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http://www.pbs.org/wgbh/nova/physics/sthttp://www.pbs.org/wgbh/nova/physics/stability-elements.htmlability-elements.html
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Nuclear DecayNuclear Decay Why nuclides decay…Why nuclides decay…
need stable ratio of neutrons to protonsneed stable ratio of neutrons to protons
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e Xe I 0-1
13154
13153
e Ar K 01
3818
3819
Pd e Ag 10646
0-1
10647
DECAY SERIES TRANSPARENCY
RadiationRadiation
Radiation-it’s the transfer of energyRadiation-it’s the transfer of energy Radioactivity-The spontaneous emission Radioactivity-The spontaneous emission
of radiation by an unstable nucleus.of radiation by an unstable nucleus.
Good vs. BadGood vs. Bad
IonizingIonizing Has enough energy to kick off an ion.Has enough energy to kick off an ion. Very high energyVery high energy
Non ionizingNon ionizing Does not have enough energy to kick off an Does not have enough energy to kick off an
ionion Low energyLow energy
He42
Types of RadiationTypes of Radiation
Alpha particle (Alpha particle ()) helium nucleushelium nucleus paper2+
Beta particle (Beta particle (-)-) electronelectron e0
-1 1-lead
Gamma (Gamma ()) high-energy photonhigh-energy photon
0concrete
Nuclear DecayNuclear Decay
Alpha EmissionAlpha Emission
He Th U 42
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parentnuclide
daughternuclide
alphaparticle
Numbers must balance!!
Nuclear DecayNuclear Decay
Electron CaptureElectron Capture
Pd e Ag 10646
0-1
10647
electron Gamma EmissionGamma Emission
Usually follows other types of decay.Usually follows other types of decay.
Transmutation Transmutation One element becomes another.One element becomes another.
Half-lifeHalf-life
Half-life (tHalf-life (t½½)) Time required for half the atoms of a Time required for half the atoms of a
radioactive nuclide to decay.radioactive nuclide to decay. Shorter half-life = less stable.Shorter half-life = less stable.
Half-lifeHalf-lifeHalf-lifeHalf-life
ln
1ln
2
f
i
m
mn
mf: final massmi: initial massn: # of half-lives
Half-lifeHalf-life Fluorine-21 has a half-life of 5.0 seconds. If you Fluorine-21 has a half-life of 5.0 seconds. If you
start with 25 g of fluorine-21, how many grams start with 25 g of fluorine-21, how many grams would remain after 60.0 s?would remain after 60.0 s?
GIVEN:
t½ = 5.0 s
mi = 25 g
mf = ?
total time = 60.0 s
n = 60.0s ÷ 5.0s =12
WORK:
mf = mi (½)n
mf = (25 g)(0.5)12
mf = 0.0061 g
Half-lifeHalf-lifeHalf-lifeHalf-life
A sample of a radioactive isotope that was initially A sample of a radioactive isotope that was initially 5000 g decayed for 10,000 years. If 625 g remains 5000 g decayed for 10,000 years. If 625 g remains after this time, what is the half-life of the isotope?after this time, what is the half-life of the isotope?
GIVEN:
t½ = ?
mi = 5000 g
mf = 625 g
total time=10000yrs
n = ?
WORK:n= n =3
n= total time ÷ t1/2
t1/2 = total time/n
t1/2= 10000 ÷ 3
t1/2 = 3333.33 yrs.
ln
1ln
2
f
i
m
mn
Or plug into the equationOr plug into the equation
and solve:and solve:
nif mm )( 2
1
Half-lifeHalf-life Half-lifeHalf-life
GIVEN:
t½ = ?
mi = 5000 g
mf = 625 g
total time=10000yrs
n = ?
