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2016/2017 > EOS 335 > Flashcards

EOS 335 Flashcards

1
Q

John Dalton

A

all matter consists of atoms

1806

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2
Q

William Prout

A

Law of Constant Proportions

1815

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3
Q

Law of Constant Proportions

A

atomic weights are integral multiples of the mass of hydrogen

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4
Q

why the Law of Constant Proportions does not always hold

A

elements with isotopes do not have integer weights

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5
Q

N

A

number of neutrons

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6
Q

Z

A

number of protons

atomic number

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7
Q

A

A

mass number

N + Z

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8
Q

M

A

atomic mass

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9
Q

I

A

neutron excess number
N - Z
3H excess = 1

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10
Q

Isotope

A

same number of protons different number of neutrons

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11
Q

Isobars

A

same mass number

N + Z

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12
Q

Isotone

A

same # neutrons, different # protons

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13
Q

amu

A

atomic mass unit
dalton
defined by 12C = 12 amu
931.5 MeV of energy

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14
Q

types of nucleosynthesis

A

Big Bang nucleo.
Stellar nucleo.
Explosive nucleo.
Cosmic ray spallation

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15
Q

Big Bang nucleosynthesis

A

primordial nucleons formed from quark-gluon plasma
first few 100µs
once cooled

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16
Q

length of nucleosynthesis

A

about 17minutes

after that T and density of universe too low for fusion

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17
Q

Nuclear synthesis of C, O, etc.

A 
in stars (Stellar nucleo.?) by nuclear fusion or nuclear fission 
up to Fe
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18
Q

formation of elements heavier than Fe

A 
neutron capture (s-, r-processes)
fusion of Fe w/ other elements must absorb E rather than release it
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19
Q

simplest atom

A

proteon
1H
stable
most abundant isotope

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20
Q

hydrogen isotopes

A

1H - proteon, stable, most common (Z = 1, N = 0)
2H - deuterium, stable (Z=1, N=1)
3H - tritium, unstable, (Z=1, N=2)

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21
Q

atom diameter

A

about ca. 10^-8 cm (1 Å)

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22
Q

size of nuclei of atom

A

ca. 10^-12 cm (10^-4 Å)

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23
Q

e-

A

electron number - # of electrons in atom

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24
Q

neutral atom

A

Z = e-

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25
Q

Binding energy vs. mass number

A

binding energy per nucleon (MeV) as a fn of Mass Number, A
Increases straight up, curves to the right = fusion = formation of elements up to (including) Fe
after Fe line is mostly straight across, goes down a bit after A = 110 = Fission

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26
Q

fusion

A

2+ atomic nuclei form 1+ different atomic nuclei and subatomic particles (neutrons and/or protons)
Difference in mass between products and reactants = release of large amounts of energy

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27
Q

fission

A

large nuclei breaks apart into two smaller nuclei, releasing a great deal of energy

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28
Q

most tightly bound nucleus

A

Fe - 8.8 MeV per nucleon binding energy

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29
Q

Isotope notation

A

^A X

e.g. superscript 13 C = mass number 13, 7 N, 6Z

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30
Q

nuclide

A

a distinct kind of atom or nucleus characterized by a specific number of protons and neutrons

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31
Q

nuclear isomer

A

same nuclide, different energy state

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32
Q

types of isotopes

A

radioactive
stable
radiogenic

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33
Q

radioactive isotopes

A

spontaneously and predictably change atomic mass

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34
Q

stable isotopes

A

do not undergo any decay

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35
Q

radiogenic isotopes

A

may be radioactive or stable

a nuclide that is produced by a process of radioactive decay

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36
Q

Neutron number vs proton number for stable nuclides

A

follows 1:1 only up to ca. Z = 20-30
N increase more rapidly than Z
need more N for heavier elements to be stable

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37
Q

Nuclear force

A

holds nucleus together
more powerful than electromagnetic force
only over VERY short distance

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38
Q

radius of nucleon

A

ca. 10^-13 cm

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39
Q

radius of 4He nucleus

A

ca. 2*10^-13 cm

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40
Q

radius of 4He atom

A

ca. 10^-8 cm

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41
Q

Nucleon radius vs force

A

small radius = repulsion
medium radius = attraction
large radius = 0

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42
Q

Segré chart

A

protons vs # neutrons
stability in the middle - darker
decreasing stability in both directions out from the dark middle
top right is completely unstable and many undiscovered

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43
Q

Known nuclides

A

ca. 3000
ca. 275 stable, 270 in nature
ca. 70 unstable (radioactive)

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44
Q

nuclei are stable on what timescale

A

> 10^15 yrs to

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45
Q

Proton/Neutron energy levels

A

have energy levels like electrons
Z:N stability depends on energy levels
even numbers most stable

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46
Q

unstable configurations

A

eventually decay to more stable ones

alpha or beta decay and other processes

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47
Q

magic numbers of protons/neutrons

A

2, 8, 20, 28, 50, 82, 126

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48
Q

what are magic numbers

A

magic # of nucleons = higher average binding energy per nucleon
more stable against decay
analogous to filled shells of electrons (e.g. noble gas)

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49
Q

why are there magic numbers

A

thought that nuclei do not homogenize, stick their component groups like friends in a class

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50
Q

valley of stability

A

atoms at edge of parabola most unstable (dripline)

centre of parabola stable, atoms w/ highest nuclear binding energy

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51
Q

cross-section across valley of stability

A

parabola of binding energies

like x-section (isobar) across Segré chart - low stability, high, low

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52
Q

why are atoms on the dripline most unstable

A

large amounts of energy are released by their decay

β decay

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53
Q

how are isotopes useful in geoscience

A

relative Pb proportions tell Earths age

U-Th-Pb measurements used to determine age of crystals

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54
Q

how Lb is used to determine age of Earth

A

relative proportions of Pb isotopes in meteorites used as proxy
age inferred from Earths bulk Pb isotope composition
determining the age of something
paleotemperature from ice cores
tracers of present processes

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55
Q

Age of Earth

A

ca. 4.56 bya

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56
Q

t = 0 for Earth

A

when it ‘coalesced’

somewhat arbitrary

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57
Q

using isotopes to tell the age of the ocean

A

measure 14C ratios
14C comes from atmosphere (fossil fuels)
tells how long since water was at surface

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58
Q

Isotopes as tracers of present processes, migration

A

you are what you eat

can track butterfly migration from rainwater source

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59
Q

nucleon

A

proton or neutron in nucleus

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60
Q

atomic mass

A

number of nucleons

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61
Q

fermi

A

10 ^ -15 m

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62
Q

strong force

A

extremely short-range force between nucleons

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63
Q

alpha particle

A

helium nucleus, commonly emitted in radioactive disintigration

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64
Q

beta particle

A

electron, emitted in some radioactive disintegrations

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65
Q

gamma ray

A

a high-energy photon
electromagnetic radiation
extremely harmful to living organisms

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66
Q

geiger counter

A

device for measuring radioactivity

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67
Q

scintillation counter

A

device for measuring radioactivity

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68
Q

MRI

A

magnetic resonance imaging

based on energy levels of H nucleus

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69
Q

N(t)

A

population at time t

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70
Q

A(t)

A

activity

number of disintegrations per second

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71
Q

becquerel

A

one disintegration per second

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72
Q

curie

A

another unit of activity

number of disintegrations/s/g radium

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73
Q

protons expel each other by

A

coulombic (electrostatic) force

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74
Q

how do we know nuclear force/strong force has to only act at very short distances

A

otherwise all matter would collapse into a single nucleus

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75
Q

nuclear force is mediate by

A

the pion

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76
Q

Pion

A

type of meson

can exist for a short amount of time

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77
Q

meson

A

intermediate mass particles which are made up of a quark-antiquark pair

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78
Q

mass decrement of an atom

A 
δm = W - M
W = sum of mass of constituent particle (e.g. 6 protons + 6 neutrons + 6 electrons)
M = actual mass of atom
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79
Q

binding energy

A

the mass converted to energy binding the nucleons
measure of nuclear stability
E=δmc^2

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80
Q

magic number features

A

isotopes and isotopes w/ m.n. are unusually common

m.n. nuclides unusually abundant in nature

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81
Q

heaviest stable nuclides

A

N=126

Z =83

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82
Q

number of stable nuclei for odd and even Z and N

A 
Z-N #
odd-odd 4
odd-even 50
even-odd 55
even-even 165
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83
Q

10^-11 seconds after the Big Bang

A

universe expanded and cooled enough for quarks and anti-quarks to condense from energy

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84
Q

10^-4 seconds after the Big Bang

A

cool enough for quarks to associate with each other and form nucleons

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85
Q

10^-2 seconds after the Big Bang

A

universe cooled to 10^11

neutrinos combined with neutrons to form electrons and protons

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86
Q

s-process

A

slow neutron capture

neutrons captured slowly (ca. 1000yrs) to produce successively heavier elements, in late generation stars

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87
Q

r-process

A

rapid neutron capture

tends to form the heavier isotopes

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88
Q

Antoine-Henri Becquerel

A

discovered radioactivity
placed U salts on photographic plates
produced image by beta particles

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89
Q

Marie and Pierre Curie

A

discovered polonium and radium by chemical separation from ores

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90
Q

Ernest Rutherford

A

discovered alpha and beta particles

showed that radioactivity involved transformation of an element in to an entirely different one

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91
Q

J.J. Thomson

A

discovered the electron

invented the first mass spec. – gave clear evidence of two isotopes of Ne

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92
Q

lowest # element that has natural decay

A

52
Te
Tellurium

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93
Q

Protons and neutrons are composed of

A

3 quarks
Proton - 2 up quarks, 1 down quark
Neutron - 1 up quark, 2 down quarks

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94
Q

Stable isotope distribution

A

relatively mixed in top 5 rows of periodic table

83-118 have no stable configurations (Period 7 and Actinide series)

