Medical Imaging Systems · Nuclear Imaging · 1 mark · Numerical answer
NaI crystals detect 120 keV gamma rays. If their half-value layer is 0.2 cm, what percentage of gamma rays passes through 1 cm of NaI, to one decimal place?
One centimetre is five half-value layers. Each layer halves transmitted intensity, giving fraction (1/2)⁵=1/32=.03125. Multiplying by one hundred gives 3.125%, rounded to 3.1%. The detected/absorbed fraction would be the complement.
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