Question

The half-value thickness of an absorber is defined as the thickness that will reduce exponentially the intensity of a beam of particles by a factor of 2. The half-value thickness in (µm) for lead assuming X-ray beam of wavelength 20 pm, µ = 50 cm^-1 for X-rays in lead at wavelength λ = 20 pm, is ______ µm.

Options

• 130

• 135

• 137

• 139

Answer 1

The half-value thickness of an absorber is defined as the thickness that will reduce exponentially the intensity of a beam of particles by a factor of 2. The half-value thickness in (µm) for lead assuming X-ray beam of wavelength 20 pm, µ = 50 cm^-1 for X-rays in lead at wavelength λ = 20 pm, is 139 µm.

Explanation:

I = I₀e^-µx

`"I"_0/2` = I₀e^-µx

µx = ℓn2

x = `(ℓ"n"2)/mu`

= `0.693/50`

= 0.01386 cm

= 138.6 µm ≃ 139 µm