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95
Q

Proton number vs neutron number, decay

A

stable region in middle
proton > neutron = beta + decay
proton

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96
Q

Isotope half-life distribution

A

> 10^15s in the middle

half-life decreases out in each direction from middle

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97
Q

Primary modes of radioactive decay

A

Alpha decay

Beta decay - positron decay, negatron decay, electron capture

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98
Q

Other forms of decay that we will not worry about

A

gamma decay
proton decay
cluster decay

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99
Q

Alpha decay is predominantly

A

in higher atomic number elements

also in Li, Be

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100
Q

Nuclide chart

A

normal plot of Z vs N
shows radioactive decay processes
nuclide has coordinates Z, N
decay will change coordinates

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101
Q

Alph decay

A

spontaneous emission of alpha particle from nucleon

occurs for nuclides with atomic number > 58 and 5He, 5Li, 6B

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102
Q

what is happening during alpha decay

A

a He nucleus is emitted (2protons, 2 neutrons)
no electrons expelled
change in mass
change in E = heat

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103
Q

change in parent from alpha decay

A

Z - 2
N - 2
A - 4
daughter product

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104
Q

mass difference between 2Z+2N and 1 alpha particle

A

equivalent to energy lost in alpha decay:
kinetic energy of alpha particle
kinetic energy of remaining nucleus - conservation of momentum and nucleus recoil)
gamma ray emitted

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105
Q

standard model (element formation)

A

quark - meson (2quarks), baryon (3q) (both hadrons)
baryon – protons, neutrons
meson – pion
lepton - electron, muon, tau, neutrinos

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106
Q

In nuclide chart what is the direction of change associated with alpha decay

A

left two, down two

Z - 2, N - 2

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107
Q

why does alpha decay only occur at high atomic numbers

A

nuclei must have masses above maximum in binding energy curve (56Fe)

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108
Q

proton mass

A

1.00728 u

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109
Q

neutron mass

A

1.00866 u

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110
Q

mass of alpha particle

A

4.00153
(but 2protons + 2neutrons = 4.03188)
mass difference is converted energy

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111
Q

238U alpha decay

A

238,92U – 234,90Th + 4,2He + Q
A - 4
Z - 2

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112
Q

alpha decay branched reactions

A

may not go to lowest energy state right away
intermediate levels are unstable
may evolve gamma emission
depends on where the alpha particle is coming from in the nucleus

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113
Q

beta decay

A

changes charge of nucleus
does not change # of nucleons
daughter product is an isobar
emission of electron or positron

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114
Q

types of beta decay

A

negatron decay
positron decay
electron capture

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115
Q

beta decay stability valley

A

stable nuclei exist in energy valley
α-decay moves nucleus down valley axis
β-decay moves nucleus down walls toward valley axis, depends on which side of the valley the parent lies (Z>N on left)

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116
Q

Negatron decay

A

β- decay
tranform neutron into proton + electron (N – P + e-)
emission of β- from nucleon, antineutrino, energy, γ-ray

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117
Q

results of β- decay

A

Z + 1
N - 1
A = A

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118
Q

movement on nuclide chart from negatron decay

A

up 1, left 1

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119
Q

40K negatron decay

A

40,19K – 40,20Ca + β- + v^ + Q
Z + 1
A = A

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120
Q

Negatron decay daughter

A

gains one proton, Z + 1

same atomic number as parent, isobaric

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121
Q

Positron decay

A

β+ decay
transformation of proton into neutron
emission of +charged electron (positron, β+) from nucleon, neutrinos, radiant energy, gamma rays

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122
Q

results of β+ decay

A

Z - 1
N + 1
A = A

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123
Q

40K β+ decay

A

40,19K – 40,18Ar + β+ + v + Q

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124
Q

movement on nuclide chart from positron decay

A

right 1, down 1

Isobaric

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125
Q

Electron capture

A

capture of extranuclear electron (e.g. K-shell capture)
electron reacts with a proton, forms neutron + neutrino
isobaric decay

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126
Q

results of electron capture

A

Z - 1
N + 1
A = A
same as β+ decay

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127
Q

how electron capture is fundamentally different than β+ decay

A

neutralize a charge rather than throwing it out

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128
Q

why is there lots of harmful rays associated with electron capture

A

excited state = gamma rays

replacement of lost electron = x-rays

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129
Q

125I electron capture

A

125,53I + e- – 125,52Te + v + Q
Z - 1
A = A

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130
Q

movement on nuclide chart from electron capture

A 
down 1
right 1
Z - 1 
A = A
same as β+ decay
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131
Q

Adjacent isobars

A

can not be stable (up/down 1, over 1)

atomic number difference must be > 1

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132
Q

two isobars have

A

different masses

different binding energies

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133
Q

one isobar is converted in to another by

A

β decay

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134
Q

stable isobars

A

must be separate by a radioactive isobar

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135
Q

branching decay

A

decay of isotope by different methods to 2 or more different daughters
e.g. 40K – 40Ar by β+ decay, or to 40Ca by β- decay
ratio of decay directions is fixed
daughters are diagonal in each direction away from parent on nuclide chart

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136
Q

branched decay equation

A

40,19K – 40,18Ar (+ β+ + e-) + 40,20Ca (+ β-) + Q

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137
Q

atomic numbers of daughters for the 4 decay processes

A

alpha = Z - 2
EC = Z - 1
beta + = Z - 1
beta - = Z + 1

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138
Q

U decay series

A

3 clocks - 238U, 235U, 232Th
U (or Th) is rate determining step
multiple alpha and beta decay steps to reach stability
paths of the diff. clocks do not overlap

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139
Q

238U decays to

A

206Pb
8 alpha decays (length of chain)
6 beta decays

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140
Q

235U decays to

A

207Pb
7 alpha decays (chain length)
4 beta decays

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141
Q

232Th decays to

A

206Pb
6 alpha decays (chain length)
4 beta decays

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142
Q

decay end member features

A

stable

high enough in atomic number to be able to avoid contamination

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143
Q

semimetals

A

B, Si, Ge, As, Sb, Te

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144
Q

non-metals

A

noble gases
halogens
C, N, O, P, S, Se

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145
Q

halogens

A

group 17
beside noble gases
F, Cl, Br, I, At

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146
Q

noble gases

A

period 18

He, Ne, Ar, Kr, Xe, Rn

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147
Q

mass spectrometer

A

separates atoms or molecules according to mass

basic parts: ion source, mass analyzer, detector

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148
Q

application of radioactive isotopes

A 
geochronology
tracers 
medical imaging - trace, treatment
energy
weapons
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149
Q

radioactive isotopes, tracers

A

agriculture - plant fertilizers
industry - engine parts
geo-processes and characters

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150
Q

elements that make good radioactive models

A

not extremely short or long 1/2t
common enough for use
well represented in typical rock groups, abundant

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151
Q

Law of radioactivity, Rutherford and Soddy

A

rate of decay of radioactive nuclides is proportional to # of that nuclide remaining at any time (t)
lots of parent = faster decay

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152
Q

Basic Decay Equation (exponential decay)

A

-dN/dt ∝ N_t

λ is proportionality constant so -dN/dt = λN_t

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153
Q

variables in basic decay equation

A 
N = number of nuclides that will decay (parent)
-dN/dt = rate of decay
λ = decay constant (time^-1)
λN = activity (A) or 'rate of decay'
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154
Q

λ

A

decay constant
probability a given constant will decay at time t
typically independent of T, P
experimentally determined, accepted by consensus, not empirical

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155
Q

integrating basic decay equation

A

-dN/dt = λN
-dN/N = λdt
-∫dN/N = λ∫dt
-lnN = λt + C
at t_0 N = N_0 – C = -lnN_0
-lnN = λt - lnN_0

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156
Q

N_0

A

N at t=0
all parent is still present
no decay has taken place yet

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157
Q

Standard/Basic decay equation, working form

A

N = N_0 e^-λt

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158
Q

half life

A 
time required for half of radio-nuclides to decay
t = T_1/2, N = No/2
No/2 = No e^-λT_1/2
1/2 = e^-λT_1/2
-ln(2) = -λT_1/2
T_1/2 = ln2 / λ
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159
Q

rate of decay is proportional to

A

N (amount of parent nuclides)
larger N = more decay
rate decreases exponentially

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160
Q

half life working equation

A

T1/2 = ln2/λ

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161
Q

max number of 1/2 lives

A

5-10

>5 half lives and theres likely not enough parent left for data analysis

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162
Q

low N

A

lower activity
lower decay
lower quality data - less accuracy

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163
Q

14C T1/2

A

5730 yrs

exhausted in ca. 70kyr

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164
Q

40K T1/2

A

1.28Gyr

good for dating 10kyr - 100’s Myr

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165
Q

238U T1/2

A

4.47Gyr

used to date Myr to Gyr

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166
Q

growth of stable daughter

A 
D* = No - N 
D* = No - No e^-λt
D* = No (1 - e^-λt)
D* = how much daughter produced with none present initially
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167
Q

example of when D* is an alright assumption

A

K-Ar dating, Ar is a gas and therefore escapes before rock solidifies

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168
Q

Growth curve of daughter

A

number of atoms vs. time, half lives
exponentially increasing
opposite to decay curve, exponentially decreasing

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169
Q

Geochronology equation

A 
D* = N(e^λt - 1)
D = Do + N(e^λt - 1)
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170
Q

If there is daughter material to start with that is not accounted for

A

rock will ‘appear’ older than it is

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171
Q

Graphing D = Do + N (e^λt -1 )

