Focus 10 Flashcards
(25 cards)
binding energy
the energy that holds a nucleus together
why are atomic masses not exact integers?
this is due to nuclear interactions between the protons and neutrons (which are collectively called nucleons)
the mass variation reflects binding energy differences via E=mcsquared
how to calculate binding energy?
E=mcsquared
main 3 modes of radioactive decay
alpha particles
beta particles
gamma emission
alpha particle decay
emission of a He nucleus
only important for Z>60 and most important for Z>83
aplha emission doesnt penetrate very far (can be stopped by paper or skin) but its ionizing capability is substantial
Beta particle decay
emission of an electron
common in lighter elements
also plays a role in heavy elements
Beta emission is always accompanied by emission of an antineutrino
antineutrino
massless and uncharged particle
emitted during beta emission
charge neutralization in beta particle decay
beta emission initially produces a positive ion of the Z+1 nucleus
but neutralization will usually quickly occur by electron transfer from nearby atoms
so to cAlculate change in mass: determine A for the positive ion rather than the neutral
gamma emission decar
emission of a photon of very short wavelength/high energy
often happens during alpha or beta decay, but it can also happen by itself
often used for cancer treatment because the gamma rays can ionize cells and kill them
gamma rays can penetrate lead and concrete
electron capture
form of decay
electron in orbital near nucleus is captured by nucleus, decreasing Z by 1, with no change in A
positron emission
form of decay
emission of an antielectron, decreasing Z by 1, with no change in A
proton emission
form of decay
decreases Z and A by 1
neutron emission
form of decay
decrease A but not Z by 1
fission
form of decay
only important for U or higher
strong force
holds protons and neutrons together in the nucleus
nuclear decay equation
N(t) = N0 e-kt
This shows exponential decay of number of nuclei N with time.
carbon-14 dating
based on the fact that a living organism exchanges C-14 with its environment, but this stops when it dies
by measuring C-14 activity, one can determine how long ago that the organism died
5700 years = half life of C-14
Tritium dating works the same way, but with a much smaller half life
how is dating of rocks done?
with Uranium-238
medical uses of radioisotopes
Tc-99 for bone scans (gamma emitter)
F-18 for PET (image tumors)
Co-60 for tumor irradiation
what is Americium-243 used for?
used in smoke dectectors to ionize smoke particles
what is plutonium used for?
powering spacecraft for long missions
units of radiation
Intensity: curie (commonly used) = 3.7x10^10 nuclear disintegrations/s
SI unit: the Becquerel = 1 disintegration/s
Dose: rad (commonly used) = exposure to radiation whoch deposits 10^-2 J of energy per kilogram of tissue
SI unit: the gray (Gy) = 100 rad
dose equivalent
Q times the dose (Q is the biological effectiveness)
dose equivalent units
roentgen (same unit as rem)
sievert (Sv, same as gray)
