. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. 818 KOCZY [CHAP. 30 (a) If Ai is much smaller than A2, Nq^ —^ N^ and the equation can be approxi- mated as follows: i\r2 = mi^{l-e-'2(), A2 (4) which gives the formula for age as 1 a;'" ' ^2A2\ (5) where Nq^ is the initial amount of the decaying nuclide and N^ the nuclide produced. This method is applicable when one of the long-lived nuclides, such as uranium or thorium, is incorporated without daughter products in a Ag/. Fig. 2. Age determination with the aid of the ratio of two
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. 818 KOCZY [CHAP. 30 (a) If Ai is much smaller than A2, Nq^ —^ N^ and the equation can be approxi- mated as follows: i\r2 = mi^{l-e-'2(), A2 (4) which gives the formula for age as 1 a;'" ' ^2A2\ (5) where Nq^ is the initial amount of the decaying nuclide and N^ the nuclide produced. This method is applicable when one of the long-lived nuclides, such as uranium or thorium, is incorporated without daughter products in a Ag/. Fig. 2. Age determination with the aid of the ratio of two radioactive elements from the same series where the decay constant of the daughter product is large compared with the decay constant of the parent element. The ordinate gives the ratio of activities of the two radio-elements. The abscissa gives the time scale in non-dimensional units as multiples of mean lifetime. The produced nuchdes with half life large enough to be used for the purposes of marine geology are, in that case, ionium (230Th), protactinium (23iPa) and radium (228R,a, 226^^). (b) In the case where Ai is much larger than A2 the equilibrium equation is approximately N'^ NoHl -^,f ), but as No'^^Nh^i', we obtain as a formula for the age iV2\ t i-i 1 + NK (6) (7) where the same notation is used as above. This equation is used when a radio-nuchde produces a stable isotope, such as potassium-40 giving argon-40, and rubidium-87 producing strontium-87. The. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hill, M. N. (Maurice Neville), 1919-. New York : Interscience Pub.
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