ionizing radiation Flashcards
Matter:
Anything that has mass and occupies a space
▪ The atom is the basic unit of all matter
▪ Nucleus: Protons + Neutrons
Atomic number (Z)
Number of protons
▪ Same as #of electrons in a neutral atom
▪ Determines the identity of the atom
Atomic mass (A)
Atomic mass (A)
▪ Number of protons + neutrons
tungsten numbers
z=184
a=74
BINDING ENERGY
The amount of energy required to remove an electron from its shell.
• Measured in electron Volts (eV)
binding energy and electron shells
Within a given atom, inner shells electrons are more tightly bound (K>L>M, etc), more energy needed
binding energy and atomic number
higher atomic number creates more electron attraction causing higher binding energy
Ionization
▪ Electron = protons →Neutral atom
▪ Process of forming a positive and negative ion by removal of an electron from an neutral atom
▪ If a neutral atom loses an electron becomes a positive ion and the free electron becomes a negative ion.
▪ To ionize an atom, we need sufficient external energy to overcome the electrostatic forces and free the electron
Radiation, theories?
▪ Is the transmission of energy through space (vacuum) andmatter
▪ It may occur in two forms: wave theory or quantum(particles) theory
▪ Wave theory: explains the propagation of radiation
▪ Quantum theory: explains the interaction of radiation withmatter.
Waves Theory:
▪ Propagation of radiation in form of waves (no mass) traveling at the speed of light
▪ Why electromagnetic? Movement of energy through space as a combination of electric and magnetic fields.
wavelength and frequency
low and high energy?
Wavelength: Distance between two successive crests
Frequency: Number of wavelength passing a particular point in time.
speed of light= product of these (constant)
High energy radiation: High frequency, short wavelength
Low energy radiation: Low frequency, long wavelength
ionizing and non-ionizing electromagnetic radiation
Non-Ionizing
▪ Does not have sufficient energy to eject an electron from the shells
Ionizing
▪ Have sufficient energy to eject an electron from the shells (some UV, x rays and gamma rays)
Quantum theory of Radiation
based on Particles not waves
▪ Quantum theory: explains the interaction of radiation with matter.
▪ Considers radiation as small discrete bundles of energy called photons.
▪ Each photon has energy (eV), mass and travels in straight lines at the speed of light.
▪ Electrically charged (except neutrons and x-rays)
Quantum theory of Radiation energy
▪ Energy: Directly proportional to frequency, inversely proportional to
wavelength.
▪ High frequency means short wavelength →High energy
▪ Low frequency means long wavelength →Low energy
Linear energy transfer (LET)
ionizing rate
▪ Rate of loss of energy from a particle as it moves through matter
▪ Depends on velocity, charge and size.
– Lower velocity, higher charge and bigger size →Greater LET
– Higher LET: Less penetration because they lose their energy after short distances
alpha particles with high LET (high mass and charge) = low penetrance
