Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 113 (8748 total)
Current session began: 
Page Loaded: 05-23-2017 10:59 AM
414 online now:
Chatting now:  Chat room empty
Newest Member: kmastes01
Post Volume:
Total: 808,871 Year: 13,477/21,208 Month: 2,959/3,605 Week: 301/933 Day: 43/154 Hour: 15/6

Announcements: Reporting debate problems OR discussing moderation actions/inactions


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Prev1
...
56789
10
Author Topic:   Uranium Dating
Percy
Member
Posts: 15615
From: New Hampshire
Joined: 12-23-2000
Member Rating: 4.4


Message 136 of 153 (574303)
08-15-2010 9:54 AM
Reply to: Message 134 by archaeologist
08-15-2010 8:35 AM


archaeologist writes:

you secularists are all the same, you want dialogue or discussion but you have to keep tilting the playing field inyour direction. if you can't wirte the rules then you do not want to play.

There are over 30 forums at EvC Forum covering a wide range of topics. You can discuss pretty much anything you like here as long you stay roughly on-topic in any given thread. This is from the Forum Guidelines:

  1. Please stay on topic for a thread. Open a new thread for new topics.

In the science forums we discuss topics from a scientific perspective, and there's even a forum for discussing alternative approaches to science: Is It Science?. If you really believe the playing field is tilted in the direction of science and would like to discuss how the rules should change then that's the place to do it.

i have proven, using a man who lost his faith, that objectivity is impossible yet you keep wanting to force it because you do not want to hear the truth nor contradictory arguments to your viewpoints.

We wouldn't be here if we didn't want to hear your viewpoints. Expressed in threads where they're on-topic, of course.

Objectivity is an ideal that science approaches by developing consensus through the gathering of evidence and making successful predictions. In science theories aren't thought true because they are widely accepted. Rather, theories become widely accepted because they are likely true due to the presence of a broadly interconnected network of persuasive supporting evidence and successful predictions.

and i can tell you that you do not know as you use assumption for fact and my point about lincoln was very simple--you can cast a shadow of a doubt on anything by using the evidence at hand.

I think you must have a mistaken impression about the nature of certainty within science. In science nothing is known for certain. This is known as the principle of tentativity. In science all knowledge is considered tentative and open to change in light of new evidence or improved insight.

This means that at EvC Forum you are welcome to cast as much doubt as you like upon anything within science. Your argument about possible contamination is an example of taking this very valid approach.

last i looked greenland wasn't the whole earth and its tempatures and situation would do a lot to alter the isotopes in those rocks. instead of going graph by graph, i will just say htins, all you did was reprint what i have already read from authors who think like you. that is not being objective but biased and presenting your point of view when you disallow mine.

If you have actual arguments against the evidence presented to you then this is the place to make them.

By the way, your views are not disallowed, but you may find that you'll have to take different views to different forums. Views that the rules of science should change are discussed in threads in the Is It Science? forum. We take this approach because otherwise those with this view use it in every thread in all the other forums, and this causes the topic of discussion in multiple threads to become whether God and Bible should be accepted as scientific evidence. In order to insure that threads stay on their original topic we centralize such views in the Is It Science? forum.

here are a couple of articles that point out the flaws of isochron dating:

http://www.answersingenesis.org/...on/v14/i2/radioactive.asp

http://www.tccsa.tc/articles/isochrons2.html

If you have an argument based upon those links then please present it yourself in your own words and use the links as references. This is rule 5 from the Forum Guidelines:

  1. Bare links with no supporting discussion should be avoided. Make the argument in your own words and use links as supporting references.

--Percy


This message is a reply to:
 Message 134 by archaeologist, posted 08-15-2010 8:35 AM archaeologist has not yet responded

    
archaeologist
Inactive Member


Message 137 of 153 (574395)
08-15-2010 5:10 PM


i have decided to refrain from posting in the science section of this website as its rules do not allow the truth to be told. secularists and evolutionists forget that they and science do not get to make the rules.

the rules have already been established by God: is it right or wrong, truth or error and you are either for God or against Him. the scientific method has no bearing on these rules nor doe sit have the authority to over-rule or change them. neither is it the final determiner of what is right or wrong, it is too limited and deals with incomplete data, and it is not immune to the sin and corruption that entered the world at adam's sin. it is also easy to manipulate, fabricate results, lie and bend to political, academic, social pressures-- rendering it moot.

