What is the meaning of the term HALF LIFE?

Question

What is the meaning of the term HALF LIFE?

Answer 1

As far as nuclear physics is concerned "half-life" refers to the time in which the total number of radioactive nucleii reduces to half its initial value due to radioactive disintegration.

   As radioactive disintegration leads to an exponential decrease in the number of atoms so the total time taken for a number of atoms to decay completely is infinite...so we use the half-life values of radioactive elements for our calculations.

Answer 2

1: the time required for half of something to undergo a process: as a: the time required for half of the atoms of a radioactive substance to become disintegrated b: the time required for half the amount of a substance (as a drug, radioactive tracer, or pesticide) in or introduced into a living system or ecosystem to be eliminated or disintegrated by natural processes

2: a period of usefulness or popularity preceding decline or obsolescence <slang usually has a short half–life>

Answer 3

Well in chemistry--its amount of time a particle takes to cut its mass in half or something like that.

I don't know for sure, but it either has something to do with chemistry or its probably just an expression that people use.

Answer 4

'Half Life' is a technical term, used to denote the time taken for a substance to reduce in weight or efficacy, to half of original value! As an expression, loosely, it is just half the total duration before the advertised expiry date!

Answer 5

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. A drug molecule that leaves plasma may have any of several fates. It can be eliminated from the body, or it can be translocated to another body fluid compartment such as the intracellular fluid or it can be destroyed in the blood. The removal of a drug from the plasma is known as clearance and the distribution of the drug in the various body tissues is known as the volume of distribution. Both of these pharmacokinetic parameters are important in determining the half life of a drug.

Answer 6

Each of these prior explanations is true.  But the significance of something having a "half-life" is not apparent - it needs to be explained.  See, a thing with a half-life doesn't just dry up or evaporate or turn into a different material or whatever, in a set amount of time.  You might think that if the half-life was six hours, that the total life was twelve hours.  That's wrong.

Instead, if half of it changes, goes away, whatever, in six hours, then in the NEXT six hours half of WHAT REMAINS goes away, leaving a quarter of the original amount.  Then in another six hours half of THAT goes away, and so on.  So in fact, it's called a logarithmic curve, and while you keep getting less and less of the material, the pace of it going away keeps getting slower and slower too - so it ends up taking a h**l of a long time for it to go away completely, because however much is left, only HALF of that amount goes away in the next six hours - or whatever the substance's "half life" is.

Most things don't behave that way.  If half of it is gone in one hour, then the rest of it will be gone in two hours.

Half-life is like compound interest, sort of,  but in reverse - it's not intuitive and requires some non-casual math to really predict how much is left after any certain period of time.