Transcript Isotopes and Forensic Science Professor Brian McGaw
Isotopes and Forensic Science
University of Lincoln presentation This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Overview
1. The forensic perspective 2. The atom 3. Radioactive and stable isotopes – properties and measurement 4. Dating techniques 5. Stable isotope applications 6. Nuclear forensic science – atomic detectives This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
1. The Forensic Perspective
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Prof Edmond Locard (1877-1966)
“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or foot prints, but his hair, the fibres from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and MORE, bear mute witness against him” This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
The Locard Principle of Exchange:
“When objects come into contact there is a transfer of particles”…….
This is a Principle that Scientists have struggled to exploit But Improvements in technology have brought new concerns… “Physical evidence cannot be wrong……..only interpretation can err” This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Trace Analysis
• Modern analytical techniques can now identify compounds containing <1ng (1 x 10 -9 g) of substance – Increasing potential for CONTAMINATION and MIS INTERPRETATION Recent high profile cases where: • Evidence was mishandled • Amount of evidence caused concern • Results may have been misinterpreted This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Drug Contaminated Banknotes:
• Cotton / linen matrix of banknotes is ideal for trapping crystals • 99% of London banknotes are contaminated with Cocaine • Spanish Euros average 335μg cocaine per note!
• £15M of drug contaminated notes are destroyed in UK each year This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
2. The Atom
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Example: Neon-20
• Positively charged nucleus consisting of protons (Z) and neutrons (N) • Electrons (e) occupy distinct energy levels around the nucleus •Atomic Mass = Z + N •Atomic Number = Z •For Neon-20, we have Z = N = 10, written as: 20 10 Ne Nucleus This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Electron
Henri Becquerel
Discovered Radioactivity in 1896 Placed pitchblende on a photographic plate and observed….
Henri Becquerel Nobel Prize (Physics) 1903 U This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Marie and Pierre Curie
• 1896 discovery of Radium and Polonium • 1903 PhD and Nobel Prize for Physics • 1903 isolation of Radium • 1908 Nobel Prize for Chemistry This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Types of radioactive decay: alpha,
α
(Z > 83)
Daughter nucleus 231 90 Th Parent nucleus 235 92 U Alpha particle (Helium nucleus) 4 2
α
2
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Types of radioactive decay: beta,
β -
(N/Z too large)
Converting N to P Daughter nucleus 40 20 Ca Parent nucleus 40 19 K Beta particle (Negatron) 0 1
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Types of radioactive decay: beta,
β +
(N/Z too small)
Converting N to P Daughter nucleus 95 42 Mo Parent nucleus 95 43 Tc Beta particle (Positron)
0 1
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Types of radioactive decay: gamma,
γ
(excited nucleus)
Parent nucleus 60 27 Co Daughter nucleus 60 28 Ni Gamma rays This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Radioactive Decay
Growth/Decay curves for radioactive elements
Proportion of parent atoms remaining 120 100 80 60 40 20 0 0 1 2 3 Time 4 5 6 Proportion of daughter atoms remaining 120 100 80 60 40 20 0 0 1 2 3 Time 4 5 6
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Parent 3 H 14 C 87 Rb 210 Pb 238 U
Half-Life
Daughter / Radiation 3 He + 0 β -1 14 N + 0 β -1 87 Sr + 0 β -1 206 Pb + 4 α +2 234 Th + 4 α +2 + γ Half-Life (Y) 12.3
5730 49 X 10 9 20.4
4.5 X 10 9 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Element
Uranium U-238 4.5*10 9 y Proactinium Pa-234 1.2 min Thorium Th-234 24.1 d Actinium
Uranium- 238 series
U-234 245500 y Th-230 75400 y Ra-226 1600 y Radium Francium Radon Astatine Polonium Bismuth Lead Rn-222 3.8 d Po-218 3.1 min Pb-214 26.8 min Bi-214 19.9 min Po-214 0.00014 s Bi-210 5.0 d Pb-210 22.3 y Po-210 138 d Pb-206 stable
Th- 232 series U-235 series
U-235 7.0*10 8 y Pa-231 32800 y Th-232 1.4*10 10 y Ac-228 6.1 h Ra-228 5.75 y Th-228 1.91 y Ra-224 3.7 d Th-231 25.5 h Ac-227 21.8 y Th-227 18.7d
Ra-223 11.4d
Pb-208 stable Pb-207 stable α
-decay Z: -2 N: -4
β
-decay Z: +1 N: +/-0 Decay series of short lived nuclides This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
3. Isotopes
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Frederick Soddy
Definition: Atoms of the same elements with different Atomic Mass Evidence: • 3 decay series end in Lead • Inability to separate ‘elements’ in the 3 decay series • Atomic Mass values not always integers (e.g. Ne = 20.2) 1913 Soddy proposed existence of ISOTOPES Frederick Soddy Nobel Prize (Chemistry) 1921 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Detection of Isotopes
Existence of ISOTOPES confirmed by Aston using the first mass spectrometer in 1919.
