AIM: Ch 2: Radiation and the Atom Flashcards
It is energy that travels through space or matter.
Radiation
Two categories of radiation of importance in medical imaging are:
Electromagnetic and particulate
T/F: EM radiation has no mass, is unaffected by either electric or magnetic fields, and has a constant speed in a given medium.
True
Maximal speed of EM radiation
2.998 x 10^8 m/s
The interaction of EM radiation can occur by:
1. Change in trajectory:
2. Removal of the radiation:
3. At very higher energies, energy to mass conversion:
- Scattering
- Absorption
- Transformation into particulate radiation
Name the form of EM radiation used for the following modalities:
1. Nuclear imaging
2. Radiography, fluoroscopy and mammography
- Gamma rays
- X-rays
It is a discrete particle-like packets or quanta of energy
Photons
____ characteristics are more apparent when EM radiation interacts with objects of similar dimensions as the photon’s wavelength.
Wave
Particle characteristics of EM radiation, on the other hand, are more evident when an object’s dimensions are much ____ than the photon’s wavelength.
Smaller
It is the intensity of the wave
Amplitude
It is the distance between any two identical points on adjacent cycles.
Wavelength
The time required to complete one cycle of a wave is the ____
Period
Number of periods that occur per second
Frequency
It is the temporal shift of one wave with respect to the other
Phase
It is defined as the energy acquired by an electron as it traverses an electrical potential difference (voltage) of one volt in a vacuum.
1 eV
Energies of photons are commonly expressed in electron volts (eV)
What region of the radiation spectrum serves as the landmark that separates ionizing radiation from non-ionizing radiation?
UV region
Ionizing radiation: wavelengths >200 nm
What wavelength will have sufficient energy to cause ionizing radiation?
> 200 nm
The minimum energy necessary to remove an electron
Ionizing energy
Ionizing energy for water
11.2 eV
The average energy expended per ion pair (W) for water and tissue equivalent gas:
30 W
Electrons emitted by the nuclei of radioactive atoms
Beta particles
Of nuclear origin, negatively charged beta-minus particles are also called ____
Negatrons
Positively charged electrons
Positrons
A neutron is an uncharged nuclear particle that has a mass slightly ____ than that of a proton.
Greater
Which particle has the greatest elementary charge, rest mass and energy equivalent?
Alpha
Neutrons are released by nuclear ____ and are used for radionuclide production
Fission
It is a common unit of mass used in atomic and nuclear physics, defined as 1/12th of the mass of an atom of 12C.
Atomic mass unit (amu)
One amu is equivalent to 931.5 MeV of energy.
It is the smallest division of an element in which the chemical identity of the element is maintained.
Atom
The outer electron shell of an atom, which determines the chemical properties of the element.
Valence shell
The energy required to remove an orbital electron completely from the atom
Orbital binding energy
What is the formula by which you can compute the highest number of electrons each shell can contain?
2n^2
T/F: For a particular electron shell, binding energy also increases with the number of protons in the nucleus (i.e., atomic number).
True
When an electron is removed from its shell by an x-ray or gamma ray photon or a charged particle interaction, a vacancy is created in that shell. This vacancy is usually filled by an electron from an outer shell, leaving a vacancy in the outer shell that in turn may be filled by an electron transition from a more distant shell. This series of transitions is called what?
Electron cascade
The energy released by each transition is equal to the difference in binding energy between the original and final shells of the electron. This energy may be released by the atom as ____ or ____
Characteristic x-rays or Auger electrons
Emissions from transitions exceeding 100 eV are called ____
Characteristic or fluorescent x-rays.
An electron cascade does not always result in the production of a characteristic x–ray or x-rays. A competing process that predominates in low Z elements is ____
Auger electron emission
The probability that the electron transition will result in the emission of a characteristic x-ray is called ____
Fluorescent yield (w)
It is the probability that the transition will result in the ejection of an Auger electron.
1-w
Auger emission predominates in ____ Z elements and in electron transitions of the outer shells of heavy elements.
Low
Nucleons = ____ + ____
Protons + Neutrons
Atomic number
Number of protons in the nucleus
Mass number
Protons + Neutrons
Atomic mass
Actual mass of the atom
Subnuclear particles are also known as
Gluons
The lowest energy state of an atomic nucleus
Ground state
Nuclei with energy in excess of the ground state are said to be in an
Excited state
The average lifetimes of excited states range from 10^-16 s to more than 100 y
Excited states that exist longer than 10^-12 s are referred to as
Metastable or isomeric states
Nuclides with the same:
1. Z
2. A
3. A-Z
4. Atomic and mass numbers but different energy states in the nucleus
- IsotoPes
- IsobArs
- IsotoNes
- Isomers
On a plot of Z versus N, these stable nuclides fall along a “line of stability” for which the N/Z ratio is approximately ____ for low Z nuclides and approximately ____ for high Z nuclides
1, 1.5
Nuclides that decay (i.e., transform) to more stable nuclei are said to be ____, and the transformation process itself is called ____
radioactive, radioactive decay (radioactive disintegration)
The EM radiation emitted from the nucleus as the excited state transitions to a lower (more stable) energy state is called a
Gamma ray
When this nuclear de-excitation process takes place in an isomer (e.g., Tc-99m), it is called ____
Isomeric transition
T/F: In isomeric transition, the nuclear energy state is reduced with decrease in A or Z.
False
In isomeric transition, the nuclear energy state is reduced with no change in A or Z
This process occurs when de-excitation energy is completely transferred to an orbital (typically K, L, or M shell) electron
Internal conversion
The energy required to separate an atom into its constituent parts is called
Atomic binding energy
Energy necessary to disassociate a nucleus into its constituent parts and is the result of the strong forces acting between nucleons.
Nuclear binding energy
T/F: The total energy of the bound particles is less than that of the separated free particles.
True
The binding energy can be calculated by subtracting the mass of the atom from the total mass of its constituent protons, neutrons, and electrons; this mass difference is called the ____
Mass defect
During nuclear fission, a nucleus with a large atomic mass splits into two usually unequal parts called fission fragments, each with an average binding energy per nucleon ____ than that of the original nucleus. In this reaction, the total nuclear binding energy ____.
Greater, increases
Number of neutrons per cm2/s
Neutron flux
