Nuclear Physics – Final Exam

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electromagnetic radiation
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fluctuating fields of electric and magnetic energies
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electric field
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x and y
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magnetic field
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x and z
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types of radiation
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heat, radio/sound, infrared, visable, ultraviolet, x-ray, gamma
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frequency (nu)
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how frequently wave peaks
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wavelength (lambda)
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length from peak to peak/wave to wave
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low energy
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low frequency/long wavelength
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high energy
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high frequency/short wavelength
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wave “packets”
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photon
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low E behaves
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like a wave
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high E behaves
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like a particle
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photon
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chargeless bundle of energy that is massless and travels at the speed of light; can be described as Einstein’s theory of relativity
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atom
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the smallest quantity of an element
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molecule
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two or more atoms
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nucleons
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protons and neutrons; held together by binding energy
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valence electrons
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outtermost electrons responsible for almost all chemical interactions and radiation interactions
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carbon
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used to define mass units (amu) at 12.000
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protons
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defines an element’s name and properties has 1 unit of positive charge
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1.00759 amu
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proton mass
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neutrons
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neutral nuclear particle with no electric charge slightly heavier than proton very unstable, breakdown to proton, electron, neutrine
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1.00898 amu
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neutron mass
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electrons
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smallest subatomic particle has 1 unit of negative charge held in orbit by binding energy p# and e# equal if electrically neutral called negatron when originating from nucleus
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0.000549 amu
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electron mass
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1-20
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1:1 ratio of proton to neutron
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20+
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1:1.6 ratio of proton to neutron
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nuclide
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proton/neutron combinations (over 1500 combinations)
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radionuclides
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unstable proton/neutron combinations
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decay modes
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unstable combinations of released energy and/or subatomic particles drive the nucleus closer to stability
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mass defect
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relationship between mass and energy seen in strong nuclear forces
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12.10266 amu
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carbon is made up of 6p, 6n, and 6e
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95.6 MeV
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energy needed to overcome binding energy
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X
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chemical symbol or element
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A
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atomic mass number (p + n)
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Z
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atomic number (number of protons)
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isotoPe
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same number of Protons (z) different mass (a)
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isoBar
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same weight/atomic mass (a) different number of protons (z)
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isomEr
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different nuclear Energy same atomic mass (a) same atomic number (z) same elements nucleus is excited state (metastable)
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isoTone
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different atomic mass (a) different atomic number (z) different elements same number of neutrons
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fission
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separation of 2 nucleus energy liberating process (200 MeV on average) may be spontaneous or induced
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fission products
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fragments of fission process usually radioactive generally have Z #’s between 30 (Zn) and 64 (Gd)
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fusion
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two light nuclei come together to form a heavier nucleus new nucleus is lighter than the sum of the 2 nuclei due to energy being released (for elements below 26Iron)
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transmutation
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changing from one element to another (n,p) is carrier free high specific activity
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fission byproduct
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produced usually from 235U products are carrier-free separated by precipitation, chromotography solvent extraction decays by beta minus moderators, control rods, and reflectors serve to mediate this reaction
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moderators
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slow neutrons down so they can interact
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control rods
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absorb the neutrons
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reflectors
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keep neutrons in core to maintain fission
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neutron activation
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generally produces beta emitters so most useful only for radionuclide generators
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linear accelerator
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accelerates subatomic particles (usually +charged) to KE high enough to overcome done by alternating voltages between 2 electrodes mostly used for research
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cyclotron
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has linear tube wrapped up into coil with a target in the center makes commercial availability possible
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a decay
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only for heavier elements, greater than 82 consists of 2 protons and 2 neutrons, helium atom w/out electron A# decreases by 4, Z# decreases by 2 biologically harmful, large size an ionizing charge short range of travel transmutation can be stopped by a sheet of paper
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B- decay
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occurs in neutron-rich nuclei Z# increases by 1 can be biologically harmful slightly greater range than alpha particle isobaric transmutation can be stopped by a layer of clothing; few mm of metal
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B+ decay
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occurs in proton-rich nuclei Z# decreases by 1 causes an annihilation reaction 1.022 MeV, 2 photons @ 511 KeV; 180 degrees apart isobaric transmutation
