Question 1: Half-life is the time taken for a quantity of a radioactive substance to decrease to half of its original amount. It is a characteristic property of each radioactive isotope and helps in estimating how long a substance remains radioactive.

Answer: Half-life is the time for a radioactive substance to reduce to half its initial amount.

Question 1: What does the term 'half-life' specifically refer to in radioactivity?

Answer: It refers to the time taken for half of the radioactive nuclei in a sample to decay.

Question 2: Explain why different radioactive isotopes have different half-lives.

Answer: Different isotopes have varying nuclear stability, which affects how quickly they decay. Factors such as neutron-to-proton ratio influence the half-life, making some isotopes decay rapidly while others remain stable for millions of years.

Question 1: A sample of radioactive isotope has a half-life of 10 hours. How much of a 100g sample remains after 30 hours?

Answer: 12.5g

Question 2: Calculate the decay constant λ for a sample with a half-life of 12 hours. (Use the formula λ = ln(2)/half-life, where λ is in hours⁻¹).

Answer: 0.0578 hours⁻¹

Question 1: Describe a simple experiment to determine the half-life of a radioactive isotope. Include safety precautions.

Answer: The experiment involves measuring the activity of a radioactive sample at regular intervals using a Geiger counter or scintillation counter. Record the activity over time until it halves. Safety precautions include wearing lead aprons, using appropriate shielding, handling samples with tongs, and working behind protective barriers to minimise exposure.

Question 1: A researcher measures the activity of a radioactive isotope over a period of time. Initially, the activity is 200 counts per minute. After 24 hours, the activity drops to 25 counts per minute. What is the half-life of this isotope?

Answer: Approximately 6 hours

Question 2: A certain isotope has a half-life of 15 hours. How much of a 160g sample remains after 45 hours?

Answer: 10g

Question 1: Explain how understanding the half-life of radioactive isotopes is important in medical radiotherapy.

Answer: Knowing the half-life helps in selecting isotopes that deliver effective doses while minimizing radiation exposure to patients and medical staff. It ensures the radioactive material decays at a predictable rate, providing safe and effective treatment.

Question 2: Describe how the concept of half-life is used in radiocarbon dating to estimate the age of archaeological samples.

Answer: Radiocarbon dating relies on the decay of Carbon-14, which has a known half-life of about 5730 years. By measuring the remaining Carbon-14 in ancient samples and comparing it to current levels, scientists can estimate how long it has been since the organism died, thus determining its age.