A

87Sr = 87Sro + 87Rb (e^λt - 1)
y (D) = c (Do) + mx (e^λt - 1)(N)
87Sr is y axis, 87Rb is x, (e^λt - 1) is slope, 87Sro is intercept
If 87Sro = D* = no daughter to begin with, then intercept is at 0
If 87Sro≠D* then there was daughter to start with

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172
Q

How to graphing D = Do + N (e^λt -1 )

A

take multiple samples in same outcrop
rock heterogeneity will give different values
plot all the values (parent, daughter)
if rocks are same age, should plot along straight line and have same to

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173
Q

In graphing D = Do + N (e^λt -1 ), the slope (e^λt -1 ) is what

A

an isochron

it means all rocks that plot along that line have the same age

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174
Q

overcoming mass spec measurement constraints

A

difficult to measure amounts discretely so isotope measurements are generally made as ratios (R)
use stable, nonradiogenic isotope for normalization

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175
Q

87Sr normalization for mass spectrometry

A

86Sr is the stable isotope = normalizer
R = Ro + R_P/D (e^λt - 1)
87Sr/86Sr = 87Sro/86Sro + 87Rb/86Sr (e^λt - 1)
just divide each term by the normalizer
normalizer must be common and not in the decay system
86Sro should technically = 86Sr (Stable)

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176
Q

R P/D plot

A 
R = Ro + R_P/D (e^λt - 1)
y = c + xm
y is the 'now' ratio
x is the Parent/Daughter 
(e^λt - 1) is the slope = isochron
c is the intercept
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177
Q

Assumptions for R vs. P/D plots

A

isotopic equilibrium of system at t=0, i.e. homogeneous value of Ro, generally thermal/diffusional constraint (blocking T)
closed system, i.e. no loss or gain of material (parent or daughter) with time

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178
Q

Rb-Sr commonly used to date

A

Rb-rich minerals: muscovite, biotite, k-feldspar

these minerals do not incorporate much Sr at time of formation

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179
Q

Rb-Sr dating compared with K-Ar

A

Rb-Sr has a greater blocking T - usually gives somewhat older age thank K-Ar (minerals formed slightly later)
minerals form at cooler T according to Bowens reaction series

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180
Q

Using isochron method for Rb-Sr

A

plot multiple rock samples 87Sr/86Sr vs 87Rb/86Sr at to
should be a horizontal line
wait… plot values again at t1
wait.. plot again at t2
should plot co-linearly to the same intercept (if same age)

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181
Q

In isochron dating methods why does the isochron become more steep with time?

A

increasing across x-axis we have rock A, B, C
rock A has the lowest N (initial amount of parent) so its Activity will be lowest
rock C has highest N which equals larger A
more atoms = more decay
the daughter product from rock C is increasing faster than the daughter product from rock A

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182
Q

blocking T

A

temperature below which a mineral becomes a closed chemical system for a specific radioactive decay series

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183
Q

what do we get from the isochron dating method

A

the age of the rock (from the slope)

the initial value, Ro (from the intercept)

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184
Q

what does it mean for rocks to be co-genetic

A

derived from same parent material

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185
Q

how do we know if rocks are co-genetic

A

same, single initial isotope ratio, Ro

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186
Q

Assumptions in radiometric dating

A

N, D have changed only as a result of radioactive decay (closed system)
there was an isotopic equilibrium within the system at the outset (homogenous 87Sr/86Sr)
Parent isotope composition not altered by fractionation at time of formation of rock
decay constant is known accurately
the isochron is not a mixing line
the analytical data are accurate

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187
Q

disintegration rate

A 
A  ≡ λ N
also activity
can be measured with scintillation counter
A = Ao e^-λt
ln A = ln Ao - λt
y = c +mx
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188
Q

Problems with isochrons

A

two sets of rocks with same age may have different Ro
difficult to fit lines of best fit
metamorphic events after formation of rocks

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189
Q

Meaningful isochrons require

A 
large P/D (e.g. 87Rb/87Sr of 5)
large range in P/D in suite or minerals (i.e., Ca + K minerals)
closed system
homogenous D
no fluids and/or metamorphic resetting
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190
Q

dN/dt depends on

A

number of nuclides available to decay
λ is fixed
-dN/dt = λN_t

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191
Q

why K-Ca-Ar work focus on Ar

A

40K/40Ar ratio much higher than 40K/40Ca

Easier to measure differences

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192
Q

Why is 40K/40Ca ratio so low (0.00011)

A

40K least abundant K isotope (0.012%)
40Ca most abundance Ca isotope (96.92%)
Ca is more abundant than K
40K has one of shortest t1/2 of long-lived radio isotopes
∴ ratio is small, signal is hard to detect

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193
Q

Potassium

A

K, Z = 19
alkali metal, group 1A (w/ Li, Na, Rb, Ce)
1 of 8 most abundant crust elements
key component in rock forming minerals

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194
Q

K isotopes

A

39K - stable, 93.3%
40K - radiogenic, 0.012%
41K - stable, 6.73%

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195
Q

Argon

A

Ar, Z = 18
noble gas, group 8 (w/ He, Xe)
mostly gaseous in atmos.

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196
Q

Ar isotopes

A

40Ar - 99.6% (radiogenic)
38Ar - 0.063%
36Ar - 0.337%
all stable

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197
Q

Ar tracer

A

36Ar - not formed from decay

40Ar/36Ar = 295.5 - any deviation = radioactivity

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198
Q

K branching decay

A

40K –> 40Ar + ß+ (positron, e.c.)

40K –> 40Ca + ß- (negatron)

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199
Q

40K –> 40Ar

A

electron capture + gamma rays (11%, 1.46MeV)
e.c. directly to ground state (0.16%)
positron + 2gamma (0.001%)
total ∆E=1.51MeV

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200
Q

40K –> 40Ca

A

negatron emission (∆E = 1.32MeV, 88.8%)

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201
Q

K-Ar-Ca λ

A

λ_T = λec (Ar) + λ_ß (Ca)

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202
Q

fraction of 40K that goes to 40Ca, 40Ar

A 
40Ca = λ_ß / λ_T*40K
40Ar = λ_ec / λ_T*40K
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203
Q

branching ratio

A

R = λ_ec / λ_ß = 0.0117

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204
Q

K-Ar-Ca equations w/ no initial daughter

A

40Ar* + 40Ca* = 40K(e^λ_t - 1)
40Ar* = (λ_ec/λ)40K(e^λ_t - 1)
40Ca* = (λ_ß/λ)40K(e^λ_t - 1)

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205
Q

40Ar_0

A

often assume Ar_initial = 0 b/c gas escapes to atmosphere

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206
Q

K-Ar benefits

A

Ar is noble gas - escapes, volatile, not bound in lattice

can measure Ar-Ar

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207
Q

Measuring 40K/40Ar

A

40Ar - melt rock - measure gas composition w/ MS

40K -sample content measured by flame photometry, atomic absorption, ICPMS

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208
Q

key principle behind K-Ar dating

A

40K/40Ar ratio related to t since rock was cool enough to trap Ar

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209
Q

Rock-forming minerals suitable for dating by K-Ar

A

feldspars, micas, amphibole (hornblende)

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210
Q

K-Ar assumptions

A

40K decays independent of P, T
40K/K_T constant in nature
40Ar* produced by in situ 40K decay since crystallization
corrections can be made for nonradiogenic 40Ar
sample in closed system since t_o - i.e. no losses or gains

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211
Q

violation example of 40Ar* produced by in situ 40K decay since crystallization assumption

A

partial melting

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212
Q

corrections for nonradiogenic 40Ar

A

36Ar from atmos. not decay - amount diffused in is proportional to 40Ar that diffused in (contamination)
40Ar/36Ar = 295.5

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213
Q

K-Ar additional assumptions

A

1 no 40Ar* has escaped
2 mineral closed quickly to 40Ar* after formation
3 no 40Ar_initial or 40Ar incorporated later
4 correction for atmos. 40Ar* leak into mineral
5 normal 39K, 40K, 41K abundances, no fractionation during formation
6 λ, λ_ec, λ_ß accurately known
7 [40K], 40Ar* accurately determined

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214
Q

40Ar* escape

A 
remelting
solution/precipitation
alteration
mechanical weathering
metamorphism
burial P/T
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215
Q

40Ar* is measured how

A

on mass spec by isotope dilution - enriched with 38Ar so there is enough material to measure
40Ar/38Ar
38Ar/36Ar (to correct for atmos. contamination)

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216
Q

Correction for Ar contamination

A

40Ar* = 40Ar_t - (295.5)(36Ar)

note that if there is no contamination 40Ar* = 40Ar_t

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217
Q

Ar example, why you need large # samples

A

Radiogenic 40Ar content vs. distance inward from pillow rim

decrease in 40Ar inward from rim - 40Ar contamination added to pillow rim

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218
Q

40Ar/36Ar vs 40K/36Ar R-P/D plot, y-intercept

A

y-int = (40Ar/36Ar)o = initial ratio = atmospheric contamination

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219
Q

Ar diffusion

A

K-Ar thermally reset if T high enough to allow Ar diffusion

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220
Q

Ar diffusion dependent on

A 
diffusion coefficient (D) - material dependent
temperature (T)
E_a = activation energy 
Arrhenius equation: D = Do * e^(-E_a / RT)
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221
Q

Ar diffusion consideration

A

closure T
cooling rate, closure rate
dependence on mineral used for dating

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222
Q

Diffusion of Ar, Temperature

A

higher T = faster diffusion (good)
in melted rock - 36Ar should escape
in cool rock Ar should stay put

