Math Problem Statement

Uranium-238, the most common uranium isotope, has a half-life of 4.5 billion years. After 10,000 years, what percentage of the original amount of uranium remains? This series of problems will build your fluency with exponential growth and decay. For each question below, write a

function modeling the scenario, and then solve the problem.

Solution

To solve this problem, we will model the decay of Uranium-238 using an exponential decay function. Here's how we can approach the problem:

Exponential Decay Function

The general formula for exponential decay is:

N(t)=N0eλtN(t) = N_0 \cdot e^{-\lambda t}

Where:

  • N(t)N(t) is the amount of the substance remaining after time tt.
  • N0N_0 is the initial amount of the substance.
  • λ\lambda is the decay constant.
  • tt is the time elapsed.

Step 1: Calculate the Decay Constant λ\lambda

The decay constant λ\lambda is related to the half-life T1/2T_{1/2} by the following formula:

λ=ln(2)T1/2\lambda = \frac{\ln(2)}{T_{1/2}}

Given that the half-life T1/2T_{1/2} of Uranium-238 is 4.5 billion years, we can calculate λ\lambda:

λ=ln(2)4.5×109 years\lambda = \frac{\ln(2)}{4.5 \times 10^9 \text{ years}}

Step 2: Model the Scenario

Now we want to find the percentage of the original amount of uranium remaining after 10,000 years. The function modeling the scenario is:

N(10000)=N0eλ10000N(10000) = N_0 \cdot e^{-\lambda \cdot 10000}

To find the percentage of the original amount remaining, we divide N(10000)N(10000) by the initial amount N0N_0 and multiply by 100:

Percentage remaining=(N(10000)N0)×100=eλ10000×100\text{Percentage remaining} = \left( \frac{N(10000)}{N_0} \right) \times 100 = e^{-\lambda \cdot 10000} \times 100

Step 3: Compute the Result

Now, let's calculate the exact percentage:

  1. Calculate the decay constant λ\lambda: λ=ln(2)4.5×109\lambda = \frac{\ln(2)}{4.5 \times 10^9}

  2. Substitute λ\lambda and t=10000t = 10000 years into the percentage formula: Percentage remaining=eλ10000×100\text{Percentage remaining} = e^{-\lambda \cdot 10000} \times 100

Let's compute this value.After 10,000 years, approximately 99.9998% of the original amount of Uranium-238 remains.

Would you like more details or have any other questions? Here are five related questions:

  1. What is the percentage of Uranium-238 remaining after 1 million years?
  2. How long will it take for only 50% of Uranium-238 to remain?
  3. How would the remaining percentage change if the half-life were shorter?
  4. What is the remaining percentage after three half-lives?
  5. How does the decay of Uranium-238 compare to that of other radioactive isotopes?

Tip: Understanding the relationship between the half-life and the decay constant is crucial for modeling and predicting decay processes accurately.

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Math Problem Analysis

Mathematical Concepts

Exponential Decay

Formulas

Exponential decay formula N(t) = N_0 * e^(-lambda * t)

Theorems

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Suitable Grade Level

High School