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Ch.21 - Nuclear Chemistry
Chapter 21, Problem 41

The cloth shroud from around a mummy is found to have a 14C activity of 9.7 disintegrations per minute per gram of carbon as compared with living organisms that undergo 16.3 disintegrations per minute per gram of carbon. From the half-life for 14C decay, 5730 yr, calculate the age of the shroud.

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1
Identify the given values: the activity of the shroud (9.7 disintegrations per minute per gram), the activity of living organisms (16.3 disintegrations per minute per gram), and the half-life of 14C (5730 years).
Use the formula for radioactive decay: \( N = N_0 e^{-\lambda t} \), where \( N \) is the current activity, \( N_0 \) is the initial activity, \( \lambda \) is the decay constant, and \( t \) is the time elapsed.
Calculate the decay constant \( \lambda \) using the half-life formula: \( \lambda = \frac{\ln(2)}{\text{half-life}} \).
Rearrange the decay formula to solve for \( t \): \( t = \frac{\ln(N_0/N)}{\lambda} \).
Substitute the known values into the rearranged formula to calculate the age of the shroud.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Radiocarbon Dating

Radiocarbon dating is a method used to determine the age of organic materials by measuring the amount of carbon-14 (14C) remaining in a sample. Living organisms continuously take in carbon, including 14C, until they die. After death, the 14C decays at a known rate, characterized by its half-life of 5730 years, allowing scientists to estimate the time since the organism's death based on the remaining 14C activity.

Half-Life

Half-life is the time required for half of the radioactive nuclei in a sample to decay. For carbon-14, this period is approximately 5730 years. Understanding half-life is crucial for calculating the age of ancient organic materials, as it provides a consistent measure of decay that can be used to relate the remaining amount of 14C to the time elapsed since the organism's death.
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Disintegration Rate

The disintegration rate refers to the number of radioactive decays occurring in a sample per unit time, typically measured in disintegrations per minute (dpm). In the context of radiocarbon dating, comparing the disintegration rates of a sample to that of a living organism allows for the calculation of the sample's age. The difference in activity levels indicates how much time has passed since the organism ceased to take in carbon.
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