Radioactivity

What holds together the protons in the nucleus? The protons in the nucleus are positively charged and want to repel each other. There is a force called the strong force, which causes the protons to be attracted to each other. The strong force is a basic force of nature that is 100 times stronger than the electric force The strong force gets weaker with distance, so it only works in the nucleus.

What is Radiation? Radioactivity is the process of nuclear decay, or the splitting of a nucleus. Large nuclei tend to be unstable and decay. This decaying process releases matter and energy which is radiation. All elements above 83 on the periodic table are radioactive.

How does the strong force help to explain radioactivity? The strong force gets weaker with distance. With larger nuclei, the strong force becomes weaker overall because the it only attracts the closest protons.

The discovery of radioactivity Radiation was discovered in 1896 when Henri Becquerel left uranium salt in a desk drawer with a photographic plate. When he developed the plate he noticed dark spots in the shape of the uranium salt. Becquerel hypothesized that that invisible rays from the salt had darkened the film Two years later, Marie and Pierre Curie discovered two new radioactive elements and a process to extract them

Types of Radiation - Alpha There are three types of radiation: Alpha, Beta, and Gamma radiation Alpha Radiation occurs when an alpha particle is emitted from a decaying nucleus An alpha particle is 2 protons and 2 neutrons Alpha particles have a positive charge

Alpha Radiation Alpha particles are much more massive than gamma and beta radiation and have more electric charge Because of their charge they exert an electric force on the electrons in atoms causing them to lose force quickly Alpha particles can be stopped by a sheet of paper Alpha particles can damage cells if they are released within the body

Transmutation Transmutation is the process of changing one element into another through nuclear decay When an atom emits an alpha particle, the nucleus has 2 fewer protons, so it is now a different element

Beta Radiation The second type of radiation occurs during beta decay A neutron decays into a proton and an electron, and the electron is emitted from the nucleus as a beta particle

Beta Radiation Beta particles are faster and more penetrating than alpha particles They can cause damage if they are released inside the body Beta particles can be stopped by a sheet of aluminum foil.

Gamma Rays Gamma rays are the most penetrating form of nuclear radiation. They are a form of energy with no mass or charge Gamma rays are usually emitted from a nucleus when alpha or beta decay occurs

Gamma Rays Gamma rays can cause the least amount of damage on their own due to their low mass and lack of charge. They do cause atoms to absorb their energy and can cause them to emit particles causing further damage. Gamma rays can be stopped by thick blocks of lead or concrete

Half Life Half life is the measure of how long it takes for half of the nuclei in a sample to decay. Half life varies greatly among radioactive materials from 1/1000 of a second to 4.5 billion years This fact can be used to determine the age of artifacts and rocks. Carbon 14 has a half life of 5,730 years and is used to date artifacts by the amount of Carbon 14 left in the sample

Detecting Radiation A cloud chamber uses water vapor to visualize the path of alpha or beta particles A bubble chamber uses superheated liquid to detect the path of particles. When a particle moves through the liquid, it causes it to boil A Geiger counter is used to measure radiation. It measures radiation through the electrical charge given off by particles interacting with a gas.

Radiation Around Us Low level radiation is emitted constantly from the Earth’s rocks, soil, and atmosphere There are traces of radioactive materials in building materials and food and water consumed by all living things

Nuclear Reactions There are two type of nuclear reactions: Fission and Fusion Nuclear Fission is when one nucleus splits into to two nuclei The mass of the resulting nuclei is slightly less than the mass of the original, as the missing mass has been converted into a tremendous amount of energy E=mc2

Fission Fission occurs through a chain reaction of neutrons striking nuclei For a chain reaction to occur, there must be a critical mass of nuclear material Critical mass is the amount of material so that each fission reaction produces another reaction

Fusion Fusion occurs when two low mass nuclei are combined Fusion occurs at high temperatures so that nuclei can overcome the repulsion force between positive charges This process releases more energy than fission The sun is constantly undergoing fusion

Uses of radiation Radiation is used in the medical field to treat and diagnose diseases Radioactive isotopes or focused gamma rays can be used to kill cancer cells Radioactive materials are also used to diagnose problems in the body X-rays are used to view the inside of the body