Tox 310
Atomic & Nuclear Structure
- Atoms are composed of a nucleus with radius ~ 10-14 m and a surrounding cloud of
electrons travelling in orbits of ~10-10
- The nucleus is composed of nucleons: protons and neutrons
- ZAX represents a nuclide, X = element symbol
- Atomic number (Z): the number of electrons and protons in an atom. It determines the
chemical properties and position of on the period table
- Mass numbers (A): total number of nucleons (A – Z = # of neutrons)
- Atomic mass: An element may exist in nature as a mixture of isotopes with different
numbers of neutrons
- Isotopes: same number of protons but different number of neutrons
- Isotones: same number of neutrons but different number of protons
- Isobars: same number of nucleons but different number of protons
- Isomers: same number protons and neutrons (differ in nuclear energy state)
Subatomic Particles
Proton (p) 11H
- Charge is +1
- The nucleus of a hydrogen atom
- Mass is 1.007277 amu
Neutron
- Charge is 0
- Mass is 1.008665 amu
Electron
- Also known as a beta particle or ray, or a beta minus particle or ray
- Charge is -1
- Mass is 0.000548 amu
- Moderately penetrating (depends on the energy)
- Can be stopped by varying thickness of metal ionizing
Positron (e+ or β+)
- Also known as a beta plus particle or ray
- Identical to an electron but with a positive charge
- Charge is +1
- Mass is 0.000548 amu
- Exist only when in motion (when they slow or stop moving, they combine with an
electron and annihilate)
- Moderately penetrating (depends on energy); can be stopped by varying thicknesses of
metal;
- Ionizing hence can cause biological damage
- upon slowing down they annihilate with electrons and release energy in the form of 2
photons
Neutrino
- Emitted with 𝛽+; minimal interaction with matter; non-ionizing
Antineutrino
, - Emitted with with 𝛽-; minimal interaction with matter; non-ionizing
Photons
- Not technically a particle but behaves as a particle at higher energies
- Charge and mass are 0
- A bundle of energy travelling at the speed of light (3.0 x 108m/s)
- Photons include x-rays and gamma rays (γ)
- The only difference between x-rays and gamma rays is their mode of origin
- X-rays arise from transitions of electrons between shells of an atom or from interactions
between electrons and nuclei
- Gamma rays are ejected from a nucleus
- Highly penetrating
Alpha Particles
- Alpha particle, 42He, an atomic particle
- Charge is +2
- The nucleus of a helium atom (2 protons and 2 neutrons)
- Mass is 4.001506 amu
- Minimum penetrability
- Low risk from external exposure but damaging if ingested or inhaled; highly ionizing
Radiation
- Radiation: any combination of subatomic particles with sufficient kinetic energy to
interact with and transfer energy to objects that intersect their path
- Radiation can be ejected by radioactive nuclides or be generated by machines
- Gamma rays, electrons, positrons, and alpha particles can be ejected from nuclei during
decay of radioactive nuclides
- Radioactive nuclides occur spontaneously or produced artificially in machines such as a
cyclotron
- X- rays, electrons and gamma rays can be generated by machines: Diagnostic x-ray tubes,
linear accelerators, Cobalt 60 therapy units
Radiation Uses
- Diagnostic imaging: radiography, computed tomography, positron emission tomography
- Therapy: Linear accelerator, Cobalt 60 therapy machine, Strontium 90 applicators.
Brachytherapy, Nuclear medicine
Radiation Protection
- Radiation has a risk of harmful effects
- Exposure of patients for diagnostic imaging and therapy (benefit to individual outweighs
risk of harm)
- Occupational exposure
- E.g., mines exposed to radon gas
Excitation and Ionization
- Excitation: involves the displacing of an orbital electron from its ground state
- Ionization: involves the removal of an orbital electron from a neutral atom
Ionizing & Non-Ionizing Radiation
- Non-Ionizing Radiation: transfers energy but does not ionize material
- Ionizing: has sufficient energy to eject one or more orbital electrons from an atom or
molecule
, - Ionizing radiation has potential for important biological effects (e.g., cell killing, DNA
mutation)
- Directly ionizing radiation causes ionization immediately and continuously as it passes
through material (charged particles: electrons, alpha particles, protons)
- Indirectly ionizing only causes ionization after some type of interaction with the
material (particles with no charge: photons, neutrons)
Particulate & Electromagnetic Radiation
- Particulate: Atomic or Subatomic particles (Electrons, protons, neutrons, alpha particles)
- Electromagnetic: photons (X-rays and gamma rays)
Electromagnetic Spectrum
- Photons are described by frequency (number of waves per second), wavelength (distance
between waves) or energy
- Longer wavelength photons (e.g., radiowaves, microwaves) are described by their wave
properties (wavelength, frequency)
- Shorter wavelength photons (e.g, x-rays, gamma rays) are described by their energy
(E=hv)
- Gamma rays, x-rays and some ultraviolet rays are ionizing radiation
- Photons all travel at the speed of light; they only differ in their wavelength and frequency
and therefore energy.
