Radioactivity MCQs With Answer

Mastering radioactivity is essential for B. Pharm students involved in radiopharmacy, diagnostic imaging, and radiation safety. This concise collection of Radioactivity MCQs With Answer covers core concepts such as nuclear decay laws, half-life calculations, units (Bq, Ci, Gray, Sievert), radiation types, detector principles, radiopharmaceuticals (Tc-99m, I-131, F-18), generator systems, dosimetry, shielding, and quality control. Questions emphasize practical applications: decay correction, effective half-life, radiochemical purity, ALARA, and tracer techniques used in pharmaceutical research and clinical practice. Clear explanations and focused examples help build competence for exams and lab work. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which law describes the exponential decrease of radioactive nuclei over time?

• First-order decay law
• Zero-order decay law
• Second-order decay law
• Logistic decay law

Correct Answer: First-order decay law

Q2. The activity A of a radioactive sample after time t is given by A = A0 e^(-λt). What does λ represent?

• Decay constant
• Initial activity
• Half-life
• Mean lifetime

Correct Answer: Decay constant

Q3. How is the half-life (t1/2) related to the decay constant λ?

• t1/2 = ln2 / λ
• t1/2 = λ / ln2
• t1/2 = e^λ
• t1/2 = 1 / λ^2

Correct Answer: t1/2 = ln2 / λ

Q4. Which unit measures radioactivity in the SI system?

• Becquerel (Bq)
• Curie (Ci)
• Gray (Gy)
• Roentgen (R)

Correct Answer: Becquerel (Bq)

Q5. Which unit quantifies absorbed dose of radiation by tissue?

• Gray (Gy)
• Sievert (Sv)
• Becquerel (Bq)
• Curie (Ci)

Correct Answer: Gray (Gy)

Q6. Which unit accounts for biological effect of radiation by weighting absorbed dose?

• Sievert (Sv)
• Gray (Gy)
• Becquerel (Bq)
• Roentgen (R)

Correct Answer: Sievert (Sv)

Q7. Which type of radiation has the highest mass and lowest penetration?

• Alpha particles
• Beta particles
• Gamma rays
• Neutrons

Correct Answer: Alpha particles

Q8. For shielding beta radiation effectively in a lab, which material is commonly used?

• Plexiglass or acrylic
• Lead bricks
• Concrete blocks
• Aluminum foil

Correct Answer: Plexiglass or acrylic

Q9. Which interaction predominates for moderate-energy gamma photons in most radiopharmaceutical detectors?

• Compton scattering
• Photoelectric absorption
• Pair production
• Thomson scattering

Correct Answer: Compton scattering

Q10. Which detector is most commonly used for counting low-energy gamma and beta emitters in radiopharmacy QC?

• Scintillation counter
• Geiger-Müller counter
• Cloud chamber
• Photographic plate

Correct Answer: Scintillation counter

Q11. Which instrument provides absolute activity measurement and is preferred for calibrating radioactivity standards?

• Ionization chamber (dose calibrator)
• Geiger-Müller counter
• Scintillation detector with no calibration
• Film badge

Correct Answer: Ionization chamber (dose calibrator)

Q12. What phenomenon reduces counts at high rates in detectors like GM tubes?

• Dead time
• Background subtraction
• Energy resolution
• Thermal noise

Correct Answer: Dead time

Q13. Which decay converts a neutron into a proton with emission of an electron and antineutrino?

• Beta-minus decay
• Beta-plus decay
• Alpha decay
• Electron capture

Correct Answer: Beta-minus decay

Q14. Positron emission during decay results in which detectable event used in PET imaging?

• Annihilation photons at 511 keV
• Alpha particle emission
• Beta-minus electrons
• Conversion electrons only

Correct Answer: Annihilation photons at 511 keV

Q15. Which radionuclide is widely used for diagnostic SPECT imaging due to its favorable half-life and gamma energy?

• Tc-99m
• I-131
• Cs-137
• U-238

Correct Answer: Tc-99m

Q16. How long is the approximate physical half-life of Tc-99m used in clinical practice?

• 6 hours
• 66 hours
• 110 minutes
• 8 days

Correct Answer: 6 hours

Q17. Mo-99/Tc-99m generator provides Tc-99m by which process?

