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 | | From: | Nelly | | Subject: | Under standing Half-Lifes (not the computer game) | | Date: | Thu, 23 Dec 2004 14:17:22 +1100 |
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 | Hi there,
I was wondering if someone could help me understand the logic behind half
lifes.
My teacher explained to me that a half life is the TIME in which it takes
for a material to break down in half ie material X takes 5000 years to get
1/2X
well thats how my teacher explained it and she tore paper to explain it
breaking in half, but my argument and she could never answer and i want to
know the reaon is that WHY is that time in a half life always the same
like all i want to knowi swhy the time in a half life is the same because
logically if there is 1/2 the amount of x should it not take less time to
decompose because there is less of it to break down?
i hope this makes sence,
please help me out
thanks
nathan
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| | From: | Daedalus | | Subject: | Re: Under standing Half-Lifes (not the computer game) | | Date: | Thu, 23 Dec 2004 16:56:32 GMT |
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| I assume you're talking about the half life of radioactive materials?
Perhaps it will help if you don't think that at the given time, half of the
atoms will just 'blink out'. Rather, the atoms decay at various periods,
which varies with the level of instability of the element that you are
looking at. (Note that the atoms don't just disappear, but change into other
atoms. For example, Berylium 11 decays into Boron 11.)
Say you have a million atoms of a material with a half life of 60 seconds.
At 1 second, some of the atoms have already decayed. at ten seconds, lots
more and so on. At 60 seconds, you only have 500 000 atoms left. At 120
seconds, you only have 250 000 left. Do the rest of the maths yourself, but
at a certain period, you will have no unstable atoms left.
This activity is NOT dependent on how much of the material is still around
the bit you are looking at. Let's say I have the million atoms again, and
somehow, I can see into the future and I know that this one particular atom
will decay after ... 185 seconds. (in fact there is no way to know this, but
stay with me) If I take that atom and put it in a jar all by itself, it will
still decay at 185 seconds. If I put it in a jar with 6 million other atoms,
it will still decay at 185 seconds. So don't worry about how much of the
material remains, it doesn't change the timing of the decay of the atom that
you are 'looking' at.
Half life is about trying to establish how much activity is still going on
after a given amount of time. It might be easier to think of it as being
based on averages.
There are lots of good web sites that will give you some background in this
stuff. Just go to ask.com, or Google, and type the question "what is half
life?"
Hope this helps.
For other readers: yes I have simplified this.I don't think Nathan needs to
go into quantum mechanics just yet. Don't bother writing to me to complain
about this.
D.
"Nelly" wrote in message
news:41ca38b4$1_1@news.iprimus.com.au...
> Hi there,
> I was wondering if someone could help me understand the logic behind half
> lifes.
>
> My teacher explained to me that a half life is the TIME in which it takes
> for a material to break down in half ie material X takes 5000 years to get
> 1/2X
>
> well thats how my teacher explained it and she tore paper to explain it
> breaking in half, but my argument and she could never answer and i want to
> know the reaon is that WHY is that time in a half life always the same
>
> like all i want to knowi swhy the time in a half life is the same because
> logically if there is 1/2 the amount of x should it not take less time to
> decompose because there is less of it to break down?
>
> i hope this makes sence,
>
> please help me out
> thanks
> nathan
>
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| | From: | Nathan | | Subject: | Re: Under standing Half-Lifes (not the computer game) | | Date: | Fri, 24 Dec 2004 15:43:59 +1100 |
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| hi there
thanks for your explination i know understand that it is not dependant on
the amount
thanks alot
nathan
"Daedalus" wrote in message
news:4NCyd.86151$K7.75874@news-server.bigpond.net.au...
>I assume you're talking about the half life of radioactive materials?
>
> Perhaps it will help if you don't think that at the given time, half of
> the atoms will just 'blink out'. Rather, the atoms decay at various
> periods, which varies with the level of instability of the element that
> you are looking at. (Note that the atoms don't just disappear, but change
> into other atoms. For example, Berylium 11 decays into Boron 11.)
>
> Say you have a million atoms of a material with a half life of 60 seconds.
> At 1 second, some of the atoms have already decayed. at ten seconds, lots
> more and so on. At 60 seconds, you only have 500 000 atoms left. At 120
> seconds, you only have 250 000 left. Do the rest of the maths yourself,
> but at a certain period, you will have no unstable atoms left.
>
> This activity is NOT dependent on how much of the material is still around
> the bit you are looking at. Let's say I have the million atoms again, and
> somehow, I can see into the future and I know that this one particular
> atom will decay after ... 185 seconds. (in fact there is no way to know
> this, but stay with me) If I take that atom and put it in a jar all by
> itself, it will still decay at 185 seconds. If I put it in a jar with 6
> million other atoms, it will still decay at 185 seconds. So don't worry
> about how much of the material remains, it doesn't change the timing of
> the decay of the atom that you are 'looking' at.
>
> Half life is about trying to establish how much activity is still going on
> after a given amount of time. It might be easier to think of it as being
> based on averages.
>
> There are lots of good web sites that will give you some background in
> this stuff. Just go to ask.com, or Google, and type the question "what is
> half life?"
>
> Hope this helps.
>
> For other readers: yes I have simplified this.I don't think Nathan needs
> to go into quantum mechanics just yet. Don't bother writing to me to
> complain about this.
>
> D.
>
>
> "Nelly" wrote in message
> news:41ca38b4$1_1@news.iprimus.com.au...
>> Hi there,
>> I was wondering if someone could help me understand the logic behind half
>> lifes.
>>
>> My teacher explained to me that a half life is the TIME in which it takes
>> for a material to break down in half ie material X takes 5000 years to
>> get 1/2X
>>
>> well thats how my teacher explained it and she tore paper to explain it
>> breaking in half, but my argument and she could never answer and i want
>> to know the reaon is that WHY is that time in a half life always the same
>>
>> like all i want to knowi swhy the time in a half life is the same because
>> logically if there is 1/2 the amount of x should it not take less time to
>> decompose because there is less of it to break down?
>>
>> i hope this makes sence,
>>
>> please help me out
>> thanks
>> nathan
>>
>
>
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