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7/23/2019 History of Radiocarbon
http://slidepdf.com/reader/full/history-of-radiocarbon 1/33
Volume
09 , Number 2, March-April 2 0 0 4
Journal of Research
of
th e National
Institute of Standards an d Technology
J. Res. Natl. Inst.
Stand.
Technol.
09 , 85-217 (2004)]
The
Remarkable
Metrological
History
of
Radiocarbon Dating [II]
Volume
09
Number
2
March-April
2 0 0 4
Lloyd
A.
Currie
National Institute of Standards
an d
Technology,
Gaithersburg,
M D
0 8 9 9 -8 37 0
U.S.A.
This
rticle
traces
he
metrological history
of
adiocarbon, rom he nitial reak-
through devised by
Libby,
to minor (evolu-
tionary) nd ajor revolutionary)
advances
hat
have brought
measure-
me nt from a
crude,
bulk
[8 g
carbon]
dating
tool, o
efined
robe or ating iny
amounts f precious rtifacts,
nd
or
molecular
dating"
t
the
0
ng to
00
\ig
level.
he
etrological dvances
ed
o
opportunities
nd
urprises,
uc h
s
he
non-monotonic
endrochronological
ali-
bration
urve nd he
b o mb
ffect," ha t
gave rise to ne w multidisciplinary areas of
application, ranging from archaeology an d
anthropology o osmic ay hysics o
oceanography
o
pportionment of
anthro-
pogenic pollutants
o
the
reconstruction of
environmental
history.
Beyond the specific topic of natural
,
it
is hoped that
this
account m ay serve as a
metaphor or young
cientists, llustrating
that
just
when
cientific
discipline
m ay
appear
to
be
pproaching
maturity,
unanti-
cipated metrological
advances
in
their
ow n
chosen ields, nd
nanticipated
nthro-
pogenic r natural hemical vents n he
environment, an pawn ew reas f
research aving xciting heoretical
nd
practical implications.
Key
ords: ccelerator as s pectro-
metry;
apportionment of fossil an d biomass
carbon;
"bomb" as a global
tracer;
dual
isotopic
uthentication;
etrological
history;
olecular
ating;
adiocarbon
dating; the urin Shroud; SR M 1649a.
Accepted:
ebruary 11,2004
Available online:
http://www.nist.gov/jres
Contents
1 . ntroduction 86
2 .
he Birth of Radiocarbon Dating 86
2. 1 Standards
an d
Validation 8
9
3. atural
Variations 90
4.
he
B om b
92
4.1
xcess
C
as
a
Global
Geochemical
Tracer
93
4. 2 he Second (Geochemical) Decay Curve
of C : sotopic-Temporal Authentication 93
5. nthropogenic
Variations;
"Trees Pollute"
9
5
5. 1
Fossil-Biomass Carbon
Source
Apportionment
96
6.
ccelerator
Mass
Spectrometry
99
6.1
he
Invention
99
6. 2 he Shroud of Turin 00
Emergence of
|X-Molar C Metrology
04
7.1 ong-Range
Transport
of Fossil
an d
Biomass Aerosol 05
7. 2
sotopic
Speciation
in
Ancient
Bones
an d Contemporary Particles 10
7.2.1 Urban Dust (SRM 649a);
a
Unique
Isotopic-Molecular Reference Material .. .211
Epilogue
14
References 15
18 5
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Volume
09 , Number 2, March-April 2 0 0 4
Journal of Research
of
th e National
Institute of Standards an d Technology
1.
ntroduction
This
rticle
s
bout
etrology,
he
cience
f
measurement. More pecifically,
t
xamines he
metrological
revolutions,
or at least
evolutionary
mile-
stones ha t
have
marked
he
istory
f
adiocarbon
dating,
ince
ts
nception
om e
0 years
go ,
o
he
present.
The series
of
largely
or
even totally unantici-
pated developments
in
th e metrology of natural * C is
detailed
in
th e several sections of this article, together
with
xamples of
th e
onsequent mergence
of ne w
an d
undamental pplications
n
road
ange
f
disciplines n
he
hysical, ocial,
nd
iological
sciences.
The
possibility
of
radiocarbon
dating
would
no t
have
existed,
had
not
*€
ha d
th e wrong half-life—a
fact
that delayed
its
discovery [1]. Following th e discovery
of this 5730 year (half-life) radionuclide
in
laboratory
experiments
by
Ruben an d
Ka me n, it
became
clear
to
W .
F.
Libby
hat
* C
should
exist
in
nature,
an d
that
it
could serve
as
a
quantitative
means
fo r
dating
artifacts
an d
vents
marking
he
istory
f
ivilization.
he
search or
atural
adiocarbon as
tself
metro-
logical
challenge,
fo r
th e
level
in
th e
living
biosphere
[ca.
2 30 Bq/kg]
la y fa r
beyond
the
then
current
state
of
th e
measurement
rt.
he
ollowing
ection
f
hi s
article reviews th e underlying concepts an d ingenious
experimental
pproaches
evised
y
ibby nd is
students
that
le d
to
th e establishment an d
validation
of
th e absolute radiocarbon
technique.
That
wa s but he beginning, however.
ubsequent
metrological an d scientific advances have included:
major
mprov ement n
*€ ecay
ounting precision
leading
to
he discovery
of
natural
*€
variations;
he
global racer
xperiment ollowing he pulse f
excess
* C
from
atmospheric
nuclear
testing;
th e
grow-
in g importance of quantifying sources of
biomass
an d
fossil
arbonaceous contaminants in th e environment;
th e revolutionary
change
from
decay
counting to atom
counting
AMS:
ccelerator mass pectrometry) plus
its
amous
pplication
o
rtifact
ating;
nd
he
demand fo r
an d possibility
of ' * €
speciation (molecular
dating)
f
arbonaceous
ubstances
n eference
materials, istorical rtifacts, nd n
he
atural
environment.
2.
he
Birth of
adiocarbon
Dating
The year before last marked th e 50th anniversary
of
th e irst
dition
f W illard
.
ibby's monograph.
Radiocarbon
ating—^published n
952
2].
ight
years
ater
ibby
as
warded
he
obel
rize n
Chemistry.
n
very
pecial ense ha t mall volume
(111 pages
of text)
captured
the essence
of th e path
to
discovery:
from
th e
initial
stimulus,
to
both conceptual
an d
quantitative
scientific
hypotheses,
to
experimental
validation,
nd
finally,
o
th e demonstration of highly
significant
pplications. he
ignificance
f Libby's
discovery,
rom
he erspective
f he obel
Commi tte e ,
is
indicated in
Fig.
,
which
includes
also
a
portrait of Libby in
th e
year
his
monograph w as pub-
lished 3].' he tatement f he obel ommittee
represents
n
unusual
degree of foresight,
n
ight
of
unsuspected
cientific
nd
etrological evolutions
that
would
take
place
in ensuing years.
Like many f
he
major
dvances n cience.
Radiocarbon
Dating
was
bom
of
Scientific Curiosity.
As
noted
by
Libby
n
his
Nobel
Lecture,
it ha d ts
origin
in
a
study
of
th e
possible effects that
cosmic
rays
might have on th e earth an d on th e earth's atmosphere"
[4].
hrough ntensive
tudy
of th e
osmic
ay
nd
nuclear
physics
iterature,
ibby made
n
mportant
series
of deductions,
eading
to
quantitative predic-
tion of
th e natural
'^ C
concentration
in
th e
living
bio-
sphere.
A s
reviewed in chapter I ofLibby's monograph,
an d
in
th e
Nobel Lecture, th e
deductive
steps included:
(1 )
Serge
Korff's discovery that cosmic
rays
generate
on
average
about
2
econdary
neutrons
pe r
cm^
of
th e
earth's
urface
pe r
econd;
2)
he nference ha t
he
large majority of th e
neutrons
undergo hermalization
an d
reaction
with
atmospheric
nitrogen
to
form '* C
via
the nuclear reaction
"*N(n,p)"*C; (3 )
th e
proposition that
th e
'* C toms
quickly
oxidize o
'^COj,
nd
ha t
hi s
mixes with th e total exchangeable reservoir of carbon
in
a
period short
compared
to
th e
ca .
8 0 0 0 year
mean
life of
' * C . Based
on
he
observed
production
rate
of
neutrons
ro m
osmic ay s
ca.
cm"^
~'),
heir near
quantitative ransformation
o
* C ,
nd
an
stimate
of
th e
global
arbon
xchangeable
eservoir
8. 5
g/cm^),
Libby
estimated
that th e
steady
state
radioactivity con-
centration
of
exchangeable
'* C
would
be
approximate-
ly
[(2
X
60)/8.5]
or
about
14
disintegrations per
minute
(dpm) per
gram
carbon
(ca.
2 30 m Bq g"'). O n c e living
matter s
ut off from hi s teady tate,
xponential
nuclear
decay
will
dominate, an d
"absolute dating"
will
follow
using
th e observed
half-life
of
' ' * C
(5568
years).^
Figure
hows Libby as
the
author
first
m et
him,
shortly after
the
latter
ntered
he
University
of
Chicago
s
graduate
tudent
n
chemistry.
Production
rate an d reservoir parameters are taken from th e Nobel
lecture 4]; these values differ somewhat from those used by Libby
in
[5 ]
an d
in
the
first edition of
his
book [2].
Th e
half-life
(5568
a) is
the
"Libby half-life" which
by
convention is used
to
calculate
"radio-
carbon
ages;"
the
current accepted
value
for the
physical
half-life is
(5730 ±
40 )
a
[5a].
1 86
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Volume
09 , Number 2, March-April 2 0 0 4
Journal of Research
of
th e National
Institute of Standards an d Technology
Seldom has a single
discovery in chemistry had
such an impact on the
thinking in
so
many
fields
of human endeavor.
-Nobel
Committee
1960
W .
F . Libby(ca.
1952)
Fig.
.
Portrait of W . F. Libby, bout the time of publication of t he irst edition of
his
monograph, Radiocarbon Dating
(1952) ,
an d
statement of
the
Nobel Committee (1960) [3].
Tw o
ritical
ssumptions
re
needed
or
bsolute
*€
dating:
onstancy of
both th e cosmic
ra y
intensity
an d
size of
th e exchangeable reservoir on average fo r
many
thousands
of years.
A graphical
summary
of th e
above
points
is
given
in
Fig.
2.
Libby first postulated th e existence of
natural
*€
in
1946 ,
at
a
level
of
0 .2
to
2 Bq/mol carbon
(1
dpm/g
to
10 dpm/g)
5] .
is
irst
xperimental
as k as
o
demonstrate
his
presence
f
natural
'^ C
n
iving
matter. The
problem
wa s that,
even
at
10
dpm/g, th e
*€
would
be
unmeasurable
he
plan was
o
earch
or
natural
*€
in
bio-methane,
but
th e
background
of
hi s
well-shielded
.9
L
Geiger
ounter
34 2
ounts
er
minute) xceeded
he xpected
ignal
by actor
of
400. Libby an d coworkers di d succeed
in
demonstrat-
ing the presence
of
' ' ^C in living m atter, however. For an
account
of their
creative
approach
to
th e
problem,
ee
their
on e page rticle n
Science, Radiocarbon ro m
Cosmi c
Radiation" [6].^
Having detected
*€ n
he
iving
biosphere,
Libby
an d is
olleagues
ad
o
evelop measurement
technique that
w as
both quantitative
an d practical.