• Radioactive decay (molybdenum parent to technetium daughter)
• Neutron activation of technetium
• Chemical synthesis
• Electron capture to produce Tc-99m directly

Correct Answer: Radioactive decay (molybdenum parent to technetium daughter)

Q18. In radiopharmacy, what does “radiochemical purity” refer to?

• Fraction of total radioactivity in desired chemical form
• Total radioactivity per unit volume
• Presence of stable contaminants only
• A measure of biological distribution

Correct Answer: Fraction of total radioactivity in desired chemical form

Q19. Which technique is commonly used to assess radiochemical purity of a radiotracer?

• Instant thin-layer chromatography (ITLC)
• Mass spectrometry without radioactivity detection
• pH titration
• UV-Visible spectroscopy

Correct Answer: Instant thin-layer chromatography (ITLC)

Q20. Effective half-life (Te) depends on which two components?

• Physical half-life and biological half-life
• Radiochemical purity and radionuclidic purity
• Detector efficiency and counting time
• Activity concentration and volume

Correct Answer: Physical half-life and biological half-life

Q21. The formula relating effective half-life Te to physical (Tp) and biological (Tb) half-lives is?

• 1/Te = 1/Tp + 1/Tb
• Te = Tp + Tb
• Te = Tp × Tb
• Te = Tp – Tb

Correct Answer: 1/Te = 1/Tp + 1/Tb

Q22. ALARA principle in radiation protection stands for?

• As Low As Reasonably Achievable
• All Levels Are Radioactive Always
• As Long As Radiation Applicable
• Atomic Limits Are Rigidly Applied

Correct Answer: As Low As Reasonably Achievable

Q23. Which is the best immediate action if a small open radiopharmaceutical vial spills on bench?

• Contain spill, cordon area, notify radiation safety, and follow spill protocol
• Wipe up quickly with dry cloth and discard
• Ignore and continue experiments
• Pour water to dilute the spill

Correct Answer: Contain spill, cordon area, notify radiation safety, and follow spill protocol

Q24. Which quantity follows Poisson statistics in radioactivity measurements?

• Counting uncertainty where SD = sqrt(N)
• Half-life of radionuclide
• Decay constant value
• Mean energy of emitted photons

Correct Answer: Counting uncertainty where SD = sqrt(N)

Q25. If a sample has an initial activity of 800 MBq and half-life 4 hours, what is activity after 4 hours?

• 400 MBq
• 200 MBq
• 800 MBq
• 100 MBq

Correct Answer: 400 MBq

Q26. Which radionuclide is commonly used in PET imaging?

• F-18
• Tc-99m
• I-131
• Sr-90

Correct Answer: F-18

Q27. What is radionuclidic purity?

• Percentage of total activity due to desired radionuclide
• Fraction of radiochemical species in desired form
• Purity of inert carrier in formulation
• Biological purity of tracer

Correct Answer: Percentage of total activity due to desired radionuclide

Q28. Which process reduces radiopharmaceutical efficacy by breaking chemical bonds due to radiation?

• Radiolysis
• Radiochemical purification
• Chelation
• Lyophilization

Correct Answer: Radiolysis

Q29. In the inverse square law for point sources, how does exposure change if distance is doubled?

• Exposure becomes one-fourth
• Exposure doubles
• Exposure halves
• Exposure remains the same

Correct Answer: Exposure becomes one-fourth

Q30. Which radionuclide is commonly used for thyroid therapy?

• I-131
• Tc-99m
• F-18
• C-14

Correct Answer: I-131

Q31. Electron capture decay results in which outcome on the nucleus?

• Proton converts to neutron by capturing orbital electron
• Neutron converts to proton with electron emission
• Emission of an alpha particle
• Spontaneous fission

Correct Answer: Proton converts to neutron by capturing orbital electron

Q32. Secular equilibrium between parent and daughter nuclide occurs when:

• Parent half-life is much longer than daughter half-life
• Parent half-life is much shorter than daughter half-life
• Both have identical half-lives
• Neither decays

Correct Answer: Parent half-life is much longer than daughter half-life

Q33. Transient equilibrium occurs when:

• Parent half-life is somewhat longer but comparable to daughter half-life
• Parent half-life is much longer than daughter half-life
• Parent half-life is negligible
• No daughter is produced

Correct Answer: Parent half-life is somewhat longer but comparable to daughter half-life

Q34. Specific activity of a radionuclide-labeled compound refers to:

• Activity per unit mass of the compound
• Total activity in the vial regardless of mass
• Number of radioactive atoms only
• Molecular weight of labeled compound

Correct Answer: Activity per unit mass of the compound

Q35. Which reagent is often used to iodinate tyrosine residues in proteins for radiolabeling?

