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MEDICAL BIOPHYSICS > RADIATION > Flashcards

RADIATION Flashcards

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USMLE® Step 1 flashcards
1
Q

RADIATION

A

-energy in transit in the form of high speed particles or electromagnetic waves
EG: gravitational waves

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2
Q

IONIZING RADIATION

A

radiation which has has sufficient energy to ionize an atom

Ionizing radiation is capable of knocking electrons out of their orbits around atoms, upsetting the electron/proton balance and giving the atom a positive charge

EG: gamma rays, neutrons

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3
Q

NON-IONIZING RADIATION

A

Non-ionizing radiation has less energy than ionizing radiation; it does not possess enough energy to produce ions.

EG: visible light, infrared, radio waves, microwaves, and
sunlight, earths magnetic field

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4
Q

ELECTROMAGENTIC RADIATION

A

the flow of energy at universal speed of light through free space or through a material medium in the form of electric and magnetic fields that make up electromagentic waves
EG: radio waves, visible light, gamma rays

POSESSES ABILITY TO EXCITE OTHER ATOMS IN THEIR VICINITY

-> flow of photons through space

-> electric and magnetic fields linked with each other at right angles and perpendicular to the direction of motion

-> there is as much energy carried by the electric component as the magnetic component and the energy is proportional to the square of the field of strength

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5
Q

PHOTONS

A

packets of energy that always move with the universal speed of light

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6
Q

WHEN IS ELECTROMAGNETIC RADIATION PRODUCED?

A

whenever a charged particle changes velocity
EG: oscillating current in radio antenna

-> any system that emits electromagnetic radiation can also absorb radiation at the same frequency

1: broad continuous spectrum of frequencies (the sun)
2: characteristic frequencies (radio transmitter)

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7
Q

WHAT IS UNIQUE ABOUT LIGHT?

A

the speed of light is always the same
3x10^10c,/sec

-> the higher the frequency the lower the wavelength and vice versa
-> the higher the frequency the higher the energy
-> can be any wavelength

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8
Q

WHAT PHOTONS MAKE IT THROUGH THE ATMOSPHERE?

A

-gamma and xray are absorbed
-infrared and ultraviolet are absorbed
-visible light and radio waves make it through

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9
Q

WHAT HAS THE SHORTEST WAVE LENGTH BUT HIGHEST ENERGY?

A

gamma waves

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10
Q

WHICH TISSUE HAS MOST RESISTANCE TO IRRADIATION?

A

neural tissue
muscle

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11
Q

WHAT IS THE SPEED OF ULTRASOUND IN COMPARISON TO SPEED OF SOUND?

A

its the same

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12
Q

WHAT IS THE DOPPLER SHIFT?

A

the change in frequency of a wave in relation to an observer who is moving relative to the wave source

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13
Q

WHAT IS A BETA PARTICLE?

A

positron

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14
Q

WHAT IS THE INVERSE SQUARE LAW OF LIGHT?

A

light intensity is inversely proportional to the square of the distance

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15
Q

CHARACTERISTICS OF LASER

A

monochromatic
polarized
coherent

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16
Q

RADIOACTIVE ATOMS

A

atoms whose nuclei is not stable
-> can spontaneously transform into new nuclei overtime

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17
Q

WHAT DOES IONIZING RADIATION DO?

A

changes the chemical nature of the radioactive atoms due to emission of nuclear particles

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18
Q

WHERE DOES GAMMA RADIATION ORIGINATE?

A

atomic nucleus

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19
Q

WHERE DOES X RADIATION ORIGINATE?

A

atomic electron cloud

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20
Q

WHAT IS THE UNIT OF ACTIVITY?

A

becquerel Bq
curie Ci

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21
Q

WHAT IS THE UNIT OF ABSORBED DOSE?

A

gray Gy = 1 joule/kg

-> amount of energy deposited per unit mass in target material

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22
Q

WHAT IS THE UNIT OF EQUIVALENT DOSE (H)?

A

sievert Sv

-> takes into account the effect of the radiation on tissue by using weighting factor
H = D X W

Sv = Gy x Q

Q = quality factor

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23
Q

ACTIVITY

A

amount of radioactive nuclei decayed or transformed per second

-> decreases exponentially with time

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24
Q

WHAT IS THE UNIT OF ENERGY OF RADIOACTIVE PARTICLES?

A

1 eV

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25
Q

WHAT IS EXPOSURE?

A

describes the absolute value of the total electrical charge of ions produced by ionizing radiation in the air, divided by the mass of the air, where the electrons where released

-> coloumb per kilogram

-> commonly used parameter to describe gamma and xray

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26
Q

WHAT IS THE QUALITY FACTOR?

