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Old 04-08-2011, 03:05 PM   #1370475  /  #1826
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Quote:
Originally Posted by Febble View Post
Dave, do you ever read more than a couple of words of anyone else's post?

Just curious.
yes of course I read </dave>
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Old 04-08-2011, 03:06 PM   #1370477  /  #1827
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Quote:
Originally Posted by Dave Hawkins View Post
That last sentence in the Cherniak paragraph above is the only one I can see that can possibly be construed to say "Saadoune was wrong" ... but hold on ... Cherniak was observing that the 75-80kJ was lower than Reiners but Reiners did HIGH TEMP work! He didn't do low temp work and Saadoune was focused on low temp behavior. So of course his 75-80kj/mol is going to be significantly lower than Reiners!

It seems that all researchers in this field (and people here as well) who have been brainwashed by this belief in "extreme extrapolation" are having a hard time getting their heads around one nagging fact about helium diffusion in zircons:

LOW TEMP = LOW ACTIVATION ENERGY
dave, what conclusions can you draw from data points that are below the machine sensitivity?
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Old 04-08-2011, 04:28 PM   #1370580  /  #1828
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Quote:
Originally Posted by Dave Hawkins View Post
Gary ...
Quote:
I think he is wrong because his model does not agree with the high-temperature experimental data of Cherniak.
So I suppose if Reich said that "oranges are spherical" you would also say he was wrong? Look, guys, don't you think Cherniak would have said Reich was wrong if he was? And Saadoune too? But what did Cherniak say?
Quote:
p. 160 - Reich et al. (2007) have simulated the diffusion of He in perfectly
crystalline zircon using molecular dynamics simulations and empirical
force field and quantum mechanical calculations. They find strong
anisotropy, with diffusion in the [001] direction the most favorable
pathway with a low activation energy for diffusion (13.4 kJ/mol).
Their calculated diffusivities for this orientation, as well as the [100]
direction, are considerably faster than those measured in the present
study (Fig. 8). However, the authors point out that these simulations
represent “tracer” diffusivities, i.e., a single atom diffusing through a
perfectly crystalline lattice free of defects, which may differ significantly
from volume diffusion coefficients representing an aggregate
movement of atoms under a chemical potential gradient; such simulations
therefore may not be predictive of bulk lattice diffusion rates.
A more recent study by Saadoune et al. (2009) obtains similar results
for “perfect” zircons, also predicting that diffusion along [001] will
be most favorable for He transport, although there are differences
among the results from these studies for migration along (100)/(010)
directions. The calculations of Saadoune et al. (2009) suggest that the
presence of point defects in zircon mayaffect He mobility, and note the
possibility of defect trapping playing a role in He transport. However,
these observations have not yet been quantitatively related to He
diffusivities, and the activation energies calculated (~75–80kJ/mol)
are considerably lower than those measured in this study and that of
Reiners et al. (2004).
Do you see Cherniak saying that Reich or Saadoune are wrong? I don't. Then you've got Cherniak's Fig. 8 and it looks to me like Cherniak's lines are sort of an average of Reich's. Which is what we would would expect from reading Saadoune. Remember ... Saadoune said that the low resistance paths would have their Ea's increased and the high resistance paths would have their Ea's decreased by point defects - which explains the difference we see between Cherniak's and Reich's data perfectly.

So here you guys are, yammering away about how wrong Reich and Saadoune are, yet the very scientist that you say shows Reich to be wrong, does not herself say Reich is wrong!

Take your blinders off.
Does Reich predict, or does he not that:

Quote:
Diffusion of He in zircon is strongly anisotropic at
temperatures below 650 K (380 C), as He diffuses
preferentially along [001]. In contrast, diffusion
becomes nearly isotropic above this temperature,
as He diffuses in both [001] and [100/[010]
directions.
And does Cherniak's data, or does it not, indicate that He in zircon is strongly anisotropic down to 300C AND up to 600C?

