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Author Topic:   Does radio-carbon dating disprove evolution?
PurpleYouko
Member
Posts: 714
From: Columbia Missouri
Joined: 11-11-2004


Message 91 of 308 (340269)
08-15-2006 12:02 PM
Reply to: Message 88 by Percy
08-15-2006 10:39 AM


Re: mean free path of Neutrons in water
By "spontaneous fission" are you referring to radioactive decay?
No I am not.
Even non-radioactive nuclei have a small chance of decaying via spontaneous fission.
Regular decay Alpha, beta and Gamma do not directly produce a neutron. The reason that Uranium is able to "go critical" ironically has absolutely nothing to do with its radioactivity. It is just that Uranium has a very high probability of spontaineously fissioning so when enough Uranium atoms are placed close together the neutrons set off a sustainable chain reaction (criticality)
When Uranium fissions, it does not follow the normal decay route buy emitting alpha or beta particles. It splits right down the middle, leaving elements around mass 100-150. See this Nuclear Fission entry at wikipedia. it is pretty accurate.
Normally the fission is caused by the nucleus combining with a thermal neutron such as the case with U235 in a reactor but the chain reaction is initiated by spontaneous fission.
from the same wiki article
quote:
All fissionable and fissile isotopes undergo a small amount of spontaneous fission which releases a few free neutrons into any sample of nuclear fuel. The neutrons typically escape rapidly from the fuel and become a free neutron, with a half-life of about 15 minutes before they decay to protons and beta rays. The neutrons usually impact and are absorbed by other nuclei in the vicinity before this happens. However, some neutrons will impact fuel nuclei and induce further fissions, releasing yet more neutrons. If enough nuclear fuel is assembled into one place, or if the escaping neutrons are sufficiently contained, then these freshly generated neutrons outnumber the neutrons that escape from the assembly, and a sustained nuclear chain reaction will take place.
A typical fission event could be something like
U235 + N ---> U236 (unstable) ---> Kr92 + Ba141 + 3N
But it is by no means certain what the outcome will be.
Hope this helps to clear up any misunderstandings

This message is a reply to:
 Message 88 by Percy, posted 08-15-2006 10:39 AM Percy has replied

Replies to this message:
 Message 96 by Percy, posted 08-15-2006 12:49 PM PurpleYouko has replied

  
PurpleYouko
Member
Posts: 714
From: Columbia Missouri
Joined: 11-11-2004


Message 92 of 308 (340272)
08-15-2006 12:06 PM
Reply to: Message 89 by crashfrog
08-15-2006 10:52 AM


Re: the usual idiocy from some evos
OMG you work at the reactor! That's awesome, we're practically neighbors. I work at the Rollins Bottoms experiment station back behind the reactor sometimes. Down past the golf course.
I wondered where you hung out
I actually run the ICPMS program at the reactor, as plasma mass spectrometry is my field. Can't help picking up stuff about the nuclear side of things though, especially when half the time I end up writing the software that they use to determine safe shipping levels.

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johnfolton 
Suspended Member (Idle past 5591 days)
Posts: 2024
Joined: 12-04-2005


Message 93 of 308 (340273)
08-15-2006 12:08 PM
Reply to: Message 82 by JonF
08-15-2006 9:01 AM


Re: the usual idiocy from some evos
The metabolic processes involved in protein breakdown result in a preferential release of 14N-enriched products and retention of 15N-enriched cellular chemicals.
The nitrogen cycle utilizes denitrification bacteria to release nitrogen of any flavor back to atmosphere.
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In the food cycle, nitrogen compounds are assimilated with little change in the relative amounts of 14N and 15N, and plants and soil microorganisms that can use atmospheric nitrogen or can metabolize nitrogen from man-made ammonium nitrate fertilizer, retain only a small enrichment of 15N over the starting 15N/14N ratio in N2 or NH4NO3. However, metabolic processes involved in protein breakdown result in a preferential release of 14N-enriched products and retention of 15N-enriched cellular chemicals. Herbivores further enrich their tissues in 15N and each consumer up the food chain eats nitrogen progressively enriched in 15N. The body mass and excreted waste of carnivores at the top of the food chain, including humans, are most enriched in 15N.
Denitrification - Wikipedia
Denitrification is the process of reducing nitrate, a form of nitrogen available for consumption by many groups of organisms, into gaseous nitrogen, which is far less accessible to life forms but makes up the bulk of our atmosphere. It can be thought of as the opposite of nitrogen fixation, which converts gaseous nitrogen into more biologically useful forms. The process is performed by heterotrophic bacteria (such as Pseudomonas fluorescens) from all main proteolitic groups. Denitrification and nitrification are parts of the nitrogen cycle.
Denitrification takes place under special conditions in both terrestrial and marine ecosystems. In general, it occurs when oxygen (which is a more favourable electron acceptor) is depleted, and bacteria turn to nitrate in order to respire organic matter

