does it take for 15/16 of the sample to decay?