You know that the half-life of a radioactive nuclide, t1/2 , tells you the time needed for half of the atoms present in a sample to undergo radioactive decay. In this case, it takes 3.6 days for any sample of this substance to decay to half of its initial mass.

How can a half-life be used to tell the age of a sample? The ratio between the radioactive form and stable form varies regularly with time. A certain radioactive element has a half-life of one hour.

For example, the biological half-life of water in a human being is about 9 to 10 days, though this can be altered by behavior and other conditions.

1. Activity after 1 half-life = 16 x 0.5 = 8 k B q.
2. Activity after 2 half-lives = 8 x 0.5 = 4 k B q.
3. Activity after 3 half-lives = 4 x 0.5 = 2 k B q.
4. Activity after 4 half-lives = 2 x 0.5 = 1 k B q.
5. Activity of the radioactive source 1 hour later = 1 k B q.

The half-life of a reaction is the time required for a reactant to reach one-half its initial concentration or pressure. For a first-order reaction, the half-life is independent of concentration and constant over time.

Half-life is defined as the amount of time it takes for half of an isotope to change into another isotope. This means that, like the decay constant, the half-life gives an estimate of the stability of a particular radioactive substance, and it can thus be used to identify unknown isotopes.

Concentration is reduced to 25%. It means it takes two half-lives to decrease the concentration of reactant from 0.8 M to 0.2 M in first-order reaction. Hence, half-life of the reaction is 12/2 = 6 hours. The half life of reaction is 6 hours.

The half-life of a reaction is the time required for the reactant concentration to decrease to one-half its initial value. The half-life of a first-order reaction is a constant that is related to the rate constant for the reaction: t1/2 = 0.693/k.

Half Lives. To determine a half life, t½, the time required for the initial concentration of a reactant to be reduced to one-half its initial value, we need to know: The order of the reaction or enough information to determine it. The rate constant, k, for the reaction or enough information to determine it.

Knowing about half-lives is important because it enables you to determine when a sample of radioactive material is safe to handle. They need to be active long enough to treat the condition, but they should also have a short enough half-life so that they don’t injure healthy cells and organs.

We use the half-life because radioactive decay is a matter of chance. When one atom will decay is anyone’s guess. If you have two identical atoms, one could decay immediately, the other could hang around for a century or a millenium. This time frame, where statistically half the atoms decay is called the half-life.

It’s simple. Half-Life 2 is still the greatest FPS ever made. The fact is that Half-Life 2 still executes its concepts, conceits and mechanics more effectively, deftly, and powerfully than almost any of its imitators have in the 10 years since. That’s why it’s still the best, and that’s why I’m still playing it.

Simply by changing the neighboring atoms that are bonded to a radioactive isotope, we can change its half-life. For such an ion, there are no longer any electrons available to capture, and therefore the half-life of the electron capture radioactive decay mode becomes infinite.

In a nutshell, the radiological half-life is important in radiation control because long-lived radionuclides, once released, are around for longer time periods than are shorter-lived species. Long-lived radionuclides released to the environment will be present for longer times than short-lived nuclides.