Assignment:
1. If the energy resolution of a particular NaI(Tl) scintillation detector is 7% for Cs-137 gamma rays, estimate its energy resolution for the 1.28 MeV gamma rays from Na-22.
2. Why are materials with low atomic number often preferred as scintillators for electron spectroscopy, while the opposite is true for gamma-ray spectroscopy?
3. The mass attenuation coefficient of NaI at 0.5 MeV is 0.955 cm2/g. Find the intrinsic total efficiency of a slab detector 0.50 cm thick at this energy. If the photofraction is 40% at the same energy, what is the intrinsic peak efficiency?
4. Listed below are a number of parameters of interest in gamma-ray spectroscopy using scintillation detectors:
a. Density of the detector medium
b. Kinetic energy required to create a scintillation photo in the crystal
c. Average atomic number of the detector medium
d. Geometry of the source-detector system
e. Gain of the photomultiplier tube
f. Quantum efficiency of the photocathode in the photomultiplier
g. Gain of the amplifier used between the detector and pulse analysis system
h. Fraction of light generated in the crystal that reaches the photocathode of the PM tube (light collection efficiency)
Identify those parameters from this list that have a major influence on the detector intrinsic peak efficiency. Repeat, but now identify those that have a major influence on energy resolution.
5. Find the ratio of the number of charge carriers created in silicon by a 1-MeV proton to the number created by the same energy deposition in air.
6. In order to reverse bias the junction, should the positive terminal of the voltage supply be connected to the p or n side of the junction? Justify your answer.
7. Indicate the functional dependence of the following properties of a p-n junction on the magnitude of the applied reverse bias:
a. Depletion width
b. Capacitance
c. Maximum electric field
8. There is often a premium on fabricating detectors with the largest possible depletion width for a given applied voltage. Explain why starting with semiconductor material of the highest available purity enhances this objective.