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223
Q

Ar Blocking temperature

A

T wt which mineral becomes ‘closed’ w.r.t. Ar loss

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224
Q

Problem w/ Ar blocking T

A

date obtained will be less than true age unless rock cooled very rapidly

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225
Q

blocking T dependent on

A

diffusion
cooling rate
grain size
grain shape

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226
Q

87Sr normalized by

A

86Sr

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227
Q

87Sr parent

A

87Rb

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228
Q

40Ar normalized by

A

36Ar

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229
Q

radiogenic argon

A

40Ar
accumulated from decay of 40K
also 39Ar but very short t_1/2

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230
Q

non-radiogenic argon

A

blank, trapped, cosmogenic, neutron induced Ar

not from decay

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231
Q

Relic Ar

A

40Ar

remains following partial resetting (partial melting) event

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232
Q

Blank argon

A

unavoidable surgical Ar introduced into MS

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233
Q

excess Ar

A

all contamination

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234
Q

trapped Ar

A

incorporated within mineral

atmospheric Ar w/ or w/o an excess 40Ar component (e.g. H2O)

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235
Q

Excess Ar

A

released from older K-bearing minerals

typically during heating event - trapped as mineral cools

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236
Q

Atmospheric argon

A

Ar from EARTHs atmosphere (different extraterrestrially)

40Ar/36Ar = 295.5

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237
Q

Neutron-induced Ar

A

produced by irradiation of sample in nuclear reactor

mostly synthetic

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238
Q

Inherited argon

A

radiogenic + non-radiogenic Ar introduced by contamination w/ older material (e.g. inclusions)

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239
Q

Argon gains

A
  1. Inherited, 40Ar/36Ar greater than 295.5, overestimate of age
  2. 40Ar doesn’t escape during thermal event - redistributed - disproportionately situated on crystal edges - amongst first to diffuse out during weathering
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240
Q

Argon Losses

A
  1. Extended cooling period - enhanced differences in edges
  2. Differential diffusional loss during reheating
  3. In 39K(n,p)39Ar, 39Ar lost from crystal rim during recoil following radiation
    underestimation of true age
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241
Q

Trouble with K-Ar

A

chemical differences

measured differently

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242
Q

avoiding K-Ar problems

A

Use 39Ar as 39K proxy by irradiating sample - turn K into Ar

39K(n,p)39Ar

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243
Q

benefit to using 39Ar as proxy for 39K

A

measured in same machine at same time

can also measure 36Ar at same time to correct for Ar*

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244
Q

Argon step heating

A

In situ conversion of 39K - 39Ar
incremental heating of sample over ‘total fusion’
allows liberation of Ar in stages
melt sample from outside-in

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245
Q

benefit of step-wise heating

A

permits age determination and identification of domains

246
Q

sample domains

A

anomalous zones/region
e.g. outside edge of sample may be different than inside
if sample closed throughout history no discrete domains, age same at each increment

247
Q

step-heating spectrum corrected for

A

non-radiogenic 40Ar (at every step) using atmospheric ratio from 36Ar measured

248
Q

result of step heating correction

A

excess 40Ar not detected

all 40Ar not corrected for is assumed to be from decay

249
Q

Ar release spectra of samples taken at varying distances from intrusion

A

intrusion = heating = Ar loss
samples closest to intrusion show lowest age corresponding with Ar loss
If no plateau is reached in spectral image than data not trustworthy

250
Q

Schematic 40Ar-39Ar age spectra representations

A

undisturbed - flat line (1 age)
slight disturbance - initial step is lower, increases to plateau
disturbed - no plateau over spectra
reset - plateau in first stages then increase
saddle-shape - presence of excess 40Ar

251
Q

Ar plots

A

heating plots/heating release spectra
Isochron plot
inverse isochron plot

252
Q

Ar inverse isochron plot

A

36Ar/40Ar vs 39Ar/40Ar
like isochron plot, does not assume non-radiogenic 40Ar/36Ar ratio, can be useful for recognizing excess 40Ar in addition to atmos. Ar
higher precision than isochron plot
more commonly used (than isochron plot)

253
Q

measured value in stepwise heating

A

(40Ar/39Ar)m = 40Ar* + 40Ar_c / 36Ar
radiogenic (40Ar*)
contamination (40Ar_c) - atmospheric and Ar entering system since closure

254
Q

Why inverse isochron has lower error

A

[39Ar] is lower than [40Ar] – any measurement inaccuracy in 39Ar/40Ar will produce large error

255
Q

‘pure’ radiogenic component of Ar

A

where 36Ar/40Ar = 0

36Ar is not formed radiogenically

256
Q

extrapolating on inverse isochron plot

A

where 39Ar/40Ar = 0 gives trapped, non-radiogenic component
39Ar ∝ 39K and 40K
corresponds to 40K/40Ar = 0

257
Q

Data in inverse isochron plot represent

A

diff T steps from one mineral (if step-heating)

or diff. spots w/i one mineral (if laser-ablation)

258
Q

inverse isochron plot, measurements w/ high radiogenic component

A

will plot close to 39Ar/40Ar axis

259
Q

Measurements of Earths age

A 
Biblical - 6016yrs
Lord Kelvin, heat flow, 1862 - 20-400Ma
John Joly, Ocean Na, 1899, 80-100Ma
Rutherford (radioactive decay), 1913 - >400Ma
Hubble, 1929, 2Ga
Patterson (Pb isotopes), 1953, 4.55Ga
260
Q

How John Joly calculated age of Earth

A

how much weathering must have had to occur for the Na in the ocean
didn’t account for evaporites

261
Q

µ

A

238U/204Pb

262
Q

238U/235U

A

137.88

263
Q

κ

A

232Th/238U

264
Q

238 decay

A

238U – 206Pb + 8(4He) + 6ß- + Q

∆E = 47.4 MeV

265
Q

235 decay

A

235U –> 207Pb + 7(4He) + 4ß- + Q

∆E = 45.2 MeV

266
Q

ω

A

232Th/204Pb

267
Q

232 decay

A

232Th –> 208Pb + 6(4He) + 4ß- + Q

∆E = 39.8MeV

268
Q

Early methods for U, Th decay

A

chemical method - assume all Pb in mineral/rock is radiogenic (often invalid)
Pb-alpha method - optical spectroscopy to measure Pb, alpha-counting to measure U, Th
U-He method - assumes U, Th minerals retain He released by decay (not always valid)

269
Q

Current U, Th methods

A

U, Th-Pb isotopic method or concordia

Common-lead (Pb-Pb) method

270
Q

Uranium

A

high incompatible - large ionic radii, large charge
mobile among last species to crystallize out
concentrates in crustal rocks

271
Q

thorium

A

high incompatible element - large ionic radii, large charge

relatively immobile

272
Q

U, Th minerals

A

Zircon (more U)
Monazite (more Th)
Apatite

273
Q

zircons

A

abundant
chemically resistant
incorporate U, Th

274
Q

Pb

A

incompatible

immobile except at low pH and high T

275
Q

Pb minerals

A

Galena
substitutes for K in feldspar, biotite
sulphides (come out of hydrothermal vents)

276
Q

U, Th level of incompatibility

A

U more than Th more than Pb

277
Q

homogeneous loss

A

238U/235U remains constant, 238U is lost in the same ratio as 235U
this relationship does not hold for U or Pb gains

278
Q

U, Th rate determining step

A

parent is rate determining - by far longest 1/2 life

279
Q

matching parents with daughters, U, Th, Pb

A

238U 235U 232Th
206Pb 207Pb 208Pb
even-even odd-odd smallest-largest

280
Q

Secular equilibium

A

T_1/2 parent much greater than T_1/2 daughter

e.g. 10-1000X

281
Q

equilibrium

A

quantity of radioactive daughter isotope remains constant b/c decay rate = production rate from parent decay

282
Q

transient equilibrium

A

T_1/2 parent greater than T_1/2 daughter

e.g. few X’s

283
Q

main difference btw transient, secular equilibrium

A

10 half-lives of daughter:
Secular - essentially no parent decay takes place
Transient - significant parent decay takes place

284
Q

secular equilibrium characteristics

A

no initial (or fixed initial) radioactive daughter (rd) material
if no initial then no initial rd decay
rd forms at ca. constant rate from parent
no substantial loss of parent over time
decay of rd once material is accumulated
increased rd material = increased activity
activity increases until it reach rate of formation
after ^ amount remains constant over time (equilibrium)

285
Q

why does increased material = increased decay

A

A Ξ λN
activity is proportional to amount
if you have more you can lose more, probability of any one particle decaying increases

286
Q

time to reach specific A (activity)

A

dependent on λ

287
Q

after n half lives, activity will be

A

f - some faction of rate of formation or saturation activity

f = 1 - (1/2) ^n

288
Q

Secular equilibrium rule of thumb

A

Secular equilibrium is typically reached by 4-5 half lives of the daughter

289
Q

real-life example of secular equilibrium

A

ca. half of U created at creation of universe is left

only Ra that exists today is a result of U decay

290
Q

Transient equilibrium characteristics

A

parent will undergo significant decay
A_d will increase and establish eq. w/ parent activity
A_d ≠ A_p; A_d = A_p * T_p / (T_p - T_d)
as T_d approaches T_p, A_d > A_p - transition eq.
at transition- A_d, A_p change w/ time
once transition equil. attained daughter decays according to T_p

291
Q

T_p

A

T_1/2 parent

T_d = T_1/2 daughter

292
Q

If T_p&raquo_space; T_d

A

A_d = A_p

secular

293
Q

Transition equilibrium

A

typically reached quicker than secular equilibrium

294
Q

Initial lead values on earth

A

known from meteorites
206Pb/204Pb = 17.21
207Pb/204Pb = 15.78
208Pb/204Pb = 37.43

295
Q

238U half life

A

4.468x10^9 yrs
4,468,000,000 yrs
4.468Ga

296
Q

235U half life

A

0.7038x10^9 yrs
703,800,000 yrs
703Ma

297
Q

232Th half life

A

14.010x10^9 yrs
14,010,000,000yrs
14Ga

298
Q

elements in U, Th decay series

A

3 series
12 elements
43 isotopes
no overlap

299
Q

changes in 207Pb, 206Pb with time

A

as rock ages, 207 grows faster
207/206 vs time = increasing hyperbola
235U decays faster