And does this, or does it not, indicate that Reich's prediction is supported by Cherniak's data?
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Old 04-08-2011, 04:51 PM   #1370613  /  #1829
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Quote:
Originally Posted by Febble View Post
Quote:
Originally Posted by Loechelt View Post
The claim in Reich's paper is that the diffusion become isotropic, not that the activation energies are the same. There is a difference, by the way.
Yes, did I imply that they were the same?
No, you did not imply that they were the same. I was addressing this comment to Dave, who did imply that they were the same.
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Old 04-08-2011, 04:53 PM   #1370615  /  #1830
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Quote:
Originally Posted by Loechelt View Post
Quote:
Originally Posted by Febble View Post
Quote:
Originally Posted by Loechelt View Post
The claim in Reich's paper is that the diffusion become isotropic, not that the activation energies are the same. There is a difference, by the way.
Yes, did I imply that they were the same?
No, you did not imply that they were the same. I was addressing this comment to Dave, who did imply that they were the same.
Ah, thanks

Yes, he did.
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Old 04-08-2011, 05:14 PM   #1370633  /  #1831
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Quote:
Originally Posted by Dave Hawkins View Post
Gary ...
Quote:
I think he is wrong because his model does not agree with the high-temperature experimental data of Cherniak.
So I suppose if Reich said that "oranges are spherical" you would also say he was wrong? Look, guys, don't you think Cherniak would have said Reich was wrong if he was? And Saadoune too? But what did Cherniak say?
Quote:
p. 160 - Reich et al. (2007) have simulated the diffusion of He in perfectly
crystalline zircon using molecular dynamics simulations and empirical
force field and quantum mechanical calculations. They find strong
anisotropy, with diffusion in the [001] direction the most favorable
pathway with a low activation energy for diffusion (13.4 kJ/mol).
Their calculated diffusivities for this orientation, as well as the [100]
direction, are considerably faster than those measured in the present
study (Fig. 8).
However, the authors point out that these simulations
represent “tracer” diffusivities, i.e., a single atom diffusing through a
perfectly crystalline lattice free of defects, which may differ significantly
from volume diffusion coefficients representing an aggregate
movement of atoms under a chemical potential gradient; such simulations
therefore may not be predictive of bulk lattice diffusion rates
.
A more recent study by Saadoune et al. (2009) obtains similar results
for “perfect” zircons, also predicting that diffusion along [001] will
be most favorable for He transport, although there are differences
among the results from these studies for migration along (100)/(010)
directions.
The calculations of Saadoune et al. (2009) suggest that the
presence of point defects in zircon may affect He mobility, and note the
possibility of defect trapping playing a role in He transport. However,
these observations have not yet been quantitatively related to He
diffusivities, and the activation energies calculated (~75–80kJ/mol)
are considerably lower than those measured in this study and that of
Reiners et al. (2004).
Do you see Cherniak saying that Reich or Saadoune are wrong? I don't. Then you've got Cherniak's Fig. 8 and it looks to me like Cherniak's lines are sort of an average of Reich's. Which is what we would would expect from reading Saadoune. Remember ... Saadoune said that the low resistance paths would have their Ea's increased and the high resistance paths would have their Ea's decreased by point defects - which explains the difference we see between Cherniak's and Reich's data perfectly.

So here you guys are, yammering away about how wrong Reich and Saadoune are, yet the very scientist that you say shows Reich to be wrong, does not herself say Reich is wrong!

Take your blinders off.
Excuse me Dave, but you have a basic reading comprehension problem here. In particular, unlike you and your behavior, there is a professional courtesy in academic writing where rarely does one come out and blantantly say that another person's work is "wrong". There are more polite and diplomatic ways of getting the point across. Perhaps you can learn a basic social lesson here? In any event, I highlighted in the quote above where Cherniak politely points out that the previous theoretical work is "wrong". I give special attention to the word considerably, because as far as technical writing etiquette goes, it is a pretty strong word.

