Автор сообщения: gorm
Дата и время сообщения: 29 April 2004 at 14:32:13:
Выкладываю статью, в которой экспериментально был опровергнуты гипотезы о возможной "карбоксилации" плащаницы во время пожара.
Требуемое пояснение к тексту: pMC означает процент от современного содержания радиоуглерода. Жарили, жарили древнее дерево в атмосфере 100% современного радиоуглерода и с серебром и без, а этот современный углерод не лезет внутрь -- обнаруживается лишь на пределе чувствительности, как доли процента. Для того чтобы эффект играл какую-либо роль, величины должны быть в сотни раз больше.
AN EXPERIMENT TO REFUTE THE LIKELIHOOD OF CELLULOSE CARBOXYLATION
R. E. M. HEDGES, CHRISTOPHER BRONK RAMSEY
Radiocarbon Accelerator Unit, Research Laboratory for Archaeology, 6 Keble Road Oxford, 0X1 3QJ, United Kingdom
Max-Planck-Instirut für Biogeochemie, Sophienstrasse 10, D-07743 Jena, Germany
Radiocarbon, Vol. 40, No. 1, 1998, p.59-60
ABSTRACT. To test the hypothesis that cellulose in linen can be carboxylated at high temperatures in the presence of CO2 water and silver, we heated two aliquots of cellulose extracted from old wood in glass ampoules, adding Ag powder to one to test its potential action as a catalyst for the carboxylation reaction. AMS measurement of the heated aliquots showed no statistically significant difference in 14C content from the "uncarboxylated" cellulose. We conclude that carboxylation is not a systematic source of error in the dating of cellulose-containing materials such as the Shroud of 'urin.
Controversy has been recently created by the claim of Kousnetsov, Ivanov and Yeletsky (1996) that cellulose in the form of a linen textile, can be carboxylated in the presence of carbon dioxide, water, and silver at elevated temperatures. This has obvious reference to potential systematic "errors in the radiocarbon dating of the Shroud of Turin (Damon et al. 1989) since the Shroud was known to experience conditions that might have resembled those investigated by Kousnetsov, Ivanov and Yeletsky (1996). While it is not credible that carboxylation can occur to the extent that "would add or replace enough original carbon atoms of the Shroud to alter the question of its authenticity (ca. 50% of atoms would need to be replaced at the time of the Chambery fire to change the date from 600B? to 2000 BP), the case that it might cause a significant systematic error, not necessary with the Shroud date, but also with other dates on cellulosic materials, is worth consideration. The chemical pro cesses proposed are not regarded by all chemists as feasible. Therefore, we earned Rut the experiment described below to test as sensitively as possible whether carboxylation migbt be induced under the most favorable conditions we could contrive.
The experimental conditions are not a replication of those by Kousnetsov, Ivanov and Yeletsky (1996) because it is impossible to know how exact the replication must be. We have tried to carry out an experiment that would give a definite result on its own but which is relevant to that of the Kousnetsov Ivanov and Yeletskv (1996). The experiment not only invalidates their claims with respect to the Shroud dating, but also makes a very strong case that the carboxylation mechanism, if it occurs at all, is very unlikely to make a significant change to the carbon composition of cellulose.
THE CARBOXYLATION EXPERIMENT
We took 5 mg of cellulose extracted from wood known to be growing >45ka BP. Two aliquots were taken, one having added a few mg of Ag powder, since this is claimed to have catalytic properties for the carboxylation reaction. Both aliquotes were sealed in glass ampoules in an atmosphere of modern (D14 = 130 pc) CO2 (2 bar pressure) and H2O (1 bar), and kept at a temperature of 200oC for 24 hr. Slight charring took place. The 14C content of the product was then measured by accelerator mass spectrometry (AMS), with the following results:
Sample 1: 14C content = 0.33+0.2 pMC
Sample 2 (including Ag): 14C content = 0.41+0.1 pMC
Previous dating of the extracted cellulose (i.e., before "carboxylation") gives values of 14C content = 0.2+0.1 pMC. The dates of the treated samples are not younger in a statistically significant sence.
Under these conditions, without any additional pretreatment of the "carboxylated" cellulose, the fraction of added or exchanged carbon content from the CO2 was not detectable, the limit being ca. 0.2 pMC. These represent extreme conditions (certainly in terms of CO2 concentrations), so that without silver -- would presumably be less liable to exchange carbon between cellulose and the atmosphere. It seems that the proposed mechanism can be entirely discounted as a detectable source of contamination and therefore a systematic error source in 14C dating, not only for the Shroud, but more importantly, for many other potential dating situations where cellulose and a degree of conflagration are involved. Similar results, albeit of less sensitivity, from experiments that are basically similar in their chemistry, have been reported by Jullm Donahue and Damon (1996).
Damon, P.E., Donahue, D.J., Gore, B.H., Hatheway, A.L., Jull, A.J.T., Linick, T.W., Sercel, P.J., Toolin, L.J., Bronk, C.R., Hall, E.T., Hedges, R.E.M., Housley, R., Law, I.A., Perry, C., Bonani, G., Trombore, S., Woelfli, W., Ambers, J.C., Bowman, S.G.E., Leese, M.N. and Tilte, M.S. 1989 Radiocarbon dating of the Shroud of Turin, Nature 337: 611-615.
Jull, A.J.T., Donahue, D.J. and Damon, P.E. 1996 Factors affecting the apparent radiocarbon age of textiles. Journal of Archaeological Science 23: 157-160.
Kouznetsov, D.A., Ivanov, A.A. and Yeletsky, P.R. 1996 Effects of fire and biofractionation of carbon isotopes on results of radiocarbon dating of old textiles: The Shroud of Turin. Journal of Archaeological Science 23: 109-122.