The
To fully appreciate the nature of th e experimental impediments an d
flashes of insight along
the
path to
discovery,
tudents re ncour-
aged to tudy th e original scientific iterature, s given
here,
rather
than
restricting attention
to
subsequent
summaries
in
textbooks.
thermal
diffusion
enrichment
technique
6]
w as
not:
t
demanded very
large
samples an d thousands of (1946)
US dollars to measure he ge of
a
ingle mummy
[4].
Development f n
cceptable
echnique
as
formidable,
s
outlined
n Table .
A
ubstantial
n-
crease
in
signal w as achieved
by converting
th e
sample
to
olid
arbon,
hich
oated
he
nner
al l
f
specially
designed
"screen wall counter;" bu t
th e back-
ground/signal
ratio
(16:1)
still
eliminated
th e
possibili-
ty
of
meaningfiil
measurements.
At his
point,
Libby
ha d
an
inspiration,
from the analysis of the nature of th e
background
adiation
4] .
e
oncluded
ha t
t
wa s
primarily
due
to
econdary,
onizing
cosmic
radiation
having great penetrating power—negative
m u
mesons
{\r). By urrounding th e
ample
ounter with osmic
ra y
uard
ounters
perating
n
n
nti-coincidence
mode , most of th e \r counts
could
be eliminated,
result-
ing
n
urther
background
eduction
by
actor
of
twenty,
o
pproximately
ounts
per minute
cpm).
The inal background
to
ignal ratio
of
0.8
or
living
carbon, made ossible he measurement f natural
(biospheric)
* C
with
precision
under 2
% Poisson
relative
standard
deviation)
with
a
total
(sample,
back-
ground)
counting time ofjust 2
d
([2],
Chap.
V ).
Fig.
3
shows
he
ow-level
ounting
pparatus
evised
y
Libby,
with
which th e
seminal '* C
dating measurements
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Volume
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Journal of Research
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th e National
Institute of Standards an d Technology
PRODUCTION OF ̂^C
p
R
O
D
U
C
T
I
O
N
D
I
S
T
R
I
B
U
T
I
O
N
D
E
C
A
Y
C o s m i c
Ray
*C 9
Equilibrium
Concent ra t ion: ̂—
10
^
Tiien: ^ ^0
14K
*N
+ e'
+
V
T ^ ^ 2
5700
years
O ne
Gram
-»
-10
counts/minute
Fig.
. raphical
epresentation
f he roduction, istribution, nd ecay f natural
(courtesy of D.
J.
Donahue).(Parameter values are approximate.)
were
made.
he
* C creen
al l
ounter
s
isible
through th e open, 8 inch thick cantilevered
steel
doors
having
a
wedge-like
closure.
The
steel
tomb
reduces
th e
background
by
about
a
factor
of
five.
The
bundle
of
nticoincidence
osmic
ay
uard
ounters,
ee n
surrounding th e central counter in
th e
figure, eliminates
some
5
%
f he
esidual ackground
rom
he
Table
1.
ibby's
Measurement
Challenge
penetrating
i
tion.
radiation, hrough
lectronic
ancella-
• osmic ra y neutron intensity: n m s
• xchangeable carbon reservoir: .5 g m
• stimated C
activity:
14
dp m ~
0.23
Bq ~ )
•
ample
size
(detector
efficiency):
g
carbon
(5.5
% )
•
stimated modem
carbon
rate 6. 2 cp m
(min~
)
• ackground rate: 0 0 cp m (unshielded), 00 cp m (2 0 cm Fe )
Assumptions:
Constant production
rate
Fixed
exchangeable C reservoir
(uniform
distribution)
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Volume
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Journal of Research
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th e National
Institute of Standards an d Technology
Fig.
.
ow-level nticoincidence ounting pparatus evised
by
Libby
fo r
t he original
measurements that
le d
to the
establishment
of
he
adiocarbon
ating
echnique
Ref
2 ],
nd
Radiocarbon
Dating
(jacket
cover)
R.
Berger
an d H .
Suess, eds., Univ.
California
Press, Berkeley (1979) .)
Perhaps
the
most valuable metrological
lesson
from
Libby's
arly
work
as
he
xtreme
mportance
f
formulating
ealistic
heoretical
stimate
or
he
sought-after signal. W i th o u t ha t
s
guideline or
designing a
measurement
process
with
adequate
detec-
tion or
quantification
apabilities,
here s
ssentially
no ossibility
ha t
atural adiocarbon ould
av e
been found by hance with th e he n urrent radiation
instrumentation.
2.1 Standards and
Validation
Once he measurement f
atural
* C
ecame
feasible, th e
immediate
task
tackled
by
Libby
an d
hi s
colleagues was
o
es t th e
validity
of
th e radiocarbon
dating
model. Th e
first
step
consisted of
determining he
zero
point
of th e
natural
radiocarbon
decay
curve—
i.e.,
th e radioactivity concentration (dpm
* C
pe r gram C )
in
living
matter,
an d
to
test fo r
significant geographic varia-
tion.
This
was
a
major
component
of the
Ph D
thesis
of
E. C . Anderson
[7];
the
result
(i?„)
wa s
(15.3 ±
0.5)
dpm/g
[255 Bq/kg] ith
o
ignificant
eviation ro m
he
hypothesis of
a
uniform
global
distribution.'*
Th e next
Th e
neutron
intensity
in the
atmosphere,
an d hence
the
produc-
tion
profile,
ha s
major
variations
vertically
(because
of
cosmic
ra y
absorption with tmospheric epth) nd atitudinally because
of
geomagnetic shielding)—See Figs. 2
an d
3 in
Ref
2] , Because
ha s uch a long me a n life (=8000 a) , however, it w as expected that
an y esidual gradients
n he
global
xchange
eservoir would
be
undetectable, given
the
3
%
to
5
%
uncertainties of
Libby's
original
measurements
(Ref 2] ,
Chap.
I).
step
w as
to
measure
th e
* C
concentrations
in selected
historical artifacts
of
known
age,
an d compare them
to
th e absolute
* C
age.
The
latter
was accomplished by
comparing th e rtifact * C oncentration
dpm/g
C )
to
that of th e iving biosphere. The bsolute ge derives
from the
inversion
of
first order
nuclear
decay
relation,
using 5.3 dpm/g an d
5568
a
as
th e parameters
of
th e
absolute natural
*€
decay
curve.
The famous result, utilizing known
ag e
tree rings an d
independently-dated
gyptian
rtifacts, s
hown
n
Chapter
I
of
Libby's
1952
monograph
an d Fig. 4
in
this
article. Although he elative measurement uncertain-
ties
re moderately arge ca.
%
o
% ), he data
provide
a
striking
validation
fo r
th e
radiocarbon
dating
method over
a
period
of
nearly 5000
years.
Note that
th e
curve
shown
is
notfit
to
the
data\ Rather,
it
repre-
sents
the
absolute,
wo-parameter nuclear
decay
func-
tion. (See [8 ] fo r detailed information on th e validation
samples
selected.)
This
initial
absolute
dating
fiinction
served
to
estab-
lish th e
method,
but
it
indicated th e
need
fo r
a
univer-
sal
adiocarbon
ating
tandard,
ince
he
eference
value or th e ntercept here
5.3
dpm/g) would vary
13-
SAMPLES OF K N O W N AGE
^ TREE RING SBO .D.)
PTOLEMY
(200
±
15 0
B.C)
TAYINAT(675±50B.C)
Jj REDWOOD
(979 ±52
B.C.)
C URVE CALCULATED
FHOM PRESENT
D A Y
POiNT
AN D
HALF
LIFE O F
RADIOCARBON
5566
±30 YEARS
SESOSTRIS 1800
6£)
ZOSER
(2700175ac)
SNEFERU(2625±75B.c)
1000
2000 3000
4 0 0 0
50 0 0
HISTORICAL
AGE (YEARS)
6000
7000
Fig. .
adiocarbon
dating
validation
urve 1952):
he
curve of
knowns"
hat
irst demonstrated ha t bsolute adiocarbon ating
worked. Th e validation points epresent
re e
ings nd historical
artifacts
ofknown age.
Th e
exponential
function is notfit to
the data,
but
derived from
the
ndependently measured
half-life
nd
he
content of
living
matter
([2], Fig.
).
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Volume
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Journal of Research
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among
aboratories,
f
he y ac h
ad e
heir wn
standards.
The
problem
w as
tackled by th e internation-
al radiocarbon community
in
th e
late
1950s,
in
cooper-
ation with he U.S. National Bureau of Standards. A
large quantity of contemporary oxalic ci d
di-hydrate
w as
repared
s B S tandard
eference
Material
(SRM)
4 9 9 0 B .
Its
* C
concentration was
ca.
5
%
above
what
as
elieved
o
e
he
atural
evel, o
he
standard or adiocarbon dating was defined
s
.9 5
times th e *€
concentration of this
material, adjusted
to
a
C
reference
value
of-19
per
m il
(PDB). This
value
is defined
as
modem carbon" referenced
to
AD
1950.
Radiocarbon
measurements re ompared o his
modem
arbon
value,
nd
xpressed
s
fraction
of
modem Z^);
nd radiocarbon
ges"
re
alculated
from fi^
using he xponential
decay
elation
nd
he
Libby half-life"
568
. The ge s
re
xpressed
n
years before present
(BP)
where
present is defined
as
A D
1950.
A
published estimate
fo r
th e '^ C
concentra-
tion f
modem
arbon"
s
iven
s 13.53
±0.07)
dpm/g 9].
n
uly 983,
replacement SRM
4 9 9 0 C
w as substituted fo r th e nearly exhausted
SRM
4 9 9 0 B .
It w as repared ro m xalic ci d erived ro m he
fermentation
of
French beet molasses
from harvests
of
1977.
opy
f
he
ertificate
Analysis
f
SRM
4 9 9 0 C ,
ogether
ith
ertinent
eferences,
ay
e
obtained from th e website: ttp://nist.gov/srm [1 0 ] . '
Libby's uccessflil
development
of th e cience f
radiocarbon
dating
ed
o
he
apid
stablishment
of
more
ha n
hundred
dating
aboratories
world-wide,
th e initiation of
a
joumal supplement that later became
th e joumal Radiocarbon, nd he stablishment of
a
continuing series
of
triennial
R A D I O C A R B O N
confer-
ences,
he
irst
f
which
ook
lace
n ndover,
Massachusetts
in
1954.
3.
Natural Variations
This
failure esulted ro m basic dvances
n
* C
metrology. New pproaches o ow-level ounting
yielded
measurement
mprecision
hat
ltimately
approached .2 %
rsd);*
nd onstruction f
he
radiocarbon
dating
alibration
urve" ro m meticu-
lously
counted
annual
tree
ring
segments
showed
that
assumptions
of
constancy within different geochemical
compartments
f th e
xchangeable arbon
eservoir,
an d over time, were invalid. (This is
a
classic example
demonstrating ha t one annot
prove
he
null
hypo-
thesis;
he
alidation urve
hat
stablished he
radiocarbon
dating
method demonstrated onsistency
(validity) only within th e rrors uncertainties)
of
th e
validation
measurements.)
Th e
failure
of
the
absolute
dating
model
was,
n
fact, a
notable
success. The
revo-
lutionary discovery
of
natural adiocarbon variations
literally
arose
out of th e noise of absolute radiocar-
bo n dating, an d
it
transformed th e study of natural * C
into multidisciplinary
cience,
giving ise o
otally
ne w scientific
disciplines
of
* C
solar
an d
geophysics.