300
Q

concordant

A

if ages obtained from independent U, Th Pb chronometers are the same
(usually do not agree- discordant)

301
Q

Dicordancy often a result of

A

Pb loss
intermediate daughter loss
caused by radiation damage from alpha decay

302
Q

common lead method

A

206-207 method
Pb-Pb method
combine 2 U-Pb geochronometers
lessen effects of open-system

303
Q

Pb-Pb method characteristics

A

does no assume Pb_0 is insignificant

often yields older date than individual system - ratio of Pb isotopes not as sensitive to Pb loss

304
Q

why is Pb-Pb ratio not as sensitive to Pb loss

A

losses tend to be isotopically homogeneous

305
Q

238U/235U

A

137.88

306
Q

Pb-Pb system

A

207Pb/206Pb = (e^λ_235t - 1) / 137.88(e^λ_238t - 1)
too complex to solve- L’Hopital
use Wetherill table

307
Q

what we can see from Pb-Pb equation

A

only dependent on age

not on P/D b/c that is a fixed ratio

308
Q

Why Pb-Pb type system is not often used with Th

A

U, Th different elements - different behaviours, processes

unequal gain/loss

309
Q

Pb-Pb system value

A

∆-relationship does not assume negligible/small starting Pb
not affected by recent alteration (Pb-loss or U-loss)
only Pb addition or aging after alteration affects measured age

310
Q

Why is Pb-Pb method not affected by Pb-loss or U-loss

A

depends only on ratios not []’s

311
Q

232Th-238U method

A

similar equation to Pb-Pb method
different elements, behave differently - unequal loss/gain
works if kappa is constant (not given)

312
Q

Where does U come from

A

supernova (collapsing star) - high E - accretion on to planet

313
Q

238U half life

A

4.468Ga

314
Q

Pb-Pb equation

A

207Pb/206Pb = (e^λ_235t -1)/137.88 (e^λ_238t -1)

315
Q

Where did Pb come from

A

R&S processes
decay
super-enriched in crust due to decay

316
Q

Where is U on Earth

A

enriched in crust relative to mantle

incompatible - stays in melt longer - doesn’t want to crystallize

317
Q

Closure temperature

A

blocking T

pt where system becomes ‘closed’

318
Q

A system is open if

A

T is is high enough for atoms to diffuse in/out of crystals

319
Q

Blocking T depends on

A 
compatibility
duration of heating
grain size
pore fluids
mineral chemistry
320
Q

Example blocking T’s

A 
U-Pb, zircon- >900ºC
U-Pb, titanite- >650ºC
Sm-Nd, garnet- 600ºC
U-Pb, apatite- 500º
K-Ar, hornblende- 500º
Rb-Sr, feldspar, biotite- 500º
321
Q

If T_1/2 of daughter is greater than T_1/2 of parent

A

equilibrium will never be reached

322
Q

238U/235U

A

137.88

323
Q

Homogenous loss

A

isotopes lost in the same proportions as in the rock before losses, e.g. Pb

324
Q

If closed system, 207Pb/204Pb vs 206Pb/204Pb

A

= straight line

325
Q

207Pb/204Pb vs 206Pb/204Pb shape of growth curve

A

distance point moves along the line

238U/204Pb (µ)

326
Q

mineral suitable for U-Th-Pb methods

A

Zircon

327
Q

what is needed in a mineral for U-Th-Pb methods

A

retain radiogenic Pb

be common

328
Q

why zircon?

A

retain radiogenic Pb- resistant to mechanical/chemical weathering, metamorphism, remains closed system, robust
be common - found in igneous, metamorphic, sedimentary

329
Q

Zircons in sedimentary

A

do not tell age of sedimentary deposit! they are inclusions

330
Q

Kober-method

A

single zircon Pb evaporation

hit Zircon w/ high T - vaporize - 2step heating

331
Q

why 2-step heating is necessary for zircon

A

rim most likely to lose Pb or have overgrowth (Ga weathering)
core most likely to preserve Pb isotope signature

332
Q

Zircon formula

A

ZrSiO4

333
Q

Zircon mineralogy

A

very hard
resistant to weathering
permits substitutions of U, Th for Zr
concentrates U/ Th, not Pb - high U/Pb

334
Q

Concordia diagram

A

206Pb/238U vs 207Pb/235U
both ratios proportional to t
basically 238U-206Pb* age vs 235U-207Pb* age

335
Q

Shape of Concordia curve

A

root curve

initially 207Pb/235U increases more rapidly, as 235U used up trend inverts 206Pb/238U increases more quickly

336
Q

When to use Concordia

A

whenever you can- gold standard

rocks/minerals w/ extremely high 238U/204Pb

337
Q

Why do 207Pb and 206Pb grow at different rates

A

differences in λ’s
low abundance of 235U
235U decays much faster (shorter T1/2) - 207 produced faster

338
Q

concordant dates

A

238U-206Pb age = 235U-207Pb age

339
Q

On Concordia diagram, the locus of all points yielding concordant dates is called

A

the concordia curve

ages are concordant

340
Q

235U half-life

A

0.704Ga

341
Q

Why is a Concordia curve not a straight line

A

207Pb ‘grows’ faster

342
Q

Any point along Concordia curve

A

represents equal age

343
Q

evolution of Concordia curve

A

doesn’t just grow along the x-axis like if you were drawing a curve
the curve actually moves up the y-axis
x-axis is not age

344
Q

What if there is complete Pb loss? (Concordia)

A

then zircon is reset to time of loss

U-Pb dates can not distinguish a ‘reset’ zircon from a crystallized zircon

345
Q

232Th half-life

A

14.01Ga

346
Q

If partial Pb loss in Concordia

A

data plot on chord that connects true age of zircon w/ age Pb loss occurred - if sufficient data

347
Q

Concordia ‘chord’

A

discordia line

348
Q

Better if Pb loss is continual or episodic

A

episodic

continual causes greater difficulties, uncertainties

349
Q

Pb gain, Concordia

A

less likely
more difficult - not homogenous
cannot be predicted - no specific age relationship
makes dates uncertain

350
Q

U gain, Concrdia

A

similar to Pb loss - discordia line (beneath concordia)

351
Q

Discordia line, intercepts

A

upper can represent age of formation of rock

lower may represent date of Pb loss if single stage, not continuous

352
Q

Where would Pb gain plot

A

above Concordia

353
Q

Metamict texture

A

fracturing in crystal
natural radiation damage
amorphous crystal
increases/allows Pb mobility

354
Q

The location of a point of the Concordia depends on

A

ONLY age

355
Q

Concordia =

A

simultaneous coevolution of 206Pb and 207Pb via 238U and 235U decay (respectively)

356
Q

Rocks/minerals that do not plot on the Concordia

A

yield discordant dates

357
Q

As rocks age (Concordia)

A

move along concordia (if no Pb, U mobility)

358
Q

If different Zircon samples from same rock lost differing amounts of Pb during same episode

A

would all plot along discordia

359
Q

decay rate is dependent on

A 
# of atoms
independent of physical characteristics (T,P)
360
Q

activity is measured in

A

atoms / unit time = disintegration rate = total activity

361
Q

N

A

number of particles

362
Q

oldest known rock in Canada

A

4.28Ga
bedrock, eastern shore of Hudson Bay
Jonathan O’Neil, McGill University
Sm/Nd technique

363
Q

2nd oldest known rock in Canada

A

4.03Ga

Gneiss, NWT

364
Q

Oldest Earth material

A

Zircon
4.37-4.41Ga
Jack Hills, W. Australia

365
Q

oldest cratons

A

ca. 4.3Ga

- materials older than cratons (e.g. zircons)

366
Q

differentiation of Earth

A

layering (e.g. mantle, crust, core..)

367
Q

importance of Earths differentiation

A

understanding ore deposits

368
Q

Earth processes that shape and determine compositional nature of planet

A

metamorphism, erosion
destroy ancient features
systems may retain some information

369
Q

Chemical differences between elements

A

valance state, ionic radius, etc.

lead to differentiation

370
Q

Uranium chemical associations

A 
lithophile
actinide series
incompatible 
concentrated in lithosphere
can substitute for other lithophilic elements
371
Q

Lead Goldschmidt classification

A

chalcophile

372
Q

chalcophile

A

metals and heavier nonmetals that have low affinity for O and prefer to bond with S as highly insoluble sulfides

373
Q

Rubidium chemical associations

A

alkali metal (Group 1A)
associates w/ Li, Na, K, Ce
substitutes for K
more incompatible than Sr

374
Q

Strontium chemical associations

A

Alkali earth (Group IIA)
associates w/ Be, Mg, Ca, Ba, Ra
Substitutes for Ca (feldspars)
more compatible

375
Q

Rb/Sr fractionation

A

by igneous processes

Rb stays in melt longer - enriches in lithosphere relative to Sr

376
Q

U/Pb, Rb/Sr differences valuable

A

can explain some of Earth’s fractionation processes

377
Q

Value in explaining Earth’s fractionation processes, Rb/Sr

A

differentiation/fractionation of alkali metals from alkali earths

378
Q

Value in explaining Earth’s fractionation processes, U/Pb

A

fact./partitioning of compatible vs incompatible elements

379
Q

Value in explaining Earth’s fractionation processes, Sm/Nd

A

describe events that lead to fractionation of REE

380
Q

Granites

A 
lithospheric, surface rocks
essential constituent of continental crust
mosaic of diff. ages 
accumulate, brake up, drift
5Ma - 4Ma
381
Q

