Physiology: X-rays Definition

X-rays Definition

• X-rays are a type of electromagnetic radiation with a wavelength between 0.01 to 10 nanometers (nm).
• They are generated when high-energy electrons collide with a metal target, such as tungsten or copper, in an X-ray tube.
• X-rays are characterized by their high energy and ability to penetrate materials, making them useful in medical imaging and other applications.

Structure of the Atom

• The atom consists of a massive, positively charged nucleus surrounded by electrons in orbits of specific diameters.
• The nucleus is composed of protons and neutrons, held together by a strong nuclear force.
• The diameter of the nucleus is approximately 5 x 10^-15 meters, while the entire atom has a diameter of about 5 x 10^-10 meters.

X-ray Production

• X-rays are produced when high-energy electrons interact with atoms in the anode of an X-ray tube.
• There are two main types of X-ray reactions: Bremsstrahlung radiation and characteristic X-rays.

Bremsstrahlung Radiation

• Bremsstrahlung radiation occurs when high-energy electrons are slowed down or "braked" by the metal target, and the energy lost is emitted as X-rays.
• The energy and frequency of the X-rays produced depend on the energy of the electrons and the atomic structure of the metal target.

Characteristic X-rays

• Characteristic X-rays occur when high-energy electrons knock inner-shell electrons out of the metal atoms in the anode.
• Outer-shell electrons fill the resulting vacancies, releasing energy in the form of X-rays with characteristic frequencies.
• Characteristic X-rays are useful in identifying specific elements in materials and can also be used in medical imaging for specific diagnostic purposes.

X-ray Spectrum

• The X-ray spectrum is a graphical representation of the intensity of X-rays as a function of their energy.
• The spectrum is typically divided into two main components: the continuous or Bremsstrahlung spectrum and the characteristic spectrum.

Filtration

• In X-ray imaging, a filter is a device that selectively absorbs certain wavelengths or energies of X-rays, while transmitting others.
• The purpose of using a filter is to modify the X-ray spectrum, optimizing image quality and reducing patient radiation dose.
• Filters can be made from a variety of materials, such as aluminum, copper, and rare-earth elements.

Interaction with Matter

• When X-rays interact with matter, they can be absorbed, scattered, or transmitted.
• The number of X-rays that are absorbed, scattered, or transmitted depends on the type of material and the energy of the X-rays themselves.
• X-rays are particularly useful in medical imaging, as they penetrate soft tissues, such as skin and muscle, but are absorbed by denser materials, such as bone.

Photoelectric Effect

• The photoelectric effect is an interaction in which an X-ray photon collides with an atom and is completely absorbed, ejecting an inner-shell electron from the atom.
• The energy of the X-ray is transferred to the ejected electron, which is then called a photoelectron.
• The photoelectric effect is important in medical imaging because it produces high-contrast images that are useful for detecting tumors and other abnormalities.

Compton Scattering

• Compton scattering is an interaction in which an X-ray photon collides with an outer-shell electron, causing the electron to recoil and the X-ray to scatter in a new direction.
• The energy of the scattered X-ray is lower than the original X-ray, and the degree of scattering depends on the angle of the collision and the energy of the X-ray.
• Compton scattering is important in medical imaging because it produces low-contrast images that are useful for detecting bone fractures and other structural abnormalities.

Pair Production

• Pair production occurs when an X-ray photon interacts with the electric field of a nucleus and converts it into an electron and a positron.
• Coherent scattering occurs when an X-ray photon collides with an atom and causes the atom to vibrate, producing a scattered X-ray with the same energy and wavelength as the original X-ray.