The most significant forms of radiation are light, heat, and ionizing radiation. Ionizing radiation can penetrate cells and create ions in the cell contents. These, in turn, can cause permanent changes in DNA (mutations). There are three basic types of radiation that humans are exposed to. An alpha particle, which is essentially a helium nucleus, cannot penetrate the skin from the outside and can do very little damage. The beta particle, the electron, can penetrate the skin to a depth of about a centimeter. Both of these particles can do very little damage from the outside, but they can be harmful if they get inside the body. The gamma ray can penetrate any part of the body, and because of its extremely high energy, it can do a lot of damage.
Some of our exposure to radiation is from background radiation (the stuff around us) like cosmic radiation and rocks and soil. From within the body, most comes from potassium-40. About 0.02% of the potassium in nature is in the form of the radioactive isotope potassium-40.
Each kind of radioactive nucleus has a fixed rate at which it decays. This rate is unaffected by most normal external conditions, such as temperature, pressure, or whether or not they are chemically combined with another substance. The amount of time it takes for half of a sample of any such radioactive material to decay is called the half-life. For example, if you had a 100-gram sample of carbon-14, it would take 5,715 years for 50 grams of it to decay. After 11,430 years only 25 grams would remain, and after 17,145 years only 12.5 grams of it would remain.
Radiation is measured in millisieverts (mSv), a unit that measures the absorbed dose of radiation.
A Geiger counter is a device designed to measure radiation. The Geiger counter detects the ionization that occurs within a low-pressure gas inside the Geiger counter. The Geiger counter’s gas is ionized briefly by the passage of a radioactive particle, which allows a brief flow of electricity. The amount of electricity can be observed on a readout, or it can be converted into the familiar clicking sound that is often associated with a Geiger counter.
Journal Entry # 31
a) Why would a source of alpha particles be
dangerous if completely trapped inside of
b) Cesium-137 has a half-life of 30 years.
What percent of a 100-gram Sample
would be left after 210 years?