At hi s opening
address
at the
12th
N obel Symposium
on Radiocarbon
ariations and Absolute
Chronology
[12] n Uppsala,
Nobelist Kai
iegbahn
mphasized
that
This
ubject
s now]
nteresting
o pecialists
in
many
different
fields,
s
an be
ee n
ro m
he
ist
of participants,
howing
rchaeologists,
hemists,
dendrochronologists,
geophysicists,
varved-clay geolo-
gists, nd
physicists" Ref.
12] ,
p.
9f).
A n
arly
version
f
he endrochronological
* C
alibration
curve, resented y
ichael
nd
alph t
he
Symposium, is given
in
Fig.
5
(Ref
[12], p. 10) . ' The
Bristlecone pine,
s
hown n he igure, ha s
made
seminal
contribution
to
th e
science
of
dendrochronolo-
gy,
an d
through that,
to
th e
study
of
natural
'* C
varia-
tions.
It
is considered by some
to
be
th e
world's "oldest
living
thing,"
with
a
single
tree
containing
annual
rings
going
back 4000
years or more. It
is
clear
from
Fig.
Already, by th e time th e
Nob e l
Prize w as
awarded.
Radiocarbon Dating appeared
to
be approaching matu-
rity,
with
a
rich
fiiture
in
application
as
opposed
to
ne w
fundamental
iscovery.
hi s
ll
hanged,
owever,
when some
of
th e fundamental assumptions proved
to
be invalid—what might be considered
as
th e "failure
of
Radiocarbon Dating.
Several
econdary
tandards
or
dating
re
vailable
hrough
th e
International Atomic
Energy
Agency.
These
materials,
designated
IAEA Cl -C8, onsist of
wood, cellulose, ucrose, nd carbonate;
they cover
a
range of 0.00 pM C to 50.6 p M C ,
an d
have been
sub-
ject o
n
nternational omparison
11].
Note ha t
pM C
percent
modem
carbon)
refers to_4i
expressed as a percentage.
Th e deciding actor
for
high
precision
measurement
was he
successfiil evelopment f C O 2 as roportional ounting, fter
several failed attempts. Co mp a re d to Libby's solid sample (graphite)
technique,
he
CO 2 method esulted
n
maller ample
izes
nd
efficiency enhancement by
nearly
a
factor
of
twenty.
Th e
relatively
imprecise
dendro-calibration
curve in
Fig. 5
extends
to ca. 50 0 0 BC . Meanwhile, the
radiocarbon
dating calibration func-
tion ha s ndergone onsiderable efinement:
t
no w omprises n
extensive
database,
nd t
ha s
become
n
ssential lement of al l
radiocarbon
ating.
he
98 6
alibration
ssue
f
he
oumal
Radiocarbon
13] ha s
ompilation
going
back
o
a.
00 0 BC .
More
recent
attempts
t
extending the
record
much further back in
time av e tilized omparisons ith ther ating methods,
notably U/Th disequilibrium
dating.
B y
this
means, calibration data
have
been
given fo r periods beyond
2 0
0 00 BC
[14].
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5600BC
r
4800
BC
4000
BC
1 1 1
3200BC
n
2400BC
o
1600BC
C D
01
800BC
AD/BC
800
AD1600
.
o o
u Q Q
o
Q (j (J Q
o o
rfi
iTl
[Q C D ro
iTl rTi
m
o
Q
O
o
o CJ O O
9
<
CO
y?
̂
IN
O 00
<
Dendro
-Age
CO fl- TT
Fig. 5. Radiocarbon Variations, discovered by comparison of high precision radiocarbon dates
with high annual) ccuracy re e ing
ates.
Th e
plot,
which overs
he
period ro m bout
50 0 0
BC
to
the
present, represents
n
early version of
t he
radiocarbon dating calibration curve
( [12] ,
p.UO).
Th e
photo
shows
the
Bristlecone
pine,
the
major
source
of
dendrodates extending
back
many
millennia
(Photo
is courtesy
of
D.
J.
Donahue) .
that he
dendrochronological
ge
hows
ignificant
departure
i-om he
bsolute
* € nuclear) ge , begin-
ning
bout
hree housand years
go ,
nd
ontinuing
through he nd
of
this
eries of measurements ca.
5000 BC). These
newly
discovered
deviations
from
th e
absolute
dating
model,
of
course,
posed
new
scientific
questions:
ha t ar e he
auses of
th e deviations,
nd
ca n
we
use them
to
better understand Nature?
In
fact,
th e dendro-calibration curve serves dual
purposes.
For
more
classic
dating
disciplines,
such
as
archaeology,
anthropology,
nd
geology
event
dating),
t
gives
n
empirical
orrection
iinction
or
he
imple
adio-
carbon ge s
BP)
derived ro m he irst order decay
relation.
or
olar
nd geophysics nd elated disci-
plines,
it
gives th e
potential fo r
th e
quantitative investi-
gation
of
th e
causes
of
th e
variations.
The N obel
Symposium
serves as
a
rich resource fo r
information about
th e natural
'^ C
variations.
A n
excel-
lent exposition of
th e hree prime causative actors s
given by Hans Suess
Ref
12], pp . 595-605). These
are:
(1 )
hanges
n
he *€
production
at e ue
o
changes
n
he
ntensity
of
th e
earth's]
geomagnetic
field; (2)... modulation
of th e
cosmic-ray flux by
solar
activity;
3)
hanges n
he geochemical adiocarbon
reservoirs an d rates of carbon transfer between them.
The major
departure
(ca. 10
% )
seen
in
Fig.
5
is
consid-
ered to be
du e
to
th e
geomagnetic
field,
corresponding
to
a
factor of tw o
change
in
its
intensity
over th e past
8 0 0 0
years
15] .
This
ha s
given major impetus
to
he
science
of archaeomagnetism.
The other wo
actors
are
onsidered
esponsible or
he
artly eriodic
fine structure
exhibited n he
curve,
with arying
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RADIOCARBON
AN D SOLAR
ACTIV ITY
lOM
1100 1150
1200
1iO
1300
:9S0
1400
4S 0 ISOO
55 0
60 0
1650 1?0C
7S 0 ISQO
It60
190O
A ir
temperatures, eastern Europe
1,000 800 600 400 200
T O D A Y
YEARS A G O
CLIMATE
Fig.
6.
Radiocarbon
Variations
an d
Climate:
the
influence of
solar activity (sunspot
record)
(top)
on
C concentrations (cosmic ra y production
rates)
an d
climate
(Maunder
Minimum
temperature
record)
(bottom)
[15,
6].
amplitudes
of
about
%
to
2
% .
See
Figs.
, 2
in
th e
Suess rticle, espectively,
or
plots of
th e
irst
order
(geomagnetic)
an d
second order
(fine
structure)
devia-
tions from the ideal exponential decay function
("radio-
carbon
age")-)
A
fascinating
link
exists
between dendrochronology
an d
adiocarbon
ge ,
elated
o
limate.
That
s,
re e
rings by their
width
time series, like
ice
cores by their
'*0
time
eries,
give
insight
into
ancient
climate
16].
This,
in
turn,
m ay
be linked
to
th e
aforementioned *€
variations
ro m
hanging
olar
ctivity nd/or
varia-
tions n
eochemical
eservoirs.
ig .
epresents
famous example of th e inter-relationships among solar
activity (sunspots),
natural
radiocarbon
variations,
an d
climate
(Ref.
[15],
Fig.
5a ;
Ref.
[16] ,
p.
615).
The upper
part
of
th e
igure
hows
he orrelation
between he
sunspot
record (circles,
an d
ca .
1 year cycles)
an d
th e
* C
variations.
The period of lo w
olar ctivity,
nd
correspondingly
increased
* C
activity,
peaking at
about
1500
AD
nd
70 0
AD
s triking.
The
ower
part
of
th e igure uggests trong ink
o
lobal limate,
represented
here
by
th e
"little
ice
age."
4.
The Bomb
Atmospheric nuclear testing
ha d
n
unintended
bu t
profound
mpact on
* C
geoscience.
t
pproximately
doubled
th e
* C
concentration in atmospheric C O j , an d
consequently
in
living
matter,
by
th e
mi d- 1960s .
This
came
bout
because
neutrons
eleased
ro m
nuclear
fission
(o r
fusion)
react with atmospheric nitrogen by
exactly
th e same
reaction,
^N(n,p)' '*C,
as
th e secondary
neutrons from cosmic rays. The " bomb pulse ofexcess
* C
was ecorded
n
ll parts of th e iving
biosphere,
from
vintage
wine
[17]
to
contemporary
tree
rings
[18] .
It
w as
characterized by
a
sharp injection
of
' *€
in th e
early
960s,
ollowed by relatively slow geochemical
decay
after
th e imited atmospheric) nuclear test ba n
treaty. Totally ne w
nd unanticipated
opportunities
o
perform
global
racer
xperiments
esulted
ro m
hi s
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90 0
80 0
70 0
60 0
50 0
400
30 0
20 0
10 0
0
-100
1950
1960
1970
Y E A R
1980
1990
Fig.
7. nput function
of
excess
("bomb")
C :
a
global
tracer
fo r
carbon
cycle
dynamics
in the atmosphere, biosphere, an d oceans [19].
sudden,
widespread
injection
of
anthropogenic
*€
into
th e biogeochemical system.
4.1 Excess C as
a
Global
Geochemical Tracer
An
extensive
world-wide
program
of
monitoring
th e
excess
tmospheric
' ^COj
egan
ith
he
nset
f
nuclear testing an d
continues
today. Results of precise
measurements of
the nput
unction
or
xcess
' ^COj
ar e hown n
Fig.
Ref[19];
Ref 20] , hap. 1,
(I. Levin, et
al.)).
U se of this known
pulse of
excess
*€
as
a
tracer
ha s
allowed scientists
to
study exchange an d
transport processes
n
he
tmosphere,
he
biosphere,
an d
th e oceans
on
cale
ha t
would
otherwise
have
been nearly
impossible.
Simple
visual xamination
of
Fig.
7
shows, fo r
example,
that th e excess atmospheric
' ' ^C
injected
in
th e
northern
hemisphere
gave an attenu-
ated signal
n
th e
outhern
hemisphere,
nd that
there
w as
a
la g time
of
approximately
2
years.
Nowhere
ha s
he
b omb
pulse been
mor e
mportant
than n urthering our understanding
of
th e
dynamics
of th e ocean. A comprehensive program G E O S E C S :
Geochemical
Ocean
Section
Study)
to
follow
th e
plume
of
excess
*€
as
it
diffused
in
th e
Atlantic
an d
Pacific
oceans
wa s
initiated
in
th e
970s.
A small example
of
th e findings is given in
Fig.
, where we
find
a
nearly
uniform
distribution
below th e mixed layer,
indicating
rapid
vertical
transport
in
the
North
Atlantic, in
contrast
to
mode l
predictions
19,
21].
The
scientific
impact
of
this massive tracer study of ocean circulation is
trik-
ing, onsidering,
or
xample,
he ne w knowledge t
brings regarding th e
effects
of
th e
oceans
on pollutant
an d
heat transport
an d
climate
[22].*
4.2
The
Second
(Geochemical) Decay Curve
of
C: Isotopic-Temporal Authentication
Geochemical elaxation of th e xcess tmospheric
* C
fter
bout
970
ha s
esulted
n
econd short-
lived)
"decay
curve"
fo r
* C
(tail
of th e
input
function.
