What does a linear attenuation coefficient of 0.18 cm⁻¹ for water indicate?

The linear attenuation coefficient is a measure of how easily a material attenuates (weakens) an x-ray beam as it passes through it. A coefficient of 0.18 cm⁻¹ for water indicates that x-ray intensity decreases exponentially with distance traveled in the material.

Using the exponential attenuation formula, the fraction of x-ray intensity that remains after passing through a thickness (x) of a material is expressed as (I = I_0 \cdot e^{-\mu x}), where (\mu) is the linear attenuation coefficient and (I_0) is the initial intensity. For a linear attenuation coefficient of 0.18 cm⁻¹, looking at a thickness of 1 cm shows that about 18% of the incident x-ray beams are absorbed. This reflects the concept that the coefficient quantifies the attenuation effect: a coefficient of 0.18 implies that approximately 18% of the x-ray photons are absorbed in that 1 cm of water.

Thus, the correct answer accurately relates the linear attenuation coefficient to the percentage of x-ray beams absorbed, making it clear that 18% of the x-ray beams do not pass through and are absorbed within a 1 cm thickness of