Chapter 5 The Types of Radiation

Types of Radiation There are two main types of radiation involved in the production of radiographs and in radiology. They are primary radiation (produced in the tube) and secondary radiation (a result of primary radiation striking another object).

Types of Radiation

Primary Radiation There are two types of primary radiation: Bremsstrahlung (AKA Braking or White radiation) Characteristic Radiation.

Bremstrahlung Radiation is a variable process that can give up a lot or little energy. They are produced by a slowing of electrons by the pull of the nucleus of an atom on the target. This results in the variable x-ray wavelengths produced (due to the conservation of energy).

Characteristic Radiation is characteristic of the material of the target. The x-ray produced is a result of excess energy from one shell to another. A fast traveling electron going toward a target will eject an electron in an atom of the target material. The resultant x-ray produced is due to the atom which has lost an electron wanting to return to stability.

Characteristic Radiation To do this an electron from an outer shell will drop into the vacancy. The excess energy which is due to the two different energy levels in dropping from one shell to another is liberated in the form of characteristic radiation.

Secondary Radiation is produced by primary radiation striking any object. There are two types of secondary radiation - scattered rays and characteristic rays.

Secondary Radiation Scattered rays are caused by x-rays striking organic substances (of less atomic weight than aluminum); they are heterogeneous and scattered in all directions. There are two types of scattered rays that occur at the energy levels we deal with:

Secondary Radiation Photoelectric effect - the incoming photon gives up all energy and emits an electron. A Characteristic event could occur. This often takes place in the patients skin at a lower energy levels. Lower energy levels have a higher probability of having interaction in the patients tissues. This is not good for patients skin dose.

Secondary Radiation Comptons effect - this takes place at higher energy levels. An incoming photon strikes an electron, usually in the outer shell . The photon is deviated from its original path. Energy is decreased. At high energy levels the photons are deflected but still make their way on to the film and produces fog. Increased kV = more compton scattering and the film becomes more gray.

Secondary Radiation Characteristic rays are caused by x-rays striking metallic substances (of greater atomic weight than aluminum); these are homogeneous (all of the same wavelength) and the wavelength is characteristic for the metal that is struck.

Secondary Radiation Scattered radiation from the soft tissues of the body is responsible for film haziness and low film contrast. The methods used for eliminating some of the scattered radiation is detailed in the next section.

Secondary Radiation Characteristic radiation is unimportant in radiography but very important in therapy. The filter interposed between the tube and the patient may itself give off a characteristic radiation softer than the rays which it filters out.

For Best Film Image: Best for Patient: Low kV & High MAS Radiation Summary For Best Film Image: Low kV & High MAS Best for Patient: High kV & Low MAS