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electron capture
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occurs in proton-rich nuclei most often a K-shell electron gets absorbed Z# decreases by 1 produces characteristic x-rays competes with positron decay isobaric transmutation
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isomeric transition
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originates from within the nucleus transition between isomers releases gamma ray nucleus termed “metastable” very long range of travel no change A# or Z#, no transmutation lead is needed to shield gamma rays
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internal conversion
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alternative to isomeric transition electron is ejected from its orbit characteristic x-ray produced by filling of vacancies no transmutation 140 KeV
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no transmutation
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isomeric transition & internal conversion
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transmutation
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the conversion of one element to another
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isobaric transmutation
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B- decay, B+ decay, & electron capture
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alpha decay schematics
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southwesterly direction; z-2
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beta minus decay schematics
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southeasterly direction; z+1
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beta plus decay schematics
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southwesterly direction; z-1
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electron capture decay schematics
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southwesterly direction; z-1
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gamma radiation schematics
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southerly direction with no change in z
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standard chart
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isobars, diagonal lower right to upper left isotopes, left to right isotones, bottom to top
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trilinear chart
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isobars, vertically adjacent isotones, diagonally adjacent upper left to lower right isotopes, diagonally adjacent lower left to upper right isomers, vertical line through hexagon
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parent
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original nuclide in any mode of decay
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daughter
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the nuclide to which a parent decays, which may be stable or unstable
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particulate radiation
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alpha, beta, positron
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non-particulate radiation/EMR
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x-rays, gamma rays
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excitation
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(near miss) E passing charged particle or EMR causes metastable excitation of outer shell e-
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ionization
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(direct hit) the particle or EMR with E greater than or equal to BE collides with e- and ejects it from its orbit, creating a positively charged atom and free e-; this is known as ion pair
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ion pair
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the ejected electron and the resultant positively charged atom caused by the removal of electrons
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ionizing radiation
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radiations that create ion pairs
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alpha particles
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rapidly lose energy as they interact with matter cause the removal of electrons from an atom large, relatively slow moving particles that travel through matter in a straight line have the ability to create hundreds of thousands of ionizations in a very short distance due to high mass and +2 charge bowling ball
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beta particles
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travel at a high speed than alpha particles their path may involve several deflections or changes in direction excitation, ionization, brems pool table ball
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beta particles – excitation
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may interact with an orbital electron electron is raised to a temporarily higher energy state energy released in the form of visible or infrared light as it returns to its original state scintillators utilize this application
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beta particles – ionization
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a beta particle collides with the orbital electron of an atom and causes it to be ejected leaves the atom without one electron and thus, a net + charge
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beta (-/+) & Bremsstrahlung
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due to charge, a beta particle may be either attracted to or repulsed by the positively charged nucleus of an atom this attraction/repulsion can cause the beta particle to change direction beta particle must slow down as it changes direction beta particle must release energy in order to slow down this energy released is known as Bremsstrahlung
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Bremsstrahlung
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braking radiation; energy released by beta particle as it slows down due to changing directions seen in radionuclides known as “pure beta emitters” Phosphorous32 is an example plastic/lucite shielding is required to lessen the Brems
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likelihood of Bremsstrahlung
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increases in higher z# materials such as lead low z# such as plastic lessens Brems
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x-rays & gamma rays
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non-particulate photons of varying wavelength, amplitude, and propagation/velocity
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Electromagnetic radiation interactions with matter
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photoelectric effect, compton scatter, pair production, photonuclear disintegration
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photoelectric effect
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low energy gammy ray inner orbital electron “photoelectron” completely absorbs the energy of the gamma ray photoelectron is ejected from orbit characteristic x-rays are given off as inner orbits are filled
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compton scatter
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medium energy gamma ray outer shell electron “compton electron” absorbs a portion of the photon’s energy remaining energy is released as a secondary gamma ray
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pair production
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high energy photon greater than or equal to 1.02 MeV interacts near the nucleus two particles are created (beta particle, positron) positron goes on to be involved in annihilation reaction just as with positron decay
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characteristic x-rays
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produced from electron cascades created when the electron in the next energy shell drops to fill the vacancy, transferring lesser BE requirements to the valance shell
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Auger electrons
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produced when either a photoelectron or a characteristic x-ray cause a secondary ionization (usually within the same orbital shell)
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factors that affect quality of images
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scatter & attenuation
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scatter
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deflection of photon due to interaction with matter: patient, air, collimator, crystal
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results of scatter
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change in direction of photon and decrease in energy of photon
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attenuation
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blocking, shielding, or absorption of photons by matter
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results of attenuation
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lower energy photons are more easily/likely attenuated appear as decreased area of uptake on images
