View Single Post
Old 04-14-2004, 06:44 AM   #7 (permalink)
Yakk
Wehret Den Anfängen!
 
Location: Ontario, Canada
Half-life, more technically, is the period of time in which any one atom of the substance has a 50% chance of decaying.

As it happens, when dealing with large quantities of a substance (and any quantity of atoms you can weigh is 'large'), this means that pretty much exactly[1] half of it decays in that period of time.

If your isotope X had a half life of 1 day, and you had one atom, after 1 day there is a 50% chance it would be gone.

After 10 days there would be a (1-2^-10)*100% chance it would be gone, or about 99.9% chance.

There would never be a 100% chance it was gone.

Interestingly, even protons have a half life. There is a period far far far far[2] in the future when there is a greater than 50% chance that every proton in the universe will have decayed, assuming something else catastrophic doesn't happen first.

Footnotes:
[1]: Basically, the odds that >51% or <49% would be left are on the same order of magnitude as the atoms in your room spontaniously assembling into a working computer. Well, not quite... =)
[2]: No, I actually didn't use enough "far"s. Not by a long shot.
__________________
Last edited by JHVH : 10-29-4004 BC at 09:00 PM. Reason: Time for a rest.
Yakk is offline  
 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73