Also, you keep avoiding the purple X's. In the work by Wolfe and Stockli, they showed that the theoretical predictions of Reich and Saadoune were a poor predictor of the helium content of zircons from the field, but the extrapolated measurements of Reiners and Cherniak were a good predictor. At least you are starting to look at one of the two papers that you have been persistently avoiding. I suppose that is progress.
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Old 04-08-2011, 05:31 PM   #1370651  /  #1832
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Quote:
Originally Posted by Dave Hawkins View Post
Take your blinders off.
PURPLE X'S!
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Old 04-08-2011, 06:16 PM   #1370724  /  #1833
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IOW, Davie-doodles, shorn of Dr. L's polite wording:

We all see Cherniak saying that Reich and Saadoune are wrong.
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Old 04-08-2011, 06:38 PM   #1370743  /  #1834
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Not least because we actually look at the data.
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Old 04-09-2011, 01:02 AM   #1371078  /  #1835
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For those who are still interested in the instrument sensitivity issue, here is some more information. First, the reference cited by VoxRat (Analytic Chemistry 1999, 71, 2059-2061) is not the most informative because it deals primarily with the heating apparatus used by Farley and not the mass spectrometer analysis itself. More detailed information can be found in some of his later papers.

Quote:
Helium diffusion from apatite: General behavior as illustrated by Durango fluorapatite

K. A. Farley

Helium was extracted from the apatites and accumulated in the chamber for periods ranging from 15 min to several weeks. The evolved helium was spiked with ~0.5 pmol of 99.3% pure 3He and measured on a Balzers Prisma quadrupole mass spectrometer after cryogenic concentration and purification. The amount of spike delivered was repeatedly cross-calibrated against a pipette that delivers a known amount of 4He determined to high precision and accuracy with a capacitance manometer. On the basis of reproducibility of standards the precision of He determinations presented here is better than 1% down to a few times the blank level. Blanks were essentially invariant with both time and temperature in the diffusion cell and were typically <1 fmol. All plotted data have been blank corrected; in general, the blank corrections are small (<2%), but in rare cases, blank correction is a substantial fraction of the total gas in a step. When blank corrections for a given data point exceeded 35% the point was ignored for plotting and interpretation.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 105, NO. B2, PAGES 2903–2914, FEBRUARY 10, 2000
A few points to note. Farley measures the helium quantity using a method called "isotope dilution", which is common in the geochronometry/thermochronometry business. Here is the issue. There is a difference between instrument sensitivity and the ability to measure quantity accurately. Let's use an example. Suppose we have an instrument with atomic level sensitivity (which AMS is not capable of doing!). Then, in theory, we could count atoms one-by-one. Let's suppose now we have 10,000 atoms in a box. Can we accurately count all of them? Well, our instrument could count all the atoms in principle, but in order to do so, we would have to insure that we could route every single atom through the system. In practice, the limiting factor is not the instrument sensitivity, but the ability to get every atom from the sample to the instrument. Isotope dilution provides the solution. In this method, a known quantity of material of a different isotopic concentration is added to the sample. Then, assuming that the sample and the isotope "spike" mix uniformly, one merely has to measure ratios instead of quantities, which is much easier to do.

Now back to Farley's measurements. He uses a 3He spike that is 99.3% pure, meaning that there is 0.7% "other stuff" in the spike, probably mostly 4He. This, undoubtedly, contributes to some of the background signal. Below is a table with some calculations and unit conversions.

