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Nuclear PhysicsNuclear Physics
Nuclear SymbolsNuclear Symbols
23592U
Element symbol
Mass number, A (p+ + no)
Atomic number, Z(number of p+)
Balancing Nuclear EquationsBalancing Nuclear Equations
nK rBanU 10
9 13 6
1 4 25 6
10
2 3 59 2 3
Areactants = Aproducts
Zreactants = Zproducts
235 + 1 = 142 + 91 + 3(1)
92 + 0 = 56 + 36 + 3(0)
Balancing Nuclear Equations Balancing Nuclear Equations #2#2
42
2 2 68 8 Ra
226 = 4 + ____222
222
88 = 2 + ___86
86
Atomic number 86 is radon, Rn
Rn
Balancing Nuclear Equations Balancing Nuclear Equations #3#3
nInU 10
1 3 95 3
10
2 3 59 2 2
235 + 1 = 139 + 2(1) + ____95
3992 + 0 = 53 + 2(0) + ____
3995
Atomic number 39 is yttrium, Y
Y
Alpha DecayAlpha Decay
Alpha production (Alpha production (): ):
an alpha particle is aan alpha particle is a
helium nucleushelium nucleus
ThHeU 2 3 49 0
42
2 3 89 2
Alpha decay is limited to heavy, radioactive
nuclei
ThU 2 3 49 0
42
2 3 89 2
242
242 orHe
Alpha Alpha RadiationRadiation
Limited to VERY large nucleii.
Beta DecayBeta Decay
Beta production (Beta production ():):A beta particle is an A beta particle is an electron ejected from electron ejected from the nucleusthe nucleus
eP aTh 01
2 3 49 1
2 3 49 0
Beta emission converts a neutron to a proton
01
2 3 49 1
2 3 49 0 PaTh
01
01 ore
Beta Beta RadiatioRadiatio
nn
Converts a neutron into a proton.
Gamma Ray ProductionGamma Ray Production
Gamma ray production (Gamma ray production ():):
92238
24
90234
002U He Th
Gamma rays are high energy photons produced in association with other forms of decay.
Gamma rays are massless and do not, by themselves, change the nucleus
Deflection of Decay ParticlesDeflection of Decay Particles
Opposite charges_________ each other.
Like charges_________ each other.
attract
repel
Positron ProductionPositron Production
Positron emission:Positron emission:Positrons are the anti-particle of the electron
1122
10
1022Na e Ne
Positron emission converts a proton to a neutron
e01
Electron CaptureElectron Capture
Electron capture: (inner-orbital Electron capture: (inner-orbital electron is captured by the nucleus)electron is captured by the nucleus)
80201
10
79201
00Hg e Au
Electron capture converts a proton to a neutron
Types of RadiationTypes of Radiation
NuclearNuclearStabilityStability
Decay will occur in such a way as to return a nucleus to the band (line) of stability.The most stable nuclide is Iron-56
If Z > 83, the nuclide is radioactive
A A Decay Decay SeriesSeries
A radioactive nucleus reaches a stable A radioactive nucleus reaches a stable state by a series of stepsstate by a series of steps
Half-life ConceptHalf-life Concept
Sample Half-LivesSample Half-Lives
STOPSTOP
NUCLEAR DECAY KINETICSNUCLEAR DECAY KINETICS
Decay KineticsDecay Kinetics
Decay occurs by first order kinetics (the rate of decay is proportional to the number of nuclides present)
ktN
N
0
lnN = number of nuclides remaining at time t
N0 = number of nuclides present initially
k = rate constant
t = elapsed timektNN o lnln
Calculating Half-lifeCalculating Half-life
kkt
693.0)2ln(2/1
t1/2 = Half-life (units dependent on rate constant, k)
ExampleExample
Determine the amount of Rn-222 that Determine the amount of Rn-222 that remains after 5.0 days if the the half-life is remains after 5.0 days if the the half-life is 3.8 days and you started with 80,000 3.8 days and you started with 80,000 particles.particles.
NNoo = 80,000 particles = 80,000 particles
k = 0.182 dayk = 0.182 day-1-1
N = ? N = ?
First find decay constant. k = ln2 / tFirst find decay constant. k = ln2 / t1/21/2
Example 2Example 2
Determine the activity of Rn-222 that Determine the activity of Rn-222 that remains after 7.0 days if the the half-life is remains after 7.0 days if the the half-life is 3.8 days and you started with 285 3.8 days and you started with 285 counts/min.counts/min.
AAoo = 285 counts/min = 285 counts/min
k = 0.182 dayk = 0.182 day-1-1
N = ? N = ?
First find decay constant. k = ln2 / tFirst find decay constant. k = ln2 / t1/21/2
Example 3Example 3
Determine the percentage of Rn-222 that Determine the percentage of Rn-222 that remains after 9.0 days if the the half-life is remains after 9.0 days if the the half-life is 3.8 days.3.8 days.
NNoo = ??? particles = ??? particles
k = 0.182 dayk = 0.182 day-1-1
N = ? N = ?
First find decay constant. k = ln2 / tFirst find decay constant. k = ln2 / t1/21/2
Nuclear Fission and FusionNuclear Fission and Fusion
FusionFusion:: Combining two light nuclei to Combining two light nuclei to form a heavier, more stable nucleus.form a heavier, more stable nucleus.
01
92235
56142
3691
013n U Ba Kr n
23
11
24
10He H He e
FissionFission: : Splitting a heavy nucleus into Splitting a heavy nucleus into two nuclei with smaller mass numbers.two nuclei with smaller mass numbers.
Energy and MassEnergy and MassNuclear changes occur with small but Nuclear changes occur with small but measurable losses of mass. The lost mass is measurable losses of mass. The lost mass is called the mass defect, and is converted to called the mass defect, and is converted to energy according to Einstein’s equation:energy according to Einstein’s equation:
E = E = mcmc22
mm = mass defect = mass defectEE = change in energy = change in energy
cc = speed of light = speed of light
Because c2 is so large, even small amounts of mass are converted to enormous amount of energy.
ExampleExample
Calculate the mass defect and energy Calculate the mass defect and energy released during this typical fission released during this typical fission reaction.reaction.
++ + +U236
92 Kr8836 n104Ba144
56 236.04556 g 87.91445 g 143.92284 g 4 x 1.00867 g
265.04556 g 235.87197 g
E = mc2 = .2917359 kg x 3.0 x 108 m/s
E = 8.752 x 107 J
FissionFission
Fission ProcessesFission Processes
Event
NeutronsCausingFission Result
subcritical < 1 reaction stopscritical = 1 sustained reactionsupercritical > 1 violent explosion
A self-sustaining fission process is A self-sustaining fission process is called a chain reaction.called a chain reaction.
A Fission ReactorA Fission Reactor
FusioFusionn
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