RAB: Ch. 2 Radiation And The Atom

Question 1

How does electromagnetic radiation (EM radiation) interaction occur?

Answer 1

1. scattering (change in trajectory)
2. absorption (removal of the radiation), or, at
3. very higher energies, transformation into particulate radiation (energy to mass conversion)

Question 2

It is commonly characterized by wavelength (l), frequency (n), and energy per photon (E). It comprises the EM spectrum over a wide rane of wavelengths, frequencies and energy per photon. Several forms of this are used in diagnostic imaging, namely Gamma Rays, X-rays, Visible light and Radiofrequency EM radiation near the FM frequency

Answer 2

Electromagnetic Radiation

Question 3

Emitted by the nuclei of radioactive atoms, are used to image the distributions of radiopharmaceuticals

Answer 3

Gamma rays

Question 4

Produced outside the nuclei of atoms, are used in radiography, fluoroscopy, and computed tomography

Answer 4

X-rays

Question 5

Produced when x-rays or gamma rays interact with various scintillators in the detectors used in several imaging modalities and is also used to display images

Answer 5

Visible light

Question 6

Used as the excitation and reception signals for magnetic resonance imaging

Answer 6

Radiofrequency EM radiation, near the FM frequency region

Question 7

This addresses the inadequacy of classical Newtonian mechanics in fully describing the behavior of atomic and sub-atomic-scale objects

Answer 7

Wave-particle duality

[There are two equally correct ways of describing EM radiation—as waves and as discrete particle-like packets or quanta of energy called photons. A central tenet of quantum mechanics is that all particles exhibit wave-like properties and all waves exhibit particle-like properties]

Question 8

The particle-like behavior of x-rays is exemplified by the classical “billiard-ball” type of collision between an x-ray photon and an orbital electron during a ___________ _________ event.

Similarly the x-ray photon’s energy is completely absorbed by, and results in the ejection of, an orbital electron (a photoelectron), in the __________ __________.

Answer 8

Compton Scattering

Photoelectric effect
[Albert Einstein received the Nobel Prize in 1921 for his explanation of the photoelectric effect]

Question 9

Wave Characteristics:
Any wave (EM or mechanical, such as sound) can be characterized by their amplitude (maximal height), wavelength (l), frequency (n), and period (t).
1. _______ is the intensity of the wave
2. _______ is the distance between any two identitcal points on adjacent cycles.
3. _______ is the time required to complete one cycle of a wave
4. _______ is the number of periods that ocur per second
5. _______ is the temporal shift of one wave with respect to the other
6. Because ______ of EM radiation is constant in a given medium, its frequency and wavelength are inversely proportional.

Answer 9

1. Amplitude
2. Wavelength
3. Period
4. Fequency
5. Phase
6. Speed

Question 10

propagates as a pair of oscillating and mutually reinforcing electric and magnetic fields that are orthogonal (perpendicular) to one another and to the direction of propagation

Answer 10

EM radiation

Question 11

Particle Characteristics:

The discrete (particle-like) packets (or quanta) of EM energy are called ______. The energies of photons are commonly expressed in _________ (eV). One electron volt is defined as the energy acquired by an electron as it traverses an electrical potential difference (voltage) of one volt in a vacuum. Multiples of the eV common to medical imaging are the keV (1,000 eV) and the MeV (1,000,000 eV)

Answer 11

Photons;
Electron volts (eV)

Question 12

Ionizing Radiation
An atom or molecule that has lost or gained one or more electrons has a net electrical charge and is called an _____.

Answer 12

Ion

Question 13

Ionizing Radiation:
In general, photons of higher frequency than the far UV region of the spectrum (i.e., wavelengths greater than 200 nm) have sufficient energy per photon to remove bound electrons from atomic shells, thereby producing ionized atoms and molecules.

Radiation in this portion of the spectrum (e.g., x-rays and gamma rays) is called _______ ________. EM radiation with photon energies in and below the UV region (e.g., visible, infrared, terahertz, microwave and radio waves) is called _______ _________.

Answer 13

Ionizing radiation

Non-ionizing radiation

Question 14

Ionizing Radiation:
This is the minimum energy necessary to remove an electron

Answer 14

Ionization Energy

Question 15

Ionizing Radiation:
As water is the most abundant (thus most likely) molecular target for radiation interaction in the body, a practical radiobiological demarcation between ionizing and nonionizing EM radiation is approximately ___ eV. While 11 eV is the lowest photon energy capable of producing ionization in water, in a random set of ionization events evoked in a medium by ionization radiation, the average energy expended per ion pair (W) is larger than the minimum ionization energy. For water and tissue equivalent gas, W is about ___ eV

Answer 15

11 eV
30 eV

Question 16

Particulate Radiation
1. ______ are found in the nuclei of all atoms. A ____ has a positive electrical charge and is identical to the nucleus of a hydrogen-1 atom
2. An atomic orbital _______ has a negative electrical charge, equal in magnitude to that of a proton, and is approximately 1/1,800 the mass of a proton
3. Electrons emitted by the nuclei of radioactive atoms are referred to as ____ ______.
4-5.. Except for their nuclear origin, negatively charged beta-minus particles (B-), or _____, are indistinguishable from ordinary orbital electrons. However, there are also positively charged electrons, referred to as beta-plus particles (B+), or _____; they are a form of antimatter that ultimately combines with matter in a unique transformation in which all of their mass is instantaneously converted to an equivalent amount of energy in the form of high-energy gamma rays
6. _______ are released by nuclear fission and are used for radionuclide production
7. An ________ _______ consists of two protons and two neutrons; it thus has a +2 charge and is identical to the nucleus of a helium atom (4He2+). ______ ______ are emitted by many high atomic number radioactive elements, such as uranium, thorium, and radium. Following emission, the ______ eventually acquires two electrons from the surrounding medium and becomes an uncharged helium atom (4He). Whereas alpha particles emitted outside the body are harmless, alpha particles emitted inside the body cause more extensive cellular damage per unit energy deposited in tissue than any type of radiation used in medical imaging.

