AIM: Ch 2: Radiation and the Atom

Question 1

It is energy that travels through space or matter.

Answer 1

Radiation

Question 2

Two categories of radiation of importance in medical imaging are:

Answer 2

Electromagnetic and particulate

Question 3

T/F: EM radiation has no mass, is unaffected by either electric or magnetic fields, and has a constant speed in a given medium.

Answer 3

True

Question 4

Maximal speed of EM radiation

Answer 4

2.998 x 10^8 m/s

Question 5

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:

Answer 5

1. Scattering
2. Absorption
3. Transformation into particulate radiation

Question 6

Name the form of EM radiation used for the following modalities:
1. Nuclear imaging
2. Radiography, fluoroscopy and mammography

Answer 6

1. Gamma rays
2. X-rays

Question 7

It is a discrete particle-like packets or quanta of energy

Answer 7

Photons

Question 8

____ characteristics are more apparent when EM radiation interacts with objects of similar dimensions as the photon’s wavelength.

Answer 8

Wave

Question 9

Particle characteristics of EM radiation, on the other hand, are more evident when an object’s dimensions are much ____ than the photon’s wavelength.

Answer 9

Smaller

Question 10

It is the intensity of the wave

Answer 10

Amplitude

Question 11

It is the distance between any two identical points on adjacent cycles.

Answer 11

Wavelength

Question 12

The time required to complete one cycle of a wave is the ____

Answer 12

Period

Question 13

Number of periods that occur per second

Answer 13

Frequency

Question 14

It is the temporal shift of one wave with respect to the other

Answer 14

Phase

Question 15

It is defined as the energy acquired by an electron as it traverses an electrical potential difference (voltage) of one volt in a vacuum.

Answer 15

1 eV

Energies of photons are commonly expressed in electron volts (eV)

Question 16

What region of the radiation spectrum serves as the landmark that separates ionizing radiation from non-ionizing radiation?

Answer 16

UV region

Ionizing radiation: wavelengths >200 nm

Question 17

What wavelength will have sufficient energy to cause ionizing radiation?

Answer 17

> 200 nm

Question 18

The minimum energy necessary to remove an electron

Answer 18

Ionizing energy

Question 19

Ionizing energy for water

Answer 19

11.2 eV

Question 20

The average energy expended per ion pair (W) for water and tissue equivalent gas:

Answer 20

30 W

Question 21

Electrons emitted by the nuclei of radioactive atoms

Answer 21

Beta particles

Question 22

Of nuclear origin, negatively charged beta-minus particles are also called ____

Answer 22

Negatrons

Question 23

Positively charged electrons

Answer 23

Positrons

Question 24

A neutron is an uncharged nuclear particle that has a mass slightly ____ than that of a proton.

Answer 24

Greater

Question 25

Which particle has the greatest elementary charge, rest mass and energy equivalent?

Answer 25

Alpha

Question 26

Neutrons are released by nuclear ____ and are used for radionuclide production

Answer 26

Fission

Question 27

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.

Answer 27

Atomic mass unit (amu) ## Footnote One amu is equivalent to 931.5 MeV of energy.

Question 28

It is the smallest division of an element in which the chemical identity of the element is maintained.

Answer 28

Atom

Question 29

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

Answer 29

Valence shell

Question 30

The energy required to remove an orbital electron completely from the atom

Answer 30

Orbital binding energy

Question 31

What is the formula by which you can compute the highest number of electrons each shell can contain?

Answer 31

2n^2

Question 32

T/F: For a particular electron shell, binding energy also increases with the number of protons in the nucleus (i.e., atomic number).

Answer 32

True

Question 33

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?

Answer 33

Electron cascade

Question 34

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 34

Characteristic x-rays or Auger electrons

Question 35

Emissions from transitions exceeding 100 eV are called ____

Answer 35

Characteristic or fluorescent x-rays.

Question 36

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 36

Auger electron emission

Question 37

The probability that the electron transition will result in the emission of a characteristic x-ray is called ____

Answer 37

Fluorescent yield (w)

Question 38

It is the probability that the transition will result in the ejection of an Auger electron.

Answer 38

1-w

Question 39

Auger emission predominates in ____ Z elements and in electron transitions of the outer shells of heavy elements.

Answer 39

Low

Question 40

Nucleons = ____ + ____

Answer 40

Protons + Neutrons

Question 41

Atomic number

Answer 41

Number of protons in the nucleus

Question 42

Mass number

Answer 42

Protons + Neutrons

Question 43

Atomic mass

Answer 43

Actual mass of the atom

Question 44

Subnuclear particles are also known as

Answer 44

Gluons

Question 45

The lowest energy state of an atomic nucleus

Answer 45

Ground state

Question 46

Nuclei with energy in excess of the ground state are said to be in an

Answer 46

Excited state ## Footnote The average lifetimes of excited states range from 10^-16 s to more than 100 y

Question 47

Excited states that exist longer than 10^-12 s are referred to as

Answer 47

Metastable or isomeric states

Question 48

Nuclides with the same: 1. Z 2. A 3. A-Z 4. Atomic and mass numbers but different energy states in the nucleus

Answer 48

1. IsotoPes 2. IsobArs 3. IsotoNes 4. Isomers

Question 49

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

Answer 49

1, 1.5

Question 50

Nuclides that decay (i.e., transform) to more stable nuclei are said to be ____, and the transformation process itself is called ____

Answer 50

radioactive, radioactive decay (radioactive disintegration)

Question 51

The EM radiation emitted from the nucleus as the excited state transitions to a lower (more stable) energy state is called a

Answer 51

Gamma ray

Question 52

When this nuclear de-excitation process takes place in an isomer (e.g., Tc-99m), it is called ____

Answer 52

Isomeric transition

Question 53

T/F: In isomeric transition, the nuclear energy state is reduced with decrease in A or Z.

Answer 53

False ## Footnote In isomeric transition, the nuclear energy state is reduced with no change in A or Z

Question 54

This process occurs when de-excitation energy is completely transferred to an orbital (typically K, L, or M shell) electron

Answer 54

Internal conversion

Question 55

The energy required to separate an atom into its constituent parts is called

Answer 55

Atomic binding energy

Question 56

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

Answer 56

Nuclear binding energy

Question 57

T/F: The total energy of the bound particles is less than that of the separated free particles.

Answer 57

True

Question 58

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 ____

Answer 58

Mass defect

Question 59

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 ____.

Answer 59

Greater, increases

Question 60

Number of neutrons per cm2/s

Answer 60

Neutron flux