# Half Life

i dont understand halflife. I just dont understand the concept but i understand radioactive decay.

The half life is really just a number that describes the rate of decay (sticking with the radioactive idea for the moment). If you draw the decay curve it seems to drop sharply then levels out. The critical thing is that it's an exponential curve. The thing about an exponential curve is that equal periods along the x-axis will give you equal ratios on the y-axis. So if you take any y-value, halve it, then compare the x-values you've got, you'll get the same values. I'd advise drawing an exponential curve out and playing with it for a bit to get the hang of it.
ianmoth
20 December 2012
As Ian says the half life is how long it takes for the quantity of the substance to half. To calculate the half life you can use a few equations. Half life = ln2/k (decay constant), Also n=noe^kt and a=aoe^kt.
22 December 2012
The half life of something is just the amount of time it takes for half of it to disappear. This could be a radioactive element, in which case the half life would be the time taken for half of it to decay, or in chemistry the time taken for one half of a reagent to be used up in a reaction. It doesn't matter how much of the substance you have, the half life will always be the same.
chemistry_guru
27 December 2012
I agree, the half life is the time taken for half of something to disappear (or at least to transform into something different). If we think of radioactivity then the half-life is the time for half of a radioactive isotope to decay. When half of the isotope is gone there will only be half as much radiation emitted.
chris_davies
12 March 2013
Carbon dating uses the fact that living things contain a small proportion of carbon 14 with the more common carbon 12. (These numbers are the atomic weights and carbon 14 has more neutrons than carbon 12.) Carbon 12 is stable, in other words it stays the same. Carbon 14 is radioactive and it decays slowly, sending out radiation when it decays. Slowly is the word because it takes something like 6000 years for half of the carbon 14 atoms to decay, or we can say that the half-life of carbon 14 is about 6000 years. If we find the ancient remains of a plant or an animal we can measure how much carbon 14 is left and so have a good idea how long it is since the plant or animal was alive.
chris_davies
12 March 2013
The Half Life of anything is the amount of time that the substance's total amount is halved. A common real world example of half life is the decay of radioactive substances.
Nilai F.
13 March 2013
half life is just the time taken for anything to half itself for eg say: how long will it take to a apple to half it self or a 1 g sugar to go 0.5 g sugar. How long will it take for a 2 g radioactive material to go 1 g. 1g is half of 2g hence the time taken to do so is called halflife. Simple :) *some things are simple just need viewing it from different angles ;)
shub91
10 January 2014
Half life is the time taken for a radioactive particle to decay to half its original weight. This concept though first applied to radioactive substances is now applied mostly in kinetics. In chemical kinetics we can state that the half life is used to measure the rate of a chemical reaction (a typical 1st order reaction), and it is the time taken for the concentration of a reactant to fall to half its initial value.
fred_ngole
11 January 2014
some of the answers below are wrong. It is NOT the time taken to half your weight!! or to half something!! this is a very common misconception. it is the time taken on average for half of the particles in a group to decay:for example if you have 1000 particles after 1 half life there will be 500. but the decayed particles may only looses a small fraction of there mass i.e an americium atom loosing 4 nuclei in alpha emission (a small fraction of the total number of nuclei)I repeat It is NOT the time taken to half itself in weight or number of particles in the atom! it is how long on average for half of the atoms in the group to decay
matt_thomas
30 January 2014
Even though half life applies to radioactive decay the concept doesn't need to have anything to do with atoms decaying.Imagine I have a million normal 6-sided dice (so when I throw the dice I can get a number between 1 and 6). Every time I throw all my dice I remove any dice that land with the  number 6. So after one throw I will only have about 1/6 of my dice. Each of the dice have a 1 in 6 chance of being removed after each throw. After two throws I'll have 5/6 * 1/6 dice left. Every time I throw the dice I remove an 1/6th of the remaining dice eventually I'll have only half the remaining dice left. The time taken for my to have only half of my original dice left is the half life.If instead of a 6 sided dice I used an 8 sided dice, still removing only the dice that land with a 6. This time I'd now be removing only 1 in 8 of the dice each time so it would take longer for my to only have half of my dice left, therefore I'd have a longer half life in this example.The half life is therefore a measure of how quickly a set of objects (which might be radioactive atoms) decay. A short half life means they're decaying quickly and a long half life means they're decaying slowly. You never know when an individual atom will decay just like you don't know when an individual dice will land 6 up  but if you have a very large sample of atoms (or dice) you do know how many will decay (or lang 6 up) in a given time frame.If instead of
mathmom
31 January 2014
A radio active element dissociates by continuous emission of  alpha or beta or gamma particle that various from element to element .The time taken for a radio active element to dissociate into  half of its initial mass is called as half life period
nagaiik
31 January 2014
halflife.png
Max P.
19 September 2015
The image in my answer below was taken from splung.com, and is a useful illustration of what we mean by 'half-life'.For any exponential decay process (e.g. radioactive decay, capacitor discharge), time how long it takes before you have half of the quantity you started with (half the number of nuclei, half the charge, etc.). In an experimental setting, you can do this repeatedly (like in halflife.png below) and take an average.
Max P.
19 September 2015