What is off focus radiation in operation of x-ray tube?

Off focus radiation is the X-rays that are emitted from areas of the X-ray tube other than the focal spot. Off-focus radiation can be caused by several factors, including:

* Electron scattering: Some of the electrons emitted from the cathode will scatter before they reach the anode, resulting in off-focus radiation.

* Bremsstrahlung radiation: Bremsstrahlung radiation is emitted by electrons that are rapidly decelerated near the anode, and some of this radiation may be off-focus.

* Characteristic radiation: Characteristic radiation is emitted by the atoms of the anode when they are ionized by the X-ray photons, and some of this radiation may be off-focus.

While lead collimation can reduce off-focus radiation by blocking the majority of the radiation emitted from the non-target area, it is necessary to consider the beam divergence (ie, the natural spreading of the x-ray beam as it travels from the tube) when designing the collimator. Beam diverges due to the fact that electrons leave the focal point at different angles to strike the anode, which in turn produces radiation as a cone-shaped distribution instead of a straight beam. As a result, the collimator must be large enough to allow for the beam divergence and still block off-focus radiation. The shape and dimensions of the collimator will depend on the specific X-ray tube and the desired size of the X-ray beam.

Off focus radiation can be a significant source of radiation exposure for patients and staff, and it is therefore important to take steps to minimize it. This can be done by using lead collimation, ensuring that the X-ray tube is properly aligned, and using shielding to block off-focus radiation.