Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Isotope Geochemistry > 1 > Flashcards

1 Flashcards

1
Q

Radioactivity

A

Decay of unstable elements through the emission of nuclear particles and radiant energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Components of atom

A

Protons (Z), neutrons(N), electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Atomic number (Z)

A

Number of protons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Mass number (A)

A

Protons (Z) + Neutrons (N) = (A)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Nuclide

A

A distinct kind of atom with a specific number of neutrons and protons. Can be uncategorized as, isotopes, isotones, and isobars.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Isotope

A

A nuclide with the same atomic number (Z) ( the same number of protons, but a different number of neutrons (N))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Isotone

A

A nuclide with the same number of neutrons (N), but a different number of protons (Z)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Isobar

A

A nuclide with the same mass number (A), but a different number of neutrons (N) and protons (Z)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Atomic weight of protons (amu)

A

1.007276467

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Atomic weight of neutrons (amu)

A

1.008664916

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Atomic weight of electrons (amu)

A

0.0005485799

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Stable nuclides

A

N = Z

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Discovery of radioactivity

A

1896 - Antoine Becquerel, Marie and Pierre Currie, Nobel Prize Physics in 1903

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Nucleosynthesis

A

Process where the first nuclides form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Oddo - Harkins Rule

A

Isotopic abundance relative to Be, the average galactic occurrence frequency of chemical elements, even atomic numbers are always higher compared to neighboring elements eg. 5B <6C> 7N

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Polygenetic Hypothesis

A

Cosmological, stellar, explosive, galactic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Cosmological polygenetic hyp.

A

Hydrogen fusion produces Helium, 0.0001s after the Big Bang nucleons formed 0.01s – 99 999 999 970oC ≈ protons and neutrons.

(n+p=2H) -> PP I

(2He + p = 3He) -> (3He +n = 4He) -> PP II

(3He +4He = 7Be) -> PP III

7Be -> 8Be -> 12C …NO
[Oddo Harkins (galactic abundance relative to Be]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Stellar polygenetic hyp.

A

Fusion in stars, Hertzsprung-Russel diagram: relative luminosity vs surface temps of Stars. Hydrogren burning (H->He). Our sun is class G

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Explosive polygenetic hyp.

A

Supernovae

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Galactic polygenetic hyp.

A

Li + Be, cosmic ray interaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Nuclear stability is a balance of what?

A

Strong nuclear force and coulombs repulsion. Strong = long-range, Coulombic = short-range

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Nuclear binding energy eq

A

E = mc^2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Mass defect

A

Difference between observed atomic mass and expected atomic mass, ectothermic due to release of energy dM = Me - Mo

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What does binding energy per nucleon tell you?

A

A metric for how tightly bound nucleons are within a nucleus (nuclide stability. Peaks at 56Fe, beyond that mass number fusion of heavier nucleons, requires energy input. (fusion <56

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Valley of stability

A

Nuclear binding energy is the greatest near the bottom = right combination of protons and neutrons to be stable. A cross section of the nuclide chart, there the center are stable nuclides and as you move outwards to transition to unstable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Major Elements

A

Reported as oxides >1.0 wt.% O, Si, Al, Mg, Fe, Ca, Ti, Na, K, P

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Trace Elements

A

<0.1 wt.% reported as ppm or ppb

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Goldschmidt Classification scheme

A

The affinity of elements to form various types of compounds. Lithophile, Chalcophile, Siderophile, Atmophile

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Lithophile

A

bound to oxygen (silicate) (ex. Li, Be, Al, Si)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Chalcophile

A

bound to sulfur (ex. Sn, Zn, Pb, S)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Siderophile

A

bound to iron (ex. Mn, Fe, Co, Ni)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Atmophile

A

gaseous behaviour ~ atmosphere (ex. H, He, C,N)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Types of decay modes

A

alpha decay, beta - decay, beta+ decay, e- capture, spontaneous fission

34
Q

Alpha decay

A

A heavy nuclide ejects a +He or (a particle) Atomic mass changes ( ex. U238 ->Th234 He4)

