Автор: Salvador Dali (---.sys.hokudai.ac.jp)
Дата: 19-07-03 18:19
На "Парахронологии" всплыла старая тема о проблематичности использования радиоуглеродного анализа для датирования исторических объектов до внедрения атомной масс-спектрометрии. Дискуссия по данному вопросу велась еще три года назад на почившем в бозе "Про & Контра", но так и не была доведена до победного конца. Теперь (в контексте приведенных ale цитат) есть повод снова порассуждать о наболевшем.
Для начала освежу некоторые моменты дискуссии трехлетней давности (примерно апрель-июнь 2000), которые сохранились на сайте Сергея Гроховского.
Примечание: у меня тогда были определенные проблемы с кодировками, поэтому часть моих сообщений, увы, нечитаема.
Salvador Dali: C14 before AMS.
[...] Итак, до второй половины 80-х годов (i.e. до AMS) для датирования нужны были десятки грамм - да, это так; если быть точнее - нижним (!) пределом было 10 десятков грамм (100 г) углерода. Насколько нам всем известно, дерево, а равно кости, торф etc. не состоят из углерода целиком, а содержат его в некоторой пропорции. Теперь посчитайте, сколько древесины или костной массы необходимо сжечь, чтобы получить 100 г углерода (и это в лучшем случае). Таким образом, практически все датировки по С14 до AMS не просто сомнительны, а скорее всего подложны.
Wally: re: C14 before AMS.
Dear Salvadore,
Indeed, before AMS appearance samples were much bigger. I have this experience myself. I did work in radiocarbon well before the arrival of AMS, so I know rather intimately the previous techniques too, namely liquid scintillators and gas proportional counters.
Liquid scintialltors required large samples, with 10s of grams (10 actually for our lab) of carbon being the lower limit. Some labs did better, having this limit at around 5 grams.
On the other hand, liquid scintillators produced results with the best experimental precision so far. It wasn't easy, but still, there existed a whole series of measurements with accuracy of 0.1-0.2%. AMS has only recently reached the state capable of rivalring those achievements.
Gas proportional counters required much less sample, with lower limit for best being at hundreds of milligrams (about 0.5 g).
Unfortunately, the relatively poor precision of results and difficulties in handling marred this experimental method.
The invention of AMS first and foremost allowed application of dating to the samples never before considered.
We now rather routinely work with samples of 100 microgram of carbon, with my best real samples were at 10-12 microgram.
That actually brought to light a different problem that we were forced to address - a question of homogenuity of the sample, of how one small part of it is representative for the whole.
So far, our studies showed that for the normal samples the limit sits at around 5 microgram of carbon or slightly less. Then the limiting factor for precision would be the possible uneven statistical distribution of 14C atoms in material, especially for the old samples.
We now are capable to chemically produce and measure a target of 1 microgram of carbon (it is a world record, our laboratory is the best in this case), but we are not pursuing this, just because of the abovementioned controvercy.
Now, to dating before AMS. Indeed, the demand for bigger samples and the destructive technique of radiocarbon processing limited the dating to a certain group of objects.
Surely, no one ever considered dating the Shroud of Turin or Dead Sea Scrolls before the coming of AMS. But what was dated?
Charcoal, big wooden artifacts (like remnants of dwellings), mummies, mammoths, bones, burried pit, other burrials where getting a 100 g of material was possible, some furniture, clothing.
Special studies were conducted on soils, including burried ones. The whole natural cycle of carbon was studied accurately, including even atmospheric samples.
By the way, the calibration curve was constructed using liquid scintillators, and with a high precision indeed.
Also, most chemical techniques and processes used in the method (except for grafitisation) were invented and perfected well before the AMS. And indeed, the very same researches who worked with older technique now very enthusiastically develope the new one.
With the arrival of AMS quite a few cross measurements were done and revealed NO discrepancy between previous and new measurements.
The improvements on calibration curve were done with new small samples, but they were tiny, the main gain was its extension further in the past.
Also, be assured that counting technique (liquid scintillators) is still widely used in radiocarbon dating having the advantage of lesser costs associated and faster turnover.
