| Topic: |
Science > Physics |
| User: |
"Bart Van Hove" |
| Date: |
06 Jun 2004 07:52:02 PM |
| Object: |
Calculate Carbon-14 w/o the original ratio |
Yes, this question is from a schoolbook, and though it's mine, it's not
homework. I'm asking because I'm genuinely curious and other students
don't agree so far.
A piece of carbon is found, it's mass is 0.025 kg. Still present are
1.1e12 C(A14,Z6) atoms. The ratio C(A14,Z6)/C(A12,Z6) *currently* is
1.3e-12
1] How many C12 atoms were present *initially*?
2] How many radioactive C14 atoms were present *initially*?
3] When did this tree die? Half-life of C(A14,Z6) is 5800 years.
My problems with these questions:
1] How can I tell without knowing what the original ratio was? Since no
C12 is disappearing, surely the C14/C12 must change in time? Accepted as
a solution by fellow students (and the book, endresults are in the back)
is dividing the 0.025 kg with the mass (in kg) of a C12 atom. Didn't the
piece of carbon used to weigh more? And if it didn't then this number
will effectively be the maximum amount of C12 that can be contained within
such a piece of carbon, implying that there was no C14 to start with!?
2] Again, how can I determine such a thing without knowing either the age
of the object (which is question 3), or the INITIAL ratio of C14/C12?
3] Haven't got a clue: don't know how much C14 there was to begin with, so
who's to tell how long it took amount X to reach 1.1e12?
Solutions the book provides:
1] 1.3e24
2] 1.7e12
3] 3.6e3 years
Bart Van Hove
.
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| User: "Michael Varney" |
|
| Title: Re: Calculate Carbon-14 w/o the original ratio |
06 Jun 2004 08:42:13 PM |
|
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"Bart Van Hove" <bartvanhove@skynet.be> wrote in message
news:pan.2004.06.07.00.52.01.689079@skynet.be...
Yes, this question is from a schoolbook, and though it's mine, it's not
homework. I'm asking because I'm genuinely curious and other students
don't agree so far.
A piece of carbon is found, it's mass is 0.025 kg. Still present are
1.1e12 C(A14,Z6) atoms. The ratio C(A14,Z6)/C(A12,Z6) *currently* is
1.3e-12
1] How many C12 atoms were present *initially*?
2] How many radioactive C14 atoms were present *initially*?
3] When did this tree die? Half-life of C(A14,Z6) is 5800 years.
My problems with these questions:
1] How can I tell without knowing what the original ratio was? Since no
C12 is disappearing, surely the C14/C12 must change in time?
www.google.com "how to use google"
www.google.com "exponetial decay"
www.google.com "decay chain" carbon
Accepted as
a solution by fellow students (and the book, endresults are in the back)
is dividing the 0.025 kg with the mass (in kg) of a C12 atom. Didn't the
piece of carbon used to weigh more? And if it didn't then this number
will effectively be the maximum amount of C12 that can be contained within
such a piece of carbon, implying that there was no C14 to start with!?
2] Again, how can I determine such a thing without knowing either the age
of the object (which is question 3), or the INITIAL ratio of C14/C12?
3] Haven't got a clue: don't know how much C14 there was to begin with, so
who's to tell how long it took amount X to reach 1.1e12?
Solutions the book provides:
1] 1.3e24
2] 1.7e12
3] 3.6e3 years
Bart Van Hove
.
|
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| User: "Old Man" |
|
| Title: Re: Calculate Carbon-14 w/o the original ratio |
06 Jun 2004 09:06:34 PM |
|
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"Bart Van Hove" <bartvanhove@skynet.be> wrote in message
news:pan.2004.06.07.00.52.01.689079@skynet.be...
Yes, this question is from a schoolbook, and though it's mine, it's not
homework. I'm asking because I'm genuinely curious and other students
don't agree so far.
A piece of carbon is found, it's mass is 0.025 kg. Still present are
1.1e12 C(A14,Z6) atoms. The ratio C(A14,Z6)/C(A12,Z6) *currently* is
1.3e-12
1] How many C12 atoms were present *initially*?
2] How many radioactive C14 atoms were present *initially*?
3] When did this tree die? Half-life of C(A14,Z6) is 5800 years.
My problems with these questions:
1] How can I tell without knowing what the original ratio was? Since no
C12 is disappearing, surely the C14/C12 must change in time? Accepted as
a solution by fellow students (and the book, endresults are in the back)
is dividing the 0.025 kg with the mass (in kg) of a C12 atom. Didn't the
piece of carbon used to weigh more? And if it didn't then this number
will effectively be the maximum amount of C12 that can be contained within
such a piece of carbon, implying that there was no C14 to start with!?
2] Again, how can I determine such a thing without knowing either the age
of the object (which is question 3), or the INITIAL ratio of C14/C12?
Researchers that do this for a living do indeed worry about
the variation of the 14 C / 12C ratio with time. There are
independent ways of determining this, but Bart ought to quit
playing the wiseacre, and assume the ratio hasn't changed
over time. It doesn't vary all that much.
Bart is given credit for realizing that the ratio might change
with time. Has Bart looked into the source of 14C in our
atmosphere ? That might give a clue as to time variation.
The half-life of radioactive nuclei doesn't vary at all, and
there's nothing smart in questioning the validity of that.
[Old Man]
3] Haven't got a clue: don't know how much C14 there was to begin with, so
who's to tell how long it took amount X to reach 1.1e12?
Solutions the book provides:
1] 1.3e24
2] 1.7e12
3] 3.6e3 years
Bart Van Hove
.
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| User: "Ian Stirling" |
|
| Title: Re: Calculate Carbon-14 w/o the original ratio |
06 Jun 2004 06:16:13 PM |
|
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Bart Van Hove <bartvanhove@skynet.be> wrote:
Yes, this question is from a schoolbook, and though it's mine, it's not
homework. I'm asking because I'm genuinely curious and other students
don't agree so far.
A piece of carbon is found, it's mass is 0.025 kg. Still present are
1.1e12 C(A14,Z6) atoms. The ratio C(A14,Z6)/C(A12,Z6) *currently* is
1.3e-12
1] How many C12 atoms were present *initially*?
2] How many radioactive C14 atoms were present *initially*?
3] When did this tree die? Half-life of C(A14,Z6) is 5800 years.
My problems with these questions:
1] How can I tell without knowing what the original ratio was? Since no
You look up the ratio of C14/C12 in the atmosphere.
The assumption is that biological organisms will take in carbon from
the atmosphere until they die.
C12 is disappearing, surely the C14/C12 must change in time? Accepted as
a solution by fellow students (and the book, endresults are in the back)
is dividing the 0.025 kg with the mass (in kg) of a C12 atom. Didn't the
piece of carbon used to weigh more? And if it didn't then this number
Neglectable.
will effectively be the maximum amount of C12 that can be contained within
such a piece of carbon, implying that there was no C14 to start with!?
2] Again, how can I determine such a thing without knowing either the age
of the object (which is question 3), or the INITIAL ratio of C14/C12?
3] Haven't got a clue: don't know how much C14 there was to begin with, so
who's to tell how long it took amount X to reach 1.1e12?
Solutions the book provides:
1] 1.3e24
2] 1.7e12
3] 3.6e3 years
Bart Van Hove
.
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