its ever changing nature has demonstrated that it, and secular science in general, does not have the ability or capibility to discover the truth and has blown its opportunity to be trusted to accomplish that task. its methods are unfair, unjust, and wrong as it seeks answers in the wrong direction and the wrong places.

creation is a one time supernatural act that will not be repeated, making it outside of secular science's scope and boundaries. Origins is not an issue for science because it cannot go back in time and observe and extrapolation backwards does not mean they got it right, it jsut means they do not want the truth.

all secular science and secular scientific method are are the blind leading the blind nothing more. any so -called christian who accepts secular science and its teachings have been deceived, lead astray from the truth and hve comrpoised their faith and it is highly doubtful they are still believers for they continue to disobey God by following the secular world into lies.

if you want to continue to sincerely and honestly discuss withme then either find me in a non-scientific forum or over at www.archiesarena.com - push the discussion button. and feel free to discuss but make sure you can accept the rules first.

secularists and evolutionists only delude themselves by saying they want discussion with creationists then make the rulse so that the creationist cannot participate correctly. it is one thing they do not understand, science has no authority to determine how something is discussed, or declare how something was done when it involves the past as they were not there. they just donot want the Bible or its truth, so they will continue to be willingly deceived.

Edited by Admin, : Fix link.


Replies to this message:
 Message 138 by Admin, posted 08-15-2010 5:15 PM archaeologist has not yet responded
 Message 139 by bluescat48, posted 08-15-2010 5:40 PM archaeologist has not yet responded

  
Admin
Director
Posts: 12503
From: EvC Forum
Joined: 06-14-2002
Member Rating: 3.3


Message 138 of 153 (574398)
08-15-2010 5:15 PM
Reply to: Message 137 by archaeologist
08-15-2010 5:10 PM


If you'd like to discuss your views about science then submit a thread proposal over in the Proposed New Topics forum. I will promote it to the Is It Science? forum as quickly as I can give it a proper review.

Edited by Admin, : Grammar.


--Percy
EvC Forum Director

This message is a reply to:
 Message 137 by archaeologist, posted 08-15-2010 5:10 PM archaeologist has not yet responded

    
bluescat48
Member (Idle past 1598 days)
Posts: 2347
From: United States
Joined: 10-06-2007


Message 139 of 153 (574403)
08-15-2010 5:40 PM
Reply to: Message 137 by archaeologist
08-15-2010 5:10 PM


the rules have already been established by God

Your rules have been established by your god. The reason you seem to change the rules of the science forums in that you are blinded by your blind faith and anything that would put a dent in your beliefs or your magic book, to you , must be false. If all people followed your narrow beliefs, the wheel wound not have yet been discovered, men would still live in caves and the dog would not have been domesticated.

{ABE} and I wouldn't be typing on this PC.

Edited by bluescat48, : added line


There is no better love between 2 people than mutual respect for each other WT Young, 2002

Who gave anyone the authority to call me an authority on anything. WT Young, 1969

Since Evolution is only ~90% correct it should be thrown out and replaced by Creation which has even a lower % of correctness. W T Young, 2008


This message is a reply to:
 Message 137 by archaeologist, posted 08-15-2010 5:10 PM archaeologist has not yet responded

    
JonF
Member
Posts: 3535
Joined: 06-23-2003
Member Rating: 3.5


Message 140 of 153 (574404)
08-15-2010 5:41 PM
Reply to: Message 133 by Percy
08-15-2010 7:39 AM


Here's a table of references to scientific papers that dated rocks from Greenland, taken from Brent Dalrymple's The Age of the Earth. Click to grow the image to readable size:

See http://www.fleming-group.com/...Dalrymple%20Table%204.1.html.

I don't believe plain old U/Pb dating is a commonly used dating method today.

I'm not actually in the field, but I do follow it. Depends on what you mean by "plain old U/Pb dating". There's lots of methods involving U-Th-Pb. U-Pb concordia-discordia dating, first developed around 1954, is the preferred method. It's very accurate because the decay constants of uranium isotopes are known more accurately than any others, and it is mostly used on zircons in which the initial lead content is essentially zero because of the physics of solidification. And even that tiny bit can be corrected for in various ways. No other method can get sub-1%accuracy.


This message is a reply to:
 Message 133 by Percy, posted 08-15-2010 7:39 AM Percy has acknowledged this reply

  
RAZD
Member
Posts: 18455
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.9


Message 141 of 153 (574804)
08-17-2010 10:13 PM
Reply to: Message 115 by archaeologist
08-13-2010 11:55 PM


Re: Uranium Halos and Redirect on 14C
Hi archaeologist, I understand you have abandoned the science threads, but I am going to answer for form sake, and for other readers of the forum.

you actually can't say that unless you think and can prove that the earth was created at the same time as the universe and all the stars and planets in it.

