Half+Life

**Review: ** **Review: ** Click here: [] (youtube video on carbon 14 decay and it's half-life)  3. __Radiographers__ use half-life information to make adjustments in the film exposure time due to the changes in radiation intensity that occurs as radioisotopes degrade.
 * Half-life is a measurement of the time it takes for **one-half** of a radioactive substance to decay (in this sense, decay does not mean to rot, but to **diminish** in quantity). *1
 * The atoms of radioactive substances, such as uranium and radium, spontaneously break down over time, transforming themselves into atoms of another element. In the process, they, or energy emitted in the form of waves. An important feature of the radioactive decay process is that each substance decays at its own rate. The half-life of a particular substance, therefore, is constant and is __not affected by any physical conditions__ (temperature, pressure, etc.) that occur around it. *1
 * 1([])
 * 1) The term **half-life** describes how long it will take for half of the atoms to is the fixed rate decay of an isotope.
 * 2) The **curie** is a unit of measurement used to describe the radioactivity of radioactive material. (1C = 3.7 X 1010 disintegrations/sec)
 * 3) The disintegration of the atoms from different isotopes can produce different amounts of radiation. *2
 * The half-lives of certain types of radioisotopes are very useful to know because they allow scientists to determine the ages of very old artifacts using a technique called **CARBON DATING** . *2
 * 1) The half-life of radioisotopes varies from seconds to billions of years.
 * 2) **Carbon-dating ** uses the half-life of Carbon-14 to find the approximate age of an object that is 40,000 years old or younger.


 * 2 ([])

3 (diagram courtesy of the University of Michigan Student Chapter of the Health Physics Society )

(N) || Notice that the graph is not linear. It is difficult to calculate the half-life or to determine how much sample would remain after a given time.
 * 4 Take a look at thorium-234. It has been determined that thorium-234 has a half-life of 24.1 days, or in other words, every 24.1 days half of the sample will decompose by beta emission into protactinium-234. Suppose that we start with a 50-g sample and measure the amount of thorium-234 that is present after every 24.1 day period. The table and chart below show the results of the measurement.
 * Time (t) || Amount in grams
 * 0 || 50.000 ||
 * 24.1 || 25.000 ||
 * 48.2 || 12.500 ||
 * 72.3 || 6.250 ||
 * 96.4 || 3.125 ||
 * 120.5 || 1.563 ||
 * 144.6 || 0.781 ||
 * 4 ([])


 * 5 The units of half-life are always time (seconds, minutes, years, etc.). If we know the half-life of an isotope (and we can measure it with special equipment), we can use the number of radiogenic isotopes that have been generated in a rock since its formation to determine the age of formation. Radiometric dating is the method of obtaining a rock's age by measuring the relative abundance of radioactive and radiogenic isotopes.


 * 5 ([])

=Radioactive Half-Life= The [|radioactive] half-life for a given radioisotope is the time for half the radioactive nuclei in any sample to undergo radioactive decay. After two half-lives, there will be one fourth the original sample, after three half-lives one eight the original sample, and so forth. (http://hyperphysics.phy-astr.gsu.edu/Hbase/Nuclear/halfli.html)


 * http://einstein.byu.edu/~masong/HTMstuff/Radioactive2.html**

This URL above shows how half life works. In this animation the slow decaying process is represented by the green bars. Like the twizzler lab that was done during class, the further into the decay that you get the smaller the amount being halved is. Another explanation for this is the fact that the remaining amount of radioactively decayed objects are slowing decreasing as the time passes.