Radioactive carbon-14 (6 protons, 8 neutrons in the nucleus) is used to estimate
ID: 473479 • Letter: R
Question
Radioactive carbon-14 (6 protons, 8 neutrons in the nucleus) is used to estimate the age of materials composed of organic carbon. It is formed by a reaction between CO2 atoms in the upper atmosphere and high energy neutrons (part of cosmic radiation) that bombards the earth. Living organic material absorbs and uses carbon dioxide from the atmosphere which contains about 1 % 14CO2 . When the organism dies, the ratio of C-14 to C-12 decrease with time as the radiocarbon decays with beta emission. The skin, bones and clothing of an adult female mummy discovered in Chimney Cave, Lake Winnemucca, Nevada, were dated by radiocarbon analysis. How old is this mummy if the sample retains 73.9 % of the activity of living tissue? The half-life of C-14 is 5730 years.
Explanation / Answer
Given half life = 5730 years
k = 0.693 / 5730 years = 0.0001204 years-1
Given initial = 100
Final C-14 = 73.9
For first order kinetics,
ln(100/73.9 ) = 0.0001204 years-1 x t
t = 2512.1 years
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