Actually, the universe is much older than the earth, as the earth appears to be formed from the debris of older stars that made heavy materials and then went nova.

This debris then would be the basis for forming the earth, the planets in the solar system and the sun,

Of course it would be possible for some debris from the universe landing on earth and being dated older than the earth, but that is not determining the age of the earth. For instance asteroids hitting the earth are dated to find an outside limit to the age of the earth: the earth formation would be younger than the remaining debris that constitutes the asteroids.

according to some theories, space particles formed and then joined together to create planets and gravity but they can't prove that nor can you prove that dating backwards is accurate.

In science nothing is proven. What we have are theories about how things came to be the way they are, based on our understanding of how things work (physics, chemistry, biology).

This results in an approximation of truth for what happened in the past.

What we can do is disprove concepts that are false, such as the young age of the earth, by finding evidence that contradicts it, such as evidence of biological life from over 30,000 years (convincingly older than any YEC earth I am aware of).

In science we discard falsified information, and this process refines our approximation of truth.

that is a bad comparison as isotopes are not sand nor do they need gravity to help them escape a body. nor are there other granals intheir way.

Yes, it is a bad analogy (all analogies are bad in one way or another), but that alone does not mean that radiometric dating is false or inaccurate.

What this is doing is comparing a (mostly) linear system of depletion of a material (sand) by a (relatively) constant rate of outflow to the radioactive depletion of a material (14C, say) by radioactive decay along an exponential curve.

A better analogy would be water flowing out a hole in a bucket, where the rate of flow is proportional to the depth of the water, as this results in an exponential curve, but this is relatively unimportant to the basic concept that each year there is less radioactive material in a sample than there was before.

but you are not verifying it, all one is using are modern ideas without any help fromancient sources to confirm. it is still all assumption, speculation and omits too many variables.

And yet the uranium halo is from an ancient source. It confirms the old age of the earth.

The reason that uranium halos confirm that the earth is old is because they cannot form the proper shells if the rate of decay is changed - that affects the alpha decay energy and that affects the distance the particle travels to make its point mark in the ring.

Each halo is made up of thousands\millions of point marks from individual alpha particles, and thus it take many many many decay events for each isotope in the decay change to form a complete halo pattern with a fully formed shell for each isotope.

I've been through the calculations, and no matter how you cut it, the formation of uranium halos takes much longer than any YEC age concept I am aware of -- hundreds of millions of years

still an assumption and ignores other possibilities for their existence. scientists are assuming that formation only goes their way and nothing or no one had a hand in their construction.

No, it is a valid conclusion based on the available evidence. The fact that evidence does not point in the direction you want is not evidence that it is false or wrong, it is evidence that what you want the evidence to show is a false concept.

There is no evidence of any other way. You can't blame science for ignoring evidence that does not exist.

let me illustrate it another way. i put salt in a jar and ask someone to date it and they come back saying because the glass is old and it takes 4 million years for salt to form to that specification, that i must have filled it 4-5,000,0000 years ago because all of their dating systems said so.

If you dated when the jar was sealed, then you would know when the salt was placed inside, and then you would know that the salt is necessarily older than that event.

And in the case of the uranium halo, the halo is the jar and the uranium is the salt, and the jar is made by the uranium as it ages. The age of the halo measures how long the uranium was in the jar.

This, of course, means that the uranium that was originally sealed in the rock where the halo formed was even older.

The earth is old. Empirical objective evidence invalidates all YEC ages I am aware of, so they are falsified concepts that need to be discarded.

Enjoy.


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

This message is a reply to:
 Message 115 by archaeologist, posted 08-13-2010 11:55 PM archaeologist has not yet responded

  
faith24
Junior Member (Idle past 853 days)
Posts: 27
Joined: 09-10-2010


Message 142 of 153 (587237)
10-17-2010 10:11 PM


I would like to add a claim if you will to this thread since i am not familiar with uranium-lead dating, so maybe someone can shine some light to this claim that was made by someone i encounter in the past. I haven't got this answer yet, so i hope someone can help collaborate on it.

As i understand, not all lead come from uranium, as they produce naturally throughout the environment. I had someone told me this would make lead unreliable. However, in this case, the half life of uranium will be used since there is no new sources to replenish uranium in the sample. Thus, the remaining of uranium will help determine the age of the sample.

