MACHINE-PRODUCED RADIATION SOURCES

a. Although there are a number of different machines designed to produce ionizing radiation, the one most commonly found, particularly in a medical facility, is the x-ray machine. X-ray machines play an important role in medical diagnosis and for this reason they are abundant. A medical center may have as many as 25 to 100 separate x-ray or fluoroscopy units.

b. X-rays, visible light, and gamma rays are all electromagnetic waves because they consist of oscillating electric and magnetic fields. These electromagnetic radiations (EMR) can be arranged on a scale of wavelength, frequency, or energy content. Electromagnetic radiations create wavelike disturbances in space similar to the disturbances created if a stone is dropped into the center of a pool of water. A series of crests and troughs are formed and these constitute an electromagnetic wave. The distance between any two successive crests or troughs is known as the wavelength (l). In a vacuum, all EMR travel at the speed of light (3 x 1010 centimeters /second). The number of waves (crests) passing a certain point per unit time is referred to as the frequency (n). The frequency will decrease as the distance between crests (wavelengths) increases.

The following equation shows this relationship.

c = ln

C represents the speed of light and is a constant value. Thus, if frequency is increased, wavelength must decrease. If wavelength is increased, frequency must decrease.

c. When discussing EMR, we refer to the energy (E) of radiation quite often and there is also a relationship between energy and frequency. This relationship can be expressed using Planck's constant (h) as follows:

E = hn

Therefore, if we increase the frequency, the energy increases. Similarly, if we consider wavelength--as the wavelength decreases, the energy increases. Thus, short-wave radiations have higher energies than long-wave radiations.

d. Electromagnetic radiation does not possess any electrical charge; that is to say, it is electrically neutral. X-rays have the same properties as gamma rays; they differ only in origin. Gamma rays are emitted from the nucleus of an unstable atom. Xrays,on the other hand, originate from transitions between electronic energy levels (orbital electron shells).