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What is the Activity of a Radioactive Sample?
Grade Level:
Class 12
AI/ML, Physics, Biotechnology, FinTech, EVs, Space Technology, Climate Science, Blockchain, Medicine, Engineering, Law, Economics
Definition
What is it?
The 'Activity' of a radioactive sample is a measure of how quickly its unstable atoms are breaking down or decaying. It tells us the rate at which a radioactive sample emits radiation. Higher activity means more atoms are decaying per second.
Simple Example
Quick Example
Imagine you have a big bowl of laddoos. If you eat 10 laddoos in one minute, your 'laddoo-eating activity' is 10 laddoos per minute. Similarly, the activity of a radioactive sample is how many 'atoms' decay per second, not laddoos!
Worked Example
Step-by-Step
QUESTION: A radioactive sample has 10,000 unstable atoms. After 1 second, 50 atoms decay. What is the activity of the sample?
STEP 1: Understand what activity means. Activity is the number of decays per unit time.
---STEP 2: Identify the number of decays. Here, 50 atoms decayed.
---STEP 3: Identify the time taken for these decays. Here, the time taken is 1 second.
---STEP 4: Calculate the activity using the formula: Activity = (Number of decays) / (Time taken).
---STEP 5: Substitute the values: Activity = 50 decays / 1 second.
---STEP 6: Calculate the result. Activity = 50 decays per second.
ANSWER: The activity of the sample is 50 decays per second.
Why It Matters
Understanding activity is crucial in fields like Medicine, where doctors use radioactive materials for imaging (like PET scans) or cancer treatment, ensuring the correct dosage. It's also vital in Space Technology for powering spacecraft and in Climate Science for dating ancient samples, helping scientists understand our planet's past.
Common Mistakes
MISTAKE: Confusing activity with the total number of radioactive atoms present. | CORRECTION: Activity is the *rate* of decay (how many decay per second), not the total count of atoms. A sample with many atoms might have low activity if they decay slowly.
MISTAKE: Forgetting the units of activity. | CORRECTION: Activity is measured in 'Becquerel' (Bq), where 1 Bq means 1 decay per second. Another common unit is 'Curie' (Ci). Always include units!
MISTAKE: Thinking that activity stays constant over time. | CORRECTION: The activity of a radioactive sample *decreases* over time as more and more unstable atoms decay. This decrease is characterized by the 'half-life'.
Practice Questions
Try It Yourself
QUESTION: A sample of Iodine-131 shows 250 decays in 5 seconds. What is its activity? | ANSWER: 50 Bq
QUESTION: A radioactive source has an activity of 120 Bq. How many atoms decay in 2 minutes? | ANSWER: 14,400 atoms
QUESTION: A radioactive material initially has an activity of 800 Bq. After 10 minutes, its activity drops to 400 Bq. If it continues to decay at this rate, what would be its activity after another 10 minutes? | ANSWER: 200 Bq
MCQ
Quick Quiz
Which of the following best describes the 'Activity' of a radioactive sample?
The total number of radioactive atoms present.
The rate at which its unstable atoms decay.
The time it takes for half of its atoms to decay.
The type of radiation it emits.
The Correct Answer Is:
B
Activity specifically refers to the *rate* of decay, meaning how many decays occur per second. The other options describe total atoms, half-life, or radiation type, not activity.
Real World Connection
In the Real World
In Indian hospitals, doctors use radioactive isotopes like Technetium-99m for medical imaging. They need to know the 'activity' of the sample to calculate the correct dose for a patient. Too high activity could be harmful, too low and the scan won't be clear. This precise measurement helps in diagnosing heart conditions or bone issues safely and effectively.
Key Vocabulary
Key Terms
DECAY: The process where an unstable atomic nucleus loses energy by emitting radiation. | BECQUEREL (Bq): The SI unit of activity, equal to one decay per second. | ISOTOPE: Atoms of the same element with different numbers of neutrons. | HALF-LIFE: The time taken for half of the radioactive atoms in a sample to decay.
What's Next
What to Learn Next
Great job understanding Activity! Next, you should learn about 'Half-Life of a Radioactive Sample'. Half-life directly relates to how activity changes over time and is super important for understanding how long radioactive materials remain active.
