09 Mar 06
To take a particular aspect of the discussion in "The origin of life Thread" I would like to find out how half-lifes of elements who's half-life is in the millions of years are measured and how accurate those measurements are. I have not yet found a website explaining this.
I would like to know if there are accurate methods that can be carried out in a lab. For example if a samle of pure Uranium is taken and then the lead content measured after 1 week will this yeild and accurate half-life measurement?
09 Mar 06
Originally posted by twhiteheadThis might get you started, the links at the bottom may yield further info too.
To take a particular aspect of the discussion in "The origin of life Thread" I would like to find out how half-lifes of elements who's half-life is in the millions of years are measured and how accurate those measurements are. I have not yet found a website explaining this.
I would like to know if there are accurate methods that can be carried out in a l ...[text shortened]... en the lead content measured after 1 week will this yeild and accurate half-life measurement?
http://en.wikipedia.org/wiki/Exponential_decay
09 Mar 06
1 edit
Originally posted by twhiteheadIt's actually pretty easy. Measure the energy output over a discrete period, say, a month. E=mc^2 lets you convert energy to mass, and from there, you can work out the half life. Easy-peasy.
To take a particular aspect of the discussion in "The origin of life Thread" I would like to find out how half-lifes of elements who's half-life is in the millions of years are measured and how accurate those measurements are. I have not yet found a website explaining this.
I would like to know if there are accurate methods that can be carried out in a l ...[text shortened]... en the lead content measured after 1 week will this yeild and accurate half-life measurement?
Oh, then go back do the same measurement 40 years later and you get the same result. Do this for multiple elements, then analyse a rock sample, and subject it to all the tests. If you've got your decay constants right, they'll all come up with the same answer. Simple.
09 Mar 06
Originally posted by twhiteheadtry this one.
To take a particular aspect of the discussion in "The origin of life Thread" I would like to find out how half-lifes of elements who's half-life is in the millions of years are measured and how accurate those measurements are. I have not yet found a website explaining this.
I would like to know if there are accurate methods that can be carried out in a l ...[text shortened]... en the lead content measured after 1 week will this yeild and accurate half-life measurement?
http://www.asa3.org/ASA/resources/Wiens.html
10 Mar 06
Originally posted by frogstompThis site has a lot of good information on dating of rocks. However the basic science that half-lifes can be measured without watching a sample for millions of years is not explained. Also the explanation of how we know that half-lifes do not vary over time is not explained.
try this one.
http://www.asa3.org/ASA/resources/Wiens.html
The arguement that dj2becker is trying to make is that half-lives are unknown and may vary over time. I would like to find a site stating the methods used to determine this and the accuracies involved.
Personally, from my small knowledge of nulcear physics, I believe that even a small change in half-life implies a change in atomic properties which would fundamentally change atoms to such a degree that it would be obvious (eg different chemical reactions)
10 Mar 06
Originally posted by twhiteheadYes, see my explanation above. You can work out the mass difference, albeit very very small based on the energy emitted, since E=mc^2. From that you can calculate the half life. Work out the half lives for several radioactive elements, then analyse the same smaple by multiple methods. If they all get roughly the same answer then the decay constants must be about right, and must not vary (if they vary it'll throw off all the ages given by differing amounts).
This site has a lot of good information on dating of rocks. However the basic science that half-lifes can be measured without watching a sample for millions of years is not explained. Also the explanation of how we know that half-lifes do not vary over time is not explained.
The arguement that dj2becker is trying to make is that half-lives are unknown an ...[text shortened]... entally change atoms to such a degree that it would be obvious (eg different chemical reactions)
10 Mar 06
Originally posted by twhiteheadThe way the halflives can be inferred is by the fact we can observe similar processes going on all of the time. Pick a half-life between 1x10^-6 seconds and 1 million years and there is probably an isotope with that halflife. Scientists can observe decay in "real time" for a great number of isotopes. If they fit the data, and if what we now see of ancient isotopes is consistent with them having had a halflife of thousands of years, then why can't they extrapolate. There is no reason to believe the rules governing them have changed since the formation of the earth.
This site has a lot of good information on dating of rocks. However the basic science that half-lifes can be measured without watching a sample for millions of years is not explained. Also the explanation of how we know that half-lifes do not vary over time is not explained.
The arguement that dj2becker is trying to make is that half-lives are unknown an ...[text shortened]... entally change atoms to such a degree that it would be obvious (eg different chemical reactions)
Change in halflife would almost certainly not affect the chemical reactivity. Most isotopes have almost identical properties. It is the number of protons (and hence electrons) that define the chemical characteristics of an isotope, not the number of neutrons (which determines its radioactivity).