- Wavelength is inversely proportional to energy
- Frequency is directly proportional to energy
Radiation Units
- Absorbed Dose: the energy absorbed from ionizing radiation per unit mass
- Exposure: the charge liberated by ionizing radiation per unit mass air
- Activity: the disintegrations of radioactive material per second
- The SI unit of energy is the Joule
- In radiological science the electron volt (eV) is used as a unit for energy
- 1eV is the energy acquired when an electron falls through 1 volt
- 1eV = 1.602 e-19 J
Atomic Energy Levels
- Electrons travel around the nucleus in orbits or shells: K, L, M, N
- The maximum number of electrons in each shell = 2n2, where n= shell number
- Valence electrons are responsible for chemical reactions and bonds between atoms
- The shells can be considered as energy levels where the energy depends on the on the
Coulomb (electrostatic) force of attraction between the nucleus (+) and the orbital
electron (-) (the electron binding energy)
- The binding energy is defined as the energy needed to remove an electron from its shell
- Electrons in shells closer to the nucleus will have a higher binding energy
- Electron binding energies are on the order of keV (thousands of electron volts)
Nuclear Energy Levels
- While atomic structure is based on electrostatic force (the attraction between negative
electrons and positive protons), nuclear structure is based on strong nuclear force
- The nucleon binding energy is the energy required to separate nucleons (protons and
neutrons) from the nucleus
- Nucleon binding energy is on the order of MeV (millions of electron volts)
Direct and Inverse Proportionality
, - Distance is very important because radiation exposure is inversely proportional to the
square of distance (inverse square law)
- Exposure ~ 1/(distance)2
- When comparing exposures at two distances, the formula used is E2 = E1 * (d1/d2)2
- Where E1 = exposure at distance 1 and E2 = exposure at distance 2
Directly Proportional
- Increases if the value increases and decreases if the value decreases
- e.g., amount you are paid ↑ as number of hours you work ↑
- e.g., amount you are paid ↓ as number of hours you work ↓
Inversely Proportional
- Decreases if the value increases and increases if the value decreases
- e.g., heat from a candle ↓ as distance from the candle ↑
- e.g., heat from a candle ↑ as distance from the candle ↓
Exponential Behavior
- The rate of change of a function is proportional to the function
- If a quantity changes by a certain factor in a given interval of time, then there will be
exponential behavior if in any other equal interval of time it changes by the same factor
Exponential Decay
- N = N0e-λt where N is the number of atoms remaining at time t, N0 is the initial number of
atoms and λ is the transformation constant
- Half-life th = 0.693/λ
Exponential Attenuation
- N = N0e-μx where N is number of photons after the beam has passed through a material of
thickness x, N0 is the initial number of photons and μ is the linear attenuation coefficient
- Half-value layer xh = 0.693/μ
Fundamentals of Nuclear Physics
Radioactivity
- Radioactive decay an atomic nucleus undergoes the spontaneous transformation from a
higher energy state to a lower energy state
- The nucleons within the nucleus are in continual motion
- As a result of the motion, collisions occur and energy is transferred between particles
- In a stable nucleus, no particle ever acquires enough energy to escape the nucleus
- In a radioactive nucleus, it is possible for a particle by a series of chance encounters to
gain enough energy to escape the nucleus and a new nucleus species is formed
- Radioactivity is governed by quantum mechanics, and is thus inherently probabilistic
- It is impossible to know which radioactive atom in a sample will decay, but the average
rate of nuclear transformation or decay for a large group of radioactive atoms can be
predicted
Stability
- 4 fundamental forces of nature
- Two, the strong nuclear force and electromagnetic force, contribute to a nucleus stability
- The strong nuclear force binds the nucleons
- The electromagnetic force acts between charged particles (like charges repel)
- The strong nuclear force is ~2 orders of magnitude stronger than the electromagnetic
force, but acts under a much smaller distance
Atomic & Nuclear Structure
- Atoms are composed of a nucleus with radius ~ 10-14 m and a surrounding cloud of
electrons travelling in orbits of ~10-10
- The nucleus is composed of nucleons: protons and neutrons
- ZAX represents a nuclide, X = element symbol
- Atomic number (Z): the number of electrons and protons in an atom. It determines the
chemical properties and position of on the period table