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half-life
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time required for half the amount of radioactivity to deplete
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ways which half-life can be expressed
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number of radioactive nuclei (N) amount of activity present (A)
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calibration time
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used to identify amount present at a predetermined time
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purpose of Nuclear Physics
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create an image representing the distribution of a radiolabeled substance within the body
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emissions recorded from radioactive substance
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administered internally recorded externally emissions must be strong enough to exit body
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80 – 500 KeV
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emissions best suited for imaging; sufficient energy to exit body
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thallium activated sodium iodide crystal
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can be stopped by scintillation material
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lead & tungsten
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can be adequately shielded and collimated
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adds counts we don’t want (changes direction & energy)
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scatter
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subtracts counts we want
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attenuation
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number of events
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disintegrations; decays because of radioactivity; too few counts degrade image
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factors that can degrade image
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scatter, attenuation, collimator performance, number of events, equipment QC
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contrast
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the ability to differentiate between target & background and different tissue layers
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thicker/denser crystal
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stops more photons increases crystal sensitivity decreases spatial resolution
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sensitivity
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stopping of photons
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spatial resolution
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measure of how close two distinct sources of activity can get and still be distinguished as separate
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gamma camera collimator
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limits and directs radiation emissions from patient
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parallel hole
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direct representation
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converging
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holes are focused toward a single point focal point located in center of field of view causes organ/image to appear magnified
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pinhole
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specific converging collimator for greatest magnification used in ped/neonatal used for thyroid imaging
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diverging
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holes focused away from large plane toward central point allows for larger object to fit within image constraints
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fan beam
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holes converge along one single line of symmetry useful in cardiac/brain SPECT images
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proportional to resolution
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hole length and diameter smaller, longer holes increases resolution
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septal thickness
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thicker will block higher energy photons will prevent image burnout
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resolution decreases
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distance is increased between patient and camera
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uniformity
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ability of camera to show uniform source as uniform image
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“flood”
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uniformity
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extrinsic flood
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done with collimator on uses a sheet source; normally 57Co done as a daily quality control
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intrinsic flood
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done with collimator off uses a point source; normally 99mTC usually performed as weekly quality control
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resolution
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ability to accurately distinguish between two point sources uses a bar phantom and 57Co sheet source done as a weekly quality control normally done in conjunction with linearity with a bar phantom
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linearity
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ability to display straight lines of activity as straight lines on an image uses the bar phantom done as a weekly quality control
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center of rotation
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corrects misalignment of SPECT images taken from multiple projections done as a weekly quality control
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planar images
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high resolution problem of super imposing structures
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multiple projection w/ SPECT
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sacrifice resolution gain better contrast
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multiple projections
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1, 2, 3 head camera 180 degree and 360 degree orbits 180 degree is beneficial in cardiac imaging
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noise
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random radiation events that provide useless information
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> 1.022 MeV
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positron decay is possible proton rich nuclei decay by either EC or B+
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cyclotron produced
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PET radiopharmaceuticals
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PET radiopharmaceuticals
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produced by bombarding with positively charged particles (protons or deuterons)
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temporal resolution
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light converted quickly
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scintillation material
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requires higher density material
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PET camera
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511 KeV
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bismuth germanate
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good stopping power based on high molecular weight poor/slow scintillator yields only a small amount of light poor energy resolution
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LSO, LYSO, GSO
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sacrifice stopping power for greater scintillation properties (more light per KeV and faster scintillation)
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PET detector arrangement
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8,000-20,000 small crystals 3-4mm and 10-30mm in length too small for individual PM tubes
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16 crystals/PMT; 4 PMT/block
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PET detector arrangement
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true coincidence
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desirable 511 KeV photons detected 180 degrees apart
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scattered coincidence
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will misrepresent actual location of event forms a triangle of detected events
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random coincidence
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two separate events scatters are both registered 180 degrees apart from each other creating an artificial event random events increase with greater activity

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