MI Image Acquisition

Question 1

Sodium Iodide (TI) is used as a scintillator crystal; what two properties make this material suitable for this and why?

Answer 1

1) High density (3,670 kg/m3)
2) High atomic number Z=53
Efficient gamma ray absorbtion.

Question 2

What advantages does a Sodium Iodide (TI) crystal have for use as a scintillator?

Answer 2

1) the signal is proportional to the energy depostited in the crystal
2) high output of photons per keV at room temperature; therefore good energy resolution
84% of 140keV photons in a 9mm thick crystal are detected
3) high count rate due to a short (0.23µs) excitation time
4) transparent, therefore, minimal light loss

Question 3

What disadvantages does a Sodium Iodide (TI) crystal have for use as a scintillator?

Answer 3

1) Fragile (mechanically and thermally)

2) Hydroscopic - is sealed in Al case, lifetime limited (goes yellow)