Radiation Measurement and Instrumentation Flashcards

A thermoluminescent dosimeter (TLD) uses which physical process to record dose?

Answer: Trapping of electrons in crystal lattice defects

TLDs work by trapping electrons in crystalline defect sites; heating the crystal releases them as measurable light proportional to absorbed dose.

The Bragg-Gray cavity theory applies to ionization chambers when the cavity:

Answer: Is small enough not to perturb the radiation field

Bragg-Gray theory requires the cavity to be small relative to the range of secondary electrons so it does not disturb the fluence of charged particles.

Which detector type is best suited for measuring fast neutrons through proton recoil?

Answer: Proton recoil scintillator (EJ-301)

Organic scintillators such as EJ-301 (NE-213) detect fast neutrons via elastic scattering off hydrogen nuclei, producing measurable proton recoil tracks.

Dead time in a Geiger-Müller tube is the period during which:

Answer: The detector cannot register a new event after a previous pulse

Dead time is the interval following a pulse during which the detector is paralyzed and cannot produce a new independent output pulse.

The energy resolution of a sodium iodide (NaI) detector at 662 keV (137Cs) is approximately:

Answer: 6–8%

NaI(Tl) detectors typically achieve 6–8% full-width at half-maximum energy resolution at 662 keV, far inferior to HPGe but adequate for many field applications.

When calibrating an air ionization chamber for exposure measurement, the calibration factor N_X converts:

Answer: Instrument reading to exposure in air

The exposure calibration factor N_X relates the electrometer reading (corrected for temperature and pressure) to the true exposure in roentgens or C/kg.

A survey meter reads 2 mR/h at 1 meter from a point source. At 3 meters, the expected reading is approximately:

Answer: 0.22 mR/h

By the inverse square law, intensity scales as 1/r²: 2 × (1/3)² = 2/9 ≈ 0.22 mR/h.