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Percy
Member
Posts: 22388
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 94 of 308 (340275)
08-15-2006 12:22 PM
Reply to: Message 90 by Coragyps
08-15-2006 11:35 AM


Re: mean free path of Neutrons in water
Coragyps writes:
Not all 238U decays through alpha particle emission. 0.00005% splits into two (sizable) nuclei and some neutrons instead.
Okay, but what we want to know is the source of trace amounts of 14C found in the ground. Could a decay sequence with a branch ratio of only 0.00005% be significantly responsible? I understand that it's a more direct process, since it bypasses the need for the alpha particle to strike a nearby low atomic weight atom, but even if only 1% of the material in the ground consists of low atomic weight elements, then there will be 200 neutrons by alpha particle collisions for every 0.00005% branch ratio decay. Even if this less likely decay path gives off 10 neutrons instead of just 1, it's still a minority process.
PurpleYouko was describing things as if the significant process is one which directly emits neutrons, and I'm trying to understand what she is saying in light of what I am reading.
--Percy

This message is a reply to:
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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 95 of 308 (340280)
08-15-2006 12:40 PM
Reply to: Message 93 by johnfolton
08-15-2006 12:08 PM


N14 /N15 ratios
Uh, so what?
You quote a bunch of details when you've been shown that:
1) The N14/N15 ration (enriched or not) is almost all N14.
2) You're fussing about miniscule amounts of C14 that are a problem when attempting to deal with anything over about 50,000 years. You've been give ample reason why there can be small amount of C14 created in situ.
You haven't though dealt with the high degree of correlation between C14 dates and other dating approachs back to about 40,000 years.
It seems you want to drag red herrings across the discussion when you can't deal with substantive issues.
Are you going to deal with them?

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 Message 93 by johnfolton, posted 08-15-2006 12:08 PM johnfolton has not replied

Replies to this message:
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Percy
Member
Posts: 22388
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 96 of 308 (340285)
08-15-2006 12:49 PM
Reply to: Message 91 by PurpleYouko
08-15-2006 12:02 PM


Re: mean free path of Neutrons in water
Okay, I see where you're coming from now, and what you say meshes neatly with what Coragyps said. So since what we're trying to do is identify the process that produces the background levels of 14C in the ground, and since spontaneous fission has a 0.00005% branch ratio for 238U, would you conclude that this process plays any significant role?
--Percy

This message is a reply to:
 Message 91 by PurpleYouko, posted 08-15-2006 12:02 PM PurpleYouko has replied

Replies to this message:
 Message 100 by PurpleYouko, posted 08-15-2006 1:56 PM Percy has replied
 Message 110 by RAZD, posted 08-15-2006 8:10 PM Percy has not replied

  
JonF
Member (Idle past 167 days)
Posts: 6174
Joined: 06-23-2003


Message 97 of 308 (340290)
08-15-2006 1:03 PM
Reply to: Message 87 by PurpleYouko
08-15-2006 10:06 AM


Re: the usual idiocy from some evos
Not to be too picky but N2 is a gas. N14 is an atom and as such can be bonded to other atoms as part of a molecule.
Yup, that's what I said in response to his "N14 is a gas" claim.

This message is a reply to:
 Message 87 by PurpleYouko, posted 08-15-2006 10:06 AM PurpleYouko has not replied

  
JonF
Member (Idle past 167 days)
Posts: 6174
Joined: 06-23-2003


Message 98 of 308 (340293)
08-15-2006 1:10 PM
Reply to: Message 95 by NosyNed
08-15-2006 12:40 PM


Re: N14 /N15 ratios
You haven't though dealt with the high degree of correlation between C14 dates and other dating approachs back to about 40,000 years.
The bottom line is that there's minuscule but barely measurable amounts of 14C where we don't a priori expect to find it; we certainly don't expect to find any remains of 14C ingested by organisms that died over 50K-ish years ago. There are various possibilities for the source of this 14C, and there are various explanations being tested. But "The Earth is less than 50K years old" is way down on the list of possible explanations, certainly below "we don't know yet", and for good reason. If we explain the 14C by a young Earth, we immediately have the problem of explaining the vast quantities (far too much for one human to comprehend) of interlocking and cross-correlating evidence for the great age of the Earth.

