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The radioactive isotope sodium-24 is used as a tracer to measure the rate of flow in an artery or vein. The half-life of sodium-24 is 14.9 hours. Suppose that a hospital buys a \(40-\mathrm{g}\) sample of sodium- 24 (a) How much of the sample will remain after 48 hours? (b) How long will it be until only 1 gram remains?

Short Answer

Expert verified
(a) Approximately 4.69 grams will remain after 48 hours. (b) It will take about 79.27 hours for only 1 gram to remain.

Step by step solution

01

Understand Half-Life

The half-life of a substance is the time taken for its quantity to reduce to half its initial amount. For sodium-24, this time is 14.9 hours. This means every 14.9 hours, the sodium-24 sample will reduce to half of its current amount.
02

Determine Number of Half-Life Periods (48 hours)

To find the remaining amount after a certain time, first determine how many half-lives have passed. For 48 hours, divide the total time by the half-life: \( \text{Number of half-lives} = \frac{48}{14.9} \approx 3.22 \) half-lives.
03

Calculate Remaining Amount After 48 Hours

Use the formula for exponential decay, \( A = A_0 \left(\frac{1}{2}\right)^n \), where \( A_0 \) is the initial amount and \( n \) is the number of half-lives. Here, \( A_0 = 40 \) grams and \( n = 3.22 \). Thus, the remaining amount \( A \approx 40 \times (0.5)^{3.22} \approx 4.69 \) grams.
04

Calculate Time for Remaining Amount to be 1 Gram

Rearrange the half-life formula to solve for time: \( A = A_0 \left(\frac{1}{2}\right)^{t/14.9} \). For \( A = 1 \) gram, \( A_0 = 40 \) grams, and solve for \( t \): \( 1 = 40 \left(\frac{1}{2}\right)^{t/14.9} \). This implies \( \left(\frac{1}{2}\right)^{t/14.9} = \frac{1}{40} \), leading to \( \frac{t}{14.9} = \log_{0.5}\left(\frac{1}{40}\right) \). Calculating gives \( t \approx 79.27 \) hours.

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Key Concepts

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

half-life
In the world of radioactive decay and nuclear physics, the concept of "half-life" is essential to understand. It represents the time it takes for a radioactive isotope to reduce to half of its initial amount. For example, consider our case with sodium-24, which has a half-life of 14.9 hours. This means, if you have 40 grams of sodium-24, after 14.9 hours, only 20 grams will remain because half of the substance will have decayed.

Understanding half-life helps in planning and predicting how long a radioactive tracer like sodium-24 will be effective in medical or industrial applications. In practice, you'll often need to calculate how many half-lives occur over a given period. This can aid in determining how much of the substance is left after a certain duration has passed.

To determine the remaining amount of a radioactive substance after several half-lives, you can use an exponential decay formula, where the number of half-lives is plugged in as an exponent. This formula is crucial when dealing with substances with a known half-life, offering a clear pathway to calculate their degradation over time.
exponential decay
Exponential decay is a process that describes the reduction of a quantity at a rate proportionate to its current value. This type of decay follows a specific mathematical model, which is widely applicable not just in physics, but also in finance, biology, and other fields. When it comes to radioactive substances like sodium-24, exponential decay describes how the atoms in the substance disintegrate over time.

The mathematical model of exponential decay is represented by the formula:
  • \( A = A_0 \left(\frac{1}{2}\right)^n \)
where \( A \) is the amount remaining, \( A_0 \) is the initial amount, and \( n \) signifies the number of half-lives. This model lets you predict the behavior of a radioactive isotope as it decreases over time, providing a forecast of its potency and usefulness.

An insightful aspect of exponential decay is that it reflects real-world scenarios where substances decrease without leaving a residue of their original state. Each half-life term represents a predictable, mathematical cut in the substance's presence, making it a reliable tool in medical diagnostics/workflows, like tracing the flow of blood using sodium-24.
sodium-24
Sodium-24 is an isotope commonly used as a radioactive tracer in medical diagnostics. Tracers help doctors visualize and measure the internal processes of a patient's body, such as blood flow in arteries or veins. Its relatively short half-life of 14.9 hours makes it well-suited for such purposes since it remains active long enough to complete procedures without prolonged radiation exposure.

Once administered, sodium-24 gives off radiation detectable by special imaging equipment. This ability allows tracking of the tracer's movement through the body. In medical scenarios, sodium-24 can be injected into the bloodstream, highlighting areas or functions needing observation.

Despite its usefulness, handling sodium-24 requires caution because, like all radioactive substances, it carries potential risks. Proper shielding and safety protocols are necessary to protect healthcare providers and patients. Understanding sodium-24’s exponential decay rate through its half-life is crucial, ensuring safe, accurate assessments and offering insights into the dynamics of bodily functions.

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