35
Q

Beta- decay

A

a neutron in the nucleus decays to a proton, an electron (b- particle and antineutrino) example (C14 -> N14 + e-) Atomic mass remains the same

36
Q

Beta + decay

A

a proton in the nucleus decays to a neutron, a positron (b+ particle and neutrino are ejected) atomic mass remains the same (example Na22 -> 22Ne + e+)

37
Q

e- capture

A

An electron is captured by the nucleus, converting a proton to a neutron and releasing a neutrino (example: K40 -> 40Ar)

38
Q

Spontaneous fission

A

spontaneous breakdown of large nuclei into two smaller nuclei (U235 -> Cs140,n,200MeV,n,Rb92)

39
Q

The probability that a given atom will decay in some time dt: eq

A

dN/dt = -lamdaN => decay rate = decay constant x parent atoms

40
Q

Behaviour of parent and daughter through time

A

Parent (radioactive) atoms decrease exponentially with time. Daughters (radiogenic) increases

41
Q

Parent eq

A

N = Noe^(-lamda t)

42
Q

Half-life eq

A

t(1/2) = ln 2 / lamda, (ln2 = 0.69314718056)

43
Q

Daughter eq

A

D = Do + N((e^lamdat)-1)

44
Q

The CNO cycle

A 
12C + p = 13N +gamma
13N = 13C +e + n
13C + p = 14N + gamma
14N+p 15O + gamma
15O 15N +e+n
15N+p 12C +4He

Occurs after He-burning

45
Q

e-process

A

Si burning (stops at mass 56, 1 day) 28Si + gam = 24Ne+4he

28 +4He 32S +gam

32S +4He = 36Ar+gam

46
Q

s-process

A

Slow neutron capture in red giants, every 1000 y, makes heavier isotopes:

22Ne +4He = 25Mg +n

141Nd +n 142Nd +gam

47
Q

r-process

A

rapid neutron capture, explosive nucleosynthesis

48
Q

p-process

A

Proton capture, lightest isotopes of an element,

less abundant than s and r process

49
Q

Benefits of zircon and chemical structure

A

ZrSiO4, very resistant to erosion, burial, high-temperature metamorphism, Hardness = 7.5, incorporates large amounts of uranium but no lead during crystallization (Do ~0)

50
Q

Decay eq of 187Re to 187Os

A

Half-life = 42.3 by

187Os = 187Oso + 187Re(e^-lamdat -1)

Isochron eq:
(187Os/188Os) = (187Os/188Os)o + (187Re/188Os)(e^-lamdat -1)

y=mx+b

51
Q

Decay rate definition

A

immutable nuclear process

52
Q

U-Pb-Th system

A

Parents:
235U (0.7G) -> 207,
238U (4.5G) -> 206,
232Th (14G) -> 208

Daughters: 204Pb, 206Pb, 207Pb, 208Pb

53
Q

U-Pb Two decay sequences

A

Concordia plot
Y axis: 206/238
X axis: 207/235

54
Q

Secular Equilibrium

A

Product of the abundance of an isotope and its decay constant are equal among all intermediate daughter products and parent isotope

N1Lam1 = N2Lam2 = N3Lam3

(ex. one 206Pb is created for every atom of 238U that decays)

55
Q

When will secular equilibrium be reached in a closed system?

A

In a time proportional to the longest half-life of the intermediate daughter product. Will remain in SE until one or more isotopes in the chain is fractionated from the others (ex chemical partitioning in mag system or low temp fractionation during chem weathering

56
Q

U-Pb age eq

A

206:

(206/204) = (206/204)o +(238/204)(e^-lamt-1)

207:

(207/204) = (207/204)o +(235/204)(e^-lamt-1)

204 is stable and removes systematic uncertainty of calculated moles

57
Q

Pb-Pb age eq

A

(207/206) = (235/238)([e^-lamt-1]/[e^-lamt-1])