5Ma granites

A

Andes, Alps, Himalayas

382
Q

Strontium granite ratios

A

87Sr/86Sr ranges 0.705 - 0.850
not homogenous
older rocks have higher ratio (decay)

383
Q

Rubidium granite ratios

A

87Rb/87Sr range: 0.5 - 3, average 1

due to incompatibility of Rb

384
Q

Basalts

A

essential constituent of oceanic crust
very young - oldest ca. 200Ma, average 80Ma
from high T mantle-melting

385
Q

Basalt Sr ratios

A

87Sr/86Sr: 0.7020 - 0.7070

younger rocks

386
Q

Basalt Rubidium ratios

A

87Rb/87Sr: 0.001

due to incompatibility of Rb

387
Q

Oceanic Basalts

A

MORB

OIB

388
Q

MORB

A

Mid-ocean-ridge basalts
upper mantle
arises from mid-ocean ridges - spreads - subjected - mantle

389
Q

OIB

A

Ocean-island basalts
lower mantle
arises from subaerial volcanism - form island chains, archipelagos

390
Q

upper mantle

A

depleted mantle material

391
Q

lower mantle

A

primary, ‘bulk earth’ material

392
Q

MORB isotope ratios

A

87Sr/86Sr - narrow range, ca. 0.7025

87Rb/87Sr - ca. 0.001

393
Q

OIB isotope ratios

A

87Sr/86Sr - narrow range, ca. 0.7035 (higher than MORB)

394
Q

Continental crust Sr ratio

A

87Sr/86Sr - 0.705 - 0.850 (granites)

395
Q

Sm decay

A 
147Sm decays to 143Nd
alpha decay (A - 4)
T_1/2 = 10^6 years - very long lived
396
Q

Sm, Nd characteristics

A 
7 naturally occurring isotopes 
only 147Sm impacts 143Nd
143Nd is stable
both are intermediate REE
similar chemical properties 
Nd enriched in lithosphere relative to Sm
397
Q

Sm, Nd similar chemical properties

A 
results of identical outer electron shell configuration
similar but importantly different ionic radii 
Sm smaller (1.04Å vs. 1.08Å)
398
Q

Sm/Nd ratios

A

chondritic - 0.32

present day - 0.1967

399
Q

Nd enriched in lithosphere

A

more than Sm, opposite of Rb/Sr

400
Q

during fractionation of magma, Sm/Nd

A

decreases

401
Q

fractionation pathway of igneous rocks

A 
ultramafic, deep mantle, high Nd - mafic - intermediate - felsic, continental, crustal, lithospheric, low ratio, low Sm
high T (first to crystallize) - - - low T (last to crystallize)
402
Q

Early stage Sm/Nd crystallization

A

mafic igneous
high Sm:Nd -close to the 0.32 chondrite end-member
calc-alkaline - basalt, andesite, dacite, rhyolite

403
Q

crustal rock Sm/Nd

A

lower than mantle rocks

404
Q

REE plot

A

chondrite normalized abundance for REEs
MORB ca. straight line around 10
upper continental crust > than MORB (ca.100) for first 3 REEs - decrease - below MORB and straightens out
-the decrease points are the radiogenic elements, unique (Nd, Sm)

405
Q

Sm decay equation

A

143Nd = 143Nd_o + 147Sm(e^λt - 1)

406
Q

Why does Sm/Nd decrease in fractionation

A

Sm stays in mantle, more compatible

407
Q

Sm/Nd normalized by

A

non-radiogenic 144Nd

408
Q

Sm-Nd theory

A

Earth isotopically homogenous at outset - initial 143Nd/144Nd ca. to that in meteorites - deviations btw measured and expected evolution through time

409
Q

CHUR

A

Chondritic Uniform Reservoir
chondritic (stony) meteorites (especially carbonaceous)
thought to represent earliest material formed in solar system before planets

410
Q

CHUR used as

A

approximation of what Earths accretionary composition was 4.6Ga

411
Q

Present CHUR 143Nd/144Nd

A

0.512638

= homogenous bulk earth

412
Q

Present CHUR 147Sm/144Nd

A

0.1967

413
Q

All meteorites have

A

same age
same 143Nd/144Nd = 0.512638
not same 87Sr/86Sr

414
Q

refractory elements

A

behave coherently, consistently

Sm, Nd, Sr

415
Q

volatile elements

A

low boiling points that are associated with a planet’s or moon’s crust and/or atmosphere
Rb

416
Q

Using CHUR to determine Earth’s differentiation

A

when lines diverge from CHUR line
Partial melt - below CHUR - SM depletion
residual solids above CHUR line - Nd, SM enriched

417
Q

143Nd/144Nd above CHUR line

A

depleted mantle (enriched, Sm more compatible then Nd)

418
Q

143Nd/144Nd below CHUR line

A

continental crust

419
Q

ε_ND

A

= [ (143Nd/144Nd)sample - (143Nd/144Nd)chur) / (143Nd/144Nd) ] x10,000
differences in 143Nd/144Nd are small

420
Q

εND for CHUR

A

= 0

421
Q

εND range

A

-20 to +14

422
Q

(+) εND

A

high Sm/Nd
high 143Nd/144Nd
enriched relative to meteorite/bulk earth

423
Q

Depaolo and Wasserburg

A

devised εND scale, 1976
easier to express and show differences
graph easier to interpret

424
Q

Combining Nd, Sr isotopes

A

negatively correlated
rocks w/ large Sm/Nd variation = mafic, ultramafic, smallest variation = felsic rock
Rb/Sr = opposite

425
Q

Nd, Sr incompatibilities

A

Rb more incomp. than Sr

Nd more incomp. than Sm

426
Q

εND vs 87Sr/86Sr

A

Bulk earth plots along 0 εND
MORB, OIB above and to left of bulk earth (+)
CC below and right of b.e. (-)

427
Q

Elemental differentiation, crust

A

melt
Sm/Nd less than 1, depleted in Sm, below b.e. line
Rb/Sr greater than 1, enriched in Rb, above b.e. line

428
Q

( - ) εND

A

low Sm/Nd
low 143Nd/144Nd
depleted relative to meteorite/bulk earth

429
Q

BABI

A

basaltic chondrite best initial

standard for ‘primitive’ mantle

430
Q

Why doesn’t OIB match bulk Earth?

A

appears to have undergone mixing (subduction)

also not one specific value

431
Q

Elemental differentiation, mantle

A

solid residue
Sm/Nd greater than 1, enriched in Sm
Rb/Sr less than 1, depleted in Rb

432
Q

Sialic

A

relatively light rock
rich in silica, alumina
typical of outer layers of earth

433
Q

Mechanisms for creating continental crust

A
  1. Accretion of oceanic crust
  2. Underplating of magmas
  3. Continental volcanics
  4. Subduction
434
Q

accretion of oceanic crust

A

not common, most subducted

add depleted material - melt - granite

435
Q

Underplating of magmas

A

depleted - remelting - granite

436
Q

Continental volcanics

A

flood basalts
300Ma later still large flood basalt provinces
old provinces may be partitioned by dykes - metamorphosed, melted

437
Q

subduction

A

accretion of arcs
most likely
now principal mechanism

438
Q

NA age provinces from

A

reworking (metamorphism, melting) of crust

addition of new crust

439
Q

Determining age provinces, use

A

Rb-Sr

new crust should have lower 87Sr/86Sr, younger

440
Q

NA Archaen craton

A

stable over geologic time scale
deep rooted ca. 70km
rifted would release massive CO2

441
Q

age provinces in NA

A

Archaen block in the middle, 2350-2700Ma (Hudsons bay) - less age as you move out in either direction
youngest on W coast (less than 440Ma)

442
Q

evolution of continental crust with time

A

consensus - crust grown at steady rate through geological time - gradual growth
growth w/ accretion

443
Q

2 component mixing, proportion present

A

f_a = A/ (A+B)
f_b = B/(A+B)
f_a + f_b = 1

444
Q

2 component mixing, end members

A

if the endmembers are known, then f_a can be calculated for any mixture

445
Q

Two component mixing hyperbola

A 
Ratio-Element Plot
87Sr/86Sr vs. Sr, ppm
two end members component A, component B
Mixture 'M' somewhere in the middle
with 2 pts can find the 3rd
446
Q

two component mixing hyperbola, Sr_A / Sr_B less than 1

A

decreasing hyperbola

447
Q

two component mixing hyperbola, Sr_A / Sr_B > 1

A

increasing hyperbola

448
Q

two component mixing hyperbola, Sr_A / Sr_B = 1

A

straight line

ONLY if end members are equal

449
Q

linearize it (2 component mixing)

A

take reciprocal of hyperbola to make it linear

87Sr/86Sr vs 1/Sr ppm^-1

450
Q

binary mixing

A

2 components, 2 isotope ratios
two elements - Sr, Nd
end members - crust, mantle

451
Q

basalt-granite binary mixing may be from

A

igneous rocks formed basalt magma assimilated granitic rocks or magma generated by melting of a mixture of granitic and basaltic source rocks

452
Q

HIMU

A

high mantle uranium
high µ
high 206Pb
µ = 238U/204Pb

453
Q

mantle array

A

graphical plot of 144Nd:143Nd against 87Sr:86Sr for igneous rocks. Rocks which have been derived from the mantle tend to plot on a straight line; those that show evidence of crustal contamination tend to fall off the line

454
Q

mantle array represents

A

mixing

and evolution?

