NRRPT Radiation Fundamentals & Detection 4

Question 1

A sealed radioactive source contains 10 mCi of Cs-137 (T½ = 30 years). Approximately how much activity remains after 90 years?

Accepted Answer

1.25 mCi

Answer

5 mCi

Answer

2.5 mCi

Answer

0.625 mCi

Question 2

In a proportional counter, what is the primary advantage over an ionization chamber?

Accepted Answer

Gas multiplication amplifying the primary ion signal

Answer

Simpler circuitry requirements

Answer

Ability to operate without applied voltage

Answer

Lower sensitivity to gamma radiation

Question 3

The photoelectric effect is the dominant photon interaction in tissue at energies:

Accepted Answer

Below about 100 keV

Answer

Between 1 and 10 MeV

Answer

Above 1.022 MeV

Answer

At all diagnostic energies equally

Question 4

Which detector is best suited for measuring low-energy beta emitters like tritium (H-3)?

Accepted Answer

Liquid scintillation counter

Answer

GM tube with thin mica end-window

Answer

NaI(Tl) scintillation detector

Answer

Pressurized ionization chamber

Question 5

What is the significance of the 'dead time' in a radiation detector?

Accepted Answer

The period after each pulse during which new events cannot be recorded

Answer

The time needed to warm up the detector before use

Answer

The decay time of the scintillation light pulse

Answer

The delay between radiation exposure and TLD readout

Question 6

Which nuclear decay mode is characterized by emission of radiation from nuclear isomers (metastable states)?

Accepted Answer

Isomeric transition (IT)

Answer

Internal conversion (IC)

Answer

Electron capture (EC)

Answer

Spontaneous fission (SF)

Question 7

The Compton edge in a gamma-ray spectrum represents:

Accepted Answer

The maximum energy transferred to the recoil electron in Compton scattering

Answer

The full energy peak shifted by detector resolution

Answer

The energy of backscattered photons from shielding

Answer

The minimum detectable photon energy