RADIATION Flashcards
RADIATION
-energy in transit in the form of high speed particles or electromagnetic waves
EG: gravitational waves
IONIZING RADIATION
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
NON-IONIZING RADIATION
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
ELECTROMAGENTIC RADIATION
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
PHOTONS
packets of energy that always move with the universal speed of light
WHEN IS ELECTROMAGNETIC RADIATION PRODUCED?
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)
WHAT IS UNIQUE ABOUT LIGHT?
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
WHAT PHOTONS MAKE IT THROUGH THE ATMOSPHERE?
-gamma and xray are absorbed
-infrared and ultraviolet are absorbed
-visible light and radio waves make it through
WHAT HAS THE SHORTEST WAVE LENGTH BUT HIGHEST ENERGY?
gamma waves
WHICH TISSUE HAS MOST RESISTANCE TO IRRADIATION?
neural tissue
muscle
WHAT IS THE SPEED OF ULTRASOUND IN COMPARISON TO SPEED OF SOUND?
its the same
WHAT IS THE DOPPLER SHIFT?
the change in frequency of a wave in relation to an observer who is moving relative to the wave source
WHAT IS A BETA PARTICLE?
positron
WHAT IS THE INVERSE SQUARE LAW OF LIGHT?
light intensity is inversely proportional to the square of the distance
CHARACTERISTICS OF LASER
monochromatic
polarized
coherent
RADIOACTIVE ATOMS
atoms whose nuclei is not stable
-> can spontaneously transform into new nuclei overtime
WHAT DOES IONIZING RADIATION DO?
changes the chemical nature of the radioactive atoms due to emission of nuclear particles
WHERE DOES GAMMA RADIATION ORIGINATE?
atomic nucleus
WHERE DOES X RADIATION ORIGINATE?
atomic electron cloud
WHAT IS THE UNIT OF ACTIVITY?
becquerel Bq
curie Ci
WHAT IS THE UNIT OF ABSORBED DOSE?
gray Gy = 1 joule/kg
-> amount of energy deposited per unit mass in target material
WHAT IS THE UNIT OF EQUIVALENT DOSE (H)?
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
ACTIVITY
amount of radioactive nuclei decayed or transformed per second
-> decreases exponentially with time
WHAT IS THE UNIT OF ENERGY OF RADIOACTIVE PARTICLES?
1 eV
WHAT IS EXPOSURE?
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
WHAT IS THE QUALITY FACTOR?
describes different qualities of radiation in regard to the biological effects it causes
-> only for humans
PHYSICAL HALF LIFE
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
BIOLOGICAL HALF LIFE
time in which a living organism eliminates 1/2 a given amount of a radionuclide
-> unit of dose is Sievert
EFFECTIVE HALF LIFE
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
ISOTOPIC NUMBER
difference between the amount of neutrons and protons in the nucleus
ISOTOPES
the same number of protons but different number of neutrons
ISOBARS
elements that have the same nucleon number but different number of protons
-> represent different chemicals
ISOTONES
elements that have the same number of neutrons but a different number of protons
WHAT IS THE MASS NUMBER ALSO KNOWN AS?
nucleon
ISOMERS
elements with the same number of protons and nucleons but differ in energy states
WHAT IS A NUCLIDE?
a collection of atoms sharing the same number of protons and neutrons, existing for at least a fraction of a second
WHAT IS A RADIONUCLIDE?
nuclides consisting of atoms with nuclei displaying higher levels of energy than those of stable nuclides
WHAT ARE ABSOLUTELY STABLE NUCLIDES CHARACTERIZED BY?
zero activity
-> its physical half life is infinitely long
-> impossible
RADIOACTIVE NUCLEI
spontaneously transforming atomic nuclei
often resulting in the emission of radiation
RADIOACTIVE NUCLIDES WITH HIGH PROTON NUMBER AND DECAY CHAINS
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
WHEN IS RADIOACTIVE EQUILIBRIUM ACHIEVED?