Of course researches now have an option to choose, and the ability to work with very small samples, thus widening the applications of dating.
I regret to say this, but I thought better of you. Never before you went into groundless accusations, always accurately considered arguments. Now, labeling the radiocarbon before AMS a hoax, a falsification doesn't make you any honour, and simply reveals your poor knowledge in the subject.
If you have facts in hands to prove your statement that all(!, not one or two) datings done before AMS were, let's say it, incorrect, you are welcome, we could discuss that. But so far I see only abusive words and label sticking.
An the second point. We date things, not interpret the results. And yes, not one or two times we had samples being much younger then expected. And we also had samples being significantly older then anticipated by submitters. But the absolute majority of samples were in agreement with traditional timescale. And of course, building a theory on one or two outliers, and turning the blind eye to and ditching the main body of data is simply un-scientific and ridiculous.
Salvador Dali: ?, ... ? ?
[нечитаемые сообщения]
Wally: re: ?, ...
With a certain effort have finally managed to read your epistle, Salvadore. Would you please, for the future, break it into larger parts?
Anyway.
Apparently you have offered NO facts that radiocarbon dates done before the AMS were incorrect.
And do not hiperventilate, it was your words - "all before AMS is a fraud".
Now, let us consider Santorini.
First of all, how big were the samples that this proffessor had gathered? All you know that they were small. But how small? 10-20 g is small enough, believe me, especially for that period of research.
Then, if you have noticed from my previous post, the gas proportional countes operate at much lesser mass demand. And the original radiocarbon method and first pioneering measurements were done on prop counters. Albeit, at a worse accuracy.
Gas proportional counters are still in use (as well as liquid scintillators method). Go to a library and have a look at Radiocarbon journal, browse through it.
About this guy from Massachusets. They didn't have a strong radiocarbon laboratory there. The best in the US were in Tucson AZ and Seattle WA.
10 and even 5 grams is the absolute low limit for the best counters like Quantulus and relatively modern samples. To play safe people always preferred to have extra material, also for possible duplicate sample.
Now, back to Santorini. By far it was not the only radiocarbon date obtained for this area. Rarely (if ever) people build chronological relations on one date.
I have addressed this topic, Santorini eruption, on this board already some time ago http://community.by.ru/cgi-bin/mb.cgi?newchrono-public+945260279
Unfortunately, the link further to my more detailed post is not working, we should ask WebOfficer for help.
Briefly, I have cited the Nature paper dating Santorini from the volcanic layer in polar ice, and also comparing the obtained value with combined radiocarbon dates.
Now, some concluding words. The availability of a mass-spec in the lab does mean nothing .if you are not an expert in a particular area. Unfortunately, the amount of excellent equipment in Japanese laboratories is widely known, together with its poor scientific applications. Not enough people and bright brains in research?
As for mass-spec, we have two in the next room, as well as 9 dedicated GC's, a mass-spec in a lab across the harbour, an AMS installation here and another in close collaboration in different town, a few decay counters (Quantulus) and gas prop counters, gamma-spectrometers and alpha-specs as well. I could forget something. Like dedicated chemistry laboratories and refrigirated rooms to work with ice samples.
I truly believe you are a professional in some field. I do like to read your post about climate, when you'd fix the encoding, not only for debating purposes, after all it is my field of research. But being a professional, you should know that when venturing in a new field, especially an experimental one, it takes a rather long time to absorb all the information to start understanding all the why's and if's of the trade. I'm 20 years in this stew, and indeed, if I'm saying something it is not just to show myself, or prove something. I truly like to give people the best possible information they can get on the subject and the most objective view on the problems.
It is good you are there in Japan. I may ask you to get some rare proceedings on ice cores and vocanic ash and tephra identification if the ordinary ways would prove unsuccessful.
Cheers. See you around. And please do not use such words as fraud or hoax unless you have an absolute proof of that. That truly is insulting for some involved in relevant studies.
Salvador Dali: 100 or 10? That's the question.
Dear Wally!