Isotope Ratio MS Magnetic sector Analysis of Neon gas achieved separation of 3 stable isotopes: Ion Source Faraday cups Detection system 20 10 Ne 21 10 Ne 22 10 Ne 90.9% 0.3% 8.8% This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Chart of the Nuclides
• A nuclide = an isotope • Narrow band of stability • For stability, N/P ratio rises with mass • All nuclides outside the band and with Z > 83 are radioactive • Elements can have from 0 – 10 stable Isotopes
100 90 80 70 60 50 40 30 20 10 0 0
β emission
10 20 30
β + emission
40 50 60 Number of protons, Z 70 80 90 100
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4. Dating Techniques
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The Clocks in the Rocks
In the beginning was the BIG BANG
Solar system / earth condensed from dust and gas
Radioactive elements decay to daughters (Parent : Daughter ratio changes with time)
With half-life can calculate the age of the earth This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Process: Dating with Isotopes
120 100 80 60 40 • Select suitable isotope 20 0 0 Parent C-14 Daughter N-14 5000 10000 15000 20000 25000 30000 35000 Time years • Clearly the 14 C 14 N system is useless ….. beyond 40,000 years • The 87 Rb – 87 Sr system is fine for 60M to 400G years!
120 100 80 60 40 20 0 0 100 Parent Rb-87 Daughter Sr-87 200 300 400 500 Time (billions of years) 600 700 800 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Process: • Ideally the crystals in the rock should contain no Sr (eg: Mica in Granite) • All subsequent Sr arises from Rb decay • Earliest rocks on Earth are 4G years old • On melt, the clock is reset when new igneous rock is formed This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Strontium Dating – the Forensic Application
0.715 --- • Sr has 4 stable isotopes • As a result of 87 Rb decay, 87 Sr levels will rise with time • 87 Sr / 86 Sr is highest in oldest rock • Sr has similar chemistry to Calcium and ends up in BONE 0.730 --- 88 Sr 7% 87 Sr 10% 86 Sr 82% 84 Sr 1% 87 Sr / 86 Sr ratios: 0.703 in young rock 0.750 in oldest rock This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Strontium Dating – Tracing
recovered from Thames
Adam
• Sept 2001, torso of 5 yr old boy • Suspected ‘muti’ style ritual killing • Gut contents suggested poisoning and UK as place of murder • Bone 87 Sr/ 86 Sr was high – Pre Cambrian levels • Police search for relatives in rural area between Benin City and Ibadan, Nigeria…arrest made in Dec 2003 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Carbon Dating
• 14 C half life = 5730 yrs • Excellent for dating organic material from 0-40,000 yrs * Nitrogen-14 Neutron capture Cosmic radiation Carbon-14 Why is there any 14 C left, & how does it work?
14 C is absorbed along with 12 C and 13 C into the tissue of living organisms in a fairly constant ratio • Assume rate. 14 C is continually being produced at the same • Whilst alive, drop dates 14 C levels remain constant. Only on death does the level start to • However, calibration is needed to get accurate Carbon-14 Soil When an organism dies 14 C converts back to 14 N by beta decay Beta decay Nitrogen-14 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Carbon-14 and Tree Rings
• Bristlecone Pine allows calibration back 7000yrs …. …..HOW?
• Calibration shows that 14 C production is variable…... WHY?
• Variation in Solar flux • Decreases caused by burning fossil fuels • Increases caused by A bombs
200 190 180 170 160 150 140 130 120 110 100
Year This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Carbon Dating – the Forensic Application
• Piltdown Man - a fake!
• Turin Shroud mediaeval (1260 to 1390AD) • Zoroastrian Mummy – post A-bomb era This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
5. Stable Isotopes
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Lead in Human Teeth
• Pb has 4 stable isotopes • Pb isotope ratios in our bodies reflect that of the environment: Data from Australian Citizens –Tooth Enamel Origin 206 Pb/ 204 Pb Australia 16.56
CIS 17.98
Balkans 18.23
UK 16.92
–Enamel - Pb content set in childhood –Dentine - 1% of Pb exchanges per annum –Jaw bone - 10% exchanges per annum Gulson et al J. Forensic Science 42, 787-791.
Isotope Origin 208 Pb 207 Pb 235 U 206 Pb 238 U 232 Th 204 Pb Big Bang Ratio 206 Pb/ 204 Pb in geology: Varies according to origin / age …..
