GATE 2020 BM – Question 60
In the shown 50 keV X-ray path, incident photon count is 2×10⁶. The ray crosses 2 cm soft tissue,0.5 cm blood and 1 cm soft tissue. Attenuation coefficients are 0.4 cm⁻¹ for tissue and 0.2 cm⁻¹ for blood. Find exiting photon count in units of 10⁶, to two decimals.
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Correct answer: 0.5 to 0.6
Explanation
Successive transmissions multiply. The total attenuation exponent is .4×(2+1)+.2×.5=1.3. Thus Nout=2×10⁶e⁻¹·³≈.545064×10⁶ photons. The requested coefficient is .55 to two decimals, not the absorbed fraction.