Вы опять взялись обвинять меня в том, что я не выложил факты о подлоге всех радиоуглеродных до-AMS’овских дат, хотя я: 1) никогда не говорил, что мое убеждение в подлоге основано на анализе обширного фактического материала; 2) никогда не обещал Вам предоставления подобного количества фактов. Вся моя аргументация (она, конечно, очень проста, и, тем не менее, весьма логична) базируется на одном единственном, но при этом крайне важном факте (упоминаемом в специальной литературе), от которого довольно трудно отмахнуться. А именно: до внедрения AMS минимальным пределом количества углерода, необходимого для датирования образца, было 100 г. Если Вы полагаете, что все датированные образцы удовлетворяли этому требованию, то есть, если Вы готовы допустить, что историки кромсали исторические реликвии на такие внушительные части для последующего уничтожения в тиглях физиков, то я преклоняю чело. Ваши требования можно объяснить только тем, что Вы действительно считаете так. Ведь если бы Вы так не считали, достаточным было просто доказать неверность моего тезиса о 100 г. Однако, Вы этого не сделали в полной мере. И даже если в дальнейшем Вы при помощи каких-либо средств английской идиоматики сможете убедить меня в том, что десяти граммов углерода вполне хватало для анализа, Вам придется еще и объяснить, почему в литературе (даже в 1985 году) речь шла о 100 г., то есть о количестве в 10 раз большем. “That guy from Massachusets”, как Вы полагаете, написал цифру 100 по причине того, что у них в институте нет хорошей лаборатории? Неужели в Массачусетских научных кругах не принято читать работы коллег из соседних штатов - хотя бы при работе над обобщающим трудом? Неужели Вы полагаете, он ничего не знает о помянутых Вами лабораториях? На основании чего Вы делаете такие выводы? Называя 5-10 г, как абсолютный минимум, считаете ли Вы, что это действительно абсолютный минимум, а не погоня за мировым рекордом? Дайте ссылку, где написано, что минимум - 5-10 г, а не 100.
Дискутировалось .ли это в научных работах, или только Ваше мнение как эксперта? Стоит ли нам всецело доверять Вам, и всецело не доверять “парню из Массачусетса”? Если мы доверяем Вам, то автоматически моя гипотеза о подлоге неверна; если мы доверяем другим данным - неправы Вы. Ни о какой фальсификации с моей стороны речи не идет. Зачем же Вы меня в ней обвинили? Не суть ли это одного из демагогических приемов (см. небезызвестную статью “Демагогия: опыт классификации”)?
[...]
Wally: re: 100 or 10? That's the question. Is it? I see it differently.
[...]
This is a serious accusation, very insulting, by the way. I have asked you for proof of a fraud, but you are turning the discussion into arguing what was the lower limit before AMS, 10 or 100 g of C.
What relevance it has to dates being fraudulent?
After all, understanding of what the small sample is was changing all the time. When we just started the AMS in our lab 9 years ago a 10 mg sample was small for us, now we call 10 microgram small and 100 microgram routine, see the difference?
The very same is for decay counting. 100 g sample was small for most labs, but a few most advanced worked sometimes with 10 g, having a 100 g as a routine.
Indeed, before the AMS a smaller number of what we conventionally call artifacts were dated then now, focusing on larger samples allowing a sacrifice of a decent portion of them.
So what? Why still were they a fraud?
Mind you, a calibration curve (the first edition of it) was constructed with decay counters. And it was measured with very high precision, much better then most modern AMS labs produce. Was it also a fraud?
To prove your statement you have to present an irrefutable information that all dates before AMS were erroneous, very erroneous, do not agree with modern ones at all.
And we are not talking of one or two mistakes, they always happen, and with modern technique also, but of the whole corpus of data before AMS.
I completely agree to you that AMS have widened the dating applications many times. But in no way it did reject the studies done before.
Even now many (most actually) labs still use decay counting, applying to AMS only if sample mass do not allow the traditional way. AMS is much more expensive with longer turnover. And never, so far, a disagreement between AMS or decay date was reported.