Can someone help verify this claim?

And here is my next question concerning the half life problem:

It takes a very long time for uranium to decay into lead. Who even lived that long to observe this? If this is not how they determine the half life, then in what method do they use to determine the half life? I think it has to do with calculations.

Edited by faith24, : No reason given.


Replies to this message:
 Message 143 by Nij, posted 10-17-2010 11:47 PM faith24 has not yet responded
 Message 144 by Chiroptera, posted 10-18-2010 7:32 AM faith24 has not yet responded
 Message 146 by JonF, posted 10-18-2010 9:04 AM faith24 has not yet responded

    
Nij
Member (Idle past 2298 days)
Posts: 239
From: New Zealand
Joined: 08-20-2010


Message 143 of 153 (587247)
10-17-2010 11:47 PM
Reply to: Message 142 by faith24
10-17-2010 10:11 PM


These are two very simple questions to answer; one depends on chemistry, the other on "basic" mathematics:

not all lead come from uranium, as they produce naturally throughout the environment. I had someone told me this would make lead unreliable. However, in this case, the half life of uranium will be used since there is no new sources to replenish uranium in the sample. Thus, the remaining of uranium will help determine the age of the sample

Whether or not lead can be formed by other sources is rather irrelevant.
Uranium-lead dating works by comparing the current ratio of uranium to lead, because of the simple fact that for every uranium atom decaying, you form one lead atom. At the beginning of the process there were no lead atoms in the structure (because we don't just scoop up a handful of dirt and stick it in a geigercounter). The measurements are (usually) made on zircons, a zirconium-silicate mineral with a formula ZrSiO4. When this mineral forms from molten rock, there is the chance of uranium sneaking into the structure of the mineral instead of zirconium, which gets trapped there after the mineral cools. But lead cannot enter the structure anywhere near as easily; it just isn't the right size. So virtually no lead is initally trapped in the mineral and we can safely assume that the initial amount is zero lead.

So, any lead present must have been formed by decay. Thus if there is a 1:1 ratio, half of the uranium has decayed, meaning one halflife has passed since the formation of the rock; if the ration is 1:3 then three-quarters of the uranium has decayed and there has passed two halflives -- the progression is in powers of 0.5 or 1/2; after n halflives there is 100 x 0.5n% of the original isotope remaining.
All we have to do is compare the ratio in the manner above to determine the number of halflives since the mineral's formation. It does get a little more complicated because the fact that not one, but two uranium isotopes might be involved: uranium-235 and uranium-238. There's a method that involves something called concordia, but I'll leave that to more knowledgeable persons.

"But wait!" you say. "How do we know what the halflife is?!" Excellent question and one that has been answered hundreds of times here already. But just for kicks, and because I want to try explaining it myself (the best way to tets your knowledge is teach someone else):



It takes a very long time for uranium to decay into lead. Who even lived that long to observe this? If this is not how they determine the half life, then in what method do they use to determine the half life? I think it has to do with calculations.

You are correct in surmising that it involve calculations.
Isotope decay follows an exponential decay pattern; the amount of material remaining at time t can be calculated by At = A0ekt where A0 is the original amount (amount at time zero), e is the natural base (about 2.7-something-or-other IIRC), k is a constant specific to that isotope (and can be worked out from an experiment by doing some fancy jiggery-pokery with calculus) and t is simply enough time (in whatever units; in this case it would be years although some do work in days, minutes, even milliseconds. Gotta be careful with that).

By doing an experiment where we begin with say 100 grams* of uranium and watching it decay over a period of 1 year, for example, we measure that there is now 99.7 grams* of uranium left. That tells us that A1 = 99.7.

So using our equation, 99.7 = 100 x ek x 1. Using the natural logarithm we can juggle the stuff until we get k on its lonesome:

99.7 = 100ek
99.7/100 = ek
0.997 = ek
ln(0.997) = ln (ek) = k = ???

All you need to do is find out what ln(0.997 is) to get k, which you can then place into the formula, and use that to work out the amount at any time you like OR figure out how much was in the original amount when given the amount at a later point.
This formula and experiment works on any isotope that can be measured accurately, not just uranium, and the general method can be extended into multiple areas of science like biology (simple population growth modelling) and physics (Newton's law of cooling).

You can find out most of this by looking up the subject in Google or checking out pretty much anything RAZD has written in the "Dates And Dating" forum.

* These are just random numbers. 1s are easy to manipulate.
** ln is notation for the natural log or logarithm to base e (normal logs use base 10).


