applications for isotope ratio analysis · 2016. 10. 20. · dating with decay systems ! principles...

| |

Dating of age and origin

19.10.16 Christoph Neff, Fabian Matter 1

Applications for isotope ratio analysis

| |

§  Dating with decay systems §  Principles of radiometric dating §  Mineral dating with Rb/Sr-Isotope system §  Principles of isochron dating

§  Dating of lunar rock 77215 §  Needed measurement §  Analytical techniques §  Analytical process §  Resulted age

§  Isotope ratio in forensics


Overview

| |





Overview

| |

Age determination based on radioactive decay


Principles of radiometric dating

N(t): number of particles at given time N0: number of particles at starting point λ: decay constant t: elapsed time

integration

| | 19.10.16 Christoph Neff, Fabian Matter 5

Principles of radiometric dating

measured in experiment unknown

known

unknown

General problem: two unknown parameters


Reminder Radiocarbon dating (lecture 3) Age determination by 14C/12C ratio Carbon Isotopes 12C: stable 14C: radioactive decay constantly reformed in atmosphere Approximate dating N0 ≈ constant (14C in steady state) Precise dating Reference data available (e.g. cellulose in tree rings)


Isotope systems used for mineral dating


84Sr (0,56 %) 86Sr (9,86 %) 87Sr (7,0 %) 88Sr (82,58 %)

85Rb (72.2 %) 87Rb (27,8 %)

Rubidium-Strontium isotope system

| |

Rubidium-Strontium isotope system for dating of minerals

§  87Rb (mother isotope M) §  radioactive nuclei decay to 87Sr §  half life: 4.81 x 1010 years (10 times longer than earth‘s age) §  4.5 bya – 50 mya

§  87Sr (daughter isotope D) §  radiogenic daughter of 87Rb

§  86Sr (reference isotope R) §  non-radiogenic isotope (stable & not formed by other decay chains)



| |

Incorporation of Strontium and Rubidium during mineral formation §  Strontium incorporation

§  86Sr and 87Sr isotopes are chemically equivalent §  same initial ratio of 87Sr/86Sr in all minerals (not same amount)

§  Rubidium incorporation §  chemically different to 86Sr and 87Sr §  initial ratio of 87Rb/86Sr different for each mineral





measured in experiment unknown

known

unknown

unknown N0 (no equilibrium as in 14-C dating) no reference data available (e.g. tree rings/cellulose in 14-C dating)

How can we determine the the age without the knowledge of N0?

| |

§  Isochron (greek: iso = same, chronos = time) §  Minerals formed at same time (out of same reservoir)


Principles of isochron dating

melt cooling

| |

separation of minerals

(density, magnetically chemically, hand-picking

size...)



87Sr/86Sr 87Rb initial stage

after solidification from same melt

(t = 0)



87Sr0/86Sr0 87Rb0

initial stage 87Sr/86Sr 87Rb

later stage

87Rb à 87Sr

| |

Amount of 87Rb decreases Amount of 87Sr increases (initial concentration D0 + decay product D*)



(1)

(2)

(1+2)

87Rb

87Sr*

(y = a + bx)

| |

§  initial 87Sr0/86Sr0 is still unknown but: §  same ratio in minerals deriving from the same melt! 19.10.16 Christoph Neff, Fabian Matter 16


(4)

unknown initial ratio (R = 86Sr = 86Sr0)

| |

à  by subtraction, unknown initial ratio cancels out à  time can be calculated without the knowledge of initial isotope ratios! à  plotting D/R against M/R gives isochrones



-

unknown but equal = slope m



Characteristics of isochron dating

§  no initial ratio needed §  sloped is correlated with age of the rock (time after solidification)



87Sr0/86Sr0 87Rb0

initial stage

87Sr 86Sr

87Sr0 86Sr0

87Rb 86Sr



87Sr/86Sr 87Rb later stage

87Rb decreases by decay

87Sr increasing over time 87Sr 86Sr

87Sr0 86Sr0

87Rb 86Sr

| |



§  Isotope ration in forensics


Overview


Lunar rocks 77215

| |

§  Decay system of Rb/Sr 87Rb/ 87Sr §  No uran-rich minerals as zircon present

§  Isochron approach 86Sr §  Dynamic range 102

§  86Sr and 87Sr: ~10 ppm 87Rb: ~ 1 ppm

§  MS-Resolution needed: R ≥ 287’000 §  m(87Rb) = 86.909180527(13) §  m(87Sr) = 86.908877497(9) §  Isobare interference

§  Simultaneously measurement


Requirement of age determination

| |

§  Inductive coupled plasma (ICP-MS) §  Resonance ionization (RIMS) §  Thermal ionization (TIMS) §  Accelerator mass spectrometry (AMS) §  Cavity ring-down spectroscopy (CRDS)


Analytical Instruments

| |

§  RIMS + Extremely selective ionization - Limited number of excitation frequencies

§  TIMS + Constant ionization + Low fractionation - Low ion yield


Ionization techniques

§  ICP §  Digestion, nebulizer

+ Long stable signal - Intensive preparation - destructive sample preparation (10-100 mg)