455
Q

mantle array, primitive mantle

A

origin
ε_UR(Sr) = 0
ε_CHUR(Nd) = 0

456
Q

mantle array quadrants

A

I - enriched in Rb, Sm
II - depleted in Rb, enriched in Sm
III - depleted in Rb, Sm
IV - enriched in Rb, depleted in Sm

457
Q

mantle array, typical depleted mantle

A

quadrant II
depleted in Rb, enriched in Sm
residual solids

458
Q

mantle array, sedimentary rocks

A

quadrant IV
Rb enriched, Sm depleted
much larger range c.w. mantle rocks
very old

459
Q

Mantle array mixing line

A

DM, EMII end members

460
Q

DM

A

depleted mantle

461
Q

EM

A

enriched mantle material
crust, sedimentary rocks end member
contaminates mantle through subduction

462
Q

FOZO

A

focus zone

emanating point

463
Q

EM and HIMU from

A

subjected ocean crust and continental crust (OC, CC)

464
Q

Sr isotope signature, Fraser river

A

runs through terrains of different ages - tributaries carry unique isotope signatures from source land - water signature changes along way
old continental signature ‘diluted’ as younger material is mixed in

465
Q

global runoff average

A

0.7119 87Sr/86Sr
10 major rivers mixed together
lower end member
younger/OC and higher [Sr]

466
Q

Ganges, Brahmaputra

A

himalayas
high [Sr]
high 87Sr/86Sr
very rapid erosion rates

467
Q

Ganges 87Sr/86Sr

A

0.7257

468
Q

Brahmaputra 87Sr/86Sr

A

0.7210

469
Q

Himalayan weathering

A

rapid uplift = rapid erosion
87Sr rich from terrigeneous sediments, orogenic granites
downstream carbonate signal dominated by high Sr signal
increasing oceans isotopic ratio (slowly)

470
Q

Himalayan drainage basins

A

large marine limestone, evaporites

low 87Sr/86Sr (0.706 - 0.709)

471
Q

Hydrothermal 87Sr/86Sr isotope signatures

A

seawater component - 0.70916

basaltic component - 0.7025

472
Q

effects of orogeny on ocean isotopic signal

A

convergence - orogeny - relief - erosion of old crust - increased ratio

473
Q

Era when continents moved to current positions

A

Cenozoic

474
Q

changes in altitude =

A

changes in weathering/erosion

475
Q

Ocean 87Sr/86Sr, Cenozoic

A

Increasing over most of duration

476
Q

through the Phanerozoic, Sr isotopes highest during

A
  • times of higher tectonism
  • greater uplift
  • greater weathering input
477
Q

Carbonate Sr sources

A

rivers - large variation
hydrothermal inputs - constant
seafloor spreading - geologically slow

478
Q

other factors that correspond with carbonate Sr changes

A 
climate changes
ocean oxidation (kind of)
479
Q

cosmic ray

A

primarily high E H, He nuclei
H = proton
He = alpha particle

480
Q

incoming cosmic ray particles

A

89% protons
10% helium
1% electrons (ß-)

481
Q

collision of particles w/ molecules

A

nuclear spallation

482
Q

nuclear spallation

A

formation of rare isotopes

radioactive or stable

483
Q

measuring cosmogenic isotopes

A

AMS

very low in abundance

484
Q

AMS

A

accelerator mass spectrometer

485
Q

cosmic rays interact with atoms

A 
in atmosphere
in crust (rarely)
486
Q

spallation creates

A

cosmogenic radionuclides

487
Q

spallation reaction

A

14N - bombarded by radiation - neutron captured - proton expelled - 14C, Z=6, N = 8
1,0n + 14,7N – 14,6C + 1,1H
14,7N(n,p)14,6C

488
Q

After formation of cosmogenic radionuclide

A

eventually reverts back to original state

14C (6p, 8n) - expel ß- particle - 14N (7p, 7n)

489
Q

Hess

A

Victor Hess, 1912, balloon flight
[ ] of cosmic rays increases w/ altitude
measured during solar eclipse

490
Q

why Hess measured cosmic rays during eclipse

A

nobody agreed with him
solar radiation blocked out
any radiation measured would be cosmic radiation

491
Q

Cosmic rays at Earth

A

concentrated at poles
ca. 4X greater near poles
electromagnetic field (dynamo effect)

492
Q

Dynamo effect

A

mechanism by which a celestial body or star generates a magnetic field
rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales

493
Q

Isotopes formed by action of cosmic rays on air

A

3H, 10Be, 14C, 26Al, 32Si, 36Cl, 39Ar, 53Mn, 59Ni, 129I

494
Q

cosmogenic nuclides governed by

A

basic decay equation

N = N_o *e^-λt

495
Q

typical N_o (cosmogenic nuclides)

A

0
short life
little-no background

496
Q

Approaches for using cosmogenic nuclides

A

Radiometric Dating

Exposure Age

497
Q

Radiometric dating of cosmogenic nuclides

A

incorporation - isolation -decay

498
Q

Exposure Age of cosmogenic nuclides

A 
direct irradiation of Si, O
especially quartz (10^6 yrs for saturation)
499
Q

3H useful for

A

tracing water on ca. 100-yr timescales

short-term water movements

500
Q

Unique about oxygen, nitrogen

A

dipoles
absorb majority of cosmogenic energy
most abundant atoms in atmosphere

501
Q

10Be

A

cosmogenically produced nuclide
readily absorbed in aerosols - rained out
remains in atmos. 1-2 weeks
adsorbed onto ocean clays

502
Q

10Be formation

A

cosmic ray + O/N (atmosphere)

spallation of O, Mg, Si, Fe (crust)

503
Q

production rate of 10Be

A

10^-2 - 10^3 atoms/cm^2/sec

0.01 - 0.001

504
Q

10Be half life

A

T_1/2 = 1.5x10^6 y

505
Q

formation of 26Al, 36Cl

A

intx cosmic ray + 40Ar (99.6%)

spallation products that reach crust (O, Mg, Si, Fe)

506
Q

26Al decay

A

26Al - 26Mg, T_1/2 = 7.16 x105 yrs

507
Q

36Cl decay

A

36Cl – 36S 00 36Ar; T1/2 = 3.08 x10^5

508
Q

26Al, 36Cl properties

A

readily absorbed into aerosols - rained out
Al immobile (like Be)
Cl geochemically mobile
useful in hydrologic studies, groundwater aging

509
Q

Be evidence

A

sediments contribute to composition of arc magma

510
Q

10Be unique because

A

atmosphere- latitudinally heterogenous due to differences in cosmic ray abundance
oceans- more uniform due to short mixing time

511
Q

mixing time of oceans

A

ca. 800 yrs

512
Q

ocean residence time of Be

A

ca. 4000 yrs

513
Q

Be mantle uses

A

short decay time - shouldn’t exist in mantle - if does, recently subjected
presence of 10Be is a source indicator

514
Q

10Be in Arc Lava

A 
OIBs = high 10Be
MORB = low 10Be
515
Q

why OIBs have high 10Be

A

mantle contamination from lithosphere subduction

516
Q

10Be sedimentation rate

A

cosmogenic nuclide production assumed constant

using production history can date sediments, ice cores, etc.

517
Q

how to date using 10Be, constant sedimentation rate

A 
10Be = 10Be_o * e^-λt
ln(10Be) = -d/a (λ)*ln(phi/a)
d = depth
a = constant sed. rate
phi = production rate
518
Q

10Be dating with non-constant sediment rate

A

10Be = [ phi(t)/a(t) ] * e^ -λt

or e^ -λ(d/a)

519
Q

combining 10Be

A

26Al/10Be = (26Al/10Be)_o e^(λ_b - λ_a)t

520
Q

why coming 16Al, 10Be

A

improve age dating

date quartz w/ different decay constants (?)

521
Q

sedimentary quartz

A

exposed at surface - develop measurable quantities Al, Be - buried - isolated from cosmic-ray flux - nuclides decay at different rates - ratio reflects burial duration

522
Q

Be-Al also used to date

A

manganese nodules

523
Q

radiogenic carbon

A

14C

one of most commonly known, used cosmogenic dating systems

524
Q

why 14C is common known/used

A

high production rate
rapid decay rate (T_1/2 = 5730yrs)
key constituent of organic matter, non-organic compounds

525
Q

14C dating method

A

detection, counting of ß rays

ACTIVITY

526
Q

14C foration

A

N–>P reaction with 14,7N

or 13,6C(d,p)14,6C - 13C collision w/ deuterium, less common

527
Q

14C decay

A

14,6C – 14,7N + ß- + v + Q

Q = 0.156MeV

528
Q

14C method

A 
A = A_o e^-λt
t(BP) = 1/λ ln(A_o/A)
t(BP) = -T_1/2 * log_2(A_o/A)
529
Q

why is it difficult to measure cosmogenic ‘background’

A

atomic weapons testing - thermal nuclear weapons
BP then, = 1950
can tell pre-post bomb

530
Q

challenges with 14C

A

variations in local/secular atmospheric production/contents
Suess Effect
Bomb carbon
Isotope Fractionation

531
Q

local variations in 14C

A

production dependent on neutron flux
increases w/ altitude to max 12-15,000 m all
ca. 4X greater at polar regions
changing sun activity
changing intensity of Earths magnetic field

532
Q

Suess Effect

A

14C A in 1900s 2% lower than 1900s due to ‘dead’ CO2 from fossil fuel combustion

533
Q

`Bomb carbon

A

nuclear bomb additions to atmos. incorporated into other pools, ages need correction

534
Q

Isotope fractionation

A

mass differences btw 14C, 12C ca. 16.7%

14C enriched/depleted in certain reservoirs

535
Q

shared/transported 14C

A

system will initially share concentration

  • dating an organisms C - you are what you eat
  • ocean obtaining atmospheres signature
536
Q

14C, volcanics

A

eruptions eject large amount of carbonate into air
increased 12C, 13C
varies exchange ratio

537
Q

magnitude of cosmic radiation depends on

A

lang altitude

E’s magnetic field strength at given t/place

538
Q

de Vries effect

A

sun activity + magnetic field = ca. 2% or more change in 14C activity
14C ‘spikes’ = sun spots

539
Q

14C dating of water masses

A

led to thermohaline circulation theory

540
Q

Depth vs. 10Be

A

increasing [ ] moving up in agreement with isotopic enrichment of ocean = deposits of old material (mts)

541
Q

most valuable tracers/technique for water studies

A

Tritium

542
Q

what is tritium

A

3,1H

543
Q

3H characteristics

A

useful for freshwater, oceans
T1/2 = 12.43 yrs
very low abundance (3x10^16% of H isotopes)

544
Q

radioactive, stable H isotopes

A 
radioactive = Tritium, 3 H
stable = Protium 1H, Deuterium 2H
545
Q

formation of 3H

A 
Spallation 
cosmogenic n,p reaction w/ 14,7N
requires fast neutron >4MeV
14,7N + 1,0n --> 3,1H + 12,6C
14,7N(n,p)3,1H
546
Q

Tritium decay

A

3,1T – 3,2H + e- + bar + Q

Q = 0.0186 MeV (low E)

547
Q

Tritium decay energy

A

low E beta radiation cannot penetrate human skin, only dangerous if inhaled or ingested

548
Q

cosmogenic production of T

A

0.5±0.3 atoms 3H /cm^2/sec

549
Q

natural amount of T

A
  1. 65kg in atmosphere

ca. 4kg total

550
Q

T.U.

