nuclear science minor program 14 upper division units from the following: chem 482 directed study in...
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Nuclear Science Minor ProgramNuclear Science Minor Program
14 upper division units from the following:
• CHEM 482 Directed Study in Advanced Topics of Chemistry
• NUSC 341 Introduction to Radiochemistry• NUSC 342 Introduction to Nuclear Science• NUSC 344 Nucleosynthesis and Distribution of the
Elements• NUSC 346 Radiochemistry Laboratory• NUSC 444 Special Topics in Nuclear Science• NUSC 485 Particle Physics• PHYS 385 Quantum Physics
What we’ve discussed last timeWhat we’ve discussed last time
• History of radioactivity
• Interactions and Force Carriers
• Standard Model and Subatomic Particles
• Structure of Matter
• Nucleus
• Chart of Nuclides
Forces in Matter Forces in Matter and and
the Subatomic Particlesthe Subatomic Particles
Chapter 1Chapter 1
Natural Decay ChainsNatural Decay Chains
http://hyperphysics.phy-astr.gsu.edu/
(4n + 0)
6 α particles4 β- particles
http://hyperphysics.phy-astr.gsu.edu/
(4n + 2)
8 α particles6 β particles
(4n + 3)
7 α particles4 β particles
The members of this series are not presently found in nature because the half-life of the longest lived isotope in the series is short compared to the age of the earth.
< 4.7 109 y
7 α particles4 β- particles
Types of Radioactive DecayTypes of Radioactive Decay
Chapter 2
Radioactive DecayRadioactive Decay
• Statistical process• Spontaneous emission of particle or
electromagnetic radiation from the atom • Unaffected by temperature, pressure,
physical state, etc• Exoergic process• Conserves total energy, linear and angular
momentum, charge, mass number, lepton number, etc.
Units of EnergyUnits of Energy
• Mass and energy are interchangeable –
E = mc2
where energy usually expressed in MeV
• 1 eV = 1.602 x 10-19 J = 1.60219 x 10-12 erg
• 1 MeV = 1.602 x 10-13 J = 1.60219 x 10-6 erg
• 1 u = 931.5 MeV/c2
Decay ModesDecay Modes• Alpha decay• Beta decay • Gamma decay• Spontaneous fission• Delayed neutron and proton emission• Two-proton decay• Composite particle emission• Double beta decay• Prompt proton decay (new)
Molecular Rotations and Vibrations Molecular Rotations and Vibrations (Bjerrum 1912)(Bjerrum 1912)
01 ħ2/I
10 ħ2/I
L= 0L= 1L= 2
L= 3
L= 4
L= 5
3 ħ2/I
6 ħ2/I
15 ħ2/I
rota
tion
axis
r1r2
r
m1
m2CM
Absorption spectrum of HCl(note the double peaking caused
by two isotopes of Cl)
λ = 3 μm = 3 x 10-4 cm, IR
moments of inertiabond and force length
VibrationsVibrations
http://wwwnsg.nuclear.lu.se
RotationRotation
http://wwwnsg.nuclear.lu.se
prolate rotor oblate rotor
Reflection Asymmetric ShapeReflection Asymmetric Shape
http://wwwnsg.nuclear.lu.se
octupole
Gamma-Ray Radiation and NucleiGamma-Ray Radiation and Nuclei
γγGermanium detector
Num
ber
of c
ount
s
Gamma-ray energy (keV)
29Cu3059
γ-rayenergy, keV
Excitationenergy, keV
Angularmomentum, ħ
γγ
γγ
Alpha DecayAlpha Decay
• 210Po 4He + 206Pb + γ
• t1/2 (210Po) = 138.4 d; Eα= 5.304 MeV
• Typically for A>150; Z > 83 (144Nd, 147Sm)
• Geiger-Nuttall rule:
Et
log
1 log 2/1
HeXX N
AZN
AZ
422
42
216Rn; 8.05 MeV, 45μs144Nd; 1.83 MeV, 2.1 x 1015 y
Conservation of Energy Conservation of Energy for Alpha Decayfor Alpha Decay
Etrans= Eα+ Erecoil
E = ½ mv2
2mE = m2v2 = (mv)2
p = mv; p2 = m2v2 = (mv)2 = 2mE
pα= precoil
2m αE α= 2mrecoilErecoil
Erecoil = (m α/mrecoil)E α
Alpha SpectrumAlpha Spectrum
NAZ X
242
N
AZ Y
Parent
Daughter
α1(20%)
α2(40%)
α3(40%)γ1
γ3 γ2 5.0 5.5 6.0 6.5 7.0 7.5
HeXX N
AZN
AZ
422
42
What we have learned last timeWhat we have learned last time
• Natural decay chains
• Excited molecules and nuclei
• Alpha decay
Alpha DecayAlpha Decay
NAZ X
242
N
AZ Y
Parent
Daughter
α1(20%)
α2(40%)
α3(40%)γ1
γ3 γ2
5.0 5.5 6.0 6.5 7.0 7.5
HeXX N
AZN
AZ
422
42
Counts
Eα (MeV)
238U 234Th + 4He2+
238U 234Th + 4He
Beta DecayBeta Decay
change a neutron to a proton
change a proton to a neutron
EC: electron capture, change a proton to a neutron
is an electron
11 N
AZN
AZ YX
11 N
AZN
AZ YX
11 NA
ZNAZ YeX
β+ is an anti-electron or positron
(negatron decay)
Unlike alpha decay, which occurs primarily among nuclei in specific areas The periodic table, beta decay is possible for certain isotopes of all elements
Negatron (Negatron (ββ--) Decay) Decay
dtSP
ytYSr
3.14
1.29
2/13216
3215
2/19039
9038
YAZ 1Daughter
β1
β2
γ
XAZParent
11 N
AZN
AZ YX
NAZ X
11 NA
Z Y
Neutron rich nuclei; Large N/Z ratio t1/2
Beta decay – Energy Beta decay – Energy spectrumspectrum
• Emax
• Antineutrino in β-
– No charge– No magnetic moment– Near zero rest mass– Spin ½– Conservation of lepton
number
β-
β+
Beta-particle energy
Num
ber
of b
eta
part
icle
s
Etrans = Enegatron + Eantineutrino + Erecoil
Antineutrino discoveryAntineutrino discovery np
1953 by F. Reines and C.L. Cowan Jr.