- Mass numbers (A): total number of nucleons (A – Z = # of neutrons)
- Atomic mass: An element may exist in nature as a mixture of isotopes with different
numbers of neutrons
- Isotopes: same number of protons but different number of neutrons
- Isotones: same number of neutrons but different number of protons
- Isobars: same number of nucleons but different number of protons
- Isomers: same number protons and neutrons (differ in nuclear energy state)
Subatomic Particles
Proton (p) 11H
- Charge is +1
- The nucleus of a hydrogen atom
- Mass is 1.007277 amu
Neutron
- Charge is 0
- Mass is 1.008665 amu
Electron
- Also known as a beta particle or ray, or a beta minus particle or ray
- Charge is -1
- Mass is 0.000548 amu
- Moderately penetrating (depends on the energy)
- Can be stopped by varying thickness of metal ionizing
Positron (e+ or β+)
- Also known as a beta plus particle or ray
- Identical to an electron but with a positive charge
- Charge is +1
- Mass is 0.000548 amu
- Exist only when in motion (when they slow or stop moving, they combine with an
electron and annihilate)
- Moderately penetrating (depends on energy); can be stopped by varying thicknesses of
metal;
- Ionizing hence can cause biological damage
- upon slowing down they annihilate with electrons and release energy in the form of 2
photons
Neutrino
- Emitted with 𝛽+; minimal interaction with matter; non-ionizing
Antineutrino
, - Emitted with with 𝛽-; minimal interaction with matter; non-ionizing
Photons
- Not technically a particle but behaves as a particle at higher energies
- Charge and mass are 0
- A bundle of energy travelling at the speed of light (3.0 x 108m/s)
- Photons include x-rays and gamma rays (γ)
- The only difference between x-rays and gamma rays is their mode of origin
- X-rays arise from transitions of electrons between shells of an atom or from interactions
between electrons and nuclei
- Gamma rays are ejected from a nucleus
- Highly penetrating
Alpha Particles
- Alpha particle, 42He, an atomic particle
- Charge is +2
- The nucleus of a helium atom (2 protons and 2 neutrons)
- Mass is 4.001506 amu
- Minimum penetrability
- Low risk from external exposure but damaging if ingested or inhaled; highly ionizing
Radiation
- Radiation: any combination of subatomic particles with sufficient kinetic energy to
interact with and transfer energy to objects that intersect their path
- Radiation can be ejected by radioactive nuclides or be generated by machines
- Gamma rays, electrons, positrons, and alpha particles can be ejected from nuclei during
decay of radioactive nuclides
- Radioactive nuclides occur spontaneously or produced artificially in machines such as a
cyclotron
- X- rays, electrons and gamma rays can be generated by machines: Diagnostic x-ray tubes,
linear accelerators, Cobalt 60 therapy units
Radiation Uses
- Diagnostic imaging: radiography, computed tomography, positron emission tomography
- Therapy: Linear accelerator, Cobalt 60 therapy machine, Strontium 90 applicators.
Brachytherapy, Nuclear medicine
Radiation Protection
- Radiation has a risk of harmful effects
- Exposure of patients for diagnostic imaging and therapy (benefit to individual outweighs
risk of harm)
- Occupational exposure
- E.g., mines exposed to radon gas
Excitation and Ionization
- Excitation: involves the displacing of an orbital electron from its ground state
- Ionization: involves the removal of an orbital electron from a neutral atom
Ionizing & Non-Ionizing Radiation
- Non-Ionizing Radiation: transfers energy but does not ionize material
- Ionizing: has sufficient energy to eject one or more orbital electrons from an atom or
molecule
, - Ionizing radiation has potential for important biological effects (e.g., cell killing, DNA
mutation)
- Directly ionizing radiation causes ionization immediately and continuously as it passes
through material (charged particles: electrons, alpha particles, protons)
- Indirectly ionizing only causes ionization after some type of interaction with the
material (particles with no charge: photons, neutrons)
Particulate & Electromagnetic Radiation
- Particulate: Atomic or Subatomic particles (Electrons, protons, neutrons, alpha particles)
- Electromagnetic: photons (X-rays and gamma rays)
Electromagnetic Spectrum
- Photons are described by frequency (number of waves per second), wavelength (distance
between waves) or energy
- Longer wavelength photons (e.g., radiowaves, microwaves) are described by their wave
properties (wavelength, frequency)
- Shorter wavelength photons (e.g, x-rays, gamma rays) are described by their energy
(E=hv)
- Gamma rays, x-rays and some ultraviolet rays are ionizing radiation
- Photons all travel at the speed of light; they only differ in their wavelength and frequency
and therefore energy.
