I Isotope Geology & Geochemistry Quiz | Practice & Exam Preparation, Exams of Geochemistry

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Preparation

1. Basics of the Atom
   • General Construc- tion of the atom
   • Z=
   • N=
   • Mass=
2. Basics of the Atom Volume and Mass
3. Basics of the Atom
   • Nuclide
   • Electron Shells
4. Basics of the Atom Atomic Mass in AMU

• Composed of an atomic nucleus which consists of neutrons & protons and the outer electron shell

Z=Proton N=neutron Mass=A=Z+N

• Volume=1/10000 of atom=volume • angstrom Mass=entire atom=1/2000 of proton mass

Nuclide Describes specific Z, N, and nucleation energy state

Electron Shells K L M N O P Q n=1 2 3 4 5 6 7 Increasing energy ’

• Standardized and defined by: ¹²Cmass/12
• Total atomic mass accounts for each isotope ³⁵Cl mass • isotopic proportions ³⁷Cl mass • isotopic proportions sum both

a unit of mass used to express atomic and molecular weights, equal to one-twelfth of the mass of an atom of carbon-12. It is equal to approximately 1.66 x 10-27 kg

Preparation Basics of the Atom Isotopes

6. Nuclide Chart
   • Isotopes
   • Isotones
   • Isobars
   • Binding Energy

Isotopes have the same Z and charge. Also behave similarly in terms of chemical behavior. However, have ditterent mass N.

Isotopes same Z Isotones same N Isobars same Z+N=A Binding Energy Negative energy lowers the total energy (proportional to m), the energy that holds a nucleus together, equal to the mass defect of the nucleus.

7. Nuclear Stability & Stable Isotopes Have lower overall energy, lower negative binding energy, Radioactivity
   • Stable Isotopes

and smaller nucleus

8. *Nuclear Stability & α emission of ⁴₂He

Radioactivity* Radioactive Iso- topes can achieve lower energy by α β⁻ β⁺

β⁻ n=P⁺+e⁻+v⁻ β⁺ P⁺=n+e⁻+v v & V⁻ take excess energy and nuclear spin

9. *Nuclear Stability & Electron Capture e⁻+p⁺=m+v

Radioactivity* Radioactive Iso- topes can achieve

Fission large nuclei split

Preparation

• High closure temperature
• Durability
• Long T½

14. Isochrons Isochrons are cogenetic samples with ditterent N
15. Common

long-lived Geochem Isotopes

16. Kinetic Energy Kinetic Energy produces radiation damage, such as: fission tacks, radiohaloes, damage to crystal lattice
17. E=MC² Changes in energy state result in lower and energy, thus lower mass
18. Examples of De- cay α and β decay
19. Examples of De- cay Fission

In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller, lighter nuclei. The fission process often produces free neutrons and gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay.

Preparation

20. *Mass defects in ra- •Release of binding energy ²₁H mass of measured P+N does not equal mea-

dioactive decay* Binding energy

sured mass of ²₁H

• Mass to energy 931.494 MeV/1V

0.1184%=2.224MeV or 1.7E14 j/kg of total mass

21. *Mass defects in ra- •Heavy nuclei tend to decay by α decay to reduce the binding energy and

dioactive decay* Emission of α parti- cle

progress down the valley, results in -2p and -2n

mass of ⁴₂He`m ass ditterent in ²³⁸U->²³⁴Th it is a ditterent of .0046 amu=1.74E12 J/kg

22. Mass defects in ra- •Isotopes with excess neutrons go up into the valley stability along isobars , dioactive decay results in -n and +p Emission of an elec- tron and antineutri- Mass of^ P`m^ a ss^ of D, it is a ditterence of .0003 AMU=3.0E11 J/kg no in n’p
23. *Mass defects in ra- •Isotopes with excess protons go down the valley of stability along isobars,

dioactive decay* Emission of a β par- ticle and neutrino

resulting in -P and +n

Neutrinos carry excess energy and gamma rays carry excess energy

Preparation

30. Isotope Fractiona- tion α
31. Isotope Fractiona- tion δ
32. Standard Isotopic Ratios
33. Rayleigh Fraction- ation
34. Rayleigh Fraction- ation Condenstation
35. Rayleigh Fraction- ation Distillation
36. Rayleigh Fraction- ation Example