10 Mar 06
1 edit
Originally posted by scottishinnzI am no *phycist, so please excuse my ignorance in these matters, but I do not quite understand this.
If they all get roughly the same answer then the decay constants must be about right, and must not vary (if they vary it'll throw off all the ages given by differing amounts).
Why would the ages given vary by different amounts if there is some constant factor applied. For example, if we could look at 2 objects falling under the influence of gravity but the gravity is at some point increased by 3x. Would we be able to observe this by comparing the relative velocities?
I guess the question really is whether halflifes are completely self determined or if they are affected by some outside factors. Will the halflife always be the same in all parts of the universe, or is the halflife we are oberving due to a specific environment that holds locally (even if for the entire galaxy)?
Hmmm, what happens during a nuclear reaction?
Does this have any effect on decay rate?
*[Edit: and clearly I am no linguist either - spelling spelling spelling, oh well - you know what I MEANT]
11 Mar 06
1 edit
Originally posted by JadeMantisAs far as we can tell the laws of physics are the same everywhere.
I am no *phycist, so please excuse my ignorance in these matters, but I do not quite understand this.
Why would the ages given vary by different amounts if there is some constant factor applied. For example, if we could look at 2 objects falling under the influence of gravity but the gravity is at some point increased by 3x. Would we be able to observe ...[text shortened]... d clearly I am no linguist either - spelling spelling spelling, oh well - you know what I MEANT]
You can't tell from the relative velocities of two falling objects that the gravitational field strength has increased by a factor of three. You can tell by looking at how their velocity changes - accelerations are absolute.
In order to affect what is happening inside a nucleus you have to put it under extreme conditions. It is possible to deform nucleii in particle accelerators, and I'd imagine that unstable nucleii would have their decay rates altered under these condidtions.
Nucleii decay because there is a lower energy state available to them, in the simplest case a neutron will decay into a proton, an electron and an anti-neutrino. The proton is a more stable configuration (if it has a finite half-life it is of the order of trillions of years). It's not clear what you mean by 'what happens during a nuclear reaction' since a decay event is a nuclear reaction, but the decay products will be more stable, otherwise the decay just plain won't happen, so the decay products have a larger half-life.
12 Mar 06
Originally posted by JadeMantisOkay, to understand all this it's best to know a little more about both nuclear structure and radioactive decay.
I am no *phycist, so please excuse my ignorance in these matters, but I do not quite understand this.
Why would the ages given vary by different amounts if there is some constant factor applied. For example, if we could look at 2 objects falling under the influence of gravity but the gravity is at some point increased by 3x. Would we be able to observe ...[text shortened]... d clearly I am no linguist either - spelling spelling spelling, oh well - you know what I MEANT]
Basically, a nucleus is comprised of two types of matter; protons, with a positive charge, and neutrons, with no charge. Since the protons all have the same positive charge, then they tend to want to fly away from each other, but are held together with neutrons by the strong nuclear force. Now in small atoms this is fine, there is roughly an equal number of protons and neutrons in any given atoms nucleus and all is well. In larger nucleii however, the number of neutrons may be significantly higher than the number of protons. If we have too many neutrons in a nucleus, or there are simply too many protons and neutrons full stop then the nucleus will break apart. The energy that is released (by the convertion of an infinitesimally small amount of matter to energy by E=mc^2) is called radioactivity.
Now, there isn't just one form of radioactivity - there are in fact a number of different types, the main three being alpha, beta and, imaginatively enough, gamma.
Alpha emissions are where a particle comprising two protons and two neutrons are expelled from the nucleus, for example in the decay of uranium-238 to thorium-234. Energy is also released.
Beta emissions release either an electron (-ve charge) or a positron (+ve charge) from the nucleus, changing a neuton into a proton which balances the mass:charge of the nucleus making it stable. This is best characterised by the production of 14N from 14C (one of the extra neutrons in 14C is converted into a proton, giving the nucleus 7 protons which converts it into a nitrogen atom).
Gamma emissions are the emission of pure energy from a nucleus as it makes a transition from one element to another. After a beta decay, there is occassionally some extra energy in the atom, in which an electron is in an outer orbital, rather than the 'ground state'. Pure energy must be released, and this is done as a gamma ray - which is not a particle, like the others.