Answer 16

1. Proton
2. Electron
3. Beta Particles
4. Negatrons
5. Positrons
6. Neutrons
7. Alpha particle

Question 17

It is the smallest division of an element in which the chemical identity of the element is maintained. The atom is composed of an extremely dense positively charged nucleus, containing protons and neutrons, and an extranuclear cloud of light negatively charged electrons. In its nonionized state, an atom is electrically neutral because the number of protons equals the number of electrons.

Answer 17

ATom

Question 18

In this model of the atom, each electron occupies a discrete energy state in a given electron shell. These electron shells are assigned the letters K L, M, N,…, with K denoting the innermost shell, in which the electrons have the lowest energies. In this model of the atom, each electron occupies a discrete energy state in a given electron shell. These electron shells are assigned the letters K L, M, N,…, with K denoting the innermost shell, in which the electrons have the lowest energies. The shells are also assigned the quantum numbers 1, 2, 3, 4,…, with the quantum number 1 designating the K shell. Each shell can contain a maximum number of electrons given by (2n2), where n is the quantum number of the shell. Thus, the K shell (n = 1) can only hold 2 electrons, the L shell (n = 2) can hold 2(2)2 or 8 electrons, and so on

Answer 18

Bohr model

[ Electrons orbit around a dense, positively charged nucleus at fixed distances (Bohr radii). Bohr combined the classical Newtonian laws of motion and Coulomb’s law of electrostatic attraction with quantum theory]

Question 19

The outer electron shell of an atom, that determines the chemical properties of the element

Answer 19

Velence shell

Question 20

The energy required to remove an orbital electron completely from the atom.
Thus, for radiation to be ionizing, the energy transferred to the electron must ______ or ______ its binding energy

Answer 20

Orbital binding energy.

Equal or exceed

Question 21

Due to the closer proximity of the electrons to the positively charged nucleus, the binding energy of the K-shell is ________ that of outer shells. For a particular electron shell, binding energy also increases with the number of protons in the nucleus (i.e., atomic number)

Answer 21

Greater than

Question 22

The energy required to move an electron from the innermost electron orbit (K shell) to the next orbit (L shell) is the difference between the binding energies of the two orbits (i.e., EbK - EbL equals the transition energy)

Answer 22

Hydrogen (Z= 1):
13.5 eV - 3.4 eV = 10.1 eV

Tungsten (Z= 74):
69,500 eV - 11,000 eV = 58,500 eV (58.5 keV)

Question 23

When an electron is removed from its shell by an x-ray or gamma ray photon or a charged particle interaction, a *_____ is created in that shell. This *_____ 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 an _____.

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 ________

Answer 23

Vacancy

Electron Cascade

Characteristic X-ray

Auger electrons

Question 24

Electron transitions between atomic shells can result in the emission of radiation in the visible, UV, and x-ray portions of the EM spectrum.

The energy of this radiation is characteristic of each atom, since the electron binding energies depend on ___.

Answer 24

Z

Question 25

Emissions from electron transitions exceeding 100 eV are called ____. These are named according to the orbital in which the vacancy occurred. (E.g. K-____________)

Answer 25

Characteristic or Fluorescent X-rays

[ If the vacancy in one shell is filled by the adjacent shell, it is identified by a subscript alpha (e.g., L → K transition = Ka, M → L transition = La). If the electron vacancy is filled from a nonadjacent shell, the subscript beta is used (e.g., M → K transition = Kb)]

Question 26

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 ____________.

Answer 26

Auger electron emission

[In this case, the energy released is transferred to an orbital electron, typically in the same shell as the cascading electron (Fig. 2-7B). The ejected Auger electron possesses kinetic energy equal to the difference between the transition energy and the binding energy of the ejected electron]

Question 27

The probability that the electron transition will result in the emission of a characteristic x-ray is called the ____________ (w). Thus, 1- w is the probability that the transition will result in the ejection of an Auger electron

Answer 27

Fluorescent yield (w)

1-w = probability that e- transition will result in ejection of an Auger electron.

Question 28

The nucleus is composed of protons and neutrons, known collectively as _______.

The number of protons in the nucleus is the atomic number (Z), and the total number of protons and neutrons within the nucleus is the mass number (A)

Answer 28

Nucleons

Question 29

The nucleus has energy levels that are analogous to orbital electron shells, although often much higher in energy. The lowest energy state is called the ground state of an atomic nucleus. Nuclei with energy in excess of the ground state are said to be in an excited state Excited states that exist longer than 10-12 s are referred to as metastable or isomeric states. Metastable states with longer lifetimes are denoted by the letter m after the mass number of the atom (e.g., Tc-99m)

Answer 29

True

Question 30

Classification of Nuclides

Answer 30

isoTOPES = aTOMIC number (Z)
IsoBARs= MASS number (A)
IsoTONE = no. Of NEUTRONes
IsoMER = Atomic and Mass no. But diff energy states in the nucleus

Question 31

The energy required to separate an atom into its constituent parts. It is the sum of the orbital electron binding energy and the nuclear binding energy

Answer 31

Atomic Binding Energy

Question 32

is the energy necessary to disassociate a nucleus into its constituent parts and is the result of the strong forces acting between nucleons

Answer 32

Nuclear binding energy