ε=α-1, ε•1000=fractionation in parts per thousand (similar to δ values), and ε useful in radiogenic isotopes

Compares the isotopic ratio in A to a standard isotopic ratio, such as the fractionation between two phases

A-b=δA-δb

Lighter molecules are enriched in vapor, condensation and evaporation (dis- tillation)

37. Kinetic Effects Isotopes may have ditterent rates of reaction resulting in enrichment of lighter isotopes in products related to dittusion

Preparation

38. Mass dependent Mass dependent ettects are most natural reactions and independent ef-¹⁸O>>¹⁶O fects ¹⁷O>>¹⁶O

¹⁸O is 2X more enriched than ¹⁷O

39. ¹⁷O ¹⁷O=δ¹⁷O-δ¹⁸O

λ characterizes the mass-dependent fractionation. λ=~.5 =~

40. Mass indepen- 0 ` dent Effects
41. Mass indepen- dent Effects Nuclear Volume Ef- fects
42. Mass indepen- dent Effects Magnetic Isotope Effects
43. Isotopologues and Clumping Theory
44. Diffusion

δ¹⁷O.`5δ¹⁸O Occurs in meteorites and in zone, and sulfur in sulfides > 2.45 Ga

Nuclear Volume Ettects mass-independent isotope fractionation due to heavy element nuclear volumes

Magnetic Isotope Ettects Isotope separate by spin and magnetic moment

Isotopologues and Clumping Theory Molecules that ditter in isotopic composition. Clumped isotopes are more abundant than single substituted isotopologues, temperature dependence in clumping produces a geothermometer, higher temperature produces less clumping

Preparation

48. Carbon Isotope Geothermometry

Carbon Isotope Geothermometry Often uses CO₂ as experimentally known values in minerals

49. Equilibrium Equilibrium The assumption when using a geothermometer is that minerals are at complete equilibrium during or after formation
50. Isotopic Equilibri- um may not be achieved if

Isotopic Equilibrium may not be achieved if reaction rates are slow at low temperatures kinetic fractionation competes with equilibrium fractionation systems may equilibrate during cooling

G of isotope exchange reactions are low, not readily driving the reactions to equilibrium

51. *Advantages of iso- Advantages of isotope geothermometry

tope geothermom- etry*

52. Mass Spectrome- try
53. Mass Spectrome- try

no volume changes creates little pressure dependence , pure phases are used with little element exchange involved

The ioniziation of atomic species and acceleration through a strong magnetic field to cause separation between similar masses individual particles detect- ed.

Mass spectrometry is an analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample. Mass spectrometry is used in many ditterent fields and is applied to pure samples as well as complex mixtures.

Small quantity of sample is injected and vaporized under vacuum sample bombarded with electron at 25-80 ev, the valence electron is ejected from ions, ions (+) are accelerated using an (-) anode toward the magnet each ion has

Preparation kinetic energy 1/2MV^2=Ev Ions enter magnetic field and their path is curved, radius of the curvature is smaller for lighter isotopes

54. Mass Spectrome- try
    • Gas
    • Solid
    • Sample
55. Mass Spectrome- try
    • Peak Jumping
56. Mass Spectrome- try
    • Static Measure- ments
57. Stable Isotope Ra- tio Spectrometry SIRMS

Gas Duel inlet system on continuous flow systems Solid Filament with separated materials Sample La-ICP-MS on sims oxygen or ceasium beams

Peak Jumping Manually changing the magnetic field to analyze ditterent masses sequentially through a single or not enough detections.

A means to acquire a mass spectrum by jumping from one mass to charge to another; measurements are made at the mass to charge of each mass spectral peak; only ions with mass-to-charge ratios of interest are measured, skipping mass-to-charge ratios that are not of interest

General multicollectors calibrated at a specific distances from each other correction for mass fractionation, noise, and mass interference needed

SIRMS Extract oxygen from rock by reaction with bromopentafluorine cause reaction with carbon to CO2. Isolated gas is heated and frozen with liquid nitrogen to travel to a glass tube, glass tube attached to mass spec.

Preparation

59. Non-radiogenic (stable) cosmochemical systems terrestrial sys- tems

terize exchange processes, track reservoir interactions, and evaluate biologic and kinetic processes

For terrestrial systems, common applications in geochronology and tracer Studies involve the following radiometric systems U-Th-Pb Rb-Sr Sm-Nd Lu-Hf Re-Os U series disequilibrium Sr, Nd, Hf, Os in seawater

In cosmochemical systems, the measurement of isotopic compositions is primarily as tracers of nucleosynthetic processes and constraining the evo- lution of the solar system. This involves measurement of the systems noted above, but also includes the decay of short lived radionuclides, as observed principally in meteorites. In addition to the systems noted above, systems of cosmochemical interest include: Fe-Ni Mn-Cr Al-Mg Zr-Mo Mo- Ru

Non-radiogenic (stable) isotope-isotope ratios are typically used to charac- terize exchange processes, track reservoir interactions, and evaluate biologic and kinetic processes: Li B Mg

Preparation

60. Spikes and Traces
61. •Spike
    • Tracer
62. Inductively Cou- pled Plasma - Mass Spectrometry ICPMS
63. Inductively Cou- pled Plasma - Mass Spectrometry
64. Magnetic sector and TIMS

Ca Fe

Isotopic ratios are measured, not concentrations, find concentrations indirectly by isotope dilution by adding a known spike solution before ionization. Back calculate the concentrations of an in the original sample isotope ratios are measured with each element separately then calculated.

Spike: adding a known amount of a present constituent Tracer: Adding a known of a substance not already present

• ICP-MS for radiogenic isotopes
• Quadrupole single collection
• Magnetic sector single and multi-collector

Quadrupole changes electrical frequencies in four rods and allows a particular mass of resonant ions to pass through to the collector

• Magnetic sector similar to TIMS with a single or multi collector

65. Laser Ablation Laser Ablation destructively technique leaving large and deep pits
66. Secondary Ion Mass Spectrome- try Sims (SHRIMP)

SIMS for radiogenic isotopes, primary ion beam composed of Cs or O. The instrument sputters the surface of materials and produces secondary ions to be analyzed. It is sensitive high resolution ion microprobe with smaller, shallower destructive pits.

Preparation

68. Electron Micro- probe Analysis
69. Uncertainties Accuracy vs. Preci- sion MSWD

Elements only - useful for U-Th-Pb dating in monzanite and xenotime

Absolute precision (400±20) or relative precision (400Ma±2%) 1σ=67% chance that a value is truly in uncertainty range 2σ=95% chance that a value is truly in uncertainty range

MSWD mean square of weighted deviates

Isochron - MWSD <2. Error chron- MWSD >2.

70. Stable Isotope Ap- Isotopes indicate the presence and magnitude of key ecological processes. plications Many ecological processes produce a distinctive isotope fingerprint. The pres- ence or absence of such processes and even their magnitude in relation to other processes are indicated by the stable isotope ratio value relative to known background values. Isotopes record biological responses to Earth's changing environmental con- dition. For cases in which substances or residues accumulate in an incremental fashion, such as in tree rings, animal hair and ice cores, isotope ratios can be used as a record of system response to changing environmental conditions or a proxy record for environmental change. Isotopes trace the origin and movement of key elements and substances. Ow- ing to isotopic fractionations associated with physical and biological reactions, nutrient and element pools within and among ecosystems often ditter isotopi- cally. As a result, the source(s) of essential elements and resources acquired by an organism are easily traced using isotope ratios. Strong geographic patterns in isotope signature variation provide the means to trace the movement or origin of a substance or component at landscape to continental scales.

