Authored by Fred J. Grieman

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Two Applications of nuclear chemistry Neutron
Activation Mossbauer Spectroscopy
Authored by Fred J. Grieman
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Previously Decay processes Beta emission n
? p e- ? (neutron rich) Positron
emission p ? n e ? (neutron
poor) Electron capture (AZEl e-) ? AZ-1El ?
(proton rich) Alpha emission AZEl ? 42He
A- 4Z-2El (heavy elements)
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The Words of Moses
Radiation decay kinetics Dead Sea Scrolls example
Between 1947 and 1956 thousands of fragments of
biblical and early Jewish documents were
discovered in eleven caves near the site of
Khirbet Qumran on the shores of the Dead Sea.
These important texts have revolutionized our
understanding of the way the Bible was
transmitted, and have illuminated the general
cultural and religious background of ancient
Palestine, out of which both Rabbinic Judaism and
Christianity arose.
A Aie-kt Controversy early Christians or
before?
http//www.usc.edu/dept/LAS/wsrp/educational_site/
dead_sea_scrolls/
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Fusion and Fission
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International Fusion Reactor in France
http//news.bbc.co.uk/1/hi/sci/tech/4629239.stm ht
tp//news.bbc.co.uk/2/shared/spl/hi/pop_ups/05/sci
_nat_iter___the_next_generation_fusion_reactor/htm
l/1.stm
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Neutron Activation
Artificially produce radioactive nuclei

• Principle
• Nonradioactive elements are made radioactive by
  bombardment by neutrons
• Measure decay of activated atoms to identify and
  to determine concentration in sample

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Neutron Activation Method

• Neutron source often a nuclear reactor, but can
  be other natural sources
• Usually detect gamma rays prompt or delayed
• count rate and gamma ray energy identify
  species
• Can also detect Beta Particle

http//www.missouri.edu/glascock/naa_over.htm
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Neutron Activation Advantages

• Very sensitive technique ppb range
• Can detect many different elements

Table I. Estimated detection limits for INAA
using decay gamma rays. Assuming irradiation in a
reactor neutron flux of 1x1013 n cm-2 s-1.
(http//www.missouri.edu/glascock/naa_over.htm)
Example 1
Example 2
 
Chem 1 Lab

• Can detect many different elements at the same
  time because gamma ray energies are different for
  different elements

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Some Applications of Neutron Activation
Analysis 1. Archaeology "fingerprinting" of
obsidian artifacts ? prehistoric trade
routes. 2. Environmental Determinations a)
Uranium/Thorium distribution due to Ore
Processing b) Hazardous Elements in Waste
Material/Coal-Char Admixtures c) Selenium in
Aquatic Species in Fresh-water Impoundments 3.
Nutritional Epidemiology a) Thyroid Cancer
Study b) Non-Melanoma Skin Cancer Study 4.
Semiconductor materials and other high-purity
materials 5. Geological science a) Rare
earth elements ? processes in rock formation
b) 30 elements measured routinely in geological
samples 15-20 elements measured by
specialized procedures
(http//www.missouri.edu/glascock/naa_over.htm)
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• Example 1 The measurement of iridium (Ir) in
  soils.
• 1979 - NAA found unusually large amounts of Ir
  in
• Italian Cretaceous-Tertiary
  boundary sediments.
• Ir very low abundance on earth,
• ? excess Ir from impact of a
  10-kilometer diameter asteroid
• Measurement led to the extinction theory of the
  dinosaurs
• ? 65 million years ago, asteroid
  or comet impact
• caused weather changes that
  caused
• the extinction of dinosaurs

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• 6. Forensics
• NAA allows very exact determination of inorganics
  at crime scences
• Example 2 JFK Assassination Analysis of bullet
  fragments
• Guinn, V.P. "JFK Assassination Bullet Analyses".
• Analytical Chemistry (1979)
  51, 484A-493A.
• Five different locations of bullet fragments.
• How many bullets? How many guns?
• Bullets made of lead with many other trace metals
• added antimony (Sb) (for hardness) and
• trace silver (Ag) found best for
  identification
• Composition of metals in bullets varies
  considerably
• from different manufacturers
• Composition of metals in bullets from

aAverage of 10 bullets from a single
box.bAverage of 50 bullets from a single
box.cAverage of 20 bullets from a single
box.dAverage of 5 bullets from a single box.
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(Table I from "Comparison of bullet lead
specimens by nondestructive neutron activation
analysis. H. R. Lukens,. B.S. and V. P. Guinn,
Ph. D. Journal of Forensic Sciences, Vol. 16,
No. 3, pp. 301308, July 1971.)
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Results

• Conclusions from combination of Sb Ag
  concentrations in bullet fragments and from
  bullets in Oswalds rifle
• Bullet fragments all came from Oswalds rifle
• All fragments came from only two bullets

NAA from UC Irvine reactor
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Chem 1b NAA experiment Determine amount of
copper in brass sample Brass - alloy of Cu
and Zn (up to 42) - corrosion resistant,
hard, easily machined Neutron Source
Plutonium/Beryllium Mixture
High energy neutron!! How would you determine
energy?
Neutron Activation Source surrounded by
water Fast neutrons slowed by collisions with
protons in H2O Neutrons activate Cu in
brass and pure Cu
Radioactive!!!
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NAA Measurement
Activity (A) (? decay) detected by Geiger-Mueller
Counter Previously N A/k amount ? to
activity To determine Cu in brass, measure
brass sample and pure Cu A(brass)/A(Cu) x100
N(brass)/N(Cu) x 100 Cu (brass) Kinetics A
Ai e-kt
ln(A) -kt ln(Ai) k rate constant (ln
2)/t1/2
Intercepts different Why? Different Cu
give different activities
Slope the same Why? Cu in both cases
slope -k use for
identification
Cu
ln(A)
A
Brass
time
time
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Mossbauer Spectroscopy Mars Mission Was or is
there water on Mars? Examine minerals
http//athena.cornell.edu/
Spirit Rover
Instrument Group
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Mossbauer Spectrscopy Absorption of ?-rays
Source
Spectrometer
Fe in compounds absorb this ?-ray (nuclear
transitions)
Motion of source changes energy of ?-ray slightly
by Doppler Effect
http//elchem.kaist.ac.kr/vt/chem-ed/spec/material
/mossbaue.htm
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• Absorption of ?-rays over range produces
  spectrum
• Spectrum is different for different compounds
• because electrons interact with nucleus
• s-electrons, especially we will learn that
  s-electrons
• have finite probability of being inside
  nucleus
• So, for example, Fe2 and Fe3 molecules
• have very different Mossbauer spectra
• Gives fingerprint that allows identification

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This Mössbauer spectrum shows the presence of an
iron-bearing mineral called goethite in a rock
called "Clovis" in the "Columbia Hills." Goethite
contains water in the form of hydroxyl as a part
of its structure. By identifying this mineral,
the examination of Clovis produced strong
evidence for past water activity in the area
that Spirit is exploring.
http//athena.cornell.edu/the_mission/ins_m
oss.html
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Lunar Rock Analysis
Fe silicates
Continue to monitor website to see results
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