Solar sys formation and meteorite evolution

Concordia plot
Y axis: 207/206
X axis: 204/206

58
Q

What are the three decay systems of U-Pb

A

238U-206Pb- HL 4.468G
235U-207Pb- HL 0.704G
232Th-208Pb- HL 14.01G

59
Q

238/235 ratio

A

137.88

60
Q

Concordant

A

When a mineral crystallizes and begins accumulating Pb* in a closed system 207/235 and 206/238 ratios evolve such that they follow the curve (which is curved because they decay at different rates

61
Q

Discordant

A

Disturbance or Pb loss resulting the ratios evolving away from the curve. t1 = igneous(crystallization), t2 metaphoric (Pb loss)

62
Q

Concordia plot axis ranges

A

Y = 0.0 - 0.7
X = 0 - 25
Points along curve = 0, 1000, 1500,2000, 2500, 3000

63
Q

Tera-Wasserburg

A

238/206 X axis,

207/206 y axis

64
Q

Define accuracy

A

measurement of the difference between an experimental result and the truth

65
Q

Define precision

A

measurement of the reproducibility of an experimental result, without regard to the truth

66
Q

What are the components of Error?

A

Random and systematic

67
Q

The random component of error

A

Random fluctuations in the signal you’re measuring can be reduced by increasing the number of observations, propagate into a value for it to be accurate

68
Q

Systematic components of error

A

remains constant or varies predictably no matter how many measurements you make. only propagate into a value when that value is to be compared with other values that are not subject to the same sys errors. Eg decay constant different amongst sys

69
Q

Metamict

A

radiation damage to zircon, these zones are richest in U and lost Pb = discordant. abrasion and annealing

70
Q

Wetherill Concordia plot

A

206/238 vs 207/235

71
Q

Isotope dilution

A

process of spiking a sample with a known quantity of one or more tracer isotopes in order to convert ratios measured by mass spec to moles in sample isotope, reference is most abundant isotope

72
Q

Internal random errors

A

affect only a single analysis, propagate through age eq (1 sigma 1-2%

73
Q

External systematic error

A

applied to set of ages ~1%

74
Q

Discordance filter cutoff

A

Tight filter 0-10%: good accuracy, age distribution bias

Loose filter 20-30%: less accuracy, less bias

75
Q

Steps to determine ages ID-TIMS vs LC-ICPMS

A

ID-TIMS: (analyze solution)
Dissolve crystal, add spike with non natural isotope, chemically purify, calibrate by comparison with spike (ID), run

LA-ICPMS: (analyze solid material in situ),
ablate/sputter crystals, measure isotope ratios, calibrate by comparison with sample standard bracketing

76
Q

Comparison of U-Pb techniques

A

idtims: 1 analysis/hr, 100-300$, 0.1-0.3 % ac, best precision and accuracy

SIMS: 4 analyses/hr, 25$, 1-2%ac, best spatial resolution

laicpms: 40-100 analyses/ hr, 4-8$, 1-2 % ac, highest efficiency

77
Q

Sample standard bracketing

A

Each sample needs to be measured more than three times, and the mean value of the measurements is calculated as the Si isotopic composition of the sample to obtain stable and reliable results

78
Q

Compatible material

A

remains in the solid component of the mantle, ex Peridotite enriched with Ni, Os, Cr

79
Q

Incompatible material

A

elements that do not fit into the crystal lattice of mantle minerals, ex Rb, K Th, Sr, Zr, are extracted from the mantle into the new basaltic crust, mantle cooling

80
Q

Depleted mantle

A

Earth’s mantle from which basaltic melt has been extracted during melting events ex at mid-ocean ridges, hot spots or island arcs

81
Q

Bulk silicate earth

A

Mantle =2/3 of Earth’s mass, 99.5% silicate earth primitive mantle

82
Q

How to calculate the atomic weight:

A

(atomic mass x abundance)n1 + (atomic mass x abundance)n2 + …

amu or Da

Isotope Geochemistry (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions