X-ray production

X-rays are produced due to sudden deceleration of fast-moving electrons when they collide and interact with the target anode. In this process of deceleration, more than 99% of the electron energy is converted into heat and less than 1% of energy is converted into x-rays.

Definitions

Generator

An x-ray generator gives power to the x-ray tube. It contains high voltage transformers, filament transformers and rectifier circuits. 

Cathode

The cathode is the negative terminal of an x-ray tube. It is a tungsten filament and when current flows through it, the filament is heated and emits its surface electrons by a process called thermionic emission.

Kilovoltage

High voltage, in the kilovolt range (1000 volts), is applied between the cathode and anode. This causes electrons to move towards the positive terminal (anode) of the tube at a velocity of half the speed of light (c).

Effective energy is the overall energy of a spectrum of photons that has the same penetrating power as a mono-energetic beam. In X-ray production, effective energy is 30 to 40% of the peak kVp applied to the X-ray tube ².

Anode

The positive terminal of the tube. It is made of a tungsten disc in ordinary diagnostic x-ray tubes and molybdenum in mammography x-ray tubes. Fast-moving electrons interact with the anode in the following ways: 

• interaction with K-shell electron: causes the production of characteristic radiation

• interaction with nucleus: causes bremsstrahlung radiation

• interaction with outer shell electrons: causes line spectrum