radiobiology I Flashcards
what is radiation biology?
-study the action(s) of ionizing radiation on living things
-excitation or ionization
why study radiobiology?
-mysterious yet powerful
-produce effects (people that worked around have side effects)
-useful
-in 1859: sir william crooke’s vacuum tube displayed a fluorescent light (cathode ray) when plucker passed high voltage current through it
what were the side-effects in the beginning?
what was the large-scale civilian nuclear melt-downs?
-the three mile islands accident in Pennsylvania, US in 1979
-the Chernobyl disaster at Chernobyl Nuclear Power plants, Ukraine, former USSR in 1986
-the Fukushima Dalichi nuclear disaster following the earthquake and tsunami in Japan, march 2011
what are major occupational exposures?
-the radium girls
-the uranium mines
-the radiotherapists and technicians
what are the four forces of nature?
-electromagnetic
-weak nuclear forces
-strong nuclear forces
-gravitational force
what are electrons?
-described as wave functions, rather than as point particles in orbits
-quantum mechanical calculations yield probabilities, unlike force, mass and acceleration calculations
-the square of the amplitude of a particle’s wave function yields the probability that particle will appear at that location. Therefore, although the maximum probability of finding an electron correspond to the electron shell model but the probability that it may reside at other locations, even in the middle in the nucleus, is not zero. This is likely the reason why in some forms of radioactive decay, nucleus of an atom can capture and electron
what is indirect vs direct ionizing radiation?
-electromagnetic/indirectly ionizing: photons (x-rays or gamma rays)
-particulate/directly ionizing except neutrons: protons, neutron, alpha particles, negative pie mesons, heavy charged ions, atomic nuclei
what are elastic and inelastic interactions with matter?
-elastic: total energy is conserved in all interactions but KE is conserved only in elastic interactions
-inelastic: some energy is used to free an electron or nucleon from a bound state
what is attenuation?
-absorption+scatter
-effective atomic number (Z) of composite materials (soft tissue=7.4, bone=11.6)
-biological matter is made up of many different elements so it does not have distinct spikes (looks smooth)
-mass attenuation coefficient 1/E^3
what is photoelectric absorption?
-photons and auger electrons released during PE interaction in tissue possess energy <0.5keV
-these lower energy photons and electrons are absorbed rapidly in surrounding tissue
what is compton absorption?
-at energies between 30keV-30MeV
-compton mass attenuation is independent of the atomic number
-more unbound electrons will attenuate more photons by compton scattering
what is pair production (Kn)?
->1.02 MeV (0.51 of positron+ 0.51 of electron)
-radio of triplet to pair production
-increases with incident photon energy
-decreases with atomic number of medium
what is triplet production (Ke)?
-10 MeV photons in soft tissue, 10% of all pair productions occur in the vicinity of an electron (2 electrons and 1 positron at >2.04 MeV)
what is the graph of neutron interactions?
nuclear photoabsorption (ph.n.)
-neutrons most dangerous because no charge so not repelled by anything
what is total attenuation?
what is nuclear potoabsorption?
not systematically calculatable
-irregular dependence of is shape and magnitude on atomic number and atomic weight
-sensitivity to isotopic abundance of the sample/matter
small angle neutron scattering
what is the medical imaging hierarchy?
what is the line of energy?
what is linear energy transfer?
-the amount of energy deposited in biological materials by ionizing radiation
-ratio of energy transferred by c charged particle (dElocal) to the target atoms along its path through tissue (dx) so keV/nanometer
-measure of the density of ionizations along the ionizing radiation/particle
-function of charge and mass
-higher LET radiation lead to more damage to microscopic cross-sections
-not sufficient to describe the net biological effect
what are the values of LET for subatomic particles?
what is the graph of ions vs radicals?
-more unstable if has an unpaired electron
-in ion: atomic shell is complete
-radicals are way more reactive because they are always intermediates
what is water radiolysis/ionization and excitation?
H=electron deficient (attracted towards electron)
O= electron rich (creates dipole)
what is the graph of water radiolysis?
what are the arrangements of water caging an electron?
hydrate electron: cluster isomers
what was the summary?
scattered can also be absorbed by biological material (ionization and excitation can both occur)