By the way, there are other reasons why the old reported dates differ from what you see now, but they have nothing to do with the sample size. And the date of 1400 BC that you have found in that book actually agrees well with this 1650 BC that I have given. I can explain the reasons if you are interested.
Now, we can continue the discussion on other topics as soon as we come to an agreement on this major one. You say that all the dates before AMS were fraudulent; I say, this is a groundless accusation and ask for proof (not the speculations WHY that MIGHT happen).
So far you have presented no support for your position. I'm asking, would you consider this statement of yours a mistake? And what arguments do you need to come to this conclusion?
And of course, I'm _not_ accusing you in any falsification, it was _you_, as I see it, who accused us in a hoax.
When finishing on this we can move to the other areas. I'd like to discuss and come to a certain consensus on paleoclimates. And if you like, the absolute minimum of material for decay counting also.
Cordially.
Salvador Dali: Yes, it is.
[нечитаемое сообщение]
Wally: re: Yes, it is. No, it is not :)
Dear Salvadore,
All right, let us discuss the dating practices before the AMS. Indeed, the samples were larger, but by far not that large as you might have thought.
Here I took an effort to reproduce a table from Polach H, Golson J and Head J, 1983. Radiocarbon dating: a guide for archaeologists on collection and submission of samples and age reporting practices. In: Australian Archaeology: A guide to Field and Laboratory techniques, ed G Connar, 3rd edition, Australian Institute of Aboriginal Studies, Canberra, 145-152.
Table. Amount of Material to be Collected for Routine dating by Radiometry.
--------------------------------------------------------------------------------
Description of Dry weight g Comments
Suitable materials Min Desirable
---------------------------------------------------------------------------------
Wood - clean or 5 25-30
rotten
Charcoal 2 10-20 Rich, black flakes
5-10 50-200 Sandy, brown
Shell 20 100 Hard shiny surface
30 150-200 Powdery or pitted
Grass, leaves 5 35-50
Paper, cloth 3 25-30
Peat, gyttja 30 80-120 Dark brown
50 150-200 Light grew-brown
Materials for special projects in collaboration with the RC Lab
Bone-apatite 500 1000 Up to 20,000 yr BP
-carbonate 200 600 Seldom valid date
-collagen 300 800-1500 Up to 10,000 yr BP
-charred 500 1500-3000 Up to 36,000 yr BP
Soil-organic matter 2000-5000 Humic acid, humin
-carbonate 100-500 Pedogenic, nodules
---------------------------------------------------
COMMENT (from the SK Gupta and HA Polach, Radiocarbon dating practices at ANU, 1985): Under the heading WEIGHT the first column gives the minimum which can be handled ROUTINELY. New developments in LS counting technology such as QUANTULUS enable 80 mg, the gas counter TUWANU 10 mg and AMS 1 mg of elemental carbon to be counted. Extension of dating to minute amounts of carbon is a new venture in radiocarbon dating applications and world wide efforts are being bade to perfect it. AMS in this aspect has been most successful. (Wolfli W., 1984, Single atom counting with accelerators, Europhysics News, 15, 1-4.)
As you see, the limit varied for different materials, ... as one could expect, and often is significantly less than your 100 grams, even for material, not for elemental carbon. And consider the last note, that this was the limit of ROUTINE samples, with pilot radiometric ones were as small as 80 mg for LS and 10 mg for gas prop counters.
Now, is this enough for you? I could have gone into arguing that even with 100 g limit there is no reason to suspect people in fraud, just the applications would have been fewer. But I thought that showing you that your information was not correct was the more convincing way.
About the authorities I’m referring to:
Henry Polach was one of the people who personally developed and perfected the radiocarbon method, the world renowned authority in all aspects of it, the initiator of the cross-labs checks, developer of the standard, and one of QUANTULUS designers, and in the end, my personal friend. He died of cancer 4 years ago.
Willy Wolfli is one of the forefathers of AMS, a head of Swiss AMS group, one of the first 3 AMS installations, the one participating in the Shroud dating. I know him personally too.