Code:
Instrument Background from Farley 2000 Journal of Geophysical Research.
Sample           Concentration  Concentration          Atoms
                        (fmol)          (ncc)
Spike                 500.0000       11.20700       3.01E+11
Spike (He3)           496.5000       11.12855       2.99E+11
Spike (other)           3.5000        0.07845       2.11E+09
Blanks                  1.0000        0.02241       6.02E+08
Reject                  2.8571        0.06404       1.72E+09
RATE #16                0.1588        0.00356       9.56E+07
RATE #17                0.0347        0.00078       2.09E+07
RATE #18                0.0906        0.00203       5.45E+07
RATE #19                0.1896        0.00425       1.14E+08
As you can see, the blank concentration is on the same order as the "other stuff" in the spike, and the 4 low-temperature samples from Humphreys' RATE experiment are well below this background level. A later paper by Reiners confirms this concentration level for experimental blanks.

Quote:
He diffusion and (U–Th)/He thermochronometry of zircon: initial results from Fish Canyon Tuff and Gold Butte

Peter W. Reiners, Kenneth A. Farley, Hunter J. Hickes

4He released from the sample in each step was measured by a quadrupole mass spectrometer using 3He isotope dilution. He blanks were determined throughout the temperature range of our experiments and showed no time or temperature dependence; cold blanks were checked prior to each run and a typical blank of 0.02 ncc (STP) of 4He ( < 0.05% of typical 4He released at 500 C) was subtracted from each step.

Tectonophysics 349 (2002) 297– 308
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Old 04-09-2011, 01:40 AM   #1371083  /  #1836
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Thanks, that clears things up somewhat.
What is the meaning/calculation of "reject" in your table? *

Do you suppose Humphreys is aware of this?
If not, it would seem he's not very competent.
If so, it would seem he's not very honest.

* ETA never mind - it's the number that the blank is 35% of...
Quote:
When blank corrections for a given data point exceeded 35% the point was ignored for plotting and interpretation.
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Last edited by VoxRat; 04-09-2011 at 02:58 AM.
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Old 04-09-2011, 03:06 AM   #1371128  /  #1837
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Quote:
Originally Posted by Loechelt View Post
Quote:
Originally Posted by Dave Hawkins View Post
Gary ...
Quote:
I think he is wrong because his model does not agree with the high-temperature experimental data of Cherniak.
So I suppose if Reich said that "oranges are spherical" you would also say he was wrong? Look, guys, don't you think Cherniak would have said Reich was wrong if he was? And Saadoune too? But what did Cherniak say?
Quote:
p. 160 - Reich et al. (2007) have simulated the diffusion of He in perfectly
crystalline zircon using molecular dynamics simulations and empirical
force field and quantum mechanical calculations. They find strong
anisotropy, with diffusion in the [001] direction the most favorable
pathway with a low activation energy for diffusion (13.4 kJ/mol).
Their calculated diffusivities for this orientation, as well as the [100]
direction, are considerably faster than those measured in the present
study (Fig. 8).
However, the authors point out that these simulations
represent “tracer” diffusivities, i.e., a single atom diffusing through a
perfectly crystalline lattice free of defects, which may differ significantly
from volume diffusion coefficients representing an aggregate
movement of atoms under a chemical potential gradient; such simulations
therefore may not be predictive of bulk lattice diffusion rates
.
A more recent study by Saadoune et al. (2009) obtains similar results
for “perfect” zircons, also predicting that diffusion along [001] will
be most favorable for He transport, although there are differences
among the results from these studies for migration along (100)/(010)
directions.
The calculations of Saadoune et al. (2009) suggest that the
presence of point defects in zircon may affect He mobility, and note the
possibility of defect trapping playing a role in He transport. However,
these observations have not yet been quantitatively related to He
diffusivities, and the activation energies calculated (~75–80kJ/mol)
are considerably lower than those measured in this study and that of
Reiners et al. (2004).
Do you see Cherniak saying that Reich or Saadoune are wrong? I don't. Then you've got Cherniak's Fig. 8 and it looks to me like Cherniak's lines are sort of an average of Reich's. Which is what we would would expect from reading Saadoune. Remember ... Saadoune said that the low resistance paths would have their Ea's increased and the high resistance paths would have their Ea's decreased by point defects - which explains the difference we see between Cherniak's and Reich's data perfectly.

