Radiation Physics and Fundamentals Flashcards

The traditional unit of radioactivity is the Curie (Ci). One Curie is defined as:

Answer: 3.7 × 10^10 disintegrations per second

One Curie equals 3.7 × 10^10 disintegrations per second, based on the activity of one gram of radium-226.

In electron capture decay, the nucleus captures an orbital electron and emits:

Answer: A neutrino and characteristic X-rays

During electron capture, a proton combines with the captured electron to form a neutron, emitting a neutrino; the resulting electron vacancy produces characteristic X-rays.

The specific activity of a radioactive material is defined as:

Answer: Activity per unit mass

Specific activity is the radioactivity per unit mass of a radionuclide or radioactive material, typically expressed as Ci/g or Bq/g.

Which of the following radionuclides is a pure beta emitter with no associated gamma radiation?

Answer: H-3 (Tritium)

Tritium (H-3) decays by beta-minus emission with a very low-energy beta and produces no gamma radiation, making external dose a minor concern but internal uptake significant.

The mean free path of a photon in a material is best described as:

Answer: The average distance a photon travels before interacting

Mean free path is the average distance a photon travels in a medium before undergoing an interaction such as photoelectric absorption, Compton scattering, or pair production.

If a radionuclide has a physical half-life of 6 hours and a biological half-life of 12 hours, what is its effective half-life in the body?

Answer: 4 hours

Effective half-life = (T_physical × T_biological) / (T_physical + T_biological) = (6 × 12) / (6 + 12) = 72/18 = 4 hours.

Secular equilibrium between a parent and daughter radionuclide occurs when:

Answer: The parent's half-life is much longer than the daughter's

Secular equilibrium occurs when the parent half-life is so much longer than the daughter's that the daughter activity equals the parent activity and remains constant.