Several specific questions about RadioCarbon Dating using AMS

Hello, I am a former YEC and am trying to find specific information about carbon dating methods and procedures. After searching the internet for the last couple of days and reading several freely available scholarly articles I have failed to find specific information explaining some things I'm curious about.

Specifically, I was reading paul giem's page http://www.grisda.org/origins/51006.htm

If one defines machine background as carbon-14 equivalent counts without a sample in place, the predictions of zero background turn out to be largely correct. Schmidt et al. (1987) were able to run their machine with an empty aluminum target holder without finding any atoms of carbon-14 in a 30-minute run, which would be equivalent to >90,000 radiocarbon years (<0.0014 pmc) if they had had a standard current of ordinary carbon. Van der Plicht et al. (1995) found an equivalent age of >100,000 radiocarbon years, and Kirner et al. (1995) obtained an equivalent age of >104,000 years.

For the record, I've seen the posts about Giem's lack of relevant background (http://talkrational.org/showthread.php?t=25497) and I'm not interested in that line of response. I'm specifically looking for articles on machine background with empty sample holders. I've been unable to find much. I can't even find a way to pay for the quoted article by Schmidt (1987) but from reading the abstract it looks more like they were testing their limits of the AMS.

So far I have found two articles with some information about empty sample holders but need some clarification. First, Gillespie and Hedges mention in their report "LABORATORY CONTAMINATION IN RADIOCARBON ACCELERATOR MASS SPECTROMETRY":

It is convenient to begin with the background of the measurement system itself; this includes the sample holder, ion source, accelerator and detector as one unit. When no sample carbon is present (either an empty holder or a bare tantalum wire) a beam current of l-5 nA is generated, with a 14C count rate less than 10% of that from the best “dead” sample. The lowest 14C/13C ratio we have measured is for geological graphite, which yields lo-15 PA of beam current at less than 0.05% of the i4C/i3C ratio for the modern reference standard. This “machine background” is equivalent to an age of about 61000 years.

Now I read this as saying that they ran the test without a sample and measured an age of 61000 yrs age. And as I understand the process the tantalum wire is normally used to hold the graphite in the sample holder but in this case it's bare or the sample chamber is empty. Right? And the machine background measured is just stray carbon molecules that are stuck in the AMS?

Also, I came across and article by D. L. KIRNER,1 R. E. TAYLORI'2 and JOHN R. SOUTHON3 "REDUCTION IN BACKGROUNDS OF MICROSAMPLES FOR AMS 14C DATING"

AMS 14C measurements were done at the Center for Accelerator Mass Spectrometry (CAMS), University of California Lawrence Livermore National Laboratory (LLNL) (Davis et a1.1990; Southon et a1.1990; 1992). Experiments carried out with the CAMS FN tandem accelerator using a GIC Model 846 ion source determined that the machine background as defined by Schmidt, Balsley and Leach (1987), i.e., with the ion source closed off from the remainder of the beam line, ≥104 ka (0 counts in 20.5 min of counting). With the ion source containing an empty aluminum target holder open to the beam transport system, a 14C count rate equivalent to .009 pMC (74 ka) was measured. The average (N=2) 14C value obtained at LLNL on natural graphite used by the UCR radiocarbon laboratory to monitor contamination from loading graphite into their target holders is 64,460 ± 3200 BP (CAMS-12338; 64,500 ± 1800 BP and CAMS-12339; 58,800 ± 1000 BP). The average (N=7) 14C value obtained on graphite powder used by the LLNL laboratory is 57,900 ± 1500 BP (.074 ± .014 pMC)

My only question here is what is meant by "with the ion source closed off from the remainder of the beam line, ≥104 ka (0 counts in 20.5 min of counting). With the ion source containing an empty aluminum target holder open to the beam transport system, a ¹⁴C count rate equivalent to .009 pMC (74 ka) was measured" in laymens terms.

Again, I'm just trying to find out more information to better understand the process. Thanks

Edited by Admin, : Convert last two textual article titles into links. Also, fix quote from last article, it looks like edits to improve the presentation accidentally garbled portions, or it was typed in manually.

Edited by Admin, : Correct portion between quotes in next to last paragraph.

First of all thanks to everyone for the quick responses. Really appreciated.

Pressie: My first response was to lol cause my area of study is IT not radiometric dating methods. Also, a year ago I would have been on here telling how much "ya'll were wrong" about this and "how much you didn't know what you talking about". Now, I am learning more and know better. Having said that, I do intend to help others in my circle of influence by presenting as factually as I can informational pieces about the processes and methods and why YEC is misleading/wrong. That's why I'm here asking questions to make sure I understand it well enough to present it correctly even though I'm not in the field.

Razd: that makes sense. I was reading a post on here (can't remember where now) by Coyote about this being similar to a scale and finding the limits.

Percy: regarding

This background measurement is very unlikely to come from "stray carbon molecules that are stuck in the AMS." They aren't specific about the cause, but it likely was just how their machine behaved....

That makes sense. I had in my mind the idea that the machine background was actual c14 but if I understand correctly now it's just the limits of the machines themselves (like a scale with set limits).