So here you guys are, yammering away about how wrong Reich and Saadoune are, yet the very scientist that you say shows Reich to be wrong, does not herself say Reich is wrong!

Take your blinders off.
Excuse me Dave, but you have a basic reading comprehension problem here. In particular, unlike you and your behavior, there is a professional courtesy in academic writing where rarely does one come out and blantantly say that another person's work is "wrong". There are more polite and diplomatic ways of getting the point across. Perhaps you can learn a basic social lesson here? In any event, I highlighted in the quote above where Cherniak politely points out that the previous theoretical work is "wrong". I give special attention to the word considerably, because as far as technical writing etiquette goes, it is a pretty strong word.

Also, you keep avoiding the purple X's. In the work by Wolfe and Stockli, they showed that the theoretical predictions of Reich and Saadoune were a poor predictor of the helium content of zircons from the field, but the extrapolated measurements of Reiners and Cherniak were a good predictor. At least you are starting to look at one of the two papers that you have been persistently avoiding. I suppose that is progress.
Two key points -

Firstly, the first "considerably" just refers to what everyone including Reich already knew - that there is a difference between tracer diffusivities in a perfect crystal. This is not Cherniak politely saying Reich is wrong. This is Cherniak re-emphasizing something everyone already knew. If Reich says that an orange is a sphere, he's not wrong in practical sense - only in a very special technical sense that no one cares about. Reich was not wrong (or at least no one has shown him to be wrong and we have no reason to believe he is wrong) about his most important point - the point which we care about in this debate - that helium flows very easily in the [001] with low activation energy at low temps. Do yo think Reich was wrong about this? If so, why?

Secondly, you really have no idea if Cherniak was politely saying Saadoune was wrong. That's just your opinion. And if she was saying that, she's not automatically right just because she agrees with you. In fact, if she is saying that, then she appears to be missing the fact that Saadoune was trying to explain low temp behavior, not high temp behavior. Do you not see this? If not, why not?

I've told you several times I don't understand how you got the purple X's.
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Old 04-09-2011, 03:10 AM   #1371133  /  #1838
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Quote:
Originally Posted by Loechelt View Post
For those who are still interested in the instrument sensitivity issue, here is some more information. First, the reference cited by VoxRat (Analytic Chemistry 1999, 71, 2059-2061) is not the most informative because it deals primarily with the heating apparatus used by Farley and not the mass spectrometer analysis itself. More detailed information can be found in some of his later papers.

Quote:
Helium diffusion from apatite: General behavior as illustrated by Durango fluorapatite

K. A. Farley

Helium was extracted from the apatites and accumulated in the chamber for periods ranging from 15 min to several weeks. The evolved helium was spiked with ~0.5 pmol of 99.3% pure 3He and measured on a Balzers Prisma quadrupole mass spectrometer after cryogenic concentration and purification. The amount of spike delivered was repeatedly cross-calibrated against a pipette that delivers a known amount of 4He determined to high precision and accuracy with a capacitance manometer. On the basis of reproducibility of standards the precision of He determinations presented here is better than 1% down to a few times the blank level. Blanks were essentially invariant with both time and temperature in the diffusion cell and were typically <1 fmol. All plotted data have been blank corrected; in general, the blank corrections are small (<2%), but in rare cases, blank correction is a substantial fraction of the total gas in a step. When blank corrections for a given data point exceeded 35% the point was ignored for plotting and interpretation.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 105, NO. B2, PAGES 2903–2914, FEBRUARY 10, 2000
A few points to note. Farley measures the helium quantity using a method called "isotope dilution", which is common in the geochronometry/thermochronometry business. Here is the issue. There is a difference between instrument sensitivity and the ability to measure quantity accurately. Let's use an example. Suppose we have an instrument with atomic level sensitivity (which AMS is not capable of doing!). Then, in theory, we could count atoms one-by-one. Let's suppose now we have 10,000 atoms in a box. Can we accurately count all of them? Well, our instrument could count all the atoms in principle, but in order to do so, we would have to insure that we could route every single atom through the system. In practice, the limiting factor is not the instrument sensitivity, but the ability to get every atom from the sample to the instrument. Isotope dilution provides the solution. In this method, a known quantity of material of a different isotopic concentration is added to the sample. Then, assuming that the sample and the isotope "spike" mix uniformly, one merely has to measure ratios instead of quantities, which is much easier to do.

