Carbon 14 has turned out to be of fundamental importance in many different sciences as is summarized in Figure 3 reproduced from the
Proceedings of the American Philosophical Society
as cited above.Part of this importance arises from the fact that it is continuously synthesized in the atmosphere by the bombardment of atmospheric nitrogen with secondary neutron radiation from cosmic rays. This produces a steady-state concentration of
14C in the atmosphere that has been relatively constant for thousands of years.
14
C-containing atmospheric carbon dioxide is incorporated in the tissues of plants and animals and thereby contributes some of the background radiation which is contained in the bodies of all living things including humans.Once trapped in living tissue, the
14C can no longer mix with the atmosphere, and it begins to disappear with its characteristic half-life of 5730 years. By making assumptions about the atmospheric concentration of 14C in earlier years - assumptions that can be checked over the past two millennia by reference to the 14C concentration in the tree rings of living trees - it is possible to calculate the age of tissue samples that are recovered by archaeologists.Alternatively, by reference to fluctuations in
14C as revealed by the tree ring record, it is possible to study prior solar activity. A controversy arose, for example, regarding a nineteenth century report by G. Sporer and E. W. Maunder that astronomical records from 1645 to 1715 showed a marked absence of sunspot activity, which was at variance with the records from other periods.Sunspots interfere with cosmic radiation, so it was predicted that cosmic radiation and, therefore, atmospheric
14C would increase if sun spots had actually decreased. Tree ring studies showed that an increase in 14C between 1650 and 1700 occurred, which was exactly as predicted from the Maunder minimum. Moreover, another increase occurred between 1450 and 1550, giving rise to the suggestion that the sun undergoes long periodic fluctuations as well as those of the well-known 11-year solar cycle.For more ancient times, preceding those for which atmospheric
14C concentrations can be directly checked by techniques such as tree ring analysis, assumptions about atmospheric 14C concentration and other factors can contain significant errors. Sample contamination also becomes a serious source of error in less well-defined artifacts.As a result of nuclear weapons tests, atmospheric
14C increased from the early 1950s to a maximum in about 1963 and has since decreased with an atmospheric half-time of about 10 years. This short atmospheric half-time has been cited by Frederick Seitz as evidence that the increase in atmospheric CO2 during the past century may not have been entirely caused by human activity, since it is equilibrating so rapidly with huge terrestrial reservoirs having CO2 contents that dwarf human production (see Access to Energy 22-1, September 1994, p 3).This increase of
14C has also been used by antinuclear activists in support of their claims that nuclear weapons testing has caused worldwide increases in cancer and that accidents in nuclear power plants could potentially make this problem worse.Actually, in view of the growing amount of experimental data about hormesis (see numerous past issues of
Access to Energy and included references), it appears most likely now that these small increases in background radiation have actually had a beneficial influence on human health. There is no direct evidence whatever in support of claimed harmful effects. These claims depend upon arbitrary and probably erroneous extrapolations from effects of very high radiation doses.
Although some scientists involved in early research on radioactivity were harmed by high doses of radiation before the dangers were clearly known, most were apparently not adversely affected. In Martin Kamen's case, he was forced to leave operation of the laboratory counting apparatus to his co-worker, because Kamen himself was often so radioactive that he disrupted the counters. Fifty years later, he shows no ill affects from the many cyclotron-produced nuclear isotopes that were induced in his clothing and body tissues.
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Vol. 23, No. 5
Newsletter: Access to Energy Newsletter Archive Volume: Issues Issue/No.: Vol. 23, No. 5 Date: January 01, 1996 01:45 PM Title: A Double Honor
Copyright © 2004 - Access to Energy Newsletter Archive
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