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orion-list Radiocarbon discussion

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To members of the Orion list, by way of introduction, Timothy
Jull of the Tucson AMS facility is widely regarded as one of
the top, and perhaps the top, scientist in radiocarbon in the
world.  As one radiocarbon scientist here in Denmark told
me, "Tim Jull is the best there is in AMS, period."  

I would like to clarify that I did not make all of the statements
that were quoted to which T. Jull responded.  Most of the 
statements were by me, but three were not.  (For those
interested, the ones with three carrot marks are from me, and 
the ones with two carrot marks are from another post by Tom 
Simms, for whose comments I am not responsible.)  Now I 
would like to follow up on a point Jull makes, in light of the 
issue of the measurement on 4QpPsA.  I wrote and Jull 

> > > > regarded by most as accurate.  The principle is a sound
> > > > one: in any battery of lab data, data points at one end or
> > > > the other of distributions _must_ be regarded skeptically.
> In a series of data on the same sample, this assertion is correct, but one
> cannot apply it to a series of different samples and just reject the ones
> which
> appear inconsistent with some other hypothesis.  
I am mystified by Jull's objection to my statement, since my
understanding is that it is routine in datings of, e.g. items from 
a particular archaeological assemblage, to regard skeptically
single dates that appear the earliest or latest in a battery.  (If
requested I can cite cases on this point.)  The logic is simply
that no individual date, even at two-sigma 95% confidence, is
infallible.  Therefore single dates at one end or another of a
distribution cannot be granted complete weight in upholding
major conclusions.  In the case of 4QpPsA, if this carbon 
date is correct there would be evidence (for the first time, in
my opinion) for a 1st century CE scribal copy of a Qumran
text.  But--it is at one end of a total distribution now of 19
Qumran text dates.  There are clear grounds to suspect an
occasional incidence of contamination affecting at least two 
of the 19 AMS datings which _neither_ Zurich's nor
Tucson's pretreatment procedures were successful in
removing.  The fact that the Tucson report found nothing
unusual about the 4QpPsA sample in terms of visible glue
contamination does not negate the unfortunate fact: which 
is that no test for contamination, no analysis of runoff, no
measurements of differently-cleaned samples, etc. was  
done.  If 2 of the 19 are conceded likely to have had their
datings affected by contamination, it is not unreasonable
to ask if there may have been 1 or 2 more.  And if we 
don't know the answer to this, then we don't know.  As 
a general statement, any other texts whose datings 
were perchance contaminated would likely show up 
at one or the other end of the total distribution of Qumran 
text dates--exactly the position on the spectrum which
4QpPsA occupies.  For these reasons, it is not simply 
arbitrary, nor is it derivative from my 1st BCE single-
generation hypothesis (even if some on this list may 
find this point difficult to grasp), to give the 4QpPsA 
dating a higher degree of scrutiny, and in the absence 
of corroboration, skepticism, than other datings which 
are well within the known spectrum of Qumran text 
AMS datings.

In the absence of evidence of non-contamination
or other corroboration, this single pPsA date is simply a 
black hole, an unknown, an uncertainty--what else can I 
say?  I don't think T. Jull would actually disagree with this 
last sentence.  I have recommended for the next battery 
that further samples from 4QpPsA, and 4QpIsaA and 
4QpHosA also (believed to be from the same scribe) be 
dated, with procedures designed to eliminate the 
contamination issue and answer this question.  If that 
original Tucson AMS dating for 4QpPsA comes up 
replicated, clean, etc. the question of the existence of 
1st century CE Qumran copies would be answered: there 
would be a secure basis to know it.  But there simply is 
not, at this time, a secure basis for knowledge of the 
existence of 1st century CE Qumran text scribal activity 
on the basis of the single existing 4QpPsA radiocarbon 
date, considered in isolation.  I would be surprised if this 
last statement, as I have carefully worded it, would find 
actual disagreement from Jull or other serious scientists.  

Relative to the issue of difficulty in interpreting the 
differences between Tucson and Zurich concerning 
the two labs' respective AMS measurements of 
identically-dated texts from the Bar Kochba era, 
Jull said:

> All of these samples were papyrus and not parchment.  I think this may be
> important to understand these differences.
Can you say what you mean by suggesting that this plays
a role in explaining the apparent striking Tucson/Zurich
offset in dating these papyrus fragments from identically-
dated texts?  In any case, I hope that T. Jull might stay 
with this discussion at least briefly as long as there are 
questions from Scrolls people on this list.

Greg Doudna

For private reply, e-mail to Greg Doudna <gd@teol.ku.dk>
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