Fig.
).
This
ha s
made possible
ne w
kind
of
radio-
carbon dating, where modem
rtifacts
nd
orgeries,
food
products,
forensic biology samples,
an d
industrial
bio-feedstocks
can be
dated
with
near annual resolution
[24].
As
a
result
of th e ne w
submilligram measurement
capability Sec.
),
hort-term adiocarbon
ating
s
beginning o
chieve
ommercial
mportance,
s
exemplified
y
ts
pplication
o
he
ual
sotopic
( C, * C )
fingerprinting an d time
stamping
of industrial
materials.
A ase
n point
s
he
ooperative
esearch
nd
Development
roject
etween he
NIST hemical
Science
nd Technology Laboratory nd he DuPont
Central
Research
nd
Development Laboratory
25].
Th e dvent
f
ccelerator as s pectrometry, s iscussed n
Sec. of
this
rticle, ha s given a major boost to ou r knowledge of
ocean irculation. nformation ained hrough he E O S E C S
program
ha s
been greatly amplified
in
the
W o rl d
O cean Circulation
Experiment
W O C E ) ,
where
equisite
ample
izes
were
educed
from
2 0 0 L
of
se a
water
each, o es s
ha n L;
nd
the
cean
circulation atabase grew by more ha n 0 0 0 0 ates uring he
1990s [23].
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A^H( )
50 0
1000
1500
2 000
Z50D
3000
3 500
4000
4500
goo
100
—I
—
prS-EMHTlt)
-100
1972
10 0
00
model
OEOSECS
7
N AlloMic
l l
j
—/w
Fig. 8.
xcess
C
an d ocean
circulation
( G E O SE C S) .
M od el
(left)
an d
experimental
(right)
vertical
transects
of
bom b
C
in the North
Atlantic
[19].
The goal
of the
project was
to
demonstrate
th e capabil-
ity o
uthenticate
nd
at e
enewable
biosourced)
feedstocks, hemical ntermediates, nd
inished
industrial
products
using
high
ccuracy
dual
sotopic
( C- 'C)
fingerprinting,
raceable
o
IST.
he
specific roject, s
utlined n
Fig. , w as
irected
toward th e unambiguous
dentification of th e
opoly-
mer polypropylene terephthalate (3GT)) produced from
th e biosourced monomer ,3-propanediol
3G),
which
w as
derived
from
com as
feedstock.
(Terephthalic
acid
(TPA)
erved
s
he omplementary
onomer.)
Isotopic discrimination was ssential because
it
is not
possible hemically
o
distinguish he biosourced 3G
an d GT ro m
xisting
ndustrial
materials
ha t
re
fossil
feedstock
(petroleum) based.
The
ability to estab-
lish nique sotopic ingerprint or
he
uPont
biotechnology materials was critical fo r th e
identifica-
tion
of
th e
product
s
unique
omposition
of
matter,
an d
o
rack
t
n
omme r c e .
The
work
epresents
frontier
of
high
ccuracy,
dual
sotope
metrology,
with
'^ C
ata
Mr < 0.01% )
erving o
iscriminate
mong
different
photosynthetic cycles,
an d
*€
data
{u, <
0.5
% )
serving
both
fo r
quantitative
fossil-biomass
apportion-
ment
an d
fo r
dating
th e
year of
growth
of th e
biomass
feedstock.
A
graphical
summary of th e results of th e project is
presented
n
Fig.
0,
which
hows he
dual sotopic
signatures f
he opolymer
3GT) nd
bio-sourced
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Corn Petroleum
i
Glucose
Xylene
i
1 , 3-Propanediol
H O C H 2 C H 2 C H 2 O H
Biomass Carbon
[3G]
Terephthalic Acid
H O O C
—̂—C O O H
Fossil
Carbon
[TPA]
O
Polymerization
O
I I
/=x
I
-t
C
^̂ C
OCH2CH2CH2O^
[3GT]
Polypropylene
Terephthalate
Fig. 9. olypropylene Terephthalate: biomass
an d
fossil feedstocks. Th e
,3,
propane-
diol
mo no me r is derived from a renewable (biomass) feedstock vi a laboratory biotech-
nology:
conversion
of glucose
or comstarch
using
a
single
microorganism.
Th e
copoly-
m er
ha s potential
arge
v olum e
demand, nd
is
useful
s
fiber, ilm,
particle,
nd
a
molded article
[25].
monomer (3G);
as well
as values
fo r
isotopic
reference
materials (SI:
SRM
4 9 9 0 B
[oxalic
acid];
S2 :
IAEA
C 6
[ANU ucrose];
3:
RM 649a
urban dust]).,
nd
pre-existing
materials 3G',
G").
he
ashed
ine
joining
th e copolymer
en d
members
(3G,
TPA)
demon-
strates
sotopic-stoichiometric
as s
alance.
ec-
tangular
egions
n
ed
define
he scope
of
claims"
(authentication
regions)
fo r th e
ne w
isotopic
composi-
tions. Th e blue x in th e figure
represents
data fo r an
independent
atch
f
he monomer—sent
o
IS T
blind to
test
th e
validity
of
th e
authentication
region
fo r bio-sourced
G.
he
esults
ho w
both
ha t
he
test was
uccessful
nd ha t he
eparate
production
batches of th e 3G monomer
ha d
unique
isotopic signa-
tures.
he pproximately en-fold xpansion
of
th e
isotopic
data
or
wo ndependent batches
A,
B)
of
corn-glucose
bottom
ight)
emonstrates
he
ual
isotopic discrimination capability
of
th e
technique. n
fact,
using th e short
term
decay
curve
of * C
(Fig.
11),
it
w as possible to date he wo batches
to
he nearest
year of
growth,
99 4
A) nd
99 6
B) , espectively.
(Standard
uncertainty
bars
shown.)
5. Anthropogenic
Variations; Trees
Pollute
The
achievement
of
high
precision,
lo w
background
counting,
iscussed
n
ec .
,
ed
lso
o
he
irst
isotopic evidence of
global pollution with fossil COj—
named
he
Suess
ffect,"
fter ts
iscoverer.
dramatic
monotonic
drop
n
he
'^C/'^C
atio
n
re e
rings
beginning
in
th e
late
9th
century, reflecting th e
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1.7
1.4
-
1 . 1
-
^
0 ,8
O
0 ,5
-
0 .2
-
TPA
-0.1
-
biomass-C
3G
S2_
Glucxjse
S3
_
3G ' (c)
„.
--
(d )
S1
--.'•
X
--
/••-••
{b )
(a )
3G T .^''
3G (e )
fossi l -
C
-2 9 -2 6 -2 3 -2 0 -1 7 -1 4 - 1 1
0.33
0.31
0,29
0.27
1.20
-25.5
-24.5 -23.5
[B ]
[A]
Glucose (a )
10.5
-10.1
-9.7
-9.3
:13
(3'X(permil)
Fig.
10 .
Unique
Isotopic
Signatures:
the
-
plane
[25]. Th e main
panel shows
dual isotopic
signatures
f:or
(1 ) NIST (SI,
S3 )
an d IAEA
(S2)
traceability standards, an d (2 ) glucose from biomass (a), the ne w bio-sourced mo no me r 3G (b) (from cornstarch), the resulting
copolymer
3G T
(d),
an d
pre-existing
products 3G',
30
(c, e). Expanded views of
the
authentication
regions (red
rectangles) fo r
t he
copolymer
(left)
an d
mo no me r
(center)
are
given
in
the
bottom panels, plus = 10-fold expansion
(right)
of
the
isotopic data fo r independent
batches
(A ,
B) of a biomass feedstock
(glucose from
com).
Th e
blue
x
represents a
blind
(3G)
validation
sample.
use of coal
during
the
Industrial
Revolution, showed
a
2 .5
%
ossil
arbon
dilution
effect
by
th e
950s
Ref
[12],
p. 89),
fter
which
t
w as
clipsed
by
he
vast
injection
of bomb arbon. Thus began
till
nother
field
of'
*€ science: th e investigation of anthropogenic
variations,
articularly
s
elated
o
nvironmental
pollution.
5.1
Fossil-Biomass Carbon Source Apportionment
Research
on
mor e pecific ocal r
ven
egional
carbonaceous
pollution
began
lowly,
because
of
th e
massive
amples
equired.
Heroic
ampling fforts
n
th e
late
950s demonstrated
th e
principle by measure-
ments
f particulate arbon
pollution
n U.S. rban
atmospheres
2 6,
7].
After
apse
of
tw o
decades.
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1.6
-
1.5
^
1.4
\
\l
~
VK^^ ̂
1 ,2
-
^^^ '̂''̂ -̂̂
LI
-
'̂̂ '̂ * ̂ ~ -̂-.
1.0
. .
1970
19SU
199(1
2000
Fig.
1. hort term
decay
urve,
epresenting geochemical elaxation of excess
atmospheric ro m nuclear testing
Levin
et
l.,
n
(Ref
19];
Ref
20],
Chap.
31).
Information
critical for the discussion
in
Sec.
7.2.1
is indicated by
the
arrow—namely, the
sampling
date
an d corresponding biomass C enrichment fo r SR M 649a (urban dust).
research
in this
area
was
renewed
by
th e
author,
stimu-
lated
by 975
rticle
n
Science eporting
ha t
he
culprit fo r
a
severe case
of
urban pollution
in
tidewater
Virginia might be hydrocarbon
missions
ro m rees
[28] .
Th e
vidence
was
hemical
nd ontrovertible:
plausible,
but
ircumstantial
vidence
uggested
ha t
th e
ir
pollution wa s
ue o hydrocarbon missions
from trees ather from automobile exhaust or evapora-
tion from
nearby
industrial an d
military storage
tanks.
The rticle
oncluded
ha t
th e
elatively unsophisti-
cated
monitoring f
organic] ollutant oncentra-
tions ... will rarely be ofvalue
in
identifying [pollutant]
sources
.. "
Recognizing
mmediately ha t *€ ould
function
as
an
undisputed
discriminator,
w e
decided
to
design miniature lo w level
counters,
capable
of
meas-
uring
just
10
m g
carbon
samples,
mor e
than tw o
orders
of
magnitude
smaller
than
those used in
th e tw o
earlier
studies.
Apart
from
forest
fires,
we
found
that th e trees
were
not
th e prime
culprits,
except fo r
th e
case
where
humans er e
using he
rees
or
uel
eview
f
research
in
this
area
in
th e ensuing 2 0 years is given
in
Ref
[29] .
O ne
llustration
of
*€
erosol
cience
s
given
n
Fig. 2.
t
is
drawn
ro m
perhaps he most xtensive
study
to
date of urban particulate pollution using
* C .
The multi-year, multidisciplinary study of th e origins of
mutagenic
erosols
n
he
tmospheres
f
everal
U.S.
ities,
ocussed
n
Albuquerque,
ew
Mexico
during th e winter of 1984-1985. The photos
show
th e
tremendous impact on
visibility from particulate
pollu-
tion
from
rush hour traffic.
Results
of th e tw o month
study of particulate carbon proved that daytime pollu-
tion
up
o
~ 65 % ) w as dominated by mot or vehicle
emissions
fossil arbon),
nd ighttime
ollution
(u p
o
~
95
% ),
by
residential
woodbuming
biomass
carbon), with th e mutagenicity
(potency)
of
th e mot or
vehicle particles mor e severe by
a
factor of three
[30].