§  Laser ablation

+ Easy preparation + low amount of sample (< 1mg) - Particle size distribution

| |

§  Detector §  Q-MS

§  R ≤ 1000

§  TOF-MS §  R ≤ 30’000

§  Double focusing SF-MS §  R ≤ 200’000

§  FT-ICR-MS §  R ≥ 2’000’000 §  Expensive acquirement/

maintenance

§  Orbitrap §  R ≈ 1’000’000


MS detection techniques


FT-ICR-MS / Orbitrap

Cyclotron movement of the ions

Stimulation Induction of charge

| |

§  AMS §  + separation of 87Rb+ and 87Sr2+

§  Cavity ring-down spectroscopy

(CRDS) §  + selective isotope

measurements §  - Sr and Rb in gas phase


Other techniques

| |

§  Crush to powder (< 100 µm) §  Separate magnetic parts §  Remove black grains by hand §  Digestion (HNO3)

§  Split in two aliquots §  Selective column chromatography

§  Spike/87Rb pass through §  Dry/solve

§  87Sr/86Sr retain on column §  Wash out the column with H2O §  Dry/solve

MC-double focusing SF-TIMS

§  Measure 86Sr/Spike-ratio

§  Measure 87Rb/Spike-ratio

§  Measure 87Sr/86Sr-ratio


Analytical procedure

| |

§  Rb-Sr age: 4374 ± 45 Ma

§  Uncertainties §  Non-representative Sample §  Post-crystallization disturbance, reheating events §  Difficult to collect precise data §  Half-life assumption

§  Lu-Hf age: 4421 ± 68 Ma §  Sm-Nd age: 4283 ± 23 Ma, 4348 ± 96 Ma, 4413 ± 63Ma

§  Not older than 4400-4500 Ma


Age of lunar rock 77215

| |





Overview

| |

§  Isotopes most often not homogenously distributed on earth §  determination of origin by specific isotopic signature §  (e.g. residence of unidentified victims) §  single isotope analysis not sufficient

§  Examples for multi-isotope analysis §  2H §  13C §  14N §  18O §  34S §  87Sr/86Sr §  207Pb/206Pb


Isotopes systems in forensics

| |

§  87Sr/86Sr ratio depends on geology (e.g. on age of rock) §  Sr in minerals à weathering à drinking water / food à human body



old rocks: higher 87Sr/86Sr ratio

young rocks: lower 87Sr/86Sr ratio

| |

§  18O/16O ratio depends on meteorology §  different masses influences evaporation and condensation rates

à 18O enriched in oceans (slower evaporation rate) à rainfall near coast have higher amount of 18O (higher condensation rate)



high

low

| |

Uptake of 18O and 86Sr/87Sr by ingestion and incorporated in:

§  tooth (encapsulated system) §  hydroxyapatite (in place of Ca) §  grow in early years of life §  food/water ingested during childhood defines isotope ratio

§  bone (dynamic system) §  mineralized collagen (in place of Ca) §  rips (spongy bone)

§  fast turnover rate: information of last 4-6 years §  femur shaft (compact bone)

§  slow turnover rate: information of last 25-30 years




Body found in Netherlands §  ratio in teeth sample do not

match with regional isotopes ratio

Matching 18O ratio with reference map gives probability of origin

à not decisive à  further exclusion with 87Sr/86Sr map


Body identified after isotope analysis: originates from south-west Poland

| |

Thank you for your attention!


Applications for isotopic ratio analysis

| |

§  Carlson RW, Boyet M, Horan M. Chondrite barium, neodymium, and samarium isotopic heterogeneity and early earth differentiation. Science 316, 1175–1178.

§  Bowen, G. J., J. R. Ehleringer, L. A. Chesson, E. Stange, and T. E. Cerling, Stable isotope ratios of tap water in the contiguous United States, Water Resour. Res. 43,

§  Laura Font, Gerard van der Peijl, Carina van Leuwen, Isis van Wetten, Gareth R. Davies, Identification of the geographical place of origin of an unidentified individual by multi-isotope analysis. Sci. Justice 55, 1, 24e.

§  Laura Font, Gerard van der Peijl, Isis van Wetten, Pieter Vroon, Bas van der Wagt and Gareth Davies, Strontium and lead isotope ratios in human hair: investigating a potential tool for determining recent human geographical movements, J. Anal. At. Spectrom., 27, 719-732.

§  Qin L, Carlson RW, Alexander CMO’D. Correlated nucleosynthetic isotopic variability in Cr, Sr, Ba, Sm, Nd and Hf in Murchison and QUE 97008. Geochim. Cosmochim. Acta 75, 7806–7828.

§  Voerkelius Susanne, Lorenz Gesine D., Strontium isotopic signatures of natural mineral waters, the reference to a simple geological map and its potential for authentication of food, Food chemistry 118, 933-940,

§  https://www.britannica.com/science/dating-geochronology §  http://www.tulane.edu/~sanelson/eens211/radiometric_dating.htm §  http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/rbsrstep.html

§  http://www.pmc.ucsc.edu/~apaytan/290A_Winter2014/pdfs/Lecture%205%20Sr.pdf §  https://curator.jsc.nasa.gov/lunar/lsc/77215.pdf

§  http://www.ia.uni-bremen.de/Lehre/MS2-2.pdf §  https://www.thermofisher.com/order/catalog/product/IQLAAEGAASFAFYMAMV


Literature

applications for isotope ratio analysis · 2016. 10. 20. · dating with decay systems ! principles...

Documents