This message is a reply to:
 Message 142 by faith24, posted 10-17-2010 10:11 PM faith24 has not yet responded

  
Chiroptera
Member
Posts: 6323
From: Oklahoma
Joined: 09-28-2003
Member Rating: 4.7


(1)
Message 144 of 153 (587260)
10-18-2010 7:32 AM
Reply to: Message 142 by faith24
10-17-2010 10:11 PM


It takes a very long time for uranium to decay into lead. Who even lived that long to observe this? If this is not how they determine the half life, then in what method do they use to determine the half life? I think it has to do with calculations.

As was pointed out, the formula describing decay is very well understood. As time passes, the amount of material that is left given by the formula

A=A02-t/h,

where A0 is the amount of the radioactive material that you start with.

A little bit of calculus, and we find that the number of decays you measure in a given amount of time, say in a second or a minute, is given by

decays per unit of time = A0 ln 2 /h 2-t/h

If the half life, h, is very long, then 2-t/h stays close to 1 during the length of time of the experiment, and so

decays per unit of time = A0 ln 2 /h

So one can measure the half life of a material just by measuring the amount of the material tha tone has, and measuring the number of decays that occur during a short amount of time.

Of course, there are practical issues in making these measurements, but as an undergraduate, I measured half lives of various radioactive materials, some of which have half-lives of millions of years.

Edited by Chiroptera, : Removed some minus signs.

Edited by Chiroptera, : Forgot the base of the exponent, heh.

Edited by Chiroptera, : Oops. Meant to write 2 instead of e.

Edited by Chiroptera, : *sigh* Will I ever get this right? Serves me right for trying to mix College Algebra with Calculus.


This message is a reply to:
 Message 142 by faith24, posted 10-17-2010 10:11 PM faith24 has not yet responded

Replies to this message:
 Message 145 by Coragyps, posted 10-18-2010 8:44 AM Chiroptera has not yet responded
 Message 147 by NoNukes, posted 10-18-2010 12:05 PM Chiroptera has not yet responded

  
Coragyps
Member
Posts: 5268
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 145 of 153 (587278)
10-18-2010 8:44 AM
Reply to: Message 144 by Chiroptera
10-18-2010 7:32 AM


Of course, there are practical issues in making these measurements...

I might point out that the decay of uranium is exceptionally well studied: all those power reactors and atom bombs around the world depend on a good knowledge of the fuel they use.


This message is a reply to:
 Message 144 by Chiroptera, posted 10-18-2010 7:32 AM Chiroptera has not yet responded

    
JonF
Member
Posts: 3535
Joined: 06-23-2003
Member Rating: 3.5


Message 146 of 153 (587289)
10-18-2010 9:04 AM
Reply to: Message 142 by faith24
10-17-2010 10:11 PM


There are four stable isotopes of lead (stable meaning they don't decay, and isotopes meaning they are the same element but with slightly different numbers of particles in the nucleus). Lead-206 is produced (on Earth) only by the decay of uranium-238. Lead-207 is produced only by the decay of uranium-235. Lead-208 is produced only by the decay of thorium-232. Lead-204 is not produced on Earth; the lead-204 we have was all here when the Earth formed. (All the isotopes are formed when stars blow up).

There are many different dating methods involving uranium. The most commonly used is concordia-discordia dating. This is almost always performed on zircons. Zircon is a mineral that easily incorporates uranium when it solidifies, but lead just doesn't fit in when the zircon solidifies. So when a zircon forms it has a little uranium but essentially no lead. (This is acknowledged by the few young-earth creationists who have a clue about how the method works). Therefore any lead we see in a zircon today is due to the decay of uranium after that zircon solidified, and we can use that knowledge to determine how long ago the zircon solidified,


This message is a reply to:
 Message 142 by faith24, posted 10-17-2010 10:11 PM faith24 has not yet responded

  
NoNukes
Member
Posts: 9529
From: Central NC USA
Joined: 08-13-2010
Member Rating: 3.2


Message 147 of 153 (587315)
10-18-2010 12:05 PM
Reply to: Message 144 by Chiroptera
10-18-2010 7:32 AM


Uranium dating does work
Chiroptera writes:

So one can measure the half life of a material just by measuring the amount of the material that one has, and measuring the number of decays that occur during a short amount of time.

For materials with long half lives, measuring decay counts or activity gives a far more accurate determination in shorter time than would waiting for a measurable amount of uranium to decay.