Particulate
carbon
aerosols
are
no w
widely
recognized
as
an
extreme
health
hazard
in
a
number
of
U.S. cities;
an d
except fo r periods dominated by
wildfires,
major
studies ncluding *€
measurements
av e
roduced
incontrovertible vidence ha t
he rban pisodes
re
dominated by
fossil carbon,
largely
from
mot or
vehicle
exhaust
[31].
Quantitative
pportionment
of
natural
nd nthro-
pogenic
sources
of
particulate
carbon,
methane,
carbon
monoxide,
nd
olatile
rganic
zone
recursors
n
th e
tmosphere, eanwhile,
as
ee n
ignificant
expansion
hanks
o
he
ensitivity nhancement
of ccelerator
as s pectrometry AMS) 32 ,
3].
Most recently,
with
th e mergence of
micromolar '^ C
A M S ,
nd G C / A M S ,
he
bility
o
date
ndividual
chemical
fractions
in
small
samples is
having
important
impacts
on both artifact ag e accuracy,
nd our under-
standing f perturbations f he uman nd
natural
environments
y
ossil
nd iomass
arbonaceous
species.
(See
Section
7) .
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1 3
Fig.
2.
Anthropogenic variations:
ossil-biomass carbon
apportionment
of particu-
late
ir
pollution
in
Albuquerque,
New
Mexico.
Photos
howing
visibility
reduction
in
early morning
(top)
an d mid-afternoon (bottom)
are
courtesy of R .K . Stevens
[30].)-
measurements quantified tmospheric
oot
ro m
motor vehicles
nd
esidential wood-
burning,
an d
helped apportion
concomitant
data on
particulate
mutagenicity.
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6.
Accelerator Mass
Spectrometry
6.1
he
Invention
The econd revolution n * € measurement cience
w as
he
discovery
of a
means
o
ount
* C atoms,
s
opposed
o *€
decays
beta
particles). The
potential
impact
on
ensitivity was
arly
ecognized:
nverting
th e first order nuclear decay relation, one finds that th e
ratio of th e
number
of
' *€ atoms
to
th e
number
of ' *€
decays
fo r
an y
given
sample
is
simply T/t),
where ris
th e
mean life (8270
a
fo r
'
*€), an d
t
is
th e counting
time
used fo r measurement of th e
disintegrations.
Allowing
for
he
ifference
n
elative
etection
fficiency
between AM S
an d
low-level
counting, and
setting
i to 2
d,
gives
a
sensitivity
enhancement
of
roughly
lO'',
in favor
of
AMS. hi s
mplies
ating
apability
f
ub -
milligram amounts of
modem carbon.
The
rize
f radiocarbon
ating
t
he
milligram
level
as
o
reat
ha t
major
fforts ere
ad e
to
efine mass
pectrometric echniques
o
ender th e
1. 2 X 10"'^
'*C/'^C
ratio
of
modem carbon measurable;
but, like Libby's initial
attempt
to
count
natural
radio-
carbon
without nrichment), atural
* €
roved
unmeasurable
y
onventional
as s
pectrometry.
Impediments ro m
molecular
ons
nd
he xtremely
close sobar
' '*N:
m/m .2x10 ^) ere ver-
whelming.
Success
came
in
1977,
however,
when
high
energy
megavolt)
nuclear
ccelerators
were used s
atomic
io n mass spectrometers 34-36].
Tw o
measure-
ment ideas
held
th e
key:
1 )
Negative carbon ions are
produced by
a
sputter io n source, using
graphite
as
th e
target.
(2 )
Following lo w energy mass selection, atom-
ic nd
molecular negative
ons re
njected nto
n
accelerator tube with
a
megavolt
potential.
The major
isobar is eliminated because nitrogen
does
no t
form
a
stable negative on . Passage of th e high nergy
on s
through
a
stripper
ga s
or foil
destroys all molecular ions
through th e "coulomb explosion,"
leaving
only
atomic
carbon ions
in
th e + 3
or
+ 4
charge
state.
'*C/'^C
ratio
measurements down
to
ca. 0"'^ ar e thus made possible.
Typical
ample
izes
re
.5
m g
o
m g;
modem
carbon
yields
0
0 0 0
ounts
n
ust ew
minutes;
an d
nstmment
ackgrounds
re
egligible
<0.2
%
modem, equivalent
to
a
*€
ag e of
>50
0 0 0
years
BP).
A diagram of th e ccelerator at one of th e eading
facilities
is
given in
Fig.
3
37].
The dramatic impact
of
high nergy
atomic
on)
as s pectrometry
s
shown
n
Fig.
4, where
t
is
lear
that
natural
* C
s
quite unmeasurable by lo w energy (conventional) mass
spectrometry
ue
o
molecular ons
xceeding he
* C ignal
y
mor e
han
ight
rders f
magnitude
(Ref.
[20],
Chap.
6]
Excellent
reviews
of
th e history,
principles,
nd
pplications
f A M S
re
iven
n
Ref
20 ]
y
. ove
Chap.
5) nd .
eukens
(Chap.
6) .
heCATIVC IO N
SWTTEft SOURCE
MAGNETtC M A S S
ANALYZER
ruiituci
EN - TA N D EM
ACCELERATOR
EI£CTROSTAT;C
DEFLECTOR 5*
MAGNETIC
4ASS
ANAL YZ E R
IMJUX
surs
Q \
STHlPPtft
IIIIIIIIIIIINIIirT^^IIIIIIIIKIIIMMI
_ UASSC.Il
/-
VMLKW
,14
J
l̂ ^̂ i i i i i l l l l l l l l l l l
ELtCTOOSTAnC
00 EI
CDC
f
•^
M :
I
A C E
OUTPUT
'•c/«c
c/'h
CO M P UT E R
H CURRENT/FREQ. h
-|CUBREHT/FIJEO~t-
^̂ ̂
C vENTS
Fig.
3.
AMS: andem
accelerator
t
ETH,
Zurich.
Negative carbon
ons,
produced with a
C s
putter
io n
ource,
undergo ow
nergy
mass
resolution
an d then are injected into th e 4. 5 MV accelerator tube.
Molecular
ions are destroyed by the stripper gas, an d emerging 8 M eV C ^
beams of C , C ,
an d
C are mass analyzed an d measured in current (stable C
ions)
an d event ( C
ions)
detectors [37].
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MASS UMBER
13
-1
1
n
xlO
-r
z
—1—
K > '
f-CH 3n
10
Kf'
\
'CH- SxlO
10-'
\
r
^CH,- 3x10' -
lo
X .̂Hl
V
s
CH;
J
^
' NH-
-f
V,
-J
L _
_yv.
Conventional
M
a.
/
'
Z
i 0
< J
-8
z 0
o
—
^9
lo'
•10
1 0
-
-n
to
-
W »
CONTEMPORARY
—
_ ^
n
-B
' C
0
-
19000 YEARS —
i
Accelerator MS
1 0 ^
j
j———
019 .20 JI
I NJ ECTOR AG NET IC
FIELD
(TESLA)
Fig. 4. onventional
top)
s ccelerator
high
nergy)
bottom)
mass
spectrometry:
/ ensitivity
s
nhanced
by m or e
ha n
ight rders
of magnitude hrough estruction f molecular ons an d nstable ~ )
(Ref 20],
Chap.
6).
A s
noted
n
he
eviews
by
Gove
nd
Beukens,
he
A M S revolution ha s extended well beyond * € , spawn-
in g totally new research re a in ong-lived sotopic
an d
ultra
race
table osmo-
nd
geo-chemistry
nd
physics through
its
capability
to
measure
'H,
*€ ,
^'Al,
^ 'Cl , '*'Ca,
an d
\,
and most recently, selected
actinides.
W ithin
on e
year of th e publications announcing
suc-
cessful
* C
A M S , another
continuing
series of interna-
tional
onferences
as
om .
he
irst
nternational
A M S
conference took
place
in
1978
in
Rochester,
N ew
York.
These conferences have continued on
a
triennial
basis,
with
each
proceedings
occupying
a
special
A M S
conference
ssue
of
th e journal, Nuclear Instruments
and
Methods
in
Physics
Research.
6.2
The
Shroud
of
Turin
The
adiocarbon
ating
f
he
urin
hroud
s
arguably th e best known
dating
application
of
acceler-
ator
mass pectrometry, t
east o
he
ay
public.
t
could
not,
or
at least
it
would not have taken place with-
out
A M S ,
because most
decay
beta)
ounting
ech-
niques
would
have
consumed
a
significant
fraction
of
this
artifact.
Although
still
a
destructive analytical
tech-
nique,
AM S required only "a postage stamp" amount
of
th e inen
loth
Ref. 20],
Chap.
5).
This particular
exercise
s
having
a
metrological mpact
well
beyond
th e radiocarbon date,
per
se. This
is
shown,
in
part,
by
widely
ccepted
tatements
1 )
oncerning
cientific
investigations of th e Shroud, nd
(2 )
ollowing publi-
cation
of th e
Nature
rticle
nnouncing adiocarbon
dating results
(Fig. 5;
Ref [38]).
1 : The
Shroud
of
Turin
s
he ingle, most
tudied
artifact
in
human
history."
14
2: The
Nature
) rticle
ha s ha d mor e
mpact
on
Shroud
research
than
an y
other paper
ever
written on
th e subject."
The article,
which
was
prepared
by
three
of
th e
most
prestigious
AM S
laboratories,
is
available to
the
gener-
al
ublic
n
he
eb www.shroud.com/nature.htm).
Together
with
public elevision
39],
t
s helping
o
create
broad
wareness
nd
nderstanding
f he
nature an d
importance
of th e A M S measurement capa-
bility.
econdly, because
of
controversy urrounding
th e meaning
of
th e adiocarbon
esult,
measurement
aspects
f rtifact
ating av e ee n
iven
ntense
scrutiny. Such
scrutiny
is quite
positive,
fo r
it
gives th e
possibility
of
added insight
into
unsuspected
phenome-
na
an d
sources
of
measurement
uncertainty.
The Turin
hroud s believed by many o be he
burial loth of Christ. The documented ecord, how-
ever, oes
back
only
o
he
Middle Ages,
o
irey,
France
ca.
35 3 AD ) with
he
irst
irm
date
being
1357
AD when
t
was
isplayed n Lirey
hurch.
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(b )
m
Fig.
1 5.
he
Turin
Shroud.
Shown
in the
montage
are:
(15a,
upper
left),
the
cover
of
the
issue
of
Nature
(1 6 February
989)
reporting
the
results
of the
measurements
by
A M S
aboratories
n
Tucson, Zurich,
nd Oxford;
nd hree
ingular
eatures
of
the rtifact:
15b,
ower
eft),
th e
=5 0 m g dating
ample
eceived
by
he
Tucson
aboratory, howing
he distinctive
weave 3:1
herringbone
will),
with
dimensions bout
m X
0. 5
cm ; (15c, upper right), th e characteristic negative image, considered by some as a remarkable piece of
mediaeval art; an d
(15d,
lower
right),
a
microphotograph
by
M ax Frei showing individual
fibers
supporting pollen grains of presumed unique origin [38, 39].
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Radiocarbon dating
was seen
immediately
as a
defini-
tive
method
o ecide
hether
he
Lirey
hroud"
could
have om e
i-om
la x grown n he
st entury
AD . Th e Shroud image, considered by some
to
be th e
skilled work of
a
mediaeval artist, hows
a
fiill length
image of a
crucified man;
but
as a
negative
image
[Fig.
