why are radiactive elements given half -lifes?

[tali122]

i assume also half life refers to how long the threat of radiation that remains but why are radiactive elements given half -lifes? what is the purpose of that rather than full life?

[fo3nix]

because radiation is an exponential function. this means that the radiation never actually goes away. it just goes lesser and lesser and lesser. but it'll always be there.

thus there is no actual measurable "full life", but there most cetainly is a measurable "half life".

[Gef]

The half-life of a radioisotope is the time it takes for one half of the isotope to decay. For example if a radioisotope has a half life of 2 days then after 4 days only one-quarter of it will be left.

[Peter Pedant]

the time to get to 50% in an exponential function is a constant, wherever you start on the curve - obviously if you start at 80 then you measure to 40 and if you start at 250 you measure to 125

and it's the same ! (ha! if it isnt, then it isnt exponential) - for that element or process....

getting to 100% if you're going by halves will take a long and less useful/illuniating time

[Hamish]

Correction to the first post. The radiation will not always be there, it just decays away very slowly.....The half life measure the time for half the radioactive atome to decay....at some point then there will be only one left, at this point the consept of a half life is meaningless and once this atom has decayed there will be no more radiation (in. v simple terms).

This can be compicated by the fact that may readio actibe elements decay into other radio active elements...

238g of U238 contains 6.022e23 radio acitve atoms, the half life is thousands of years I think, do the maths - OK it is essencially for ever. But technecium 99 Tc99 has a half life of just a few days so not quite so long I think.