• involves the nucleus
• the nucleus opens, protons and neutrons are rearranged
• opening the nucleus releases a great amount of energy that holds the nucleus together called "binding energy"

Chemical Reaction

• involves electrons, not protons and neutrons

1. solar radiation
2. cosmic radiation
3. cosmogenic radionuclides
4. inhaled radionuclides
5. terrestrial radionuclides

• primordial - from before the creation of the earth

• cosmogenic - formed as a result of cosmic rays interactions

• human produced - enhanced or formed due to human actions

Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.

There are numerous types of radioactive decay. 

The general idea:

An unstable nucleus releases energy to become more stable

1. Alpha
2. Beta
3. Gamma

“RULES”

• Uranium-238 decays in 14 steps to lead-206.  The half-life for the process is 4.5 billion years

Radioactive nuclides decay by 4 processes:

• use to detect radioactive substances

Radiation Units

• Roentgen: a unit for measuring the amount of gamma or x rays in the air

• Rad: a unit for measuring absorbed energy from radiation

• Rem: a unit for measuring biological damage from radiation

• 0-25 No effects
• 26-50  small decrease in white blood cell count
• 51-100 significant decrease in white blood cell count, lesions
• 101-200 loss of hair, nausea
• 201-500 hemorrhaging, ulcers, death in 50% population
• >500 death

Alpha radiation is the weakest. It can be stopped by a piece of paper and posses no threat to any human tissue.

Beta radiation is strong, but still not lethal. It can be stopped by most clothing or fabrics. 

Gamma radiation is the strongest. It can only be stopped by lead. It posses great harm to tissue that it comes in contact with.

Alpha - these are fast moving helium atoms. They have high energy, typically in the MeV range, but due to their large mass, they are stopped by just a few inches of air, or a piece of paper. 

Beta - these are fast moving electrons. They typically have energies in the range of a few hundred keV to several MeV. Since electrons are might lighter than helium atoms, they are able to penetrate further, through several feet of air, or several millimeters of plastic or less of very light metals. 

Gamma - these are photons, just like light, except of much higher energy, typically from several keV to several MeV. X-Rays and gamma rays are really the same thing, the difference is how they were produced. Depending on their energy, they can be stopped by a thin piece of aluminum foil, or they can penetrate several inches of lead. 

Marie Sklodowska Curie began studying radioactivity and completed much of the pioneering work on nuclear changes. Curie found that radiation was proportional to the amount of radioactive element present, and she proposed that radiation was a property of atoms (as opposed to a chemical property of a compound).Marie Curie was the first woman to win a Nobel Prize and the first person to win two (the first, shared with her husband Pierre and Becquerel for discovering radioactivity; the second for discovering the radioactive elements radium and polonium).

The discovery of x-rays by William Conrad Roentgen in November of 1895 excited the imagination of a generation of scientists who rushed to study this phenomenon. Within a few months, Henri Becquerel found that both uranium metal and salts of this element gave off a different form of radiation, which could also pass through solids. By 1898, Marie Curie found that compounds of thorium were also "radioactive." After pain-staking effort she eventually isolated two more radioactive elements[image]polonium and radium[image]from ores that contained uranium.

In 1899 Ernest Rutherford found that there were at least two different forms of radioactivity when he studied the absorption of radioactivity by thin sheets of metal foil. One, which he called alpha ([image]) particles, were absorbed by metal foil that was a few hundredths of a centimeter thick. The other, beta (� particles, could pass through 100 times as much metal foil before they became absorbed. Shortly thereafter, a third form of radiation, gamma ([image]) rays, was discovered that could penetrate as much as several centimeters of lead.

Wilhelm Conrad Roentgen on December 22 1895, "photographed" his wife's hand, revealing the unmistakable image of her skeleton, complete with wedding ring. Roentgen's wife had placed her hand in the path of X-rays which Roentgen created by beaming an electron ray energy source onto a cathode tube. Roentgen's discovery of these "mysterious" rays capable of producing an image on a photographic plate excited scientists of his day, including Becquerel. Becquerel chose to study the related phenomena of fluorescence and phosphorescence. In March of 1896, quite by accident, he made a remarkable discovery.

Becquerel found that, while the phenomena of fluorescence and phosphorescence had many similarities to each other and to X-rays, they also had important differences. While fluorescence and X-rays stopped when the initiating energy source was halted, phosphorescence continued to emit rays some time after the initiating energy source was removed. However, in all three cases, the energy was derived initially from an outside source.