Radio Active Isotopes

2. The Use of IsotopeThe Use of Isotope
Geochemistry in ForensicGeochemistry in Forensic
GeologyGeology
Radioactive IsotopesRadioactive Isotopes

3. Nucleus of the AtomNucleus of the Atom
 Contains protons and neutronsContains protons and neutrons
 Contains most of the mass of the atomContains most of the mass of the atom
(determined mostly by protons and(determined mostly by protons and
neutrons)neutrons)
 Electrons are distributed around theElectrons are distributed around the
nucleus in shells and orbitalsnucleus in shells and orbitals

4. ElectronsElectrons
First subatomic particleFirst subatomic particle
discovereddiscovered
1897 J.J. Thomson used the1897 J.J. Thomson used the
cathode ray tube to discover thecathode ray tube to discover the
electronelectron
Has a negative charge (-1)Has a negative charge (-1)
Mass = 9.110 x 10Mass = 9.110 x 10-28-28
gg

5. ProtonsProtons
Observed by E. Goldstein in 1896 andObserved by E. Goldstein in 1896 and
J.J. Thomson named later discoveredJ.J. Thomson named later discovered
its propertiesits properties
Has a charge of +1 equal inHas a charge of +1 equal in
magnitude, but opposite in charge ofmagnitude, but opposite in charge of
an electronan electron

6. ProtonsProtons
Thomson is given credit for showingThomson is given credit for showing
that atoms contain both negativelythat atoms contain both negatively
and positively charged particlesand positively charged particles
Relative Mass of 1 AMU (1.673 x 10Relative Mass of 1 AMU (1.673 x 10-24-24
g)g)

7. NeutronsNeutrons
Third major subatomic particleThird major subatomic particle
discovered (1932 Jamesdiscovered (1932 James
Chadwick)Chadwick)
No charge (neutral)No charge (neutral)
Relative Mass of 1 AMU (1.675Relative Mass of 1 AMU (1.675
x 10x 10-24-24
g)g)

8. IsotopesIsotopes
While atoms of the same elementWhile atoms of the same element
have the same atomic number (# ofhave the same atomic number (# of
protons) they may have differentprotons) they may have different
numbers of neutronsnumbers of neutrons
Creates different isotopes of sameCreates different isotopes of same
elementselements
Isotopes are atoms of the sameIsotopes are atoms of the same
element having different masseselement having different masses

9. Nuclide SymbolsNuclide Symbols

10. Nuclide SymbolsNuclide Symbols

11. Natural IsotopesNatural Isotopes
Every element has naturally occurringEvery element has naturally occurring
isotopesisotopes
Hydrogen has 3 naturally occurringHydrogen has 3 naturally occurring
isotopesisotopes
Protium is the most abundant isotope ofProtium is the most abundant isotope of
hydrogen (99.985%) has 1 proton, 0hydrogen (99.985%) has 1 proton, 0
neutrons, and 1 electronneutrons, and 1 electron

12. Natural IsotopesNatural Isotopes
Deuterium (0.015%) has 1 proton, 1Deuterium (0.015%) has 1 proton, 1
neutron, and 1 electronneutron, and 1 electron
Tritium (0.0001% ?) has 1 proton, 2Tritium (0.0001% ?) has 1 proton, 2
neutrons, and 1 electronneutrons, and 1 electron

15. IsotopesIsotopes
Two CategoriesTwo Categories
– Unstable – isotopes that continuously andUnstable – isotopes that continuously and
spontaneously break down/decay inspontaneously break down/decay in
other lower atomic weight isotopesother lower atomic weight isotopes
– Stable – isotopes that do not naturallyStable – isotopes that do not naturally
decay but can exist in natural materialsdecay but can exist in natural materials
in differing proportionsin differing proportions

25. Geologic TimeGeologic Time
Absolute or Radiometric DateAbsolute or Radiometric Date - Finds age- Finds age
of object in years before present basedof object in years before present based
on an absolute scale derived fromon an absolute scale derived from
radioactive isotopesradioactive isotopes

