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http://epa.gov/radiation/understand/ionize_nonionize.html
http://www.medicalradiation.com/facts-about-radiation/what-is-radiation/ionizing-radiation
HOLY FAMILY UNIVERSITY
RADIOLOGIC SCIENCE PROGRAM
RADS-215 IMAGING PHYSICS I: X-RAY PHYSICS
RADIATION: Radioactive Decay, Ionizing Electromagnetic and Cosmic/Extraterrestrial
I. RADIATION (Radiant Energy):
A. DEFINED -
•Energy transportation through space and time facilitated by the combination of electric
and magnetic fields.
•Energy emitted/transmitted in Wave (photon) or Particle (mass) form.
•A process by which particles (protons/neutrons/electrons) and/or photons
(X/gamma rays) are emitted/transmitted.
•An energy transfer or release from an atom as the result of nautral (radioactivity) or
artificial (ionizing) means.
NOTE: Not all forms of Radiant Energy (radiation) are capable of producing ionization that
may lead to biologic damage. (See Electromagnetic Spectrum)
B. TYPES OF -
1. Radioactive Decay (Radioactivity)-
•The ability of certain Nuclides (atoms/proton and neutron combinations), having
unstable nuclei (proton and neutron combinations), to change their inherent atomic
structure through random releases of atomic particles (protons/neutrons/ electrons)
which allow the atom to change/form into other Nuclides/Atoms.
226
Ra
222
Rn +
4
α++ (Alpha particle)
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•Each chemical element’s nucleus contains a specific number of protons (atomic #/Z).
Their is an “optimum” number of neutrons that should also be included within the
nucleus for the atom’s nucleus to exist in a stable state. If too few (or many) neutrons
are contained within the nucleus, particles (Alpha or Beta) &/or electromagnetic
radiation (Gamma rays) will be emitted by the nucleus until the nucleus reaches a
stable state. α
•Types of Radiation/Radiant Energy emitted through Radioactive Decay:
•Alpha Particle -
(Large mass /+2 Charge)
(
4
He++
)

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•Beta Particle - (e-) negatron OR (e+) positron
(Small mass / Charge)
•Gamma Rays - (Electromagnetic waves/Photons)
(No mass / No Charge)
2. Extraterrestrial/Cosmic-
•Primary Cosmic rays (Helium nuclei, protons, neutrons, high energy electrons, and
Gamma rays) interact with the Earth’s atmosphere causing ionizations and/or atom
splittings which produce mesons (+, -, N), high energy electrons, and Gamma
rays that penetrate down to the Earth’s surface.
3. Electromagnetic (EM) Radiation-
•EM waves are typically produced by the motion of electrically charged
particles. These waves are also called "electromagnetic radiation" because they have
the characteristic properties of electromagnetic photons. They travel
through empty space (i.e., vacuum) as well as through gas and other matter.

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•EM radiation has a “dual personality." In addition to behaving like waves, EM photons
also behave like moving particles (i.e., alpha, beta), but have no mass & no charge.
•EM photons having the highest energies (eV/keV) have the shortest
wavelengths (λ) and highest frequencies (ν). (see Wave & Particle Theories)
3a. Ionizing Electromagnetic Radiation-
•EM photons (X or Gamma Radiation) that, upon interacting/colliding with bound
orbital electrons of atoms, cause ionization (i.e., remove electrons).
•EM photons are simply “bundles of energy” having No Mass & No Charge traveling
through space and time.
•EM photons travel in wave form - producing both electric and magnetic components.
•EM photons travel at the Velocity of Light – 3 x 108
m/s or ~186,000 mile/s in a vacuum.
•EM photons can be produced Artificially/man-made (X-rays) or occur Naturally
through radioactive decay (e.g., Gamma rays).
•Specific Frequencies (ν) and Wavelengths ( λ) control EM photon Energies (keV) - that
may be sufficient to cause Ionization.
3b. Non-Ionizing Electromagnetic Radiation-
•Radiowaves, Microwaves, Infrared, Visible light/White light, and
Ultraviolet light are types of “Radiant Energy” that also travel through space and
time at the Velocity of Light.
•Travel in in wave form - producing both electric and magnetic components.
•Travel at the Velocity of Light – 3 x 108
m/s or ~186,000 mile/s in a vacuum.
•Specific Frequencies (ν) and Wavelengths ( λ ) also control photon Energies (eV) - but
are not sufficient to cause Ionization.
Nonionizing EM radiations Ionizing EM radiations

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C. LIKELIHOOD OF RADIATION’S INTERACTION WITH MATTER -
1. Alpha Particle 4
He
++ (helium nucleus) 4α++ -
•Due to its extremely large physical mass/size, the alpha particle has a greater likelihood for
having interactions with matter.
•Having a large mass, the alpha particle generates great:
•momentum (p = m•v)
•kinetic energy (K.E. = 1/2mv2 )
•Einstein's Equation (E = mc2 ) - Mass can be converted to Energy and vice versa.
•Having a relatively high charge (+2), the alpha particle is electrostatically attracted to
bound orbital electrons - increasing its likelihood for having interactions with matter.
•• Highly Ionizing ••
2. Neutron (Fast OR Slow) -
•Due to its large physical mass/size, neutrons have a greater likelihood for having an
interaction with matter.
•Having a relatively large mass, the neutron generates great:
•momentum (p = m•v)
•kinetic energy (K.E. = 1/2mv2 )
•Einstein's Equation (E = mc2 ) - Mass can be converted to Energy and vice versa
•Being absent of charge, the neutron’s interaction with matter is more random than alpha.
•• Highly Ionizing ••
3. Beta Particle ((e-) Negatron OR (e+) Positron) -
•Due to its small physical mass/size, the beta particle has little likelihood for having an
interaction with matter.
•Having a relatively small mass, the beta particle generates little:
•momentum (p = m•v)
•kinetic energy (K.E. = 1/2mv2 )
•Einstein's Equation (E = mc2 ) - Mass can be changed into Energy & vice versa
•Having a charge ((e-) negatron OR (e+) positron), the beta particle is electrostatically
attracted to either the atomic nucleus - where it can undergo a rapid deceleration,
producing Bremsstrahlung x-rays OR bound orbital electrons - increasing its likelihood
for having an interaction with matter.
•• Low Ionizing capablities ≥ Ionizing Electromagnetic Photons ••
4. Ionizing Electromagnetic Radiation (IER) -
•Photons (X or Gamma Radiation) are simply bundles of energy (keV) having NO Mass &
NO Charge traveling through space and time in straight lines.
•Being absent of mass & charge, X & Gamma Radiations’ interactions with matter are
totally random.
•Since X & Gamma photons is absent of mass & charge little kinetic energy (keV) is
transferred to matter during interactions.
•• Low Ionizing capabilities compared to particulate radiations ••
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