A

tritium units

notation for reporting [T]

551
Q

1 T.U. =

A

1 atom 3H / 10^18 atoms H

= 7.1 dissintegrations 3H / min L of water

552
Q

TU in surface water

A

10 TU (10^-15)

553
Q

T synthetic production

A
  • nuclear reactors using neutrons

- particle beam accelerators

554
Q

why synthesize T

A

very low natural abundance - impractical

weapons use

555
Q

T synthesis

A
  1. Neutron activation of Lithium-6

2. Neutrons react with 3He in particle beam accelerator

556
Q

T synthesis, 1. 6Li

A

N smashes Li in 2
exothermic - does not require high E neutrons
results in T2 gas (like H2)
N - strike Li/Al target - reacts w/ 6Li - produce T
6,3Li + n –> 4,2He + 3,1T

557
Q

T synthesis, 2. particle beam

A

N bonks a proton off and replaces it
N react w/ 3He in particle beam accelerator - produce T, H
cascading system - feeds itself - runaway rxn’s
3,2H + n – 3,1T + 1,1H

558
Q

CANDU

A

Canadian Deuterium Uranium reactor
T production in heavy water
D captures a neutron, makes deutero-tritiated water

559
Q

CANDU reactions

A

double substitution
D2O + n — TDO
singly substituted
DHO + n – THO

560
Q

how CANDU is special

A

system bathed in heavy water - buffer = lower production of waste = safer
In the even of a system failure - D2O floods chamber quenching nuclear reaction

561
Q

US T production

A 
225kg produced 1955-1988
1996 had decayed to 75kg 
2003 production resumed
2011 nominal production, maintain equilib.
2016 max production, recover reserve
562
Q

Tritium practical uses

A

military applications
flare light source, emergency lights, exit signs, luminous watch/clock dials
fuel for nuclear ‘fusion’ (experimental)

563
Q

two most common earth science applications of T

A

dating of relatively recent, short-lived elements

tracing, tracking relatively recent hydrologic/water based processes and events

564
Q

natural T cycle

A

3H formed in lower stratosphere - remains 1-10yrs - enters troposphere - oxidizes to form HTO - rains out in 5-20days

565
Q

change of natural T abundance

A

nuclear testing

566
Q

[T] before, after nuclear testing

A 
pre-1953 = less than 25T.U. (typically 5)
1964 = more than 2200T.U. (typically 1000)
567
Q

post-nuclear testing T geoscience

A

eliminated use of natural T

pulse-chase type experiment

568
Q

PTBT

A

Partial Test Ban Treaty - 1964
US, USSR agreement to stop aboveground testing
then France started, then PRC

569
Q

HTO ‘Pulse-chase’ experiment uses

A

reconstruction of T delivery history by identification/measurement of bomb peak
penetration rates of HTO (diffusion, advection, piston velocity)

570
Q

problems with HTO pulse-chase

A

T decay means signal decreases rapidly w/ t

natural dispersion of H2O makes difficult to ID peak w/ time and distance from source

571
Q

solution to HTO problems

A

use 3He

572
Q

3He solution

A

measure simultaneously w/ T
ID T peak as the sum of 3H + 3He
calculate age from 3H/3He ratio

573
Q

3He

A

tritiogenic helium
also low abundance, 1.4x10^-4 % of He
produced mostly by T decay

574
Q

calculating 3H

A 
3H = 3He_o * 3H(e^-λt - 1)
3He/4He = (3He/4He)_o + 3H/4He(e^-λt - 1)
575
Q

T tracer, ocean water masses

A

old H2O = low T
young H2O = high Tritium
how ocean circulation was discovered (and nobody believed them!)
can be measured as loss of parent (T) or gains of daughter (3He)

576
Q

why might 3He be advantageous as the measured species over 3H

A

not taken up by biological organisms - doesn’t react

577
Q

how can you measure water recharge rate

A

age structure

incursions

578
Q

World Energy use by source

A 
oil 37%
coal 25%
gas 23%
nuclear 6%
biomass 4%
hydro 3%
solar 0.5%
wind 0.3%
geothermal 0.2%
579
Q

biggest potential issues with nuclear power

A

what to do with waste

potential weapon danger

580
Q

change in energy sources

A

relatively static over the last 30 years

581
Q

majority of nuclear reactors

A

E NA
France
SW Asia

582
Q

Canada nuclear power

A

19 reactors, Ontario
16% of Electricity
only half of power generated is used in Canada
used to be world leader - 22% of world output
overtaken by Kazakhstan, 2009

583
Q

Inequality of nuclear power

A

non-renewable
U not available in every country
would result in same political battles as fossil fuels

584
Q

Uranium production in Canada

A

production from worlds largest McArthur River mine, N SK
expected to increase from 2013, new mine
mostly in WCSB

585
Q

WCSB

A

western canadian sedimentary basin

concentrated U deposits

586
Q

why is U concentrated in WCSB

A

U deposited in lithos. - rain - leeching - U oxide is soluble (unique) - transports w/ water - concentrates - reduced - drop out

587
Q

Nuclear fueld cycle

A 
mining and milling -- U concentrate
convert concentrate into UO2 or UF6
enrichment 
fuel fabrication
electricity generation
optional chemical reprocessing
disposal - recovered or permanently stored
588
Q

mining and milling of uranium

A

produce concentrated uranium = yellowcake

589
Q

why does U have to be concentrated in to yellowcake

A

mined U not directly useable for power

590
Q

UO2

A

uranium dioxide

used in heavy water reactors

591
Q

UF6

A

uranium hexafluoride

light water reactors

592
Q

Nuclear fuel cycle, enrichment

A

increases proportion of 235U

593
Q

why increase proportion of 235U

A

rare, fissile

594
Q

fuel fabrication of U

A

manufactured in to fuel pellets

595
Q

typical U pellet

A

ca. 7g

E = 3.5 oil barrels, 17,000 ft^3 natural gas, 1,780 lbs coal

596
Q

Uranium fuel manufacturing

A 
last stage before use in reactor
compress UO2 powder into cylinder
bake at 1700ºC - hard ceramic pellet
stack pellets in to thin tubes - fuel rods
group into bundle - fuel assembly
597
Q

typical pressurized water reactor

A

193 fuel assemblies
51,000 fuel rods
18 fuel pellets
ca 5yrs

598
Q

fissionable

A

material can undergo nuclear fission
typically ß decay
mostly actinides

599
Q

fissile

A

able to sustain a chain reaction w/ low E neutrons

600
Q

fissile isotopes

A

235U
233U
239Pu
241Pu

601
Q

Fissionable chain reaction

A

only sustainable w/ fast neutron

unless fissile

602
Q

Fissile rule

A

Heavy isotopes

  1. Z between 90 - 100 (actinides)
  2. 2Z - N = 43 +/- 2
603
Q

fertile

A

not fissile but easily upgraded to fissile

604
Q

fertile U

A

238

605
Q

fissionable process

A

unstable mix of Z/N
slow, low E N hits - low E
fast, high energy N, (cosmic ray, spallation) - massive destruction - perpetuate reaction

606
Q

Oklo, Gabon

A

U deposit behaved as natural nuclear fission reactor ca. 1.8Ga
few 100,000 yrs
100kW power output average

607
Q

Canadas nuclear power program 2016

A

5 plants, 3 provinces, 19 active power reactors, mostly ontario, all CANDU design, ca. 16.5% of E
Bruce Nuclear Generating Station, Ont
Pickering NGS, Ont
Darlington NGS, Ont
Gentilly-2 Nuclear Facility, Quebec (shut down)
Point Lepreau GS, NB

608
Q

Nuclear waste

A

biggest problem is intermediates - nonactinide radionuclides
short decay times, T_1/2 =50 yrs
= high E = gamma radiation

609
Q

interim nuclear waste storage

A

removed radioactively, thermally hot for several yrs
rods in barrels in H2O to cool
the moved to longer term storage

610
Q

Canada interim storage

A

on land - dry storage

611
Q

long term disposal plans

A 
drop from ship into sediment (would leech out of container)
vitrify 
store in Yucca mt in an open system 
reprocess
breeder reactors
612
Q

Th power

A

3-4X more abundance than U (in crust)
not fissile but fertile
232Th - 233U is more efficient than 238U - 239Pu
does not require isotopic separation
minimal radioactive waste
anti-theft
abundant in ocean - available to more nations

2016/2017 (15 decks)

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