The Naked Scientists

The Naked Scientists Forum

Author Topic: what does 'HALF LIFE' mean exactly ?  (Read 5539 times)

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
what does 'HALF LIFE' mean exactly ?
« on: 08/03/2006 11:18:57 »
I have just seen another_someones and Daveshorts answer a question where the term of ' half life ' was used.

Now I can guess what half life means quite a few times an I know I could probably look it up but for the sake of me and others (ok..probably just me then)..Dave, George can you explain to me exactly what ' half Life' means and why they just can't say something will last a certain amount of time ?

Please remember who you're explaining it too, so words with three or less syllables will be greatly appreciated !!

Thanking you in advance

Neil


Men are the same as women, just inside out !


 

Offline Ophiolite

  • Hero Member
  • *****
  • Posts: 716
  • Thanked: 6 times
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #1 on: 08/03/2006 12:49:00 »
Atoms, as you know, have a nucleus that is made up of a number of protons and (in everything except hydrogen) neutrons. Crudely put the neutrons stop the mutually repulsive protons from flying apart. The more protons you have the more neutrons you need to stop this happening. Most of the existing combinations of neutrons and protons are stable. They will sit there for billions of years quite unchanging. [Their electron shells will be happily engaging in all sorts of interactions with other atoms, forming all sorts of common and bizarre chemicals and getting cycled and re-cycled through the biosphere, hydrosphere, lithosphere, etc, but the nucleus will remain pristine and unchanged.]

A few combinations of neutrons and protons are unstable. They have a tendency to come apart, ejecting, for example, an alpha particle (two protons and two neutrons) and leaving behind a different nucleus, that is consequently a different element. We don't know why a particular nucleus chooses a particular time to fly apart. There is no little clock sitting inside it, timed to go off at a specific data and hour. But we have found that if we take a large enough sample of atoms, that we can determine the probability that some of them will change during a given period of time.

The easiest way of expressing this is to talk of that elements half life. (Strictly speaking I should be talking of an isotopes half life. Isotopes of the same element have the same number of protons, but different numbers of neutrons.)Imagine I start out with 1024 kg of an isotope having a half life of one hour. This means that in one hour the probability that any one specific nucleus will come apart is 50%. Now I cannot predict what will happen to that specific nucleus. I just know there is the same chance it will come apart inthe hour as that it will stay together. However, I do know that at the end of the hour half of the isotope will have come apart. I just don't know which half.

At the end of this hour I now have 512 kg of the isotope left. During the following hour, the chances that any one nucleus comes apart is still 50%. Again, I cannot predict accurately for this one nucleus, but I can predict the average result for all of them. At the end of that one hour I shall have 256 kg, and at the end of the next hour, 128 kg. Seven hours later I shall be down to 1kg.

Does that help?
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #2 on: 08/03/2006 13:30:52 »
quote:
Originally posted by Ophiolite


Does that help?



YES !..Thank you !!

Men are the same as women, just inside out !
 

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #3 on: 08/03/2006 14:29:51 »
is it not a cool PC game!
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #4 on: 08/03/2006 15:51:04 »
Yes....it's that also with an exceptional sequel...(not that I've played it)
 

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #5 on: 08/03/2006 16:10:33 »
Philosophical question is your half life half full or half empty?

What you do speaks so loudly that I cannot hear what you say.
 

Offline wolram

  • Sr. Member
  • ****
  • Posts: 103
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #6 on: 08/03/2006 17:05:56 »
Neil, your (half life) is related to the amount of questions you ask, who am i talking to ?

A born optomist
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #7 on: 08/03/2006 17:28:37 »
quote:
Originally posted by wolram

Neil, your (half life) is related to the amount of questions you ask, who am i talking to ?

A born optomist



*grinning* I'm not entirely too sure how to take that !! :D:D

Men are the same as women, just inside out !
 

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #8 on: 08/03/2006 18:06:58 »
Half of the harm that is done in this world is due to people who want to feel important.
George Eliot
(1819-1880) [Mary Ann Evans] English Novelist, Poet


What you do speaks so loudly that I cannot hear what you say.
 

Offline Ophiolite

  • Hero Member
  • *****
  • Posts: 716
  • Thanked: 6 times
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #9 on: 08/03/2006 18:30:53 »
The other half is done by people who are important.
Ophiolite
(1948- )
 

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #10 on: 08/03/2006 18:32:27 »
Dimidium facti qui coepit habet (Horace)

What you do speaks so loudly that I cannot hear what you say.
« Last Edit: 08/03/2006 18:34:07 by Hadrian »
 

Offline Ophiolite

  • Hero Member
  • *****
  • Posts: 716
  • Thanked: 6 times
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #11 on: 08/03/2006 23:02:52 »
Supersit Dimidium: rursum hoc incipe, et efficies.
 

Offline Ray hinton

  • Sr. Member
  • ****
  • Posts: 476
    • View Profile
    • http://uk.geocities.com/rayhinton56@btinternet.com/photopagetan.html
Re: what does 'HALF LIFE' mean exactly ?
« Reply #12 on: 09/03/2006 00:24:17 »
vorsprung durch technic,miene junge, [|)]

its the drugs,y-know.
 

Offline Broca

  • Sr. Member
  • ****
  • Posts: 162
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #13 on: 11/03/2006 00:19:15 »
neil...if we inject you with an isotope that has a half life of 6 hours...that means that if i inject you with 10 mci   in 6 hours it will only give off energy of half that  or 5 mci and 6 hours after that 2.5 and so on...in very layman terms it has to do with the energy potency.
Before being a teacher...I was a nuke med tech...I got to give a glow to many! :-)
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: what does 'HALF LIFE' mean exactly ?
« Reply #14 on: 11/03/2006 04:08:08 »
quote:
Originally posted by Broca

neil...if we inject you with an isotope that has a half life of 6 hours...that means that if i inject you with 10 mci   in 6 hours it will only give off energy of half that  or 5 mci and 6 hours after that 2.5 and so on...in very layman terms it has to do with the energy potency.
Before being a teacher...I was a nuke med tech...I got to give a glow to many! :-)



Thanks Broca !!.....and "OUCH !!" ...thanks for the jab !! :)


Men are the same as women, just inside out !
 

The Naked Scientists Forum

Re: what does 'HALF LIFE' mean exactly ?
« Reply #14 on: 11/03/2006 04:08:08 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums