Вопрос по РУ.


Автор сообщения: АнТюр
Дата и время сообщения: 28 February 2005 at 12:11:53:

Уважаемые господа!

Я не совсем понимаю смысл фразы 'The observed concentrations indicate
variable amounts of in-situ 14C from cosmic-ray spallation of oxygen.' из нижеприведенного абстракта. Поясните, пожалуйста, о каком 'in-situ 14C' идет речь и какое он имеет отношение к 'oxygen'.

Благодарю.

С уважением,

Анатолий


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ORIGINAL REFERENCE:
Jull, A.J.T., D. Lal, D.J. Donahue, P. Mayewski, C. Lorius, D. Raynaud and
J.R. Petit, 1994, Measurements of cosmic-ray-produced 14C in firn and ice
from antarctica, Nuclear Instruments and Methods in Physics Research Section B:
Beam Interactions with Materials and Atoms, Volume 92, Issues 1-4,
3 June 1994, Pages 326-330. doi:10.1016/0168-583X(94)96028-3


ABSTRACT:
We have studied the levels of 14C in firn and ice from two regions accumulating
ice in Antarctica, Dome C, and Newall Glacier. The observed concentrations indicate
variable amounts of in-situ 14C from cosmic-ray spallation of oxygen.
14C appears to be produced as both CO and CO2 in variable amounts, but our results
suggest rapid conversion of 14CO to 14CO2. Much of the in-situ 14C is retained
which results in a significant modification of the 14C/12C in ice derived from
trapping of air at and below the firn-ice transition zone. This means that
direct dating of accumulating ice cannot be used without correction for the
in-situ 14C. In Newall ice, we see some evidence for an enhancement in in-situ 14C
at or near the time of the Maunder Minimum. Results for Dome C firn and ice indicate
higher levels of in-situ 14C in older ice. This is due either to a reduced
accumulation rate in the past, or possible variations in cosmogenic 14C production.
The levels of in-situ 14C in firn and ice, and its impact on 14C dates on
trapped CO2 in ice are discussed.



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