Positron (Positron (ββ++) Decay) Decay change a proton to a neutron
11 N
AZN
AZ YX
β+ is an anti-electron, or positron
min 3.20
605.2
2/1115
116
2/12210
2211
tBC
ytNeNa
• Proton rich nuclei• Similar spectrum as in negatron decay • Change a proton to a neutron positive electron is emitted by the nucleus and an orbital electron originally present in the parent atom is lost to form a neutral daughter atom.• equivalent to the creation of a positron-electron pair from the available transition energy• 2 x 0.511 MeV = 1.02 MeV necessary to create 2 electrons• β+ decay is possible only when the energy of the transition is greater than 1.02 MeV
The fate of the positronThe fate of the positron• Conversion to pure energy by
positron annihilation
• After the positron slows down to energies comparable to that of surroundings
• Formation of 1, 3, or 0 annihilation photons, depending on the spin orientation of the electron-positron pair
• If the spins are parallel triple state
• If the spins are anti-parallel a single state
• Positronium “atom” light “isotope” of hydrogen, with the positron substituting for the nuclear proton
• Ortho positronium; paralell spins10-7 s
• Para positronium; anti-parallel spins 10-10 s
Electron Capture (EC orElectron Capture (EC orεε))
EC: electron capture, change a proton to a neutron
11 NA
ZNAZ YeXexcited nucleus
+ x-rays or Auger electrons + inner bremsstrahlung
dtIrPt
dtYbLu
2.10 ; electronsAuger raysx
70.6 ; electronsAuger raysx
2/118877
18878
2/1172
7017271
Gamma DecayGamma Decay
• Pure γ decay
• Internal conversion (IC)
• Pair production (PP)
h 5.4
d 8.249
2/111549
11549
2/111047
11047
*
tInIn
tAgAg
XX
m
m
AZ
AZ
Pure Gamma-Ray EmissionPure Gamma-Ray Emission
γ99.8%
β1, t1/2 = 1.17 m
0.2%β2, t1/2 = 6.70 h
92U91Pa
234U
234mPa
234gPa
2 keV < E < 7 MeV; monoenergetic
Internal ConversionInternal Conversion
The excited nucleus transfers the energy to an orbital electron, which is then ejected from the atom (monoenergetic).
EIC electron = Etrans – BEatomic electron
IC and gamma decay are competing processes
Internal conversion coefficient (α)
α= Fraction of decays occurring by gamma emission/Fraction of decays occurring by IC
Pair ProductionPair Production
• E > 1.02 MeV
16mO 16O
Etrans = 6.05 MeV
t1/2 = 7 x 10-11 s
eeXX AZ
AZ
*
Spontaneous Fission DecaySpontaneous Fission Decay
neutrons 215260
9838
25298 NdSrCf
Induced Fission ReactionInduced Fission Reaction
neutrons 29436
14056
123592 KrBanU
Oklo, Gabon – Oklo, Gabon – A natural fission reactorA natural fission reactor
• 235U natural abundance is well known: 0.00720 ± 0.00001
• Uranium deposit where self-sustained nuclear chain reactions have occurred.
• 235U abundance 0.00717, about 3 standard deviations below the accepted value.
• The only process which can lead to reduction of U is fission by low-energy neutrons.
• 2 x 109 y, 235U (~3%) reactor moderated by groundwater.
• Fission product isotope signatures Nd, Ru
Geological Situation in Gabon leading to natural nuclear fission reactors:
1. Nuclear reactor zones2. Sandstone3. Ore layer4. Granite
Fossil Reactor 15, located in Oklo, Gabon. Uranium oxide remains are visible as the yellowish rock.
Source: NASA
OkloOklo
Estimations
• 5 tonnes of 235U were fissioned.
• Total energy released 2 x 1030 MeV or 108 MW∙h. A contemporary power reactor can operate at 103 MW.
• Average power 0.01 MW, operating for 106 y.
Important feature:
the fission products are still in place in the reactor zone and have migrated very little. Despite climate changes, no substantial movement of the fission products has taken place over the past 2 x 109 y.
Confirmation: Nd signatureConfirmation: Nd signature
• natural neodymium contains 27% 142Nd• the Nd at Oklo contained less than 6% but contained more 143Nd• the isotopic composition matched that produced by the fissioning of 235U.
Delayed-Neutron EmissionDelayed-Neutron Emission
• Following beta decay of fission products such as 140Ba and 94Kr
• 87Br 87Kr 86Kr + n + β-
neutron rich
Delayed-Proton EmissionDelayed-Proton Emission
• Production of precursor: 54Fe(p,2n)53Co
• Decay by proton emission: 53Co 52Fe +p
Double-Beta DecayDouble-Beta Decay
• 130Te, 82Se stable to ordinary beta decay, but unstable toward 2-beta decay
• Simultaneous 2 beta emission
2
28236
y 104.18234
13054
y 105.213052
20
21
KrSe
XeTex
x
Two-Proton DecayTwo-Proton Decay
• 22Al (1960), 54Zn (2005)
• 45Fe (2003, 2007)
• 48Ni
End of Chapter 2End of Chapter 2
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