Now back to Farley's measurements. He uses a 3He spike that is 99.3% pure, meaning that there is 0.7% "other stuff" in the spike, probably mostly 4He. This, undoubtedly, contributes to some of the background signal. Below is a table with some calculations and unit conversions.

Code:
Instrument Background from Farley 2000 Journal of Geophysical Research.
Sample           Concentration  Concentration          Atoms
                        (fmol)          (ncc)
Spike                 500.0000       11.20700       3.01E+11
Spike (He3)           496.5000       11.12855       2.99E+11
Spike (other)           3.5000        0.07845       2.11E+09
Blanks                  1.0000        0.02241       6.02E+08
Reject                  2.8571        0.06404       1.72E+09
RATE #16                0.1588        0.00356       9.56E+07
RATE #17                0.0347        0.00078       2.09E+07
RATE #18                0.0906        0.00203       5.45E+07
RATE #19                0.1896        0.00425       1.14E+08
As you can see, the blank concentration is on the same order as the "other stuff" in the spike, and the 4 low-temperature samples from Humphreys' RATE experiment are well below this background level. A later paper by Reiners confirms this concentration level for experimental blanks.

Quote:
He diffusion and (U–Th)/He thermochronometry of zircon: initial results from Fish Canyon Tuff and Gold Butte

Peter W. Reiners, Kenneth A. Farley, Hunter J. Hickes

4He released from the sample in each step was measured by a quadrupole mass spectrometer using 3He isotope dilution. He blanks were determined throughout the temperature range of our experiments and showed no time or temperature dependence; cold blanks were checked prior to each run and a typical blank of 0.02 ncc (STP) of 4He ( < 0.05% of typical 4He released at 500 C) was subtracted from each step.

Tectonophysics 349 (2002) 297– 308
So are you taking the position that those three lowest data points just happened to line up exactly as we would expect them to (all in a nice row forming a low slope), knowing what we now know from Reich and Saadoune's work?
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Old 04-09-2011, 04:05 AM   #1371149  /  #1839
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Quote:
Originally Posted by Dave Hawkins View Post
Quote:
Originally Posted by Loechelt View Post
For those who are still interested in the instrument sensitivity issue, here is some more information. First, the reference cited by VoxRat (Analytic Chemistry 1999, 71, 2059-2061) is not the most informative because it deals primarily with the heating apparatus used by Farley and not the mass spectrometer analysis itself. More detailed information can be found in some of his later papers.

Quote:
Helium diffusion from apatite: General behavior as illustrated by Durango fluorapatite