15c]. ' Prior
to
the
AM S
measurements, th e
Shroud
was
subject
to
intensive examination by
photography,
spec-
troscopy,
rt
an d textile analysis, nd palynology
38 -
40].
The
unique
herringbone twill
[Fig.
5b ] is
consid-
ered
onsistent
with
st Century
ate;
nd pollen
grains
found
on th e cloth
[Fig.
5d ]
are
stated
by
M ax
Frei
to
have originated Irom
a
plant found only in th e
region
of
Jerusalem.
Radiocarbon
dating
of
th e
loth,
however,
yielded result
of
126 2 o 38 4
A D 9 5
%
confidence
interval)
[38].
Apart
from sampling,'" the AMS measurements were
performed taking th e strictest quality
control
measures.
Figure
5c
an d 5d
images
are
from the
documentary
prepared
by
the British Broadcasting Corporation which is hereby acknowledged
[39]; Fig.
5b
is courtesy of D.
J.
Donahue.
Th e
critical, non-AMS
issue
relates
to
sample
validity.
Th e
origi-
nally
greed
upon
ampling
protocol wa s o
have
nvolved
even
laboratories,
wo
measurement
techniques decay
an d
atom AMS]
counting), an d multiple samples representing different regions of the
cloth.
Shortly before
the
event, however,
the
scheme
was
changed to
restrict he number
of laboratories al l
A M S)
nd
he number
of
samples o hree,
al l
aken
from
he
am e ocation.
he
ampling
location,
near
a
comer
of
the
Shroud,
an d
near
an
area
damaged by
the
ire
of
53 2
AD , s onsidered
n
unfortunate hoice, because
of
the
possibility of exogenous arbon ro m
he
ire,
epairs,
nd
organic contamination from
handling
through
the
ages
[40, 41].
Organic
contamination cannot be
dismissed.
Recent observations
indicate
the
presence
of
a
bacterially-induced
bioplastic coating
on
Shroud ibers, s ha s ometimes been ound n m u m m y wrapping
fabric
(leading
to
ertoneous
dates).
According
to
[42]
(Gove,
et
al.),
such bioplastic contamination would not have been removed
by
the
conventional
pre-treatment
methods applied
to
the
Shroud samples.
Qualitatively,
such
contamination would
lead
to
a
more
recent
date;
quantitatively,
if
the
contamination
were all from
the
6t h
Century, it
would need to represent roughly 70 % of the carbon present, to shift
a irst entury
ate
o he bserved esult. Fo r ecent,
at e
0 th
Century contamination, oughly 40 % ontamination carbon would
be required.) n a
20 0 2
review
article
posted
to
the
shroud website,
www.shroud.com/pdfs/rogers2.pdf,
38], ogers nd moldi
question the bioplastic hypothesis, on the basis of
detailed chemical
analysis of fibers ro m
the
"Raes ample" which was aken from a
region djacent o ha t of th e
amples.
uantitatively, hese
authors suggest
that
the
coating
would
contribute only
a
few
percent
to he ample arbon;
qualitatively,
he y believe
ha t t
s
poly-
saccharide
gu m
(probably
G um Arabic)
ha t
would
be
removed
by
the pretieatment hemistry. Nevertheless, Rogers
nd
Amoldi
question
he
alidity f
he
ample, artly ecause f
he
presence f
otton nd ther hemical ifferences etween
he
adjacent
(Raes)
sample
an d
th e
main
shroud
material.
Three highly
competent
laboratories
were
selected:
th e
University
f Arizona,
xford niversity,
nd
he
Swiss
ederal
nstitute
f
echnology
E TH ]
n
Zurich. amples
f he hroud,
lu s
hree
ontrol
samples of
known
ge , were
distributed
blind
o
he
three aboratories. Control of
this
operation
distribu-
tion
of samples,
collection
of results)
was
th e responsi-
bility
f
Michael
ite
f he
ritish
Muse um.
he
accuracy nd precision of the nterlaboratory data fo r
th e control samples were outstanding,
leaving no
doubt
as o
he
quality
of
th e AM S
measurement echnique
(Fig.
6) .
ample-1
Shroud)
esults,
however,
were
just marginally consistent a mong the three laboratories,
prompting
th e
uthors
of
Ref
38 ] o
tate
ha t
it
is
unlikely
that
th e
rrors
quoted
by
th e
aboratories
or
sample-1
ully
eflect he
overall
catter."
Consistent
with th e discussion
in
Sec. 2, th e "'C
ag e
measurements
are reported in "' '*C years BR Transformation of
these
ages
to
calendar
ages
m u s t
take
into
account
th e
natu-
ral
'C
ariations, sing
he
endrochronological
calibration
curve
[13].
The transformation is shown
in
Fig.
7,
which
demonstrates
also
an interesting aspect
of he on-monotonic alibration unction:
amely,
exclusion
of th e
period
between
1312
AD an d
1353
AD
from
he
5 %
onfidence
nterval.
n
ddition,
n
interesting ink xists etween his
igure nd
Fig. Maunder Minimum), n ha t he
am e olar-
activity-induced '* C
variations
are
represented.
A c om-
parison
f
he
wo igures
hows
ha t
he
adio-
carbon date
69 1
BP),
ear he
nd
of
a
ignificant
calibration urve protrusion
Fig.
7) , orresponds
o
th e en d of
th e
3 th
century
warm
period
having
high
solar
activity
(Fig.
6) .
Consistency
of
th e
A M S esults
with
he xisting
(Lirey) documentation seems compelling, bu t
a
wave
of
questioning
ha s
followed—not
of
th e
AM S
method,
bu t of
possible
rtifacts
ha t ould have
ffected he
linen
an d invalidated th e
'* C
result
(Ref
40],
Chap. ,
Refs.
[41],
[42]).
A sampling
of
th e
creative
hypotheses
pu t forward is given in Table 2. The
first,
fo r example,
is
based
on
the
premise
that nuclear reactions
involving
th e ubstantial
mount
f
deuterium
ontained
n
human
body
could
produce neutrons, which
might
then
produce excess
'* C through th e
(n,p)
reaction,
making
th e ge oo young. The proposed deuteron eactions,
however,
re
ither ualitatively
r uantitatively
inaccurate—barring
an
unnatural
burst
of high
energy
photons photofission). Th e hird
proposal aises he
question
f non-contemporaneous rganic
atter—
whether from ncompletely
removed
arbon ontami-
nation
from
"oil,
wax,
tears,
an d
smoke"
that th e
cloth
ha d
een
xposed
o, r ro m
acterial
ttack
nd
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*
D'Anjou cope
Cleopatra m u m m y
- Nub ian
tomb
Turin
si i roud
4BB
3BB
2 8
IBBB
2B B B 24 B
Radiocarbon
Ag e
(yr
BP )
Fig. 1 6.
M S
dating results ( blind )
fo r the Turin
Shroud
(sample-1)
an d three
control
samples of known
ag e
samples-2,3,4),
ro m he hree
A M S
aboratories:
Z Zurich) ,
O
Oxford) ,
nd
A
Arizona).
Dates re
expressed as
"Radiocarbon
Years" before
present
(BP); uncertainties
represent
95 % confidence intervals
[38].
1 0 5 0
Calendar age BP)
850
50
450
300 t
900
1100
300
Calendar
age
AD )
1 5 00
Fig.
17 .
ransformation
of
the
Radiocarbon
A ge
(BP)
to
the
Calendar
A ge AD )
f
he hroud. he C ge
95%
I)
f
69 1
±31)
B P corresponds o two-valued alendar
ag e
s resuh of
the
non-
monotonic adiocarbon dating alibration urve. As ndicated n
he
figure,
he
projected
alendar
ge
anges
re : 1262-1312)
AD
nd
(1353-1384)
AD
[38].
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Table 2. reative Hypotheses
Excess
C
from
deuterium
spontaneous
fission;
cold
tusion
C isotopic fractionation/ exchange
(fire
of 1532 A D)
biased sampling; age depends on location
Bioplastic
coating;
non-contemporaneous
with
linen
pretieatment chemistry
deposit over th e ges. Apart from th e
ffects
of such
factors
on the Shroud,
th e issue
oforganic
reactions an d
non-contemporaneous contamination
of
ancient
materi-
al s
can be
a
very
serious
an d
complex
matter,
deserving
quantitative nvestigation
of
th e
possible
mpacts
n
measurement
ccuracy.'"
esearch
uestions
f
hi s
sort,
ncluding
he
lassic problem of
dating
ncient
bone, form one of th e ke y stimuli fo r th e development
of molecular dating"—the
topic
of th e
following
sec-
tion.
7.
Emergence
of
^-Molar
^ C
Metrology
Radiocarbon
metrology
is
at th e
very
m o m e n t
in
th e
midst
of
still
nother
revolution,
nvolving
th e
dating
(o r
sotopic
peciation)
f
pure
hemical
ractions:
"molecular dating."
or trace pecies, uch
s
poly-
cyclic
romatic
hydrocarbons
PAHs),
or
remote,
ow
concentration
samples,
such
as
th e soot
or
pollen in th e
free
troposphere
or
in
ice
cores, th e sensitivity of
A M S
is challenged
to
its
ultimate.
n
order
to
understand th e
nature of th e
challenge
it is interesting
to
consider th e
limiting
factors. n
recent
tudy
t
was
hown that
10
%
oisson
error"
standard uncertainty)
an
e
achieved with 0 .9 ng modem carbon,
whereas
machine
background
is
equivalent
to
0 .2
ng
or
less
[43].
Sample
processing blanks, however,
m ay ange
ro m
ag
o
15
|ag
or
more,
nd
they
m ay consist
of
both
biomass
carbon an d fossil carbon
[44].
Thus, th e ultimate limit-
in g actor or very mall ample AM S s he overall
isotopic-chemical blank.
nvironmental studies of '
*€
in
individual
chemical compounds
ca n
be
successful
at
th e Hg
to 0
ng level, but only with stringent control
of
th e
variability of
th e blank.
hi s is in sharp contrast
with mall ample, ow-level ounting where he
Poisson modem
arbon
imit ca.
3
m g)
nd ack-
ground
limit (ca.
5
m g
equivalent)
fa r
exceed
th e
typ-
ical
sample
preparation blank (ca. 40 ng ) [29 ] ."
Some
llustrations
f pure
ompound
dating"
y
NIST an d collaborators are
given
in Table 3. Th e
first
item refers
to
th e
aforementioned
ag
capability,
using
"dilution
AMS."
For thermally stable
species
uch
as
soot
an d
pollen, we
have
th e
possibility
of
controlling
th e
ample
preparation
blank
o es s
ha n
.2
|ag
by
applying
a
"thermal discriminator" at
a
critical
stage of
th e
process.
icrogram evel
^ C oot tudies have
already
been
successful
in Greenland snow; an d
pollen
studies
hold
great promise fo r
ice
core dating,
an d
per-
haps
even
fo r
dating
th e pollen
foimd
by M ax Frei on
th e
Turin Shroud.'^
An mportant
measurement ssue
fo r ice ore pollen
relates
to
th e amount needed fo r
a
given
ating recision.
o
iv e
ough
stimate:
assuming
0
ng
arbon
er
ollen rain, ollen
ag e f
0 0 0 years, nd % oisson mprecision
(o=400 years); one would need
o
ollect bout
00
pollen
grains.
This
might
be
ccomplished
n
ew
hours,
using
the
hand
picking"
microscope technique
ofLongetal.
[48].
14
Table
3 .