J Head then was the head of ANU radiocarbon laboratory, now he is retired, but is still working in Wollongong University, lecturing and consulting. Also a good friend of mine and co-author of a few mutual papers.
Tell me if you are satisfied, and can we now move forward to other questions closing this hoax accusations?
Best regards.
Salvador Dali: This time I surrender... but...
С интересом ознакомился с любезно присланной Вами таблицей (спасибо, все понятно и без word’а). Не стану отрицать, что приведенные цифры произвели на меня впечатление. И мне не хотелось бы подозревать кого-либо в подлоге, подтасовке и поиске выгоды, хотя коммерция – штука страшная, посильнее чем Фауст какого-то там Гете; в самом деле, чем меньше вес образца, тем больше обращений в лабораторию с просьбой датировать то или это; спрос рождает предложение, реклама двигатель торговли и пр.; а процедура датировки для всех страждущих небесплатная, так что мотив для преступления определенно есть. Но мотив не доказывает самого факта подлога, поэтому, как говорится, за отсутствием состава преступления я вынужден снять свое обвинение и публично извиниться перед Вами и остальными специалистами по РУ-анализу. Однако, Вы прекрасно понимаете, что если в источниках вдруг случайно обнаружится другая точка зрения по поводу минимальной массы, нам с Вами вновь придется вернуться к этому вопросу, а подозрение в фальсификации большинства датировок, логично следующее из положения о 100 г, опять встанет на повестку дня. Надеюсь, Вы не решили, что я пытаюсь таким образом выразить демонстративное недоверие к Вашему сообщению. Я конечно же доверяю Вам; просто у меня осталось некоторое смутное сомнение относительно репрезентативности информации. Ну, хотя бы потому, что присланные Вами данные – это середина 80-х гг., а огромная масса датировок была сделана (и вряд ли пересмотрена, не так ли?) в 50-е/60-е гг. Хотя, мои сомнения можно объяснить и с чисто психологической точки зрения, как реакцию на фрустрацию. Ну, да ладно. Полагаю, в этом вопросе пока можно ставить если не точку, то по крайней мере точку с запятой;
Перейдем к следующим вопросам. А именно к анализу применимости РУ метода на примере Санторина (см. одно из предыдущих сообщений). С 1400 и 1650 все более или менее понятно. Но – вопрос: почему эта дата говорит о времени гибели минойской цивилизации? На мой взгляд, здесь кроется серьезная методологическая проблема. Дата 1650 до н/э – это время гибели растения, хотя может статься, что куски дерева, обнаруженные в шахте, - это внутренние части очень старого дерева, то есть они могут быть на тысячу лет древнее, чем время гибели дерева. Затем, обнаруженный артефакт, изготовленный из дерева, мог использоваться на протяжении столетий и даже тысячелетий, и к извержению не имеет никакого отношения. Единственное, о чем свидетельствует такая дата, так это о факте, что извержение произошло позже гибели дерева. А на сколько позже – сказать однозначно нельзя. Из написанного выше видно, что в данном случае вполне вероятна ошибка в 1000 – 2000 лет, плюс погрешность самого метода, плюс вулканический район (вспомните Вашу дискуссию с А.Захаровым по этому поводу) – все это тоже вносит свой вклад. В результате, в вопросе датировки минойской культуры мы не можем полагаться на дату 1650 ВС – АБСОЛЮТНО. Почему ее использовали? Потому что она оказалась близка к предварительной археологической датировке по керамике (если мне не изменяет память), сопоставленной с египетской. А хронология Египта – по сей день предмет ожесточенных споров. Но уже взяв РУ-дату за основу, можно теперь говорить, что она подтверждает и хронологию Египта. Недурно, да?
Что Вы думаете по этому поводу?
С искренним уважением,
Salvador
Wally: But?
Dear Salvadore,
To wrap up the issue of weight limits, I want to comment here that your number of 100 g is not that incorrect at all. When a person was writing a review he might have used a certain averaged number. After all for different classes of samples numbers differ, and for bones for instance are in hundreds of grams, He was not describing specifically the procedure, I believe, rather for illustartive purposes only, that's why that number might appear.
