What is an atom's half-life?

Answer 1

The term half-life is one we apply to radioactive materials to talk about how quickly they decay. The half-life is the time it takes for half of a given sample of the unstable substance (whatever it may be) to undergo radioacitve decay. The way it works is quite simple, and though the numbers are statistically derived, they are pretty darn accurate. Let's look more closely.

A sample of a radioactive nuclide (radiocarbon or carbon-14 for example) is made up of atoms with unstable nuclei. These nuclei will "fall apart" (decay radioactively) spontaneously, and each one can decay at any moment. What we don't know is when a givennucleus will decay. But if we watch a large number of these nuclei, we can count the decays across a period of time, and then come up with a rate of decay. We convert this into the length of time it takes for half of the given sample to decay. This length of time will be the half-life for that particular radionuclide. Each radionuclide has a unique half-life, as you might expect.

A half-life is based on the decay rate of a particular isotope of a given element. It is a natural characteristic of that given radionuclide, and it is the amount of time it takes for a sample of it to decay to the point where half of it is gone and half the original sample remains. Use the links below to related questions to learn a little more.

Drugs also have a half-life. Some drugs stay longer in the system, some disapate quickly. If the doctor wants to maintain a level of the drug in the body it maybe necessary to prescribe a dose every several hours or once or twice a day depending on how long the half-life of the drug is.

From Wikipedia..

The duration of action of a drug is known as its half life. This is the period of time required for the concentration or amount of drug in the body to be reduced by one-half. We usually consider the half life of a drug in relation to the amount of the drug in plasma. A drug's plasma half-life depends on how quickly the drug is eliminated from the plasma.

Half life is the time duration in which half of the radioactive element would undergo decay. Suppose just for understanding purpose let us say half life is 3 hours.

Say we have 4096 atoms fresh

Now after 3 hours half of this ie 2048 have got decayed

In the next 3 hours ie totally in 6 hours half of this ie 1024 would get decayed and 1024 would remain

Now in the next 3 hours half of this ie 512 would get decayed

In the next 3 hours 256 and then 128, 64, 32, 16, 8 and so on

But in reality there would millions of atoms.

Answer 2

Strictly it is the half life of a particular isotope of the element.

The half life of a radioactive isotope is the time taken for the number of radioactive atoms in the sample to decay to one half.

Half lives vary hugely, from times like 10-21 seconds, to the very long, approaching the age of our solar system at 4.5x1012 years.