Now to make sure I understand correctly, the following article
"THE CARBONATE 14C BACKGROUND AND ITS COMPONENTS AT THE LEIBNIZ
AMS FACILITY" (1998) by MARKUS SCHLEICHER, PIE TER M. GROOTES, MARIE JOSEE NADEAU and AXEL SCHOON which states:

We tested the background of the AMS system using a pure graphite powder with a very low 14C concentration… which eliminates all but storage and pressing as possible blank contributions. It consistently gives the lowest 14C concentrations we observe in any target, and is measured weekly to check the level and stability of the machine background. These measurements yield a background of 0.03 ± 0.015 pMC, equivalent to 65 ka 14C, similar to machine backgrounds reported for other AMS systems (e.g., Vogel et a1. 1987 Beukens 1990; van der Borg et al. 1997; Kretschmer et al. 1997; Kirner et al. 1995; Grootes et al. 1986; Gillespie and Hedges 1984). Beam stops inserted at the mid-section of the recombinator (Nadeau et al. 1997; Fig. 1) allow the breakdown of this background into counts from the scattering of ions that reach the accelerator via the mass-12 or mass-13 path, and ions that follow mass 14 (12CH2, 13CH), under otherwise normal operating conditions. No counts were observed in the detector over a 40-min period when the mass 13 and 14 paths were blocked, while a normal 12C- beam was injected into the accelerator. This puts an upper limit of 0.0013 pMC, equivalent to 90.5 ka 14C, if one count had been observed, to the combined background contributions of mass-12 charge exchange/scattering and electronic noise. Blocking only the mass 14 beam, four counts were detected in a 67-min period, resulting in a background of 0.0031 pMC and equivalent age of 83.4 ka. This is similar to the observations of Beukens (1990). The observed 0.03 pMC machine background is thus for ca. 90% made up by contributions from mass-14 charge exchange/scattering and true 14C. These contributions appear to be of similar magnitude but will vary with the degree of contamination of the ion source. As stated above, the 0.03 ± 0.015 pMC is an upper limit for the machine background, since the carbon powder may also contain some residual 14C, and additional 14C may have been introduced during storage and target pressing.

indicates that they were testing the machine for background readings using a known powder with low c14 concentration and received a total background of .03 ± .015 Pmc (percent modern Carbon) total due to electronic noise, stray particles, and possible introduction of (modern?) carbon14 during preparation of the sample. So the background here measured is mostly possible contamination and machine background from scattered particles?

"stray carbon molecules that are stuck in the AMS."

I think I was thinking of ion source memory here which I understand as absorbtion of C02 in the reduction system where the sample is reduced to graphite?. I originally thought they meant in the AMS sputtering source, but think I misunderstood at first.

I want to thank everyone again for the great responses and help. I look forward to reading your replies.

Edited by PhiloNibbler, : No reason given.

Thin, by GRI do you mean Global Research Inititive? and SDA Seventh Day Adventists?
If so, not sure about the GRI connection to my first post but my background is more evangelical non-demon christian. In HS I went to a private Christian school and that's where most of my exposure to YEC (mostly bad, old arguments) came from. Also I was an avid AIG fan until Ken Ham's debate and I fact-checked him on the e-coli issue.

Percy: ah, lol. my only reason for using that source is AIG/ICR quote Giem as a study of sources and not the sources directly. I working my way through his material but lot of details and I plan to look at all 70 of his cited sources directly as well

Edited by PhiloNibbler, : No reason given.

Purple: Thanks very helpful. Glad to have your expertise. So from what I read I understand that when Snelling from AIG says:

Among their proposed explanations is that the AMS instruments do not properly reset themselves between sample analyses. But if this were true, why would the instrument find zero atoms when no sample is in it?

(he doesn's source this claim but I think it'd be from Giem based on other articles)

that's wrong because there is always some possible contamination [as well as background noise] and what you actually are measuring is a baseline measurement of these before and after to ensure good reliability of the the sample readings.

I know I'm repeating myself but I also know my YEC friends will challenge me when I challenge them

Coyote: That's interesting. That makes it harder to fact check cause then the reader would have to know whether that person properly collected samples to avaoid bias. Of course that's true for every field of study.

A perfect example would be the problems with the young volcano rocks Snelling/Austin sent in imporperly to be tested for K40/AR40 knowing they would fail.

Percy:

purposefully misrepresenting the data knowing that fellow creationists will either ignore the misrepresentations or not even notice them

Aside from Baumgarder's motives I do think you're correct that most creationists do not attempt to read/understand the issues better because they simply rely on people like Ken Ham and Snellings, and Baumgarder to answer their questions and assume they are knowledgeable and being truthful. Of course it aligns with their interpretation of scripture.

kbertsche: Thanks for the great response. I'll read over it tonight. I've come across your work before and found it interesting. One thing I did pick up on is how YEC sources portray all radiometric samples as closed systems and then accuse scientists of the same assumptions.

Percy: When I first found out the truth, I thought the worst of them, esp. Ken Ham and those who definitely should know better like Baumgardner and Snellings. But after reading Glen Morton's demon. The belief is real, but it's hard to tell how much they're deceiving themselves and how much they're knowingly deceiving others. Sadly, Ham sounds a little too much like a used car sales man when he does his presentations and makes me think the latter is true more than the former.

Baumgardner has no excuse for accepting such specious declarations about sample contamination. It's inexplicable.

Totally right about that. A great example is when you point out factual errors that having nothing to do with their interpretation - such as miscopied sources - they still refuse to edit it to make it correct. How lazy is that? If I wrote something and someone pointed out I had misspelled a name or copied a quote wrong, I'd fix it and thank that person right away. Even magazines when their reporting information like a review of video games will issue corrections when pointed out. It just shows they don't really care about the truth or they don't actually read the original sources that their fellow YECs use. Totally, irresponsible.

Of course, the run of the mill YEC has no idea they're being deceived because Morton's demon won't let them see the truth. I was on a YEC forum and had pointed out the during the Ham/Nye debate Ham had flipped a chart to make it unreadable to the audience (it actually disproved his point) and I found the original source which Ham provided during the presentation. When I pointed it out to them- and one person in responding asked whether the evo source had copied it from Ham! I about fell on the floor from shock.