WORK:
mf=mi(1/2)n
625g = (5000) (1/2)n
.125=(1/2)n
ln(.125)÷ln(1/2) =nn=3 then plug into n=total time ÷ t1/2
FF issionission
splitting a nucleus into two or more splitting a nucleus into two or more smaller nucleismaller nuclei
1 g of 1 g of 235235U = U = 3 tons of coal3 tons of coal
U23592
FF issionission chain reactionchain reaction - self-propagating reaction - self-propagating reaction critical masscritical mass - -
the minimum the minimum
amount of amount of
fissionablefissionable
material needed material needed
to sustain a to sustain a chain reactionchain reaction
FissionFission
Uranium-235 is the only naturally Uranium-235 is the only naturally occurring element that undergoes fission.occurring element that undergoes fission.
Uranium - 235
FissionFission
Why does fission produce so much energy?Why does fission produce so much energy?
Small quantities of mass are converted into Small quantities of mass are converted into appreciable quantities of energy.appreciable quantities of energy.
E = mc2
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FusionFusion combining of two nuclei to form one nucleus of larger masscombining of two nuclei to form one nucleus of larger mass thermonuclear reaction – requires temp of 40,000,000 K to sustainthermonuclear reaction – requires temp of 40,000,000 K to sustain 1 g of fusion fuel = 1 g of fusion fuel =
20 tons of coal20 tons of coal occurs naturally in occurs naturally in
starsstars
HH 31
21
Fission vs. FusionFission vs. Fusion
235235U is limitedU is limited danger of meltdowndanger of meltdown toxic wastetoxic waste thermal pollutionthermal pollution
fuel is abundantfuel is abundant no danger of no danger of
meltdownmeltdown no toxic wasteno toxic waste not yet sustainablenot yet sustainable
FISSION
FUSION
Nuclear PowerNuclear Power
Fusion ReactorsFusion Reactors (not yet sustainable) (not yet sustainable)
Nuclear PowerNuclear Power
Fusion ReactorsFusion Reactors (not yet sustainable) (not yet sustainable)
Tokamak Fusion Test Reactor
Princeton University
National Spherical Torus Experiment
Synthetic ElementsSynthetic Elements Transuranium ElementsTransuranium Elements
elements with atomic #s above 92elements with atomic #s above 92 synthetically produced in nuclear reactors and acceleratorssynthetically produced in nuclear reactors and accelerators most decay very rapidly most decay very rapidly
Pu He U 24294
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Radioactive DatingRadioactive Dating
half-life measurements of radioactive half-life measurements of radioactive elements are used to determine the age elements are used to determine the age of an objectof an object
decay rate indicates amount of decay rate indicates amount of radioactive materialradioactive material
EXEX: : 1414C - up to 40,000 yearsC - up to 40,000 years238238U and U and 4040K - over 300,000 yearsK - over 300,000 years
Nuclear MedicineNuclear Medicine
Radioisotope TracersRadioisotope Tracers absorbed by specific organs and used to absorbed by specific organs and used to
diagnose diseasesdiagnose diseases
Radiation TreatmentRadiation Treatment larger doses are used larger doses are used
to kill cancerous cells to kill cancerous cells in targeted organsin targeted organs
internal or external internal or external radiation sourceradiation source
Radiation treatment using-rays from cobalt-60.
Nuclear WeaponsNuclear Weapons
Atomic BombAtomic Bomb chemical explosion is used to form a chemical explosion is used to form a
critical mass of critical mass of 235235U or U or 239239PuPu fission develops into an uncontrolled fission develops into an uncontrolled
chain reactionchain reaction
Hydrogen BombHydrogen Bomb chemical explosion chemical explosion fission fission fusion fusion fusion increases the fission ratefusion increases the fission rate more powerful than the atomic bombmore powerful than the atomic bomb
OthersOthers
Food IrradiationFood Irradiation radiation is used to kill bacteriaradiation is used to kill bacteria
Radioactive TracersRadioactive Tracers explore chemical pathwaysexplore chemical pathways trace water flowtrace water flow study plant growth, photosynthesisstudy plant growth, photosynthesis
Consumer ProductsConsumer Products ionizing smoke detectors - ionizing smoke detectors - 241241AmAm
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