RSO Radiation Physics and Fundamentals 1 — Questions and Answers
Question 1: Which type of radiation has the greatest ionizing power but the least penetrating ability?
- Beta particles
- Gamma rays
- Alpha particles (Correct answer)
- Neutrons
Correct answer: Alpha particles
Alpha particles are highly ionizing due to their large mass and double positive charge, but they are stopped by a few centimeters of air or a sheet of paper.
Question 2: The SI unit of radioactivity is the Becquerel (Bq). One Becquerel is defined as:
- One disintegration per minute
- One disintegration per second (Correct answer)
- One joule per kilogram
- One coulomb per kilogram
Correct answer: One disintegration per second
One Becquerel equals one nuclear disintegration (decay event) per second.
Question 3: Which of the following best describes gamma radiation?
- High-speed electrons emitted from the nucleus
- High-speed helium nuclei
- High-energy electromagnetic radiation (Correct answer)
- High-speed protons
Correct answer: High-energy electromagnetic radiation
Gamma radiation consists of high-energy photons (electromagnetic radiation) emitted from the nucleus during radioactive decay.
Question 4: The half-life of a radioactive isotope is the time required for:
- Half the atoms to become stable
- The activity to decrease to half its original value (Correct answer)
- Half the radiation to be absorbed by shielding
- The dose rate to decrease by half at a fixed distance
Correct answer: The activity to decrease to half its original value
Half-life is the time for the activity (number of decays per unit time) of a radioactive sample to decrease to half its initial value.
Question 5: Which nuclear process results in the emission of a positron (β+)?
- Alpha decay
- Beta-minus decay
- Beta-plus decay (Correct answer)
- Gamma decay
Correct answer: Beta-plus decay
Beta-plus decay occurs when a proton converts to a neutron inside the nucleus, emitting a positron and a neutrino.
Question 6: An RSO is working with a source of I-131, which has a half-life of approximately 8 days. If the initial activity is 40 mCi, what will the activity be after 24 days?
- 20 mCi
- 10 mCi
- 5 mCi (Correct answer)
- 2.5 mCi
Correct answer: 5 mCi
24 days equals 3 half-lives (24/8 = 3), so the activity decreases by half three times: 40 → 20 → 10 → 5 mCi.
Question 7: Which statement correctly describes the relationship between photon energy and penetrating ability for X-rays and gamma rays?
- Higher-energy photons are less penetrating
- Lower-energy photons are more penetrating
- Higher-energy photons are more penetrating (Correct answer)
- Photon energy has no effect on penetrating ability
Correct answer: Higher-energy photons are more penetrating
Higher photon energies correspond to greater penetrating ability because higher-energy photons are less likely to interact per unit path length through matter.
RSO Radiation Physics and Fundamentals 1
Which type of radiation has the greatest ionizing power but the least penetrating ability?