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Using a half-life example, how many radioactive nuclei remain in a sample after three half-lives if the sample started with 3 million nuclei?
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After three half-lives, the number of nuclei will be: 3 million ÷ 2 (first half-life) ÷ 2 (second half-life) ÷ 2 (third half-life) = 375,000 nuclei.
How is activity measured and what is the unit used?
Activity is measured in becquerels (Bq), where one becquerel equals one decay per second.
What kind of radiation can be emitted during the decay process of unstable isotopes?
Unstable isotopes can emit alpha particles, beta particles, or gamma rays during the decay process.
For a radioactive sample with an initial activity of 6400 Bq and a half-life of 10 hours, what will be the activity after 30 hours?
After 30 hours, which is three half-lives, the activity will be: 6400 Bq ÷ 2 (first half-life) ÷ 2 (second half-life) ÷ 2 (third half-life) = 800 Bq.
What is the definition of half-life in terms of radioactive decay?
Half-life is the time taken for the number of radioactive nuclei in a sample, or the activity, to halve.
What is the definition of unstable isotopes?
Unstable isotopes are isotopes which decay to become more stable by emitting radiation such as alpha particles, beta particles, or gamma rays.
Describe what happens to the rate of decay as more isotopes decay.
As more isotopes decay, the number of unstable particles left decreases, leading to a decrease in the overall rate of decay (activity).
What is the role of the Geiger-Muller tube in measuring activity?
The Geiger-Muller tube measures activity by recording all decays (alpha, beta, gamma) reaching it per second, producing a count rate which estimates the activity.
What does a decay curve represent and how does the shape of the curve typically appear?
A decay curve represents the declining activity (measured in becquerels) over time, and the curve typically appears as a declining, curved line because the rate of decline decreases over time.
How do you determine the half-life of a material using a decay curve?
Identify the time it takes for the activity to halve on the decay curve. For example, if activity drops from 600 Bq to 300 Bq in 2 hours, the half-life is 2 hours.
Why do different samples have decay curves with varying steepness?
Different samples have different half-lives, resulting in varying rates of decline, which is illustrated by the varying steepness in their decay curves.
How can one compare the half-lives of two different samples?
One can compare the time it takes for their activities to halve by examining their decay curves or calculating the halving times for each.
Explain how the decay process is characterized in terms of predictability.
The decay process is completely random and unpredictable for individual isotopes.
If a sample’s activity decreases from 800 Bq to 400 Bq in three hours, what is the half-life of the sample?
The half-life of the sample is three hours because the activity halved from 800 Bq to 400 Bq in that time.
Why do radioactive materials become less dangerous over time in terms of activity?
Radioactive materials become less dangerous because their activity decreases over time as more isotopes decay and emit radiation, reducing the remaining unstable isotopes.
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