# Photon Energy and Compton

1. Jul 12, 2004

### Mc?

The textbook used in an x-ray physics class states that:

1) The probability of compton interactions occurring in tissue decreases with increasing photon energy (1/e)

2) The probablity of Photoelectric (PE) interactions occurring in tissue decreases with increasing photon energy by 1/e cubed.

3) The number of compton interactions relative to PE increases with increasing photon energy based on the relationship of 1/e to 1/e cubed

The author then gives a table that list the percentages of compton and PE interactions at various kVp settings that states:

a) At 50 kVp, >99% of the photons are absorbed and 21% of the interactions are compton

b) At 100 kVp, 96% of the photons are absorbed and 63% of the interactions are compton

Based on the information in the table it appears the actual number of Compton interactions will increase with an increase in photon energy.

100 Photons produced @ 50 kVp - 99% absorbed and 1 transmitted - 20.8 Compton (21% of 99)

100 photons produced @ 100 kVp - 94 absorbed and 6 transmitted - 59 Compton (63% of 94)

What does increasing photon energy do to the actual number of compton interaction occuring in tissue?

Thank you.

Mc?