The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.
The inverse of the half-life is called the decay <hl>CONSTANT</hl> . The half-life of a specific isotope is a constant and never changes
Too complex to even begin to describe. Most of the articles I researched were very technical and readable only by people who understand mathmatics. Here is a link to the easiest to understand description that I could find.
Here's a link to an abstract of a very technical article which describes
http://www.springerlink.com/content/421313u3011394v5/ The Determination of Radioactive Decay Constants</a target="_blank">> from 1957.
Note that was written in 1957. We've come a long way since then. Next is a copy of a <hl>lab report from a college physics class</hl> in which they determined the half-life of 80Br in 2008 using a Geiger counter.
http://www.physics.umn.edu/courses/getfile.html?id=18614&name=ExampleLabReport.pdf The Half-life of 80Br</a>
http://www.chem.purdue.edu/gchelp/howtosolveit/Nuclear/Half_Life.htm Kinetics of Radioactive Decay.</a>
Half-life. New World Encyclopedia. 2 Apr 2008, 08:18 UTC. 4 Mar 2009, 04:05
<bqi>The half-life of a process can be readily determined by experiment. Some methods do not require advance knowledge of the law governing the decay rate, whether it follows an exponential or other pattern of decay.
Most appropriate to validate the concept of half-life for radioactive decay, in particular when dealing with a small number of atoms, is to perform experiments and correct computer simulations. Validation of physics-math models consists of comparing the model's behavior with experimental observations of real physical systems or valid simulations (physical and/or computer simulations).
When studying radioactive decay, the exponential model does not apply for a small number of atoms (or a small number of atoms is not within the domain of validity of the formula or equation or table). A similar experiment is performed with isotopes that have very short half-lives.</bqi>
Here's the title of an article describing how a half-life is determined.
<bq>Precise and accurate determination of alpha decay half-life of 244Pu by relative activity method using thermal ionization mass spectrometry and alpha spectrometry</bq>
No point in even providing a link to that one!
The ONLY way Young Earth Creationists can maintian their conceit that the earth is 6000 years old is to claim that decay rates are not constant. Believe it or not, they do just that. It's the only possible way the real age of the earth can be discredited.
They are the only ones making this claim and have been througly discredited by all scientists working with Radioactive Decay. It isn't even an issue with real scientists There is no question, no controversy about constant rates of decay.
If half-lives were not constant, then the Atom Bomb would have imploded instead of exploded. (need to check this out).
Do you get it? This is standard stuff for those who know what they are doing. College students in Freshman Physics classes are now able to determine half-lives.