K. A. Farley

Helium was extracted from the apatites and accumulated in the chamber for periods ranging from 15 min to several weeks. The evolved helium was spiked with ~0.5 pmol of 99.3% pure 3He and measured on a Balzers Prisma quadrupole mass spectrometer after cryogenic concentration and purification. The amount of spike delivered was repeatedly cross-calibrated against a pipette that delivers a known amount of 4He determined to high precision and accuracy with a capacitance manometer. On the basis of reproducibility of standards the precision of He determinations presented here is better than 1% down to a few times the blank level. Blanks were essentially invariant with both time and temperature in the diffusion cell and were typically <1 fmol. All plotted data have been blank corrected; in general, the blank corrections are small (<2%), but in rare cases, blank correction is a substantial fraction of the total gas in a step. When blank corrections for a given data point exceeded 35% the point was ignored for plotting and interpretation.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 105, NO. B2, PAGES 2903–2914, FEBRUARY 10, 2000
A few points to note. Farley measures the helium quantity using a method called "isotope dilution", which is common in the geochronometry/thermochronometry business. Here is the issue. There is a difference between instrument sensitivity and the ability to measure quantity accurately. Let's use an example. Suppose we have an instrument with atomic level sensitivity (which AMS is not capable of doing!). Then, in theory, we could count atoms one-by-one. Let's suppose now we have 10,000 atoms in a box. Can we accurately count all of them? Well, our instrument could count all the atoms in principle, but in order to do so, we would have to insure that we could route every single atom through the system. In practice, the limiting factor is not the instrument sensitivity, but the ability to get every atom from the sample to the instrument. Isotope dilution provides the solution. In this method, a known quantity of material of a different isotopic concentration is added to the sample. Then, assuming that the sample and the isotope "spike" mix uniformly, one merely has to measure ratios instead of quantities, which is much easier to do.

Now back to Farley's measurements. He uses a 3He spike that is 99.3% pure, meaning that there is 0.7% "other stuff" in the spike, probably mostly 4He. This, undoubtedly, contributes to some of the background signal. Below is a table with some calculations and unit conversions.

Code:
Instrument Background from Farley 2000 Journal of Geophysical Research.
Sample           Concentration  Concentration          Atoms
                        (fmol)          (ncc)
Spike                 500.0000       11.20700       3.01E+11
Spike (He3)           496.5000       11.12855       2.99E+11
Spike (other)           3.5000        0.07845       2.11E+09
Blanks                  1.0000        0.02241       6.02E+08
Reject                  2.8571        0.06404       1.72E+09
RATE #16                0.1588        0.00356       9.56E+07
RATE #17                0.0347        0.00078       2.09E+07
RATE #18                0.0906        0.00203       5.45E+07
RATE #19                0.1896        0.00425       1.14E+08
As you can see, the blank concentration is on the same order as the "other stuff" in the spike, and the 4 low-temperature samples from Humphreys' RATE experiment are well below this background level. A later paper by Reiners confirms this concentration level for experimental blanks.

Quote:
He diffusion and (U–Th)/He thermochronometry of zircon: initial results from Fish Canyon Tuff and Gold Butte

Peter W. Reiners, Kenneth A. Farley, Hunter J. Hickes

4He released from the sample in each step was measured by a quadrupole mass spectrometer using 3He isotope dilution. He blanks were determined throughout the temperature range of our experiments and showed no time or temperature dependence; cold blanks were checked prior to each run and a typical blank of 0.02 ncc (STP) of 4He ( < 0.05% of typical 4He released at 500 C) was subtracted from each step.

Tectonophysics 349 (2002) 297– 308
So are you taking the position that those three lowest data points just happened to line up exactly as we would expect them to (all in a nice row forming a low slope), knowing what we now know from Reich and Saadoune's work?
dave, what conclusions can you draw from data points that are below instrument sensitivity?
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Old 04-09-2011, 04:28 AM   #1371164  /  #1840
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Two key points -

Firstly, the first "considerably" just refers to what everyone including Reich already knew - that there is a difference between tracer diffusivities in a perfect crystal. This is not Cherniak politely saying Reich is wrong. This is Cherniak re-emphasizing something everyone already knew. If Reich says that an orange is a sphere, he's not wrong in practical sense - only in a very special technical sense that no one cares about. Reich was not wrong (or at least no one has shown him to be wrong and we have no reason to believe he is wrong) about his most important point - the point which we care about in this debate - that helium flows very easily in the [001] with low activation energy at low temps. Do yo think Reich was wrong about this? If so, why?
How about

Quote:
such simulations therefore may not be predictive of bulk lattice diffusion rates?
Bulk lattice diffusion rates in real crystals is the point we care about in this debate, not tracer atom diffusivities in a perfect crystal. (Remember not so long ago how you tried to argue that Humphreys' was right because of crystal defects. Now you are trying to agrue that Humphreys' is right because of a theory based upon perfect crystals.)