26. Geologic TimeGeologic Time
 Radioactive Isotopes used in Geologic DatingRadioactive Isotopes used in Geologic Dating
ParentParent DaughterDaughter half-life (y)half-life (y)
 U-238U-238 Lead-206Lead-206 4.5 billion4.5 billion
 U-235U-235 Lead-207Lead-207 713 million713 million
 Thorium 232Thorium 232 Lead 208Lead 208 14.1 Billion14.1 Billion
 K-40K-40 Argon-40Argon-40 1.3 billion1.3 billion
 R-87R-87 Sr-87Sr-87 47 billion47 billion
 C-14C-14 N-14N-14 57305730
 Half-life = time it takes for 1/2 of the parent massHalf-life = time it takes for 1/2 of the parent mass
to decay into the daughter massto decay into the daughter mass

27. Geologic TimeGeologic Time
Carbon 14 DatingCarbon 14 Dating
– A cosmic ray neutron (n) collides with an atomA cosmic ray neutron (n) collides with an atom
of atmospheric Nitrogen (of atmospheric Nitrogen (1414
N) which decays intoN) which decays into
1414
C and hydrogen (p=proton)C and hydrogen (p=proton)
1414
N + n =>N + n => 1414
C + Hydrogen (proton)C + Hydrogen (proton)
– 1414
C is rapidly oxidized toC is rapidly oxidized to 1414
COCO22 which iswhich is
continuously taken up into living organismscontinuously taken up into living organisms

28. Geologic TimeGeologic Time
Carbon 14 DatingCarbon 14 Dating
– When the organism dies it stops taking inWhen the organism dies it stops taking in 1414
CC
which disappears as it decays towhich disappears as it decays to 1414
NN
1414
C =>C => 1414
N + Beta (beta comes from aN + Beta (beta comes from a
neutron going to a proton)neutron going to a proton)

30. Geologic TimeGeologic Time
1414
Carbon DatingCarbon Dating
– Dating is accomplished by determiningDating is accomplished by determining
the ratio ofthe ratio of 1414
C to non-radioactiveC to non-radioactive 1212
CC
which is constant in living organismswhich is constant in living organisms
but changes after the organism diesbut changes after the organism dies

33. ForensicForensic 1414
Carbon CasesCarbon Cases
Dead Sea Scrolls – 5-150 AD
Stonehenge – 3100 BC
 Hezekiah’s Tunnel - 700 BC

34. ForensicForensic 1414
Carbon CasesCarbon Cases
● King ArthurKing Arthur’’s Table ins Table in
Winchester Castle,Winchester Castle,
EnglandEngland 1414
C dated to 13C dated to 13thth
century ADcentury AD
●● Cave painting atCave painting at
Lascaux, FranceLascaux, France
1414
C dated to 14,000 BCC dated to 14,000 BC
●● Rhind Papyrus onRhind Papyrus on
Egyptian mathEgyptian math 1414
C datedC dated
to 1850 BCto 1850 BC

35. ForensicForensic 1414
Carbon CasesCarbon Cases
● The Shroud of Turin was
14
C dated 1260-1390 AD
which suggests that it is a fake
● However, recent evaluation
shows that the sample measured
was from a medieval patch and/or
that it was seriously contaminated
with molds, waxes, etc
●New estimates date the shroud from
1300-3000 ybp bases on vanillin
retention

36. ForensicForensic 1414
Carbon CasesCarbon Cases
Nuclear testing during 1955-63 put large amounts ofNuclear testing during 1955-63 put large amounts of
1414
C into the atmosphere which was incorporated intoC into the atmosphere which was incorporated into
the enamel of human teeth. Because such testingthe enamel of human teeth. Because such testing
stopped thestopped the 1414
C input ended and theC input ended and the 1414
C in the teethC in the teeth
decayed at a fixed rate allowing dating of the teethdecayed at a fixed rate allowing dating of the teeth

37. THANKS FOR WATCHING!!!THANKS FOR WATCHING!!!
Credits : Harsh, Harnish and Sai Shaumik