Download Concept Lecture Outline – Radioactivity and Nuclear Reactions

Section 9: Concept Lecture Outline – Radioactivity and Nuclear Reactions
A. Radioactivity
1. Radioactive elements
a. All elements beyond #83 are radioactive, but isotopes of many others
are, also.
b. The nuclei of radioactive elements are unstable.
c. Radioactivity is the emission of high energy radiation or particles from the
nucleus of an unstable atom.
2. A nuclide is the nucleus of an isotope with a certain atomic number and mass.
a. Represented by atomic notation.
b. Stability of nuclides:
1) Less massive elements are stable if their neutron-proton ration is about
1 to 1.
2) More massive elements are stable if their neutron-proton ratio is about
3 to 2.
B. Nuclear Decay
1. Types of nuclear radiation:
a. Alpha particles
1) The same as a helium nucleus.
2) Has the least penetrating power (can be stopped by paper).
3) Has a charge of +2 and a mass of 4 amu.
b. Beta particles
1) A very high speed electron.
2) Has moderate penetrating power (can be stopped by aluminum foil).
3) Has a charge of -1 and virtually no mass (0 amu).
c. Gamma rays
1) Electromagnetic waves of the highest energy.
2) Has the highest penetrating power (can be stopped by lead or thick
concrete).
3) Has no charge and no mass.
2. Transmutation
a. Transmutation is the process of one element changing into another by nuclear
decay of alpha or beta particles.
b. Alpha decay causes a decrease in the atomic number by 2 and the mass
number by 4.
c. Beta decay causes no change in the mass number, but the atomic number
increases by 1.
3. Half-life is the amount of time it takes for half the nuclides in a radioactive sample to
decay.
a. Vary widely by element.
b. Carbon-14 is 5730 years.
c. Uranium-238 is 4.5 billion years.
d. Polonium-214 is 0.001 second.
4. Radioactive dating is a method to find the approximate age of something based on
measuring the percentage of a radioactive nuclide remaining in a sample.
C. Nuclear Reactions
1. Nuclear fission
a. Fission is the process of splitting a large, unstable nucleus into two smaller
nuclei.
b. Either 2 or 3 neutrons are also produced with the products.
c. These neutrons act as "bullets" to ram into other unstable nuclei and split them,
resulting in a chain reaction.
d. All nuclear reactors in the world are fission reactors.
1) They cannot "blow up" like an atom bomb.
2) They produce radioactive waste which must be stored safely.
2. Nuclear fusion
a. Fusion is the process of combining two smaller nuclei into one larger one.
b. This process requires tremendous amounts of heat.
c. It has been impossible to control fusion (so far).
d. Fusion would be much better than fission.
1) It produces many times more energy.
2) It has virtually no harmful radioactive waste.
D. Nuclear Medicine
1. Tracers are radioisotopes that are put into a person's body to allow doctors to easily
monitor a bodily process.
2. Ionizing radiation therapy can be used to kill cancerous cells, but has side effects.
Physical Science standards met in this unit:
Structure of Atoms
1. The nuclear forces that hold the nucleus of an atom together, at nuclear distances, are usually
stronger than the electric forces that would make it fly apart. Nuclear reactions convert a fraction
of the mass of interacting particles into energy, and they can release much greater amounts of
energy than atomic interactions. Fission is the splitting of a large nucleus into smaller pieces.
Fusion is the joining of two nuclei at extremely high temperature and pressure, and is the process
responsible for the energy of the sun and other stars.
_______a. Compare and contrast fission and fusion reactions showing how they are processes
that convert matter to energy.
_______b. Describe fusion as the process that fuels the sun and other stars.
_______c. Understand the consequences of the development of nuclear applications such as the
atomic bomb, nuclear power plants, and medical technologies.