Preparation

71. Standards
72. D/H Fractionation in water liquid-va- por
73. Oxygen Measurements of the ratio of oxygen-18 to oxygen-16 are often used to interpret changes in paleoclimate. The isotopic composition of oxygen atoms in the Earth's atmosphere is 99.759% 16O, 0.037% 17O and 0.204% 18O.[4] Because water molecules containing the lighter isotope are slightly more likely to evaporate and fall as precipitation,[5] fresh water and polar ice on earth contains slightly less (0.1981%) of the heavy isotope 18O than air (0.204%) or seawater (0.1995%). This disparity allows analysis of temperature patterns via historic ice cores.

An atomic mass of 16 was assigned to oxygen prior to the definition of the unified atomic mass unit based upon 12C.[6] Since physicists referred to 16O only, while chemists meant the naturally-abundant mixture of isotopes, this led to slightly ditterent mass scales between the two disciplines.

74. Oxygen Isotope More Standards
75. Oxygen Isotope 18O/16O fractiona- tion in water

Preparation

81. Sulfur Geothermometry
82. Sulfur Organic Effects
83. all four sulfur iso- topes

Sulfur Geothermometry fraction occurs by kinetic ettects of microbial sulfate reduction and by exchange reactions sulfate-sulfide or sulfide-suflide gives a geothermometry application

A-values known with respect to H2S a-b=AE6/T²

Organic Ettects Sulfate reducing bacteria produce ³²S-depleted sulfide bac- teria uses ³⁴S in formation of sulfide to sulfate

all four sulfur isotopes is useful for rocks >2.4 Ga due to mass independence fractionation in O2-depleted atmosphere with H2 or CH4 (reducing) atmos- phere

84. Carbon ¹²C=98.83% ¹³C=1.07% Generally measured as CO₂ after reaction with phosphoric organic compounds oxidized to form CO
85. Carbonate Reser- voirs
86. Carboante Frac- tionation
87. Carbon Geother- mometry
88. Organic Carbon

Carbonate Reservoirs Organic, sedimentary carbonates

carbonate fractionation occurs through exchange reactions within inorganic carbon system CO2(g) bicarbonate -carbonate or through kinetic isotope ettects in photosynthesis where ¹²C is concentrated

Carbon Geothermometry between DIC and CO2 or between minerals can be used for geothermometry

Preparation Kinetic fractionation through photosynthesis prominent C3 or C4 or CAM plants produced. Aquatic plants are more complex with DIC incorporated δ¹³C somewhat indicative of geologic reservoirs

89. Cosmogenic Nu- clides

Cosmogenic nuclides Good for young systems in surficial processes, such as glaciers, landslides, and lava flows

90. Cosmogenic: Spal- Cosmogenic: Spallation lation
91. ¹⁴C comsogenic dating schemes in biological materi- al
92. Carbon Decay Rate example
93. Cosmogenic Iso- topes

Cosmic rays of high energy atomic nuclei of primarily H and He encounters the earth, striking a nucleus and shattering the nucleus into pieces producing stable nuclei, unstable nuclei, protons, neutrions, muons, prion

¹⁴C comsogenic dating schemes in biological material ¹⁴N+n=¹⁴C+P ¹⁴C is incorporated into plants from CO2 updtake and consequently transferred to plant eating organisms, CO2 update and ¹⁴C decays to ¹⁴N allowing dating

In the upper atmosphere several radioactive isotopes are produced when cosmic rays collide with atmospheric molecules at high speed. These isotopes are known as cosmogenic isotopes. The production rate of the cosmogenic isotopes depends on the strength of the cosmic radiation, which again varies with the strength of the Earth magnetic field and with the solar activity. Therefore, records of cosmogenic isotope production rates are invaluable for