Chapter 20: Problem 26
A radioactive substance undergoes decay as follows:
Short Answer
Expert verified
Decay constant , half-life days.
Step by step solution
01
Understand the decay model
Radioactive decay follows the first-order kinetics, described by the equation , where is the mass at time , is the initial mass, and is the decay constant. We are given the masses over time, and need to find .
02
Use the decay formula
Using the masses at each time, set up equations based on , , etc. Solving these will help estimate . A common way is using the first time point to simplify: .
03
Calculate decay constant
Divide the mass at day 1 by the initial mass: . Then, solve for using . Taking the natural logarithm on both sides, .
04
Calculate the half-life
The half-life is calculated using the relation . Plugging in the value of , days.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
First-Order Kinetics
When we talk about radioactive decay, it's essential to understand first-order kinetics. This means the rate at which the substance decays is proportional to the amount of substance present. In simpler terms, as the mass decreases over time, the speed at which it breaks down also declines. This characteristic is captured by the exponential decay equation . Here, is the mass at any given time , is your starting mass, and is known as the decay constant.
- Proportional decay rate
- Exponential decrease over time
- Key contributors: initial mass and decay constant
Decay Constant
The decay constant is a fundamental factor in first-order kinetics. It represents how quickly a radioactive isotope disintegrates. A larger indicates a faster decay, whereas a smaller suggests a slower process. You can identify by investigating the change in mass over time. By re-arranging the exponential decay formula , we can take the natural logarithm of both sides to solve for . This allows you to determine the unique rate of decay for different isotopes, which is vital for applications like radiometric dating or understanding nuclear waste behavior.
- Indicates speed of decay
- Can be calculated using observed data points
- Helpful in isotope identification
Half-Life
The half-life of a radioactive isotope is the time required for half of the isotope to decay. It's a crucial parameter as it tells us how long a substance remains active or hazardous. The relationship between the half-life and decay constant is given by . Understanding this concept helps us predict how quickly a substance loses its radioactivity.
- Time for half the sample to decay
- Gives insight into stability of isotopes
- Calculated directly from decay constant
Natural Logarithm
Natural logarithms are used frequently in the context of radioactive decay to transform exponential decay equations into linear ones, making it easier to solve for unknown variables. Specifically, the natural logarithm helps in finding the decay constant by rearranging into . By plotting over time, radioactive decay processes can be represented as a straight line, simplifying analysis.
- Translates exponential to linear relationships
- Simplifies solving decay equations
- Essential for k determination and half-life calculations
Radioactive Isotopes
Radioactive isotopes, often called radioisotopes, are variants of chemical elements that are unstable due to an imbalance in their nucleus. This instability makes them prone to spontaneous decay, emitting radiation as they transform into more stable atoms over time.
Here are key aspects:
- Serve as tracers in the medical field
- Used for dating ancient artifacts
- Power sources for nuclear reactors and weapons