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Originally Posted by Dave Hawkins View Post
Secondly, you really have no idea if Cherniak was politely saying Saadoune was wrong. That's just your opinion. And if she was saying that, she's not automatically right just because she agrees with you. In fact, if she is saying that, then she appears to be missing the fact that Saadoune was trying to explain low temp behavior, not high temp behavior. Do you not see this? If not, why not?
I have shown that Saadoune's mathematical calculation of the Ea (activation energy) values to be in error. This is not just my opinion, Dave.
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Old 04-09-2011, 04:33 AM   #1371168  /  #1841
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So are you taking the position that those three lowest data points just happened to line up exactly as we would expect them to (all in a nice row forming a low slope), knowing what we now know from Reich and Saadoune's work?
So are you taking the position that if three points "just happen" to line up somehow, the fact that they're way below the limit of detection is not important - or even worth mentioning?
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Old 04-09-2011, 04:34 AM   #1371169  /  #1842
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Old 04-09-2011, 04:35 AM   #1371170  /  #1843
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Old 04-09-2011, 04:36 AM   #1371172  /  #1844
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Old 04-09-2011, 04:37 AM   #1371174  /  #1845
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Old 04-09-2011, 04:37 AM   #1371175  /  #1846
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Old 04-09-2011, 04:43 AM   #1371178  /  #1847
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One thing you will find gary is that Dave is not averse to changing his model over and over again as the discussion progresses. This is exactly what he did in my own discussion with him on deposition of the grand canyon and dimetrodon footprints. During that time he changed his model several times, drawing on sources who couldn't even get basic facts right:

http://talkrational.org/showthread.php?t=2909
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Old 04-09-2011, 07:31 AM   #1371236  /  #1848
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Dave, why don't you actually read people's posts? You keep raising issues that have already been addressed, and asking for explanations that have already been given.
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Old 04-09-2011, 07:37 AM   #1371237  /  #1849
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Quote:
Originally Posted by Dave Hawkins View Post

So are you taking the position that those three lowest data points just happened to line up exactly as we would expect them to (all in a nice row forming a low slope), knowing what we now know from Reich and Saadoune's work?
For myself, yes.

You claim that the reason the line changes in gradient is because there is a change in anisotropy at that temperature, citing Reich, from isotropy above 380C to anisotropy below.

Cherniak showed that diffusion had the same, significant, degree of anisotropy above and below that point, so it cannot account for Humphreys change of slope.

The fact that the low temperature data points "happen to line up" is not at all surprising, as I have explained.

Several times. When you reach the sensitivity floor or ceiling of measurement methods, what tends to happen is that linear relationships are flattened.

Exactly as we see here.

Deal with it.

Then with the purple Xs please.

Last edited by Pingu; 04-09-2011 at 07:52 AM. Reason: typo
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Old 04-09-2011, 10:49 AM   #1371265  /  #1850
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Quote:
Originally Posted by VoxRat View Post
Quote:
Originally Posted by Dave Hawkins View Post
...
So are you taking the position that those three lowest data points just happened to line up exactly as we would expect them to (all in a nice row forming a low slope), knowing what we now know from Reich and Saadoune's work?
So are you taking the position that if three points "just happen" to line up somehow, the fact that they're way below the limit of detection is not important - or even worth mentioning?
If the three points in question are below the LOD and (obviously) near the inherent noise/backgound level of the experimental set-up, then they are almost certain to be on a flattish line because that zone will be quite narrow.

Any dose response graph of results from an analytical method, where the analyte concentrations tested include those above, at, and below the LOD or LOQ of the method will show that flattening at the low end. I see 'em every day
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