nuclear physics 2 Flashcards
radionuclides decay in a manner that conserves ___________________
charge, number of nucleons and energy
what are the several modes of radioactive decay?
-alpha decay
-beta decay (electron or positron, accompanied by a neutrino)
-electron capture (an alternative to Beta plus decay)
-gamma decay (photon, massless, electromagnetic radiation)
-internal conversion (an alternative to gamma decay)
what is the decay expression?
what is the table of disintegration particles?
what are the properties of alpha particles?
-minimal penetrability (<0.1mm in tissue, a few cm in air)
-low risk from external exposure, but damaging if ingested or inhaled
-highly ionizing
what are the properties of electrons?
-modertately penetrating (depends on energy)
-can be stopped by varying thickness of metal
-ionizing
what are the properties of positron?
-moderately penetrating (depends on energy)
-can be stopped by varying thicknesses of metal
-ionizing
-upon slowing down they annihilate with electrons and release energy in the form of 2 photons
what are the properties of photons?
-travels at speed of light in vacuum
-gamma rays when emitted from nuclear processes
-x-rays when emitted from processes outside the nucleus
-highly penetrating
-stopped by several cm of dense metal (Pb, W) or several feet of concrete
what is the general decay diagram?
what is disintegration energy?
-the energy different (ie mass difference) between the parent nuclide and decay products can be calculated to determine 1, whether the decay is energetically possible and 2. the kinetic energy shared between the daughter nuclide and the emitted radiation
-mass, m, is related to energy, E, using einstein’s equation E=mc2
what is alpha decay?
-nucleus emits an alpha particle (2 protons and 2 neutron (He nucleus))
-typically occurs with heavy nuclides> nuclide becomes more stable by decreasing its mass
-daughter: atomic number (Z) decreases by 2, number of neutrons decreases by 2, mass number (A) decreases by 4
-alpha particles emitted from nucleus with discrete energies
what is the alpha decay diagram?
what is a smoke alarm (alpha decay ex)?
-Am-241 (T1/2=432 yr) decays, emitting alpha particles
-alpha particles are detected
-if smoke present, alpha particle detection decreases and alarm sounds
what is radon (alpha decay ex)?
-Rn-222 (T1/2=3.8d) gas, a decay product of Ra-226, can accumulate in buildings
-gas inhaled, alpha-mediated damage to lungs
-leading environmental cause of cancer
what are radium girls (alpha decay ex)?
-women hired to paint clock dials with luminescent substance containing Ra in the 1910s
-1920s women used their lips to point their paintbrushes, ingesting Ra
-the high-Z radionuclides in the Ra decay scheme preferentially deposited in the bones and resulted in alpha-induced damage causing fractures, bone necrosis, anemia, cancer and death
what is beta minus decay?
-beta-minus particle (electron) and an antineutrino emitted
-occurs when radionuclides have an excess number of neutrons (neutron-rich)
-daughter: number of neutrons decreases by one and number of protons increases by one (a neutron becomes a proton)
-isobaric transition (A remains the same)
-energy shared between electron and antineutrino (continuum of energies)
what is beta-plus decay?
-beta-positive particle (positron) and a neutrino emitted
-occurs when radionuclides have an excess number of protons (neutron-poor)
-daughter: neutron number increases by one and proton number decreases by one (a proton becomes a neutron)
-isobaric transition (A remains the same)
-energy shared between positron and neutrino (continuum of energies)
-positron goes on to annihilate with electro and release more energy (in the forms of two photons)
what is electron capture?
-an alternative to positron decay (neutron-deficient radionuclides)
-nucleus captures and orbital electron, with the conversion of a proton into a neutron and the simultaneous ejection of an antineutrino
-typically an inner shell (higher energy) electron is captured (closer to nucleus)
-atomic number is decrease by one
-isobaric transition (A doesnt change)
-the capture of the orbital electron creates a vacancy in the electron shell, which if filled by an electron from a lower energy shell, which results in the emission of characteristic x-rays or Auger electrons
what are the characteristics of x-rays and Auger electrons?
-when a hole is left in an inner electron shell, an electron from a lower energy shell fill its place
-this is accompanied with a release in energy equal to the binding difference between the two electron shells
-energy carried off by an x-ray (characteristic x-ray) or an electron from an outer shell (Auger electron)
-typically a cascade of characteristic x-rays or auger electrons occurs
what are the beta-minus, plus and electron capture decay diagrams?
what is gamma decay?
what is internal conversion?
-competes with gamma decay
-the energy of the gamma is transferred to an inner-shell electron which is ejected from the atom
-results in the emission of characteristic x-rays or auger electrons
-isobaric and isometric
what is isomeric decay diagrams?
what are the biological half-life and the effective half-life?
what are the two type of radiation therapy treatment?
what is an example of external beam radiation therapy?
cobalt-60 source
what is the cobal-60 source?
Co-60 provides:
-high energy gamma rays (mean energy of 1.25 MeV), improved penetration to treat deep-seated tumors with less skin damage
-relatively long half life (5.26 years)
-high specific activity (small source size, better geometry)
-initial activity (5000 Ci)
-produced in a nuclear reactor by activation of Co-59 with thermal neutrons
what is brachytherapy?
-seeds (sealed) containing radioactive substances are implanted into the tumor
-either implanted temporarily (high activity) or permanently (low activity)
-deliver a high dose of radiation directly to the tumor
-often used to treat prostate or gynecological cancer
what is an example of brachytherapy?
treat prostate cancer
what is nuclear medicine imaging versus conventional medical imaging?
what is a bone scan?
Tc-99m bound to bone-seeking drugs
-Tc-99=metastable state of Tc-99 T1/2= 6 hrs, produced in radionuclide generator, gamma emmited
-pianar (2d) projection images
-used to image a variety of conditions metastaic cancer, arthritis, skeletal trauma, infection
what is PET?
positron emission tomography
-tomographic images (3D)
-most common tracer used in PET is fluorodeoxyglucose (FDG), an analogue of glucose with F-18
-F-18 cyclotron-produced, emits positron that annihilate with an electron and produce 2 photons that are detected t1/2=110 min
-uptake of the tracer indicates tissue metabolic activity (indicates location of a tumour)
