X-rays is a form of electromagnetic radiation which is part of the electromagnetic spectrum. They have short wavelengths ranging between 10 to 0.01 nanometres. The energy of X-rays, like all electromagnetic radiation, is inversely proportional to their wavelength as given by the Einstein equation:
E = hν = hc/λ
Where E = energy
h = Planck's constant
ν = frequency
c = velocity of light
λ = wavelength
Therefore, X-rays have very high energies (Nelson, 2008).
X-rays are widely used in various fields today; however their most prominent use is the medical field.
Production of X-rays
X-rays are usually generated in an X-ray tube. This tube consists of an evacuated chamber with tungsten filament at one end of the tube (cathode), and a very hard metal target at the other end (anode). The electric current running through the tungsten filament is supplied by a high voltage supply, which causes it to expel fast moving electrons. Electrons are required to propel at high speeds as energy possessed by X-rays photons is dependent on the velocity of electrons (NDT Resource Centre, n.d.). The electrons are focused to a small spot on the anode; hence, they acquire high kinetic energy level upon reaching the target. X-ray photons are then produced in the form of Characteristic X-rays or Bremsstrahlung X-rays upon striking atoms in the metal target (Nelson, 2008).
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Bremsstrahlung, German word for 'braking radiation', is the process that produces the most X-ray photons (Sprawls, n.d.). As electrons emitted from the cathode are accelerated towards the metal target, these electrons with high energies interact with atoms of the metal target. The electrons penetrate the metal material and travel closely to the nucleus of target. They then deflect away due to electromagnetic interaction and at the same time, slowed down by the attractive force from the nucleus. During this encounter, high energy lost by electrons appears in the form of higher energy and frequency of emitted X-ray photons according to Law of Conservation of Energy (Sprawls, n.d., Nobel Prize Organization, n.d.). Refer to Figure1.
Figure 1: The generation of Bremsstrahlung X-rays
Characteristic X-rays are produced through K-shell emission. This interaction involves the collision between the emitted electrons travelling at high speeds and the orbital electrons in atoms of metal targets. This only occurs if the incident electron has kinetic energy greater than the binding energy of electron within the atom. The incident electron will lose all its energy instantaneously. When the collision occurs, the orbital electron is knocked out by high speed electrons from cathode. The dislodged electron results in a vacancy which is then filled by another electron from higher energy level (Sprawls, n.d.). As electrons make transitions to lower energy levels, Characteristic X-rays are generated with quantum energy equal to the transition (Connolly, 2007). Since collision between emitted electrons and the orbital electrons leads to loss of energy, by Law of Conservation of Energy, this results in the release of X-ray photons of energy equal to the energy loss (Connolly, 2007). Maximum energy and frequency of Characteristic X-rays depends on the energy of incident electrons. Refer to Figure2.
Figure 2: Generation of Characteristic X-rays
Applications of X-rays
The applications of X-rays revolve around medical imaging, for example: radiography and fluoroscopy.
The applications of X-rays are based on their ability to pass through matter of different substances. Their penetrating ability depends on the density of the matter; hence, this allows X-rays to provide a powerful tool in the medical field for mapping internal structures of human body (Nelson, 2008). It helps in diagnosing and treating numerous medical conditions. X-rays with high energy produced through X-ray tubes are allowed to pass through our body and then strike an X-ray detector. This detector, a special X-ray film, has been coated with a sensitive material and linked to a computer monitor. The film, also known as radiograph, creates an image showing shadows where our bones, organs and other dense masses of the X-rays absorbed. Parts of the body appear as black or white on the film (Rad Town USA, n.d.; Kurtus, 2007). As bones have relatively high density hence; it is more difficult for X-rays to penetrate compared to tissues, therefore will be absorbed. This property will enable doctors to determine position of fractures in bones as they will leave different images on the detector due to different density (Nelson, 2008; Food and Drug administrator Organization, 2009).
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Fluoroscopy is a method that provides real-time X-ray imaging. It follows the same concept as radiography. A fluoroscope works by capturing continuous series of images produced at a maximum rate of 25-30 images per second, hence, transmitting the information to a screen to display detailed motion in our body. The X-rays beams are usually provided to different sections of the body during fluoroscopy (International Atomic Energy Agency, 2010). Blood travelling through blood vessels, diaphragm moving up and down or food moving through the digestive tract can all be observed. Fluoroscopy is usually done during other diagnostic procedures for example, cardiac catheterization, whereby the condition of coronary arteries and the flow of blood through them can be evaluated (Modern Medical Modalities Corporation, n.d.).
Side effects of X-rays
As X-rays are ionizing radiation, these rays are capable of damaging living cells and the DNA of the cells by removing electrons from atoms of the cells (ionization) (Rad Town USA, 2009). This can subsequently lead to mutation in the DNA and cause random cell division which increases the rate of forming a cancerous tumour. Therefore, X-rays may bring about profound effects to living tissues (Wise, n.d.). However, the effects of X-rays in pregnant women are said to hold more risks compared to other people. The unborn child is more sensitive to the effects of radiation exposure because the cells of the developing baby are rapidly dividing and growing into specialized organs and tissues (American Society of Radiologic Technologists, 2010).
Although X-rays is said to have potential devastating effects on an individual such as genetic damage and cancer, chances of being harmed from medical x-rays are actually extremely small (Kurtus, 2007)
X-rays, whether generated in the form of Bremsstrahlung or Characteristic X-rays,
brings many substantial benefits to us in the medical field especially
in the health aspect. By radiography or fluoroscopy, this enables us to observe
internal structures of our body, which allows medical doctors to determine the
position of damage in the body. Through this, doctors can carry out medical
treatments to the patients and this increases the quality of life of many people.
Despite the benefits, side effects of X-rays are unavoidable. Therefore, it is important that
precautions are taken during X-ray tests to avoid any devastating effects on the patient.