• Chloramine-T
• Sodium borohydride
• EDTA alone
• Hydrochloric acid

Correct Answer: Chloramine-T

Q36. What is the minimum photon energy required for pair production to occur?

• 1.022 MeV
• 0.511 MeV
• 10 MeV
• 100 keV

Correct Answer: 1.022 MeV

Q37. Which personal dosimeter is reusable and commonly used for gamma monitoring of staff?

• Thermoluminescent dosimeter (TLD)
• Film badge once discarded
• Geiger-Müller counter strapped to chest
• Survey meter only

Correct Answer: Thermoluminescent dosimeter (TLD)

Q38. Which of the following best describes “tracer principle” in pharmaceutical studies?

• Using a radioactive label in trace amounts to follow chemical or biological pathways
• Measuring bulk therapeutic doses with radioactivity
• Replacing drugs with radioactive analogs for therapy
• Detecting only stable isotopes in formulations

Correct Answer: Using a radioactive label in trace amounts to follow chemical or biological pathways

Q39. Which quality control parameter ensures the radionuclide is not contaminated with long-lived impurities?

• Radionuclidic purity
• pH measurement
• Sterility test
• Viscosity

Correct Answer: Radionuclidic purity

Q40. Which indexing is correct: 1 curie (Ci) approximately equals how many becquerels (Bq)?

• 3.7 × 10^10 Bq
• 1 × 10^6 Bq
• 3.7 × 10^6 Bq
• 1 × 10^3 Bq

Correct Answer: 3.7 × 10^10 Bq

Q41. For gamma shielding, which material provides best attenuation per thickness?

• Lead
• Wood
• Plastic
• Aluminum

Correct Answer: Lead

Q42. In radiopharmacy, generator elution yields Tc-99m as a form of which chemical species used for labeling?

• Pertechnetate (TcO4−)
• Tetramethylammonium
• Technetium metal
• Tc-oxide nanoparticles only

Correct Answer: Pertechnetate (TcO4−)

Q43. Which is the primary regulatory principle for releasing radiopharmaceuticals to patients?

• Compliance with radiation safety, sterility, and quality control limits
• Only visual inspection
• Assuming generator output is always pure
• Relying solely on manufacturer certificate without testing

Correct Answer: Compliance with radiation safety, sterility, and quality control limits

Q44. Counting efficiency of a detector is defined as:

• Detected counts divided by emitted disintegrations
• Background counts per minute
• Total activity in the source
• Half-life divided by detector area

Correct Answer: Detected counts divided by emitted disintegrations

Q45. Which method is commonly used to separate free pertechnetate from labeled Tc-99m compounds in QC?

• Instant thin-layer chromatography (ITLC)
• Gel electrophoresis with no radioactivity detection
• pH paper strip
• Gas chromatography

Correct Answer: Instant thin-layer chromatography (ITLC)

Q46. Which term refers to radioactivity remaining after decay correction to a specified reference time?

• Decay-corrected activity
• Residual radioactivity without correction
• Biological activity only
• Specific activity measured at synthesis

Correct Answer: Decay-corrected activity

Q47. Which interaction dominates for low-energy photons in high-Z materials used in detectors?

• Photoelectric absorption
• Compton scattering
• Pair production
• Raman scattering

Correct Answer: Photoelectric absorption

Q48. In counting statistics, if you record 10,000 counts in a measurement, what is the approximate standard deviation?

• 100
• 10
• 1,000
• 10,000

Correct Answer: 100

Q49. Neutron activation is used to produce some radionuclides. Which facility is typically required?

• Nuclear reactor
• Standard clinical X-ray machine
• Centrifuge
• Mass spectrometer

Correct Answer: Nuclear reactor

Q50. Which practice reduces personnel exposure when handling radiopharmaceutical syringes?

• Using syringe shields and tongs and maximizing distance
• Holding syringe directly for better control
• Keeping fingers close to the needle during preparation
• Removing shielding to speed up work

Correct Answer: Using syringe shields and tongs and maximizing distance