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The half life of carbon-14 is 5730 years. If one starts with 100 milligrams of carbon-14, how much is left after 6000 years? How long do we have to wait before there is less than 2 milligrams?

Short Answer

Expert verified
50.7 mg remains after 6000 years; wait approximately 30,000 years for less than 2 mg.

Step by step solution

01

Understanding Half-Life

The half-life of a substance is the time it takes for half of the substance to decay. Carbon-14's half-life is 5730 years, meaning every 5730 years, half of the original amount of carbon-14 decays.
02

Decay Formula

The decay process of a substance can be described with the exponential decay formula: \[ N(t) = N_0 \times \left( \frac{1}{2} \right)^{\frac{t}{T}} \]where \( N(t) \) is the quantity remaining after time \( t \), \( N_0 \) is the initial quantity, and \( T \) is the half-life.
03

Calculating Remaining Carbon-14 After 6000 Years

Let's use the decay formula with \( N_0 = 100 \) mg, \( T = 5730 \) years, and \( t = 6000 \) years:\[ N(6000) = 100 \times \left( \frac{1}{2} \right)^{\frac{6000}{5730}} \]Calculating this gives:\[ N(6000) \approx 100 \times 0.507 \approx 50.7 \text{ mg} \]
04

Setting Up Inequality For Less Than 2 mg

To find when the quantity is less than 2 mg, we set up:\[ 100 \times \left( \frac{1}{2} \right)^{\frac{t}{5730}} < 2 \]
05

Solving the Inequality

Solve for \( t \) using natural logarithms:\[ \left( \frac{1}{2} \right)^{\frac{t}{5730}} < \frac{1}{50} \]Taking logarithm base \( rac{1}{2} \),\[ \frac{t}{5730} > \log_{0.5} \left( \frac{1}{50} \right) \]\[ t > 5730 \times \frac{\ln 50}{\ln 2} \]Calculating gives \( t \approx 30000 \) years.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Half-Life
The concept of half-life is fundamental when dealing with radioactive substances such as Carbon-14. Half-life refers to the time required for half of the unstable atoms in a substance to decay. This is a predictable rate of decrease which helps scientists understand how substances reduce over time.

The half-life is essential for quantifying exponential decay, especially for radioactive compounds. For Carbon-14, its half-life is 5730 years. This means that every 5730 years, half of the Carbon-14's initial quantity decays. If you start with 100 milligrams, after 5730 years, you'll have 50 milligrams remaining.

Calculations based on half-life are common and valuable in many scientific fields, such as archaeology and geology, for dating ancient objects.
Logarithms
Logarithms are a critical mathematical tool when working with exponential decay, allowing us to solve complex equations more easily.

In the context of exponential decay, logarithms help determine the time it takes for a substance to reach a certain quantity. When exponential functions are involved, such as with the formula for decay: \[ N(t) = N_0 \times \left( \frac{1}{2} \right)^{\frac{t}{T}} \] where solving for time \( t \) becomes necessary, logarithms are invaluable.

To make calculations easier,
  • Taking the logarithm of both sides of an equation helps isolate variables.
  • Logarithms convert multiplication into addition, simplifying equations exponentially.
For example, finding when a quantity is less than a specific amount, logarithms help by providing a straightforward method to solve the relevant inequality.
Carbon-14 Dating
Carbon-14 dating, also known as radiocarbon dating, is a powerful tool used to determine the age of an object containing organic material by using the properties of Carbon-14. This isotope naturally occurs in the atmosphere and is absorbed by living organisms throughout their lifetime.

When the organism dies, it ceases to absorb Carbon-14, and the isotope begins to decay at a known rate. By measuring the remaining Carbon-14 in a sample and comparing it to the expected initial amount, scientists can estimate how long it has been since the organism died. This is made possible by understanding Carbon-14's half-life, which is 5730 years. With this decay rate known,
  • It allows the dating of artifacts up to tens of thousands of years old.
  • Provides vital information in archaeology, helping to understand historical timelines.
Thus, Carbon-14 dating gives us insights into the past, complementing historical and archaeological research.

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