Question

1. The absorption of x-rays in a patient occurs via the photoelectric effect, which produces an electron and a photon. Describe this absorption process in about 3-4 sentences and a diagram. What is the fate of these products?

2. The optimal x-ray energy for producing high contrast images is approximately in the range 20-40 keV. In terms of what we know about how x-rays interact with atoms, discuss the main mechanisms that determine this optimal range and what happens to the images for energies outside this range.?

Answer 1

Answer:

(1.)

• Description of the absorption process :

The absorption of x-rays in a patient occurs via the photoelectric effect. The process of this photoelectric effect is as follows:

When energetic X-ray incident on atom, the X-ray photons interact with the inner shell ( K - shell ) and gives its energy to the inner shell electron and that electron ejects from the atom. This ejected electron is called the photoelectron.

Due to this ejection of photoelectron, a void is created in K - shell and an electron from higher energy shell ( L - shell) comes to fill that void ( in K - shell ) releasing some energy. This released energy gives rise to characteristic photons causing secondary radiation.

• The fate of the products :

   The photoelectron produced during this process has very low energy still it continues to interact with inner shell electrons as long as it has some energy and then it is completely absorbed.

The characterisctic photon produced during X-ray absorption also has very low energy. It can not leave the body and gives rise to secondary scatter radiation.