The following equation shows this relationship.
C = λν
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 = hν
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. X-
rays, on the other hand, originate from transitions between electronic energy levels
(orbital electron shells).
2-5. X-RAY TUBE
a. All modern x-ray tubes are known as Coolidge tubes (Figure 2-1). In this
tube, electrons are supplied by an electrically heated filament. The electrons are
accelerated by a high electric field to the anode or target. When an electron strikes the
target, part of its energy is degraded to heat (~99%) and the remainder goes toward
producing x-rays. As the voltage (potential) is increased, the minimum wavelength
radiated decreases, thus producing higher energy x-rays. Very few electrons give up
their total energy in a single encounter; therefore, many photons of energy lower than
that expected will be produced.
b. The current, which heats the filament, is sometimes referred to as the tube
current. As the current is increased, the number of electrons produced is increased.
Increasing the number of electrons increases the number of x-rays produced.
Therefore, we can say that an increase in the tube current increases the quantity of x-
rays. Tube current is expressed in terms of milliamperes (mA).
c. In expressing x-ray energies, it is customary to state the peak kilo-voltage
(kVp) used. Increasing the potential, or kVp, increases the acceleration and the energy
of the electrons. This results in the production of higher energy x-rays. If electrons are
accelerated across a potential of 100 kVp, we can produce x-rays having a maximum
energy of 100 kilo electron volts (keV). So we can say that increasing the kVp will