For that reason, I don't think Nij's method of measuring the remaining U238 is used for determining really long half lives. Nij's method also would require the painful step of separating out the remaining U238 from a tiny amount of decay products. I think it would take something on the order of a million years for the U238 to decay enough to allow an accurate measurement using this method.

What is important is that you don't have to wait for half of the uranium to decay to determine the half life.

faith24 writes:

As i understand, not all lead come from uranium, as they produce naturally throughout the environment. I had someone told me this would make lead unreliable. However, in this case, the half life of uranium will be used since there is no new sources to replenish uranium in the sample. Thus, the remaining of uranium will help determine the age of the sample.

As has been mentioned, the Ur-Pb method are used in situations where the initial presence of lead can be ruled out. I don't sure how just using the remaining uranium would work because we don't directly know the initial amount of uranium. We'd have to infer it from measurements of daughter products.


This message is a reply to:
 Message 144 by Chiroptera, posted 10-18-2010 7:32 AM Chiroptera has not yet responded

Replies to this message:
 Message 148 by Nij, posted 10-18-2010 9:48 PM NoNukes has responded

    
Nij
Member (Idle past 2298 days)
Posts: 239
From: New Zealand
Joined: 08-20-2010


Message 148 of 153 (587459)
10-18-2010 9:48 PM
Reply to: Message 147 by NoNukes
10-18-2010 12:05 PM


Re: Uranium dating does work
Mass, radioactivity count, whatever. Just substitute the quantity, the formula still works exactly the same because the pattern is still exactly the same: an exponential decay.

I don't sure how just using the remaining uranium would work because we don't directly know the initial amount of uranium. We'd have to infer it from measurements of daughter products

I'm fairly sure RAZD has slapped this down before too. We don't need to know the original absolute amount; we only need relative amounts i.e. the ratio of uranium to lead, and these can be calculated from the current relative amounts by the simple fact that x uranium atoms turn into exactly y lead atoms; it's a "stoichiometric relationship".
This message is a reply to:
 Message 147 by NoNukes, posted 10-18-2010 12:05 PM NoNukes has responded

Replies to this message:
 Message 149 by NoNukes, posted 10-18-2010 11:45 PM Nij has not yet responded

  
NoNukes
Member
Posts: 9529
From: Central NC USA
Joined: 08-13-2010
Member Rating: 3.2


(1)
Message 149 of 153 (587469)
10-18-2010 11:45 PM
Reply to: Message 148 by Nij
10-18-2010 9:48 PM


Re: Uranium dating does work
Nij writes:

Mass, radioactivity count, whatever. Just substitute the quantity, the formula still works exactly the same because the pattern is still exactly the same: an exponential decay.

Yes the formulas do work, but some methods for measuring half life are are impractical regardless of what the algebra suggests.

It's very difficult to measure the half life of U238 using the method you describe. After one year of decay 100 grams of U238 would become 99.9999999845 grams of U238 with the decay nuclei still mixed in with the sample. You cannot measure the U238 accurately enough to determine the half-life of U238 even after 1 year.

On the other hand, U238 does emit enough alpha particles (tens of thousands per second per gram) to count over a reasonably short period of time in which the decay rate is constant. For that reason, making an activity measurement is the better approach for determining long half lives.

quote:
I'm fairly sure RAZD has slapped this down before too. We don't need to know the original absolute amount; we only need relative amounts i.e. the ratio of uranium to lead, and these can be calculated from the current relative amounts by the simple fact that x uranium atoms turn into exactly y lead atoms; it's a "stoichiometric relationship".

I agree that only the relative amounts are needed for dating purposes. Not disputing that at all.

The paragraph you quoted above was from my addressing a completely different question posed by faith24, namely, whether we could compensate for the situation where lead other than decay products was present simply by measuring the remaining amount of uranium present. My answer is that you cannot compensate in that fashion.

Edited by NoNukes, : Add a little detail


This message is a reply to:
 Message 148 by Nij, posted 10-18-2010 9:48 PM Nij has not yet responded

    
samreddevilz 
Suspended Member (Idle past 1336 days)
Posts: 7
Joined: 06-10-2013


Message 153 of 153 (701461)
06-19-2013 3:15 PM
Reply to: Message 9 by Coyote
11-19-2008 10:54 AM


Re: Sources
Nice One. Thnx.
This message is a reply to:
 Message 9 by Coyote, posted 11-19-2008 10:54 AM Coyote has not yet responded

    
Prev1
...
56789
10
Newer Topic | Older Topic
Jump to:


Copyright 2001-2015 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2017