Basic Atomic Structure and the X-ray Tube

• The atom is considered the basic building block of matter
• The atom as three fundamental components: electrons, neutrons, and protons
• The atom has a nucleus made of protons and neutrons
• Orbiting the nucleus are electrons in defined energy levels and distances from the nucleus
• The proton has a positive electrical charge
• The neutron has no electrical charge
• The electron has a negative electrical charge
• The electron moves extremely fast in its orbit and has a significant amount of kinetic energy
• Electrical charge is a characteristic of matter
• If an atom has an equal number of protons and electrons there is no net charge since they are equal and cancel each other out
• If there are more protons than electrons there is a positive charge and if there are more electrons than protons there is a negative charge
• The nucleus is held together by a strong nuclear force, creating a binding energy
• The law of electrostatics: like charges repel each other and opposites attract
• The binding energy creates a very strong attraction in the nucleus that overcomes the natural tendency for like charges to repel
• The binding energy is what holds the protons and neutrons together to form the nucleus of the atom
• Nucleons are protons and neutrons within the nucleus
• The mass of the nucleus is always less than the sum of the masses of nucleons because some of the mass is converted to energy to hold the nucleus together
• The difference in the nucleus mass is called the mass defect
• The mass defect represents the energy necessary to hold the nucleus together
• Binding energy is also a measure of the amount of energy necessary to split an atom (to break it apart)
• Nuclear binding energy happens when a particle strikes the nucleus with energy equal to the nucleus' binding energy
• Nuclear bindng energy is expressed in megaelectron-volts (MeV)
• The force of attraction between the electrons and protons keeps the electrons in orbit
• The electrons are held in their orbits by electron binding energy
• The closer the electrons are to the nucleus, the stronger is its binding energy (expressed in electron-volts (eV))
• Both nuclear binding energy and electron binding energy are key determinations of x-ray production
• Characteristic interactions involve the removal of orbital electrons from atoms
• The penetrating strength (energy) of the x-ray photon produced depends on the difference in electron-binding energies of the electron shells involved
• Bremsstrahlung interactions involve attraction to the nucleus of the atom, and the penetrating strength (energy) of the x-ray photon produced depends on nuclear binding energy
• An atom has defined energy levels, each at a different distance from the nucleus. These energy levels are called electron shells and describe a sphere around the nucleus
• Electrons do not all occupy the same orbit at the same distance from the nucleus
• Electrons orbit three dimensionally around the nucleus and not in a single plane
• Each electron shell of an atom is lettered beginning with K nearest to the nucleus and moving outward with L, M, N, O, P, and so on
• The K shell has the greatest electron-binding energy
• Binding energy decreases with each subsequent shell
• The maximum number of electrons that may occupy each shell can be found by using the formula 2n^2, in which n represents the shell number, beginning with the K shell as 1
• Electromagnetic radiation has no mass, carries energy in waves as electric and magnetic disturbances in space, and travels at the speed of light
• The electromagnetic spectrum is a way of grouping the different electromagnetic radiaitons
• All of the members of the electromagnetic spectrum have the same velocity (the speed of light) and vary only in their energy, wavelength, and frequency
• The members of the electromagnetic spectrum from lowest energy to highest are radiowaves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays