Tutorial quiz Instructions: Answer the following questions. Show all work for calculations. Multiple Choice Questions 1. Which of the following types of radioactive decay does not change the atomic number of the element? (a) (A) Alpha decay (b) (B) Beta decay (c) (C) Gamma decay (d) (D) None of the above 2. The half-life of a radioactive substance is 5 hours. If you start with 80 g of the substance, how much remains after 15 hours? (a) (A) 40 g (b) (B) 20 g (c) (C) 10 g (d) (D) 5 g 3. If the decay constant of a substance is 0.001 s−1 , what is its half-life? (a) (A) 100 s (b) (B) 693 s (c) (C) 1000 s (d) (D) 2000 s Short Answer Questions 1. Define the term half-life and explain its significance in radioactive decay. 2. A sample has an initial activity of 400 Bq. If the decay constant is 0.002 s−1 , what will its activity be after 500 seconds? (Use the activity decay equation). 3. Explain how radiation exposure is measured and list two ways to minimize radiation exposure. 1 Solutions: Pop Quiz on Radioactive Decay Multiple Choice Answers 1. (C) Gamma decay Explanation: Gamma decay releases energy but does not change the number of protons or neutrons. 2. (C) 10 g Explanation: After 5 hours: 80/2 = 40 g After 10 hours: 40/2 = 20 g After 15 hours: 20/2 = 10 g 3. (B) 693 s Solution: Using the half-life formula: t1/2 = ln 2 0.693 = = 693 s λ 0.001 Short Answer Solutions 1. Definition of Half-Life: The half-life t1/2 is the time required for half of a radioactive substance to decay. It is a characteristic property of each radioactive isotope. 2. Activity Calculation: Given A0 = 400 Bq, λ = 0.002 s−1 , and t = 500 s, we use: A = A0 e−λt A = 400e−(0.002)(500) A = 400e−1 A ≈ 400 × 0.368 A ≈ 147.2 Bq 3. Radiation Exposure Measurement: - Radiation exposure is measured in Sieverts (Sv). - Ways to minimize exposure: • Increasing distance from the radiation source. • Using shielding materials like lead or concrete. • Reducing exposure time. 2