NRRPT Radiation Fundamentals & Detection 3

Question 1

The half-value layer (HVL) of a gamma-ray beam is 2 cm of lead. What thickness reduces the intensity to 12.5% of the original?

Accepted Answer

6 cm

Answer

12.5% = (1/2)³, so three HVLs are needed: 3 × 2 cm = 6 cm of lead.

Question 2

In neutron activation analysis, what process produces radioactive isotopes from stable elements?

Accepted Answer

Radiative neutron capture (n,γ)

Answer

Radiative neutron capture (n,γ) adds a neutron to a stable nucleus, forming a heavier isotope that is often radioactive.

Question 3

What does the energy resolution of a radiation detector describe?

Accepted Answer

The ability to distinguish between two close energy peaks

Answer

Energy resolution is the ability of a detector to separate two photon energies that are close together, expressed as FWHM/peak energy.

Question 4

A radionuclide has a physical half-life of 8 days and a biological half-life of 24 days. Its effective half-life is approximately:

Accepted Answer

6 days

Answer

Effective half-life = (T_p × T_b)/(T_p + T_b) = (8 × 24)/(8 + 24) = 192/32 = 6 days.

Question 5

Which radiation type has the highest linear energy transfer (LET) in tissue?

Accepted Answer

5 MeV alpha particles

Answer

Alpha particles have very high LET (~80 keV/μm in tissue) due to their large mass and charge compared to beta particles and photons.

(NRRPT) National Registry of Radiation Protection Technicians Practice Test