- Wavelength is inversely proportional to energy
- Frequency is directly proportional to energy
Radiation Units
- Absorbed Dose: the energy absorbed from ionizing radiation per unit mass
- Exposure: the charge liberated by ionizing radiation per unit mass air
- Activity: the disintegrations of radioactive material per second
- The SI unit of energy is the Joule
- In radiological science the electron volt (eV) is used as a unit for energy
- 1eV is the energy acquired when an electron falls through 1 volt
- 1eV = 1.602 e-19 J
Atomic Energy Levels
- Electrons travel around the nucleus in orbits or shells: K, L, M, N
- The maximum number of electrons in each shell = 2n2, where n= shell number
- Valence electrons are responsible for chemical reactions and bonds between atoms
- The shells can be considered as energy levels where the energy depends on the on the
Coulomb (electrostatic) force of attraction between the nucleus (+) and the orbital
electron (-) (the electron binding energy)
- The binding energy is defined as the energy needed to remove an electron from its shell
- Electrons in shells closer to the nucleus will have a higher binding energy
- Electron binding energies are on the order of keV (thousands of electron volts)
Nuclear Energy Levels
- While atomic structure is based on electrostatic force (the attraction between negative
electrons and positive protons), nuclear structure is based on strong nuclear force
- The nucleon binding energy is the energy required to separate nucleons (protons and
neutrons) from the nucleus
- Nucleon binding energy is on the order of MeV (millions of electron volts)
Direct and Inverse Proportionality
, - Distance is very important because radiation exposure is inversely proportional to the
square of distance (inverse square law)
- Exposure ~ 1/(distance)2
- When comparing exposures at two distances, the formula used is E2 = E1 * (d1/d2)2
- Where E1 = exposure at distance 1 and E2 = exposure at distance 2
Directly Proportional
- Increases if the value increases and decreases if the value decreases
- e.g., amount you are paid ↑ as number of hours you work ↑
- e.g., amount you are paid ↓ as number of hours you work ↓
Inversely Proportional
- Decreases if the value increases and increases if the value decreases
- e.g., heat from a candle ↓ as distance from the candle ↑
- e.g., heat from a candle ↑ as distance from the candle ↓
Exponential Behavior
- The rate of change of a function is proportional to the function
- If a quantity changes by a certain factor in a given interval of time, then there will be
exponential behavior if in any other equal interval of time it changes by the same factor
Exponential Decay
- N = N0e-λt where N is the number of atoms remaining at time t, N0 is the initial number of
atoms and λ is the transformation constant
- Half-life th = 0.693/λ
Exponential Attenuation
- N = N0e-μx where N is number of photons after the beam has passed through a material of
thickness x, N0 is the initial number of photons and μ is the linear attenuation coefficient
- Half-value layer xh = 0.693/μ
Fundamentals of Nuclear Physics
Radioactivity
- Radioactive decay an atomic nucleus undergoes the spontaneous transformation from a
higher energy state to a lower energy state
- The nucleons within the nucleus are in continual motion
- As a result of the motion, collisions occur and energy is transferred between particles
- In a stable nucleus, no particle ever acquires enough energy to escape the nucleus
- In a radioactive nucleus, it is possible for a particle by a series of chance encounters to
gain enough energy to escape the nucleus and a new nucleus species is formed
- Radioactivity is governed by quantum mechanics, and is thus inherently probabilistic
- It is impossible to know which radioactive atom in a sample will decay, but the average
rate of nuclear transformation or decay for a large group of radioactive atoms can be
predicted
Stability
- 4 fundamental forces of nature
- Two, the strong nuclear force and electromagnetic force, contribute to a nucleus stability
- The strong nuclear force binds the nucleons
- The electromagnetic force acts between charged particles (like charges repel)
- The strong nuclear force is ~2 orders of magnitude stronger than the electromagnetic
force, but acts under a much smaller distance