Molecular Dating ( C M S
at
the
microgram level)
• ilution AMS quantifies
0 .9
ng modem
carbon
( 1 9 9 9 )
-
oot/
pollen
blank
controllable to
-0.2 ng
(o
=
60 ng )
- hallenge: dating pure pollen grains from the Shroud
• ossil nd biomass aerosol sources characterized in remote
atmosphere/
cryosphere (2.9 ng
biomass soot
quantified)
•
ndividual
amino
acids
dated
in
ma mmo t h
bones
(LC/AMS)
• ndividual
poly
cyclic aromatic hydrocarbons dated in atmo-
spheric particles
an d
marine sediment (GC/AMS)
There is a
profound
difference between
background-limited
decay
counting
an d
blank-limited A M S, that m ay no t
be
widely appreciat-
ed . Although
the
ultimate imitation in each
case
s B" variability,
when B represents
the
instrumental background
it
tends
to be
reason-
ably
well
controlled,
and under th e
best of
circumstances,
Poissonian
[45]. An extia degree
of
caution is needed, however,
when
the limit-
ing B is
an
isotopic-chemical blank. A t best, it might
be
assumed
normal;
then
replicate-based
detection
tests
an d
confidence
intervals
ca n
be constructed
using Student's-t. If
the
blank
does
not
represent
a homogeneous
r
stationary
tate
as
reagent
blank,
well-mixed
environmental
or
biological
compartment,
etc.),
such tests
an d
inter-
vals an
be otally misleading.
Non-stationary
blanks m ay
xhibit
(geochemically meaningful) structure, or they m ay
be
ertatic, reflect-
ing
a transient source of
contamination [46].
12
Molecular
dating"
of
the
pure cellulose fraction of
the
Shroud,
or
of the
associated
pollen,
could
furnish
an
interesting
consistency
test
for the
published radiocarbon
date. t would
be
especially
interest-
ing to pu t
a
"time stamp" on pollen whose point of origin ha s already
been
scribed o ocation 0
km
o 0 km as t
nd
es t f
Jerusalem [47].
uc h
measurements are
made
feasible
by the
reduc-
tion
of
requisite
sample
sizes
by
a
factor
of
te n
or
more,
from
what
AM S
dating
equired
ixteen
years go . Th e
question of
non-
contemporaneous iber ro m
6t h
entury epairs, or xample,
could
be
ddressed by ne w measurements n just 00
xg
of
fibers
(=50,
cm linen
fibers)
from
the
main
part of
the
Shroud.
Th e
expected standard
uncertainty
would
be
equivalent
to
approximately
12 0 radiocarbon
years
([43],
Eq .
).
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7.1 Long-Range
Transport
of Fossil
and
Biomass
Aerosol
Ongoing
multidisciplinary,
multi-institutional research
on oot articles n
emote
nd aleo-atmospheres,
which s
bsolutely
ependent
n
he mall ample
dating
apability, s ndicated n ig .
8.
he
pper
portion of th e figure relates
to
climate
oriented
research
on he ources nd ransport f ossil nd iomass
aerosol
o
he
emote
Arctic
49];
he
ower
portion
relates
to
atmospheric and paleoatmospheric
research at
Alpine
high
altitude
stations
an d ice cores
[50,51].
In
th e
remainder of this section we present some
of
th e high-
lights
an d
measurement
challenges
of
the
first
project,
on
th e
long-range
transport
of
carbonaceous particles
to
Summi t ,
Greenland.
Cooperative research on this project, between NIST
an d he Climate Change Research Center t he
University of
N ew Hampshire
(UNH),
began
in
994.
It
was catalyzed by th e discovery
ofan
unusually heavy
loading of
soot
on
on e
of th e
ir
filters used or 'Be
sampling
at Summit, Greenland by Jack Dibb of UN H
[52] .
Th e Summi t soot
ha d been
ascribed
to
th e combi-
nation
of
intense boreal wildfire ctivity
n
th e ower
Hudson's
Bay
region
of
Canada
an d
exceptional
atmos-
pheric transport
to
central
Greenland.
Measurement
of
' ' ^C in th e filter sample yielded
definitive
evidence fo r
biomass
burning
as
th e
source
of th e soot. O n
one
da y
only
(5
August
1994),
th e biomass
carbon increased by
nearly
an
order
ofmagnitude, with
scarcely
an y
change
in he ossil arbon oncentration n
he
ilter.
Supporting data fo r th e
origin
of th e biomass
burning
carbon
am e ro m acktrajectory nalysis,
V H RR
(infrared)
atellite
magery
of
th e ource
egion,
nd
T O M S ultraviolet)
atellite
magery that w as
bl e
o
chart
th e
ourse
of
th e
oot
particles
ro m th e
ource
wildfires
to
Summit.
The
several
parts of this
remark-
able
event
are
assembled
in
Figs. 9,
2 0
[29,49,52]. '^
Since snow
an d
ice
ca n serve
as
natural
archives
fo r
atmospheric vents, one m ay xpect
to
ind hemical
evidence
of prior
years'
fire seasons
in
snowpits, fim,
an d ultimately
ice
cores.
This
is
illustrated
in th e upper
right portion of
Fig.
8,
which hows depth profile
sampling
in
a
snowpit at Summit, overlaying an energy
dispersive spectrum an d SE M image of
a
char
particle
found
near he 99 4 ire
horizon
n
9 9 6
nowpit
[29] .
An
organic
tracer
of
conifer combustion, methyl
dehydroabietate, was
found
also at th e same depth
[53].
Atmospheric science entered
a
ne w phase at Summit
during
he W int er-Ov er" roject
1 9 9 7 -1 9 9 8 )
54].
Fo r he
irst ime,
direct
ampling
of
ai r
nd
urface
snow took place over th e polar winter, extending
from
June
997 o
April
998.
A pecial chievement of
micro-molar
* C
"dating"
was
th e first
seasonal
data
fo r
carbonaceous
articles,
eposited ith
he
urface
snow.''*
he
easonal
ecord or
iomass
arbon
particles, shown in
Fig.
2 1 , was
striking
[55].
The large
spring eaks, n articular, onsisted rimarily f
biomass
arbon:
.7 6
M
=
0.03)
modem
arbon
mass
fi-action
(/M)
or
sample-1
(WOl),
an d
0.94
(0 .01)
mass
fraction
or ample-8
W08).
eyond
he
ossil-
biomass pportionment, however, ay questions bout
th e ature nd
rigin
f he
arbonaceous
erosol.
Especially intriguing
ar e
contrasts
between
the samples
showing
ummer
sample-4
W04)]
nd
pring
[sample-8 W08)] biomass-C maxima
n
Fig. 1 . To
explore hese, multi-spectroscopic pproach was
taken,
through
which
insights
an d
supporting evidence
were
derived
ro m
variety
of
analytical
echniques.
Results or
ne f
he microanalytical echniques
employed, aser
icroprobe ass pectrometry
(LAMMS), re
hown
in
Fig.
2. '^ The igure uses
principal
omponent projection
o ummarize
multi-
variate
(multi-mass)
contrasts between
the
summer
an d
spring
biomass peaks.
t
shows that
th e
three summer
(W04)
ub-samples
en d
o
avor
„"
luster
on s
(n-even),
ypical
of
condensed
arbon
tructure
an d
graphite),
whereas
th e
three spring
(W08)
sub-samples
exhibit
a
mor e
complex,
oxygenated
structure
uch
as
occurs with biopolymers.
Th e
bserved
Fig.
0 ) vs nferred Fig. 9 ) paths of
the
m ok e
plume present
n
nteresting
ontrast.
Th e
T O M S
atellite
mage
shows
the
smoke
approaching
the
southern
tip
of
Greenland
on
3,
4
August
9 94
nd
departing
toward
Iceland
on
6
August .
Th e back-
trajectory m od el mployed n
Ref
52 ] places he pproach
t
somewhat igher atitude,
nd
f ourse rovides
o
eparture
information.
Th e
icro-molar
apability as ssential or his o rk
because of
the
extremely
small
concentrations of
particulate carbon
in the
surface
snow,
especially
during
the winter (<10 ng
C/ kg
snow).
Microanalytical
methods,
such as LA M M S ,
are
crucial
fo r gaining
chemical
nsight n ndividual particles,
r
when
nly very mall
snow (o r
ice) samples
of
remote aerosols are available, or
needed fo r
high resolution studies. n contrast to he ng capability of the most
sensitive ul k nalysis echniques, A M M S , an provide seful
chemical
data
on as
little
as 2 0
pg
of carbon species
[57].
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Summit,
Greenland
- Particle (9 0 %
C )
from
1 9 9 4
fire
horizon
- Biomass-C aerosol
seasonal
cycle
reported
(20 0 3)
[6
to
40
|ig/kg snow]
Mt.
Sonnblick
Austria
(3106
m )
Global
Atmospheric
W a tch
Observatory
-''*C "dating"
of
soot
in the free
troposphere
[W eissenbok,
2 0 0 0 ]
Fig. 1 8.
ubmicromolar C apportionment of
anthropogenic
an d
natural
carbonaceous
aerosols at remote sites in
Europe
an d
Greenland
provides
knowledge
of
their
impacts on
present
an d paleoclimate [49-51].
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̂
f e
^
^
o
> Z
3 s
O
w
^
o
O
W
B
^
o
Si'o
^
I
'o
2 ?
° s
O
3
1 5
a
>
o
8
Q
3
208
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Summit S n ow
-- Winter
Over
(1997-1998)
50
30
40
-
c
o
o
E
o
ff l
10
spring
Augus t
S u m m e r
Spring
̂
/
/
/
/
/
/
/
/
/
W i nt er
4
Samp le
Fig. 2 1 . First evidence of
a
seasonal pattern in biomass carbon aerosol in surface snow in central Greenland
[55, 56]. Fundamental differences were found between th e biomass carbon peaks in s u mme r (sample-4 [W04]),
an d spring (sample-8
[W08])
vi a
"multi-spectroscopic" macro- an d
micro-chemical
analysis.
Findings from other techniques:
•
hermal-optical nalysis.
istinctive
easonal
volatilization/decomposition
patterns
were
seen as
samples
were
heated in
a
tream
on
helium.
The
summer
ample W04)
ha d
predominant high
temperature
peak
at
=560
°C
an d
little
evidence
of
charring
(4 % ),
whereas
th e
spring
sample
(W08)
ha d
predominant peak
t
=410
°C
nd major
charring
(1 9
% ). Thermal analysis of
a
powdered
wood
oak)
eference material
howed
thermal
peak
t
he pproximately
am e emperature
s
W08,
with
21
%
charring,
mplying
th e
presence
of
a
major cellulosic component in this sample.
• on hromatography. ire racers NH/, ^)
accompanied W04; oil racers Ca^,
Mg^)
accompanied W08
• acktrajectories.
or
W04, trong
transport
was
indicated
ro m
regions
of annual wildfires n th e
Canadian Northwest;
or
W08,
trong ransport
was indicated from th e agricultural
regions
of th e
upper idwest—both
epresenting
ransport
distances
of some
8 M m .
•
lectron
probe icroanalysis.
or
W04, p
o
9 0
% C
mass
raction) was observed in
individ-
ual,
im
ize
particles, with
C
>
O or he most
abundant (core) particles;
or
W08,
maximum C
particles
ha d
a
C:0
ratio
consistent
with
cellulosic
biopolymer,
an d C
<
O
fo r
th e
core particles.
