Production of x-rays
The production of x-rays occurs as a result of a sequence of events. The evacuated x-ray tube is a device for producing free electrons from heated tungsten filament. this process of production of x-rays called thermionic emission.
Prerequisite for x-rays production
These are the requirements for x ray production-
- Source of electron
- Method of accelerating electron
- An Obstacle free path for passage of high-speed electron
- Target in which electrons can interact, releasing energy in the form of X-rays.
- An envelope (tube) to provide a vacuum environment, eliminating air molecules which are obstacles for electron stream and preventing rapid Oxidation of elements.
Basically X- ray tube consists of cathode (-ve ) side and anode (+ve) side, encased in a glass envelope which is evacuated to form a vacuum.
Process of x-rays production
The production of x-rays occurs as a result of a sequence of events. The evacuated x-ray tube is a device for producing free electrons from heated tungsten filament. The electrons remain in a constant agitated motion and their number increases as the temperature of the filament increased.
The electrons are focused towards the anode with the help of focusing cup made up of Molybdenum. Now, the filament or the cathode is given a very high negative electric potential and the target or the anode is given an equally high positive electric potential. The resulting strong electrical field causes the cloud of electrons near the filament to rush up at a high speed through the vacuum tube and bombard the target at the focal spot.
The movement of electron from cathode to anode is called as Tube current. This results in several types of interactions with the target material in the x-ray tube. More than 99% of the kinetic energy of electrons is converted into thermal energy. Approximately less than 1% of the remaining kinetic energy is irradiated as X-rays.
When the exposure is terminated, x-rays are no longer present in the room or in the patient since, the x-rays travel at the speed of light. X-rays produced are traveling in all directions. The lead housing surrounding the x-ray tube will absorb most of the x-radiation. The useful x-rays are those x-rays that pass through the tube window and help to produce the radiograph. The useful x-rays that leave the tube housing are called the ‘primary x-ray beam’.