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Isotope Fractionation
• The Chemistry of elements is largely determined by its electronic structure • But differences in mass give rise to kinetic and equilibrium effects RESULT: In photosynthesis some plants discriminate AGAINST 13 C Stable Carbon Isotopes: 12 C – 98.89% 13 C - 1.11% Light isotope: - forms weaker bonds - is more reactive - as CO 2 will diffuse faster This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Fractionation via Photosynthesis
• 2 major photosynthesis pathways: C 3 and C 4 plants • C 3 discriminate much more than C 4 plants RESULTS: CO 2 (air) = 1.11% 13 C C 4 plants = 1.10% 13 C C 3 plants = 1.08% 13 C Examples of C 3 Plants: Wheat, Barley, Rice, Oats, Sugar Beet …in fact most nutritionally important plants.
Examples of C 4 Plants: Sugar Cane and Maize.
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Measuring C-13 Levels
Species Mass • Use Isotope Ratio Mass Spectrometry (IRMS) 12 C 16 O 2 44 13 C 16 O 2 45 Isotope Ratio MS • Very Precise (+/ 0.0005% 13 C) Magnetic sector Ion Source Key Features: - Measured as CO 2 - Dual Inlet - Triple Collector - Measured v. Ref Gas Faraday cups Detection system This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Stable Isotopes – Some Forensic Applications
Food / Drink adulteration • Malt is expensive • Sugar is cheap!
• Both ferment to produce alcohol • Temptation to adulterate!
Fermentation: Sugars C 2 H 5 OH Sugar Source δ 13 C Malt (UK) -25.9
Maize -13.0
Sugar Cane -12.0
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Wines Whisky
Adulteration: Alcoholic Beverages
Wine Bootleg Port/Brandy Cz Bootleg Whisky Beer Sugars -30 Malt German Malt Blended Scotch -20 Δ 13 C per mil v. PDB UK B’bon Maize/Cane This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License -10
Adulteration: Maple Syrup
Same approach has been used for honey, fruit juice, olive oil and maple syrup -10 δ 13 C By combining 2 H: 1 H ratios with 13 C: 12 C ratios we can achieve greater DISCRIMINATION -20 Beet Cane Maple ‘Maple’ Adulterated syrup shown to contain 40% Beet sugar -30 90 2 100 H ppm Martin et al (1996) J Agric Food Chem, 44, 3206.
110 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Nakamura et al (1992) Biomed Mass Spectrom, 8, 390.
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δ 13 C -18
Travelling German Business Men
USA -20 -18 Japan -20 1 2 Weeks 3 4 Nakamura et al Biomed Mass Spectrom, 8, 390.
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Sources of Heroin
It is important to establish: • Geographical source • Evidence of ‘batch’ synthesis of Heroin
H O O H O N CH 3
Morphine Heroin
H 3 C O O H 3 C O O O N CH 3
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Geographical Source of Heroin
Drug source Lebanon Lebanon Thailand Turkey Turkey Heroin -30.9
-31.4
-32.2
-31.4
-32.7
δ 13 C Morphine -28.7
-28.9
-30.5
-29.7
-29.6
From: Besacier et al (1997)J Forensic Science, 42, 429 2.2
(H-M) 2.5
1.7
1.7
3.1
Acetyl source Lab 1 Lab 1 Lab 2 Lab 2 Lab 3 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
6. Nuclear Forensic Science – the Atomic Detectives
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Trafficking Nuclear Materials
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Man-made Radioactive Isotopes
• Smuggled Plutonium – can identify the reactor type in which the fuel was originally radiated and the type of plant where the material was subsequently reprocessed In 1997, two pieces of stainless steel contaminated with alpha-emitters were found in a scrap metal yard in Germany. Source was identified as a fast-breeder reactor in Obninsk, Russia This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Weapons-grade Plutonium
• The isotopic composition of plutonium can indicate INTENT In 1994, a small lead cylinder discovered in a garage in Tengen on the Swiss-German border was found to contain plutonium metal, isotopically enriched to 99.7% Weapons-grade Pu-239 This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Radioactive Fingerprints
• Preserving the conventional chain of evidence whilst dealing with radioactive samples can be problematic For example – lifting fingerprints and swiping for radioactive contamination cannot both be carried out The first ever radioactive fingerprint has recently been identified on an object contaminated with alpha-emitting isotopes This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Conclusions
• ‘Crime is a complex interaction of people and things at different points in time and space’ ( RE Stockdale, Science Against Crime ).
• Isotopes provide a powerful and new approach for investigating diverse crimes.
• Need for careful standardisation / calibration • Enormous research and development opportunities.
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Acknowledgements
• • • • • • • JISC HEA Centre for Educational Research and Development School of natural and applied sciences School of Journalism SirenFM http://tango.freedesktop.org
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