Because we are working at an extremely small scale the nucleus isn't affected by many of the same things that affect us, like gravity. Only the electrostatic, strong and weak nuclear forces affect the nucleus and nuclear decay. For the rate constant of nuclear decay to change would require the alteration of one of these forces. Since all nucleii are bound by the same rules, but are different masses, they all decay at their own unique rate. A change in the strong nuclear force would have to affect all radioactive elements by an exactly proportional amount in order to fool radiometric dating into yielding the same, but incorrect, date for the planet / universe, etc. This is all well and fine, except for the fact that (a) we have no evidence for any fundamental change in that laws of physics over the last 18 billion years, (b) we have alot of evidence (from spectral analysis of distant starlight (which is necessarily old)) that the decay constants have not changed over time, and (c) the universe couldn't have formed in the way it has if the strong nuclear force was altered, for two reasons. One, if the strong nuclear force was weaker then large atoms could not form, and possibly small ones too, because they'd constantly be falling apart, with the concommitant nuclear radiation that would be emitted. Two, if the strong nuclear force were stronger, nuclear reactions wouldn't occur, and the sun wouldn't function, except under greater pressure.
Fortunately for us, the rate constant hasn't changed, and we live on a planet heated by radioactive decay in the sun, and from radioactive decay in the planets core. But, to the creationists out there who'll try and say "look, proof of god" i'll remind you of this, this is not proof of god, just proof that these conditions exist.
13 Mar 06
Originally posted by scottishinnzThanks for the thoughtful summary!
Okay, to understand all this it's best to know a little more about both nuclear structure and radioactive decay.
Basically, a nucleus is comprised of two types of matter; protons, with a positive charge, and neutrons, with no charge. Since the protons all have the same positive charge, then they tend to want to fly away from each other, but are held ...[text shortened]... ind you of this, this is not proof of god, just proof that these conditions exist.
13 Mar 06
Originally posted by scottishinnzCOOL, a nice summary in language I can understand to boot... 🙂
A change in the strong nuclear force would have to affect all radioactive elements by an exactly proportional amount in order to fool radiometric dating into yielding the same, but incorrect, date for the planet / universe, etc.
OK, highly unlikely then.
This is all well and fine, except for the fact that (a) we have no evidence for any fundamental change in that laws of physics over the last 18 billion years,
Would it be a change in the laws of physics, or is there something influencing this rate. Sortof like the fact that gravity is not the same everywhere - no change in the laws, its just affected by different mass and distance from that mass in different locations? If some sort of "energy sink" passed near the planet, could it cause such a change - similar to a black hole affecting light? Not saying any of these things happened, just wondering if we are talking 99,8% or 99.9% certainty that the decay rates are right. 😀
Does spectral analysis reliably cancel out this possibility?
Fortunately for us, the rate constant hasn't changed, and we live on a planet heated by radioactive decay in the sun, and from radioactive decay in the planets core. But, to the creationists out there who'll try and say "look, proof of god" i'll remind you of this, this is not proof of god, just proof that these conditions exist.
"Hey look, proof!"
Sorry, couln't resist... 😛
13 Mar 06
Originally posted by JadeMantisLol, love the "look, proof" bit!
COOL, a nice summary in language I can understand to boot... 🙂
[b]A change in the strong nuclear force would have to affect all radioactive elements by an exactly proportional amount in order to fool radiometric dating into yielding the same, but incorrect, date for the planet / universe, etc.
OK, highly unlikely then.
This is all well a ...[text shortened]... oof that these conditions exist.
"Hey look, proof!"
Sorry, couln't resist... 😛[/b]
I can't see anything that would alter the decay constant. The only way you might be able to do it would be to expose your radioactive elements to a neutron stream, but that'd cause your radioactive material to go into a run away reaction, and explode. I can see how one method could be fooled - it's easy, just use a isotope with a half life of a billion years to date a 25 year old rock, but when you have 7 or 8 methods yielding the same date....
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13 Mar 06
Originally posted by twhiteheadThe isotope concentrations can be measured very accurately, but isotope concentrations are not dates. To derive ages from such measurements, unprovable assumptions have to be made such as:
To take a particular aspect of the discussion in "The origin of life Thread" I would like to find out how half-lifes of elements who's half-life is in the millions of years are measured and how accurate those measurements are. I have not yet found a website explaining this.
I would like to know if there are accurate methods that can be carried out in a l ...[text shortened]... en the lead content measured after 1 week will this yeild and accurate half-life measurement?
1. The starting conditions are known (for example, that there was no daughter isotope present at the start, or that we know how much was there).
2. Decay rates have always been constant.
3. Systems were closed or isolated so that no parent or daughter isotopes were lost or added.