TOPIC: BASICS OF X-RAY
🌟 IMPORTANT POINTS TO REMEMBER
🔹Hard rays: X-rays having shorter wavelengths have great penetrating power and are called hard rays.
🔹Soft rays: X-rays having longer wavelengths possess less energy and less penetrating power. These are called Grenz rays.
🔹Thermionic emission: It can be defined as the phenomenon of emission of electrons by metal when it is heated. The electron stays in an electron cloud until a high-voltage circuit is activated. The electron emitted under this action is called thermion.
🔹Bremsstrahlung radiation: It is defined as X-ray radiation produced when high-speed electrons are suddenly stopped at the target. It is the primary source of X-ray production from an X-ray tube. This process of rapidly decelerating the high-speed electron gives rise to bremsstrahlung or braking radiation. It is called bremsstrahlung, the German word for breaking radiation. It is also called general radiation, white radiation or brems radiation.
🔹There are two types of collision, direct heat and near miss.
🔹Characteristic radiation: The X-rays that result from this process have discrete energies characteristic of the target atoms; hence, they are called characteristic rays.
🔹Photon lines: The photon lines are named K and L depending on the shell from which they have emitted.
🔹Critical voltage: Characteristic K lines are not produced by X-ray tubes with tungsten targets operating at less than 69.5 V referred to as critical voltage. As the energy of incident electron increases above the threshold energy, the percentage of characteristic radiation is also increased.
🔹Line spectrum: In the case of characteristic radiation, there is generation of line spectrum.
🔹X-ray spectra can be of the following types: continuous spectrum, line spectrum and combined spectrum.
🔹Inverse square law: The intensity of an X-ray beam at a given point, i.e. number of photons per cross-sectional area per unit time, is dependent on the distance of the object from the focal spot.
🔹Heel effect: The intensity of the X-ray beam on the anode side of the X-ray tube is significantly less than that on the cathode side. It is called the heel effect. The reasons for this effect to occur are self-absorption and inverse square law.
🔹X-ray can cause ionisation, chemical effects, biological effects, photographic effects, colour changes, heating effects and fluorescence.
🔹Half-value layer: It is the required thickness of a material which reduces the beam intensity to one-half. Aluminium and copper are the materials that are commonly used to describe the half-value layer.
🔹Factors that control the X-ray beam are tube voltage, kVp, exposure time, tube current, milliampere seconds, atomic number of target and source to film distance.
🔹Coherent scattering (Thompson effect, Rayleigh scattering, elastic scattering, unmodified scatter or classic scattering): When a low-energy X-ray photon passes near an atom’s outer electron, it may not be absorbed but scattered without a loss of energy. It is called as coherent scattering.
🔹Compton effect (inelastic scattering, modified scattering or incoherent scattering): It occurs when a photon interacts with a free or loosely bound outer electron.
🔹Photoelectric effect: It is pure absorption interaction predominating with low-energy photons. It is a form of absorption of X-ray photons by matter. As this effect occurs under the influence of light, it is called the photoelectric effect.
🔹Pair production: When a photon having energy more than 1.02 MeV passes near the nucleus of an atom, it is subjected to a strong nuclear field. A photon may interact with the electric and magnetic fields of the nucleus in such a way that the photon is stopped and its energy is converted into two particles, a positive (positron) and negative (electron) pair.
📌 USES OF X-RAY RADIATION
- Radiology: Diagnosis in the dental and medical field.
- Radiotherapy: Treatment of neoplasm.
- Industrial and art radiography: Examination of gross structure (casting, welds, old painting, etc.). X-rays are also used to detect faults, cracks, flaws, and gas pockets in finished metal products.
- Spectroscopy: Identification of elements, and their atomic number and structure.
- Radiobiology: Alteration of cells and tissues for experimental purposes.
- Crystallography: Analysis of molecular structure is done with the help of X-ray.
- Sterilisation: Preservation of food.
- Digital radiography: X-rays can activate the charge-coupled device (CCD) used in digital radiography.
- Xeroradiography: X-rays can neutralise electric charges in selenium-coated plates.
- Detective department: X-rays are used by detective agencies for the detection
📌 MULTIPLE CHOICE QUESTIONS (MCQs)
💡X-rays with shorter wavelengths have great penetrating power and are called
a. Soft rays
b. Grenz rays
c. Hard rays
d. None of the above
Answer: c
💡The phenomenon of emission of electrons by metal when it is heated is called
a. Ionisation
b. Excitation
c. Thermionic emission
d. None of the above
Answer: c
💡The process of rapidly decelerating the high-speed electron gives rise to
a. Bremsstrahlung radiation
b. Characteristic radiation
c. Heterogenous radiation
d. None of the above
Answer: b
💡The X-rays produced by the process of displacement of electron from a shell of target atom by a bombarding electron is called as
a. Grenz rays
b. Hard rays
c. Characteristic rays
d. None of the above
Answer: c
💡The efficiency of X-ray production will increase with
a. Increasing electron energy
b. Decreasing electron energy
c. Increasing atomic number of target
d. Both a and c
Answer : d
💡The spectrum consisting of X-ray photons of low energies is called
a. Continuous spectrum
b. Line spectrum
c. Combined spectrum
d. None of the above
Answer: b
💡The distance considered when exposing the dental radiograph includes
a. Target to source distance
b. Target to object distance
c. Target to film distance
d. All of the above
Answer : d
💡The intensity of X-ray beam on the anode side is significantly less than that on the cathode side, which is called
a. Bragg effect
b. Heel effect
c. Compton effect
d. Photoelectric effect
Answer: b
💡Minimum kilovoltage required for dental radiography is
a. 65–100
b. 50–90
c. 40–60
d. 55–65
Answer: a
💡The materials which are commonly used to describe half-value layer are
a. Copper and tungsten
b. Lead and copper
c. Aluminium and copper
d. Molybdenum and tungsten
Answer: c