A

describes different qualities of radiation in regard to the biological effects it causes

-> only for humans

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27
Q

PHYSICAL HALF LIFE

A

average time required for the decay of exactly 1/2 the atoms in a given amount of radioactive isotope

-> unit is time and depends on type of isotope

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28
Q

BIOLOGICAL HALF LIFE

A

time in which a living organism eliminates 1/2 a given amount of a radionuclide

-> unit of dose is Sievert

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29
Q

EFFECTIVE HALF LIFE

A

the half life of a radionuclide in a biologic organism from the combination of biologic elimination and radioactive decay

-> always shorter than physical half life

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30
Q

ISOTOPIC NUMBER

A

difference between the amount of neutrons and protons in the nucleus

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31
Q

ISOTOPES

A

the same number of protons but different number of neutrons

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32
Q

ISOBARS

A

elements that have the same nucleon number but different number of protons
-> represent different chemicals

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33
Q

ISOTONES

A

elements that have the same number of neutrons but a different number of protons

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34
Q

WHAT IS THE MASS NUMBER ALSO KNOWN AS?

A

nucleon

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35
Q

ISOMERS

A

elements with the same number of protons and nucleons but differ in energy states

36
Q

WHAT IS A NUCLIDE?

A

a collection of atoms sharing the same number of protons and neutrons, existing for at least a fraction of a second

37
Q

WHAT IS A RADIONUCLIDE?

A

nuclides consisting of atoms with nuclei displaying higher levels of energy than those of stable nuclides

38
Q

WHAT ARE ABSOLUTELY STABLE NUCLIDES CHARACTERIZED BY?

A

zero activity
-> its physical half life is infinitely long
-> impossible

39
Q

RADIOACTIVE NUCLEI

A

spontaneously transforming atomic nuclei
often resulting in the emission of radiation

40
Q

RADIOACTIVE NUCLIDES WITH HIGH PROTON NUMBER AND DECAY CHAINS

A

parent nuclide transforms into a daughter nuclei
-> over time the new atom with different energy state can transform and give rise to another radioactive atom
-> after a number of transformations the decay change leads with a stable nuclide

EG: radium, actinium, thorium

41
Q

WHEN IS RADIOACTIVE EQUILIBRIUM ACHIEVED?

A

when the same number of paternal and daughter nuclei within a decay chain are being transformed per unit time
-> physical 1/2 life of paternal nuclide needs to be longer than that of daughter nuclide

42
Q

ALPHA DECAY

A

-only occurs in heavy natural radionuclides
-2 protons and 2 neutrons
-identical to helium atom
-both have double positive charge
-total number of nucleons decreases by 4
-elements moves 2 to the left on periodic table
-atomic decreases by 2, mass decreases by 4
-not very penetrable , very heavy
-energy completely absorbed by bodily tissue
-stopped by piece of paper

Examples of alpha emitters include radium, radon, uranium and thorium

43
Q

CAN RADIOACTIVE DECAY BE ACCELERATED BY TEMPERATURE, ELECTRIC CHARGE, PRESSURE OR GRAVITATION?

A

no

44
Q

BETA DECAY

A

-number of nucleons remain the same
-unstable due to neutron number (neutron rich)
-proton number increases by 1
-neutron is turned into a proton and an electron + antineutrino are emitted from the nucleus
-more penetrable than alpha
-negatively charged
-stopped by plastic or metal

Examples of pure beta emitters include strontium-90, carbon-14, tritium and sulphur-35

BETA PLUS = positron, proton number decreases by one, neutron formed, positron and neutrino released

BETA MINUS = an electron form the nucleus, emitted from neutrons in the core

45
Q

GAMMA RADIATION

A

-does not change proton or neutron number
-very high energy levels and highly penetrative
-stopped by lead
- Gamma decay takes place when there is residual energy in the nucleus following
alpha or beta decay, or after neutron capture (a type of nuclear reaction) in a nuclear reactor. The residual energy is released as a photon of gamma radiation.

Examples of gamma emitters include iodine-131, cesium-137, cobalt-60, radium-226 and technetium-99m

46
Q

ISOMERIC TRANSITION

A

transition from metastable to ground state

47
Q

ION PAIR

A

positively charged ion + electron

48
Q

PRIMARY IONIZATION

A

number of ion pairs created by ionizing particle

49
Q

SECONDARY IONIZATION

A

ionization caused by liberated electrons

50
Q

PAIR ANNIHILATION

A

subatomic particles collide with its antiparticle and create more particles

51
Q

WHAT ARE EXAMPLES OF PHOTON RADIATION?

A

gamma and xray
-can travel longer and penetrate deeper than alpha and beta
-xray lower in energy than gamma
-only differ in location

52
Q

WHAT IS THE SOURCE OF NEUTRONS?

A

spontaneous fission
-NUCLEAR REACTOR

-Neutron radiation is best
shielded or absorbed by materials that contain hydrogen atoms, such as paraffin wax and plastics. This is because neutrons and hydrogen atoms have similar atomic weights and readily undergo collisions between each other

-as strong as gamma / photons

53
Q

POSITRON EMISSION

A

A type of radioactive decay in which a proton is converted to a neutron, and it
releases a positron

54
Q

MASS NUMBER

A

number of protons and neutrons

55
Q

WHAT MACHINE IS USED TO OBTAIN PROTONS?