Also, an addition here, the samples with lesses masses could still be treated and dated, that is for your suspision in commercialism. The only difference is that lesser masses would often give slightly increased errors, that's all. When people are quoting masses they can routinely work with they usually mean the optimal errors, the best they could achieve. If the submitter agrees to slightly worse results, then lesser samples could be treated.
This is as all true for radiometric measurements. For AMS the limit is more rigid, at a certain mass the measurement is simply not possible at all, no number would be produced.
Sure, those numbers were really the best. And in the 60's they were bigger. But not much, 2-3 times only. Also, note the sizes for gas prop counters. In the 60's gas counters were the main instrument used.
I will return to the issue of Santorini tomorrow, if you wouldn't mind. It is getting rather late and I have go home and cook dinner, I'm starving, to be frank.
In the mean time I'd like to hear your understanding on why 1400 BP that you have quoted and 1650 BP of mine are in agreement. I fear you might again have a certain misunderstanding here.
Regards.
Salvador Dali: Velleicht das nachste mal
Dear Wally!
?? ?? ? ??, ? ? ?? ?? ??. ?? ?? ?, ?? ? ? . It seems there’s no misunderstanding here:
Klein, J., J.C.Lerman, P.E.Damon, and E.K.Ralph 1982. Calibration of radiocarbon dates. Radiocarbon #24, 103-50.
? ? ?? ? ? .
Wally: re: OTBET
I am sorry, Salvadore (and Gorm), this is not yet on Santorini.
But I want to finish this topic raised once and for all.
Here is another table from a very different source.
R.Gillespie. Radiocarbon User's Handbook. Oxford University, Commettee for Archaeology, Monograph Number Three. Oxford books, 1984.
Richard Gillespie, Senior Chemist, Research Laboratory for Archaeology and the History of Art. Oxford University.
Quote:
2.3 How much sample to collect.
The list in Table 1 gives an idea of how large a sample of different materials most laboratories like to receive. Obviously the weights differ for newer small sample systems, and conventional laboratories will sometimes process smaller samples then normal. The listed weights refer to samples relatively free from soil, sand, artifacts, modern roots and other foreign matter. Some of the carbon in samples will be lost during chemical pretreatment and processing (see Chapter 3) in the laboratory. This must be borne in mind when submitting samples for dating. Most laboratories encourage the collection of larger samples, and where possible the submission of different materials related to the same event. In this way, the user can retain part of critical samples for later duplication of results to check anomalous dates, to replace samples lost in the post or laboratory, and for other analyses (such as stable isotopes, microscopy, etc.). Some laboratories will be interested in dating different materials from the same horizon, or from related features, for research purposes. ...
end of quote.
Quote of table begins:
Table 1. Optimum sample weight to collect.
...........Approximate weights
Material...Coventional(g).Minicounter(g).AMS (mg)
Charcoal....5-10...........0.1-0.5.......10-100
Wood, dry...10-20..........0.5-1.........50-100
Wood, wet...40-80..........1-2..........100-200
Bone.......100-500........10-50........500-5000
Shell.......50-100.........0.5-2..........50-100
Carbonates.100-200.........2-10..........100-200
Peat, .dry...50-100.........1-3...........100-200
Peat, wet..100-200.........3-5...........200-500
Sediment,dry.100-200.......3-5..........500-5000
Sediment,wet.200-500.......10-50......1000-10,000
Note that these are only approximate weights for samples free of soil, sand, artifacts, etc.; in some cases smaller sizes will be acceptable for dating but may cost more and have lower precision in the age. If the sample is likely to be contaminated and/or more then 20,000 years old, double the amount given above. When in doubt, consult the laboratory.
End of Table quote.
As one can see, the samples we are interested, i.e. historical artifacts and remnants of vegetation are relatively small. It is the geophysical samples of soils and related that are relatively large for conventional counters.
Salvadore could obviously have a liberty of doubt and is free to search for other information, but really, it would hardly be different from that being presented already.
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Тема будет продолжена.
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