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Percy
Member
Posts: 22388
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 99 of 308 (340301)
08-15-2006 1:17 PM
Reply to: Message 93 by johnfolton
08-15-2006 12:08 PM


Re: the usual idiocy from some evos
Hi JF,
You seem to be missing a key point. The amount of 15N found in our atmosphere is 0.366%. Enrichment refers to processes that increase the level beyond this, and if you look at Figure 1 from your Environmental Tracers: Identifying the Sources of Nitrate Contamination in Groundwater link and read the accompanying description in the text you'll see that the highest levels of 15N are found in human sewage. This level maxes out at around +25, so let's translate this into a percentage of 15N.
The +25 corresponds to an increase in 15N of 2.5% (you'll discover this by reading the text of the article), which means that the highest ratio we ever see of 15N is 0.366% + 2.5% which equals 2.866%. The highest levels of 15N we ever encounter are 2.866%, and the lowest levels of 14N are 97.134%, more than 30 times higher. And that's in human sewage. As Figure 1 makes clear, the levels of 15N are much lower in soil and plants.
So since at least 97% of all nitrogen is always 14N, you cannot cite a deficiency of 14N as a reason for doubting the production of 14C from 14N by natural radiation within the ground, because no such deficiency of 14N exists.
--Percy

This message is a reply to:
 Message 93 by johnfolton, posted 08-15-2006 12:08 PM johnfolton has replied

Replies to this message:
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PurpleYouko
Member
Posts: 714
From: Columbia Missouri
Joined: 11-11-2004


Message 100 of 308 (340318)
08-15-2006 1:56 PM
Reply to: Message 96 by Percy
08-15-2006 12:49 PM


Re: mean free path of Neutrons in water
since spontaneous fission has a 0.00005% branch ratio for 238U, would you conclude that this process plays any significant role?
It's a bit hard to determine whether it does or not.
U238 is pretty stable. It has a half life of 4.47 Billion years (4.47E9) and a Fission half life of 8E15 years (That's where the ratio comes from)
lets do the math and see.
First we need to know a ballpark figure for Uranium concentration in soil. Googling around, I came up up with this site that claims a maximum of 11ppm in South Dakota. I really don't know if this is typical or not but let's take 10ppm as the norm just for the hell of it.
That means that for every kilogram of soil, there are 10 miligrams of Uranium.
1 mol of Uranium (238g) = 6.02E23 atoms (Avagadros number)
Therefore 10 miligrams of soil would contain 2.52E19 atoms of Uranium (sounds a lot doesn't it?)
It would take 1 half life of 8E15 years to cut this value in half (if all the decay was via fission)
So to calculate the number of atoms lost due to fission alone per year, we would simply divide half the present number of atoms by the half life.
This gives us a value of 3151 fissions per year for 1Kg of soil
That is 8.6 fissions per day.
(I have assumed a linear rather than exponential decay for simplicity here. An exponential decay would mean a slightly higher rate NOW and a much lower rate LATER)
Trying to estimate how many of those fissions would result in a Neutron colliding with a N14 atom is a bit beyond me but it is an interesting point that the thermal cross section of N14 is considerably higher than average at 1.8 Barns units. Most isotopes are less than 1.
So in answer to your question, yes I think it could potentially be a significant contributor to the C14 levels in soil.
One other thing too. C12 can capture a Neutron to form C13 (another stable isotope) then this can capture a second Neutron to become C14 so we have another possible route other than via N15. The pathway is very minimal though.

This message is a reply to:
 Message 96 by Percy, posted 08-15-2006 12:49 PM Percy has replied

Replies to this message:
 Message 101 by Coragyps, posted 08-15-2006 2:19 PM PurpleYouko has replied
 Message 103 by Percy, posted 08-15-2006 2:58 PM PurpleYouko has replied

  
Coragyps
Member (Idle past 734 days)
Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 101 of 308 (340324)
08-15-2006 2:19 PM
Reply to: Message 100 by PurpleYouko
08-15-2006 1:56 PM


Re: mean free path of Neutrons in water
And if this is saying what it appears to be:
Look at radium 226 there - it has
"Mode of decay: 14C
Branch ratio: 3.2E-9 %
Decay energy: 28.199 MeV"
It gives us a direct source of 14C from radium - and ALL the uranium-238 that goues through the "normal" decay pathway goes through 226Ra for a little while - 1600 years half-life. There's never much radium present in the crust, but it's always being replaced by decay down the 238U chain.