A

cyclotron

56
Q

MAXIMUM DOSE DEPTH

A

R100 m

57
Q

HALF DOSE DEPTH

A

R50 m

58
Q

THERAPEUTIC RANGE

A

R80 m

59
Q

EXPOSURE RATE

A

X

60
Q

EXPOSURE POWER

A

ampere per kg

61
Q

POPULATION INVERSION

A

there should be more atoms in the metastable state than in the ground state from pumping system in laser

62
Q

WHAT DOES LASER STAND FOR?

A

light amplification by stimulated emission of radiation

63
Q

ENERGY OF IONIZING RADIATION

A

E = mc^2
#m = mass
#c = speed of light

unit = electron volts eV or MeV

64
Q

X-RAY

A

-photons emitted not from nucleus but from electron cloud due to changes of electrons energy
-cathode electrons under high voltage strike anode made from heavy element with very high energy
-electrons deflected due to opposite charges and this decreases electrons energy creating an x-ray

EG: bremsstrahlung or characteristic radiation

65
Q

HOW ARE NEUTRONS REMOVED FROM NUCLEUS?

A

-fission
-collision
-shielded by thick layers of concrete or water
-react weakily with material
-neutral particles in nucleus
=in neutron emission, proton number decreases by 1

66
Q

NEUTRON INDUCED FISSION

A

bombardment with a neutron resulting in the splitting of the nucleus into neutrons and gamma rays

67
Q

PHOTOELECTRIC EFFECT

A

-collision between x-ray / gamma rays and a bound atomic electron
-photon disappears
-bound electron ejected
-incident energy shared between ejected electron and remaining atom
-photon energy must be greater than the atomic binding energy

68
Q

WHAT IS USED TO MEASURE EXPOSURE OF ONLY GAMMA AND X-RAY IN AIR?

A

roentgen R
rad R (measures absorbed dose)

69
Q

STOCHASTIC EFFECTS

A

= cancer
-DNA changes
-random basis based on probabilities
-no dose threshold
-effect independent of dose
-probability of effect increases with dose

70
Q

DETERMINISTIC EFFECTS

A

= tanning
-cell killing
-specific to particular tissues
-threshold
-related directly to dose received
-severity of effect is dose dependent

71
Q

WHAT IS THE EFFECTIVE DOSE UNIT?

A

sievert

-> takes into account the various sensitivity of tissues to radiation using tissue weighting factors
-> multiple organs effected from different radiations
-> stochastic effects
-> quantification of risk

72
Q

LINEAR DOSE RESPONSE MODEL

A

-suggests that any increase in dose, no matter how small, results in an incremental increase in the risk for cancer

73
Q

LATENT PERIOD

A

-period of time between exposure to radiation and the detection of cancer

74
Q

HORMESIS

A

-unproven theory that a low level of ionizing radiation helps immunize cells against DNA damage and decreases the risk of cancer
-> activates the bodies DNA repair mechanisms

75
Q

LINEAR NO THRESHOLD MODEL

A

-cancer is directly proportional to the dose level of ionizing radiation

76
Q

COLLIMETER

A

-used in x-ray, gamma, neutron

77
Q

WHAT IS THE SOURCE OF IONIZING RADIATION FOR THE GAMMA KNIFE?

A

-large number of cobalt sources
-used in brain surgery

78
Q

WHAT IS THE HOUNSFIELD SCALE USED IN?

A

CT
WATER = 0
AIR = -1000
BONE = 1000

79
Q

HOW CAN ENERGY OF PHOTONS BE EXPRESSED?

A

E = hf

80
Q

MOST DANGEROUS SCAN FOR PREGNANT WOMAN?

A

CT

81
Q

ADVANTAGE OF MRI

A

the use of non ionizing radiation
-> its radiofrequency waves

82
Q

WHEN EXAMINING DEEP BODY STRUCTURES WHAT IS USED?

A

-high pulse repetition frequency
-low ultrasound frequency

83
Q

WHICH INTENSITY OF AC CAUSES VENTRICULAR FIBRILLATION?

A

50-100mA

84
Q

WHICH INTENSITY OF AC CAUSES PARALYSIS AND RESPIRATORY ARREST?

A

20-50mA

85
Q

WHICH INTENSITY OF AC CAUSES INTERNAL ORGAN DAMAGE?

A

2A

86
Q

WHAT ELECTRICAL CURRENT HAS THE MAXIMAL STIMULATING EFFECTS ON THE HUMAN BODY?

A

low frequency AC

87
Q

WHAT IMAGING PROCESS IS BASED ON PROCESSING OF RADIATION THAT IS EMITTED FROM WITHIN THE PATIENTS BODY?

A

-processes using gamma cameras such as SPECT (2D images -> single photon emission

MEDICAL BIOPHYSICS (9 decks)

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