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Ch.20 - Nuclear Chemistry
Chapter 20, Problem 65

What is the 14C activity in decay events per minute of 1.0 g of a 3000-year-old wooden object? All living organisms contain an equilibrium concentration of radioactive 14C that gives rise to an average of 15.3 nuclear decay events per minute per gram of carbon. (14C, t1/2 = 5715 years)

Verified step by step guidance
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Step 1: Understand the problem. We need to find the current activity of 14C in a 1.0 g sample of a 3000-year-old wooden object. We know the initial activity in living organisms is 15.3 decay events per minute per gram.
Step 2: Use the half-life formula to determine the decay constant (k). The half-life (t_{1/2}) of 14C is 5715 years. The decay constant k can be calculated using the formula: k = \frac{0.693}{t_{1/2}}.
Step 3: Calculate the number of half-lives that have passed in 3000 years. This can be done by dividing the age of the object by the half-life of 14C: \text{Number of half-lives} = \frac{3000}{5715}.
Step 4: Determine the remaining fraction of 14C using the formula: \text{Remaining fraction} = (0.5)^{\text{Number of half-lives}}.
Step 5: Calculate the current activity of 14C in the sample. Multiply the initial activity (15.3 decay events per minute per gram) by the remaining fraction to find the current activity in decay events per minute for the 1.0 g sample.
Related Practice
Textbook Question
Potassium ion, K+, is present in most foods and is an essen-tial nutrient in the human body. Potassium-40, however, which has a natural abundance of 0.0117%, is radioactive with t1/2 = 1.25 x 10^9 years. What is the decay constant of 40K? How many 40K+ ions are present in 1.00 g of KCl? How many disintegration/s does 1.00 g of KCl undergo?
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Textbook Question
The electronic systems on the New Horizons spacecraft, which launched on January 19, 2006, and reached its closest approach to Pluto on July 14, 2015, were powered by elec-tricity generated by heat. The heat came from the radioac-tive decay of 238Pu in the 11 kg of 238PuO2 fuel onboard. The generator provided 240 W when the spacecraft was launched. If the power output is directly proportional to the amount of 238Pu in the generator, what was the power output when the spacecraft reached Pluto? The half-life of 238Pu is 87.7 y.
303
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Open Question
The radioisotope 226Ac can decay by any of three different nuclear processes: alpha emission, beta emission, or electron capture. (a) Write a balanced nuclear equation for the decay of 226Ac by each decay mode.
Textbook Question
Uranium-238 has a half-life of 4.47 * 109 years and decays through a series of events to yield lead-206. Estimate the age of a rock that contains 105 mmol of 238U and 33 mmol of 206Pb. Assume all the 206Pb is from the decay of 238U.
1021
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Textbook Question
The age of an igneous rock that has solidified from magma can be found by analyzing the amount of 40K and 40Ar. Potassium-40 emits a positron to produce argon-40 and the half-life of 40K is 1.25 * 109 years. What is the age of a rock whose 40Ar/40K ratio is 1.42?
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Textbook Question
Why does a given nucleus have less mass than the sum of its constituent protons and neutrons?
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