This message is a reply to:
 Message 100 by PurpleYouko, posted 08-15-2006 1:56 PM PurpleYouko has replied

Replies to this message:
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PurpleYouko
Member
Posts: 714
From: Columbia Missouri
Joined: 11-11-2004


Message 102 of 308 (340332)
08-15-2006 2:50 PM
Reply to: Message 101 by Coragyps
08-15-2006 2:19 PM


Re: mean free path of Neutrons in water
Hmmmm. Interesting. I hadn't thought of that.
Check This site out
Apparently C14 is listed as a known COPC (Contaminent Of Potential Concern) in nuclear fuel rods as it is one of the direct fission products of U235
You will find table 2 (the list of COPCs) about a third of the way down the page.
I managed to find quite a number of sites that confirm this too.
Very interesting. I wonder if there are any more ways to make C14?

This message is a reply to:
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Percy
Member
Posts: 22388
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 103 of 308 (340335)
08-15-2006 2:58 PM
Reply to: Message 100 by PurpleYouko
08-15-2006 1:56 PM


Re: mean free path of Neutrons in water
PurpleYouko writes:
This gives us a value of 3151 fissions per year for 1Kg of soil
That is 8.6 fissions per day.
Yeah, but the decay process yields more than 15 million alpha particles per day. Even if only 0.001% (a thousandth of a percent) of them collide with a low atomic weight nucleus, that's still more than 10 times more neutrons than the spontaneous fission process.
That 0.001% value is, of course, pulled out of thin air. I can only argue for it because it is so tiny as to make it likely that the actual value is larger. The actual value would be a function of the concentrations of low atomic weight elements in the ground material. For example, the complete absence of low atomic weight elements would make the percentage equal to 0, but that isn't likely since oxygen and carbon are very common elements in the ground.
--Percy

This message is a reply to:
 Message 100 by PurpleYouko, posted 08-15-2006 1:56 PM PurpleYouko has replied

Replies to this message:
 Message 104 by PurpleYouko, posted 08-15-2006 3:12 PM Percy has not replied

  
PurpleYouko
Member
Posts: 714
From: Columbia Missouri
Joined: 11-11-2004


Message 104 of 308 (340336)
08-15-2006 3:12 PM
Reply to: Message 103 by Percy
08-15-2006 2:58 PM


Re: mean free path of Neutrons in water
Yeah, but the decay process yields more than 15 million alpha particles per day. Even if only 0.001% (a thousandth of a percent) of them collide with a low atomic weight nucleus, that's still more than 10 times more neutrons than the spontaneous fission process.
I don't know a lot about this alpha particle path. Do you have any good information links on it?
Anyway, I'm not trying to say that spontaneous fission is the only possible route for C14 formation or even the major possible route. I just wanted to point out that it is one of several possible routes that should not be ignored.
I just found This while i was googling around.
It is an online calculator that works out the number of neutrons produced from Uranium under various conditions. I'm not even sure i am using it right though. It doesn't seem to agree with the rate that I worked out earlier.
Ah well. maybe i got it wrong

This message is a reply to:
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Matt P
Member (Idle past 4774 days)
Posts: 106
From: Tampa FL
Joined: 03-18-2005


Message 105 of 308 (340347)
08-15-2006 5:04 PM
Reply to: Message 99 by Percy
08-15-2006 1:17 PM


Re: the usual idiocy from some evos
Hi Percy,
One quick correction to your calculation. Isotopic deviations are reported as parts per thousand deviation from a standard. So a deviation of 25 parts per thousand actually corresponds to:
25 = 1000*{(15N/14N)sample - (15N/14N)standard}/(15N/14N)standard
which, when you calculate through, gives an enrichment of 15N of 0.01%, to a total abundance of 0.376% 15N.
This is mainly being nitpicky, but illustrates the point you make even moreso than before.
15N levels of 2% have been found in some interstellar grain material, but they're exceedingly rare.

This message is a reply to:
 Message 99 by Percy, posted 08-15-2006 1:17 PM Percy has not replied

  
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