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
ALPHA DECAY
-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
CAN RADIOACTIVE DECAY BE ACCELERATED BY TEMPERATURE, ELECTRIC CHARGE, PRESSURE OR GRAVITATION?
no
BETA DECAY
-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
GAMMA RADIATION
-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
ISOMERIC TRANSITION
transition from metastable to ground state
ION PAIR
positively charged ion + electron
PRIMARY IONIZATION
number of ion pairs created by ionizing particle
SECONDARY IONIZATION
ionization caused by liberated electrons
PAIR ANNIHILATION
subatomic particles collide with its antiparticle and create more particles
WHAT ARE EXAMPLES OF PHOTON RADIATION?
gamma and xray
-can travel longer and penetrate deeper than alpha and beta
-xray lower in energy than gamma
-only differ in location
WHAT IS THE SOURCE OF NEUTRONS?
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
POSITRON EMISSION
A type of radioactive decay in which a proton is converted to a neutron, and it
releases a positron
MASS NUMBER
number of protons and neutrons
WHAT MACHINE IS USED TO OBTAIN PROTONS?
cyclotron
MAXIMUM DOSE DEPTH
R100 m
HALF DOSE DEPTH
R50 m
THERAPEUTIC RANGE
R80 m
EXPOSURE RATE
X
EXPOSURE POWER
ampere per kg
POPULATION INVERSION
there should be more atoms in the metastable state than in the ground state from pumping system in laser
WHAT DOES LASER STAND FOR?
light amplification by stimulated emission of radiation
ENERGY OF IONIZING RADIATION
E = mc^2
#m = mass
#c = speed of light
unit = electron volts eV or MeV
X-RAY
-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
HOW ARE NEUTRONS REMOVED FROM NUCLEUS?
-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
NEUTRON INDUCED FISSION
bombardment with a neutron resulting in the splitting of the nucleus into neutrons and gamma rays
PHOTOELECTRIC EFFECT
-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
WHAT IS USED TO MEASURE EXPOSURE OF ONLY GAMMA AND X-RAY IN AIR?
roentgen R
rad R (measures absorbed dose)
STOCHASTIC EFFECTS
= cancer
-DNA changes
-random basis based on probabilities
-no dose threshold
-effect independent of dose
-probability of effect increases with dose
DETERMINISTIC EFFECTS
= tanning
-cell killing
-specific to particular tissues
-threshold
-related directly to dose received
-severity of effect is dose dependent
WHAT IS THE EFFECTIVE DOSE UNIT?
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
LINEAR DOSE RESPONSE MODEL
-suggests that any increase in dose, no matter how small, results in an incremental increase in the risk for cancer
LATENT PERIOD
-period of time between exposure to radiation and the detection of cancer
HORMESIS
-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
LINEAR NO THRESHOLD MODEL
-cancer is directly proportional to the dose level of ionizing radiation
COLLIMETER
-used in x-ray, gamma, neutron
WHAT IS THE SOURCE OF IONIZING RADIATION FOR THE GAMMA KNIFE?
-large number of cobalt sources
-used in brain surgery
WHAT IS THE HOUNSFIELD SCALE USED IN?
CT
WATER = 0
AIR = -1000
BONE = 1000
HOW CAN ENERGY OF PHOTONS BE EXPRESSED?
E = hf
MOST DANGEROUS SCAN FOR PREGNANT WOMAN?
CT
ADVANTAGE OF MRI
the use of non ionizing radiation
-> its radiofrequency waves
WHEN EXAMINING DEEP BODY STRUCTURES WHAT IS USED?
-high pulse repetition frequency
-low ultrasound frequency
WHICH INTENSITY OF AC CAUSES VENTRICULAR FIBRILLATION?
50-100mA
WHICH INTENSITY OF AC CAUSES PARALYSIS AND RESPIRATORY ARREST?
20-50mA
WHICH INTENSITY OF AC CAUSES INTERNAL ORGAN DAMAGE?
2A
WHAT ELECTRICAL CURRENT HAS THE MAXIMAL STIMULATING EFFECTS ON THE HUMAN BODY?
low frequency AC
WHAT IMAGING PROCESS IS BASED ON PROCESSING OF RADIATION THAT IS EMITTED FROM WITHIN THE PATIENTS BODY?
-processes using gamma cameras such as SPECT (2D images -> single photon emission