The
eight
f multi-spectroscopic
vidence
hu s
indicates ha t he u m m e r W04) nd pring W08)
biomass particles do not
epresent
he
ame
yp e of
biomass.
Rather,
the W04
particles appear
to
include
a
soot
omponent
ro m
ig h
emperature
ombustion
(motor
vehicles,
wildfires).
The
W08
particles, whose
carbon derives almost entirely from biomass, appear
to
have
a
major
biopolymer
component, such as
cellulose
an d
other
bio-materials
associated
with
soil
an d
vegeta-
tive carbon.
These
findings
are
consistent
with
work by
Puxbaum nd
olleagues,
who have ound by direct
chemical
nalysis, ignificant mounts f ellulose,
bacteria,
an d fiingal
spores
in
atmospheric particles
[58,
59].
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o
c
o
3
2
-
1
-
8
-2
-3
C2H2O-
_t _i _
-2
1
2
Conponent
1
W04
08
Fig. 2 . C A biplot of laser microprobe mass pectral data; ompositional ontrast
between
particles
from
he
u m m e r biomass
peak
W04, ed : „~ luster
on s
avored)
nd
he
pring biomass
peak
(W08,
green:
xygenates favored) [55].
7.2
Isotopic
Speciation
in Ancient Bones and
Contemporary Particles
The ating f
ncient
ones as een otably
unreliable because of diagenesis an d isotopic contami-
nation ha t
ccur
ith illennia f
nvironmental
exposure.
Molecular
dating
of
individual
amino
cids
in such bones ha s proven
to
be one
of
th e m o s t effec-
tive
means
to
overcome
this
problem.
Figure
23
shows
dramatically
ow
he
pparent
adiocarbon
ge
f
th e
ent
Mammot h
hanged
ro m a.
0 0 0
BP
o
ca .
1 0 0 0 BP,
s
he
ated
hemical
raction
as
refined from th e crude collagen fraction
to
th e
individ-
ual amino acids. The known radiocarbon ag e is
given
as
= 11,000
BP,
based on ssociation
with
Clovis
ulture
artifacts, nd
iostratigraphy
60].
Note ha t
he
calibrated
or
orrected alendar
ge ,
derived ro m
th e adiocarbon alibration urve 13], s oughly
1500
years
older
than th e
radiocarbon ag e
fo r
this
time
period.)
The
ommonly
dated
organic
ractions
ro m
bones
weak
ci d
nsoluble
ollagen
C O L L ]
nd
gelatin GEL]) gave ge s hat were t odds with he
archaeological
vidence—suggesting ecent umate
contamination. W h e n
th e
diagenesis-resistant
molecu-
lar components
were
solated (individual
mino cids
an d
he
ollagen
ydrolysates
XAD-HYD]),
ge
concordance
mong
he
ndividual mino cids
an d
with
he
rchaeological
vidence
ndicated
elia-
bility. H ad ontamination ro m bio-intrusive material
having
ifferent
hemical
amino
cid)
attern
occurred, mino cid ge
eterogeneity would
have
been xpected
60].
This work ould
no t
have
been
accomplished without th e ability
to
date 0 |ag
carbon
fractions.
A n
historical
footnote related
to
this work involves
th e
question
of
th e
ncestors
of
th e North American
Clovis
ulture.
Since th e
Clovis
ites give th e earliest
unequivocal data on he peopling of th e
Americas,
it
ha s
been of
enormous
nterest
to
ind
a
geochrono-
logical ink
o
n
arlier
ulture.
he
most
popular
belief
ha t
he
lovis
rogenitors
ad
rrived
ve r
th e Bering
Land
Bridge" ro m Siberia
ha s
ecently
been put into doubt, however, with new '* C vidence
that one
of th e most
likely
pre-Clovis
sites
in
northeast-
em
iberia
s
0 0 0
ears
ounger
ha n
reviously
believed. Dating
t
=1 3
0 0 0 alendar
years
go ,
t
s
doubtful that migration could have ranspired quickly
enough
o
give ise
o
he Clovis ulture 13 60 0
o
12
60 0
alendar
ears
P) n he orth
American
Southwest
[61] .
2 1 0
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O
8
t
9 -
X
LU
O
10
o
11
-
LU
O
O
L U
C D
I
Q
<
>
X
I
a
<
DENT
MAMMO I I
Q .
<
C 5
ir
C L >.
<
> - -I _i
1-
I
C 3 <
~I
SAMPLE
T
Fig. 3. Molecular
Dating"
of
individual mino cids n ncient
bone. adiocarbon ge s f o mmo nl y ated collagen, elatin)
fractions were
20 0 0
to
3000
years to o young as
a
result of
environ-
mental egradation; ure molecular ractions amino
cids)
were
self-consistent
an d in
agreement with
the
Clovis
culture
ag e
[60].
7.2.1
Urban
Dust
(SRM
1649a):
Unique
Isotopic-Molecular
Reference
Material
SRM
649a s NIST's
most
ighly
haracterized
natural matrix
Standard
Reference
Material,
nd
t s
th e only
on e
fo r
which
there
ar e
certificate
values
or
* C
in individual chemical
fractions
an d pure molecular
species. he carbon ortion f he
ertificate
f
Analysis
w as
eveloped hrough
n
xtensive
nter-
national nterlaboratory
comparison,
nvolving
eighteen
teams f
nalytical
xperts
ro m
leven
nstitutions
[62] .
Th e
particle-based
S RM ,
which
ha s
been
charac-
terized
fo r
nearly 2 0 0
chemical
species
an d
properties,
serves
as
n
essential quality
assurance
material fo r
a
remarkably broad range
of
disciplines,
from
th e
moni-
toring of pesticides, PCBs,
nd
particulate mutagenic
activity
o
asic
rganic
eochemistry
o
sotopic
apportionment
of
carbonaceous
particles.
A dramatic
illustration
f
he *€ sotopic
eterogeneity
n
hi s
reference material s
iven n Fig.
4.
he biomass
carbon mass fractions are seen
to
range
from
about
2
%
(aliphatic xtract)
o
8
% total arbon). hus, he
aliphatic raction
erives
ssentially
=9 8
% )
ro m
fossil
uel
missions,
nd ,
on verage,
ossil
ources
account fo r some
60
%
of the carbon in
these
particles.
Note
hat he
Certificate
of
Analysis
63 ]
provides
* C at a
xpressed
n
he
roper eference
nits s
fraction
of
modem carbon
(Z^).
To emphasize th e more
meaningful
ossil-biomass
arbon
ource
ichotomy,
however, we have hosen o present he nformation
here
n
erms
f
he
raction
f
biomass
arbon.
Conversion
is
based
on
th e
post-bomb enrichment
of
' ' ^C
n
he
iving
iosphere,
s
hown
n
ig .
1.
Sampling or SRM
649a ook place n
976-1977;
th e
enrichment
factor
fo r
biomass
carbon
at
that
time,
indicated by
th e re d
arrow
in
the
figure,
was
.35.
O ne
of
th e most mportant outcomes
of
th e SRM
1 64 9 a
ntercomparison
xercise
w as
he
et
of
data
obtained fo r "elemental carbon"
(EC).
EC (sometimes
known
s
black
arbon")
s
outinely monitored
n
urban
nd ural
erosols,
nd t s
of
major
oncern
because of
its
presumed
mpacts
on
health,
visibility,
an d limate radiation
bsorption).
RM
649a
potentially
an
erve
s
ey
aboratory
uality
assurance eference
aterial
or
C easurement.
Results
of
th e
largest
intercomparison
to
date
of
EC
in
a
niform
eference
aterial,
owever,
ndicate
severe measurement problem:
elative values or he
reported
data span
a
range
of 7.5,
showing
very
signif-
icant
method
ependence. hree lusters f
esults
for
the
mass fraction
of
EC
(relative
to
total-C), reported
as
nformation alues
n he Certificate of Analysis,
are 0.075, 0.28, an d 0.46. (For th e 'C data in
Fig.
2 4,
cluster-1 EC
ha s
been
labeled soot an d
cluster-3 EC ,
"char."
'* C
as ot etermined
n
luster-2 C .)
The
iindamental
problem
s
ha t EC
s
ot pure
substance,
o
unique
true
value"
or
EC
m ay
no t
exist,
n
principle."'
S o m e
interesting
insights
into
th e
meaning
of certain
of
th e
EC
results
follow,
however,
from
th e
'* C
EC speciation
data.
Although a
true (Certified)
EC
value
may be
beyond
reach, com -
patibility ofresults from
laboratories
using
the
same
method
suggests
the ossibility f method-specific
"operational")
C eference
Values
fo r
this
SRM.
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Urban Particulate Reference
Material
(SRM 1649a)
(prototypical
isotopic-chemical aerosol
reference/Q A
material)
i ^ C SPECIATION
CARBON BIOMASS-C
%
total
38
polar
32
elemental
char 11
soot
4
aromatic
13
aliphatic 2
Pyrene
3
Benzo(g/;/)perylene
6
(U
=
6 aromatic];
thers
<1)
Fig.
2 4.
NIST
Standard
Reference
Material
649a
("urban
dust").
Photograph
of
the
bulk reference
material
an d
derived filter
samples"
fo r QA
of atmospheric elemental carbon (EC).
C
data
listed indicate the mass
fraction (% )
of
biomass-C
in the
several chemical
fractions
[2 9 ,
62].
Isotopic
consistency.
easurement
of
*€ n
multiple
chemical
ractions
offers he possibility
of
tw o
very
interesting
an d
important consistency
tests:
1 )
assess-
ment
of
isotopic-chemical
consistency
mong
hemi-
cally-related ractions,
nd
2 )
ssessment of overall
isotopic-mass alance.
he
irst
es t s
llustrated
by
comparison
of
th e
*€
content
of
th e
EC
fraction with
that
of
th e
PA H
fraction
(o n average). To th e extent that
both
omponents
riginate
ro m he
am e
ource,
acetylenic
re e
adicals hat enerate
olyaromatic
structures
n
he
laming
tage
f
ombustion,
ne
would expect similar
*€
composition.
Such is th e case
fo r
* C
in
cluster-1 EC (labeled soof in
Fig.
24),
but
not
or
luster-3
C
labeled
char").
he
ac k f
isotopic
consistency
fo r
cluster-3
EC
is
th e stimulus fo r
th e
ifferent
abel,
ince
his
manifestation
f EC
necessarily eflects different m ix of fossil-biomass
sources ha n he
laming
tage C ,
hich erives
primarily from fossil
fuel
carbon.
Regarding he
econd
est, he
* C
data n Fig.
4
demonstrate
hat sotopic-mass
alance
annot
e
achieved with th e current isotopic-chemical data. Since
th e
biomass
arbon
raction
on
verage
38
%
mass
fraction)
exceeds
that of
ll
other
measured
fractions,
there
must e ignificant missing iomass arbon
component. This matter
is addressed
in
[62],
where
it
is
suggested ha t unmeasured biopolymers m ay ccount
fo r mor e han 45
%
of th e
esidual
non-extractable,
non-EC)
carbon mass.
Cellulose
is
one
excellent
candi-
date
[58].
GC/AMS. inally, th e molecular dating" of
individual
PA H
n
RM
649a
pitomizes
ne
f
he
atest
advances
in
micromolar
'* C
measurement
science:
he
capability
o
ink hromatographic
solation
f
pure
chemical compounds
to
AM S determination
of
' '^C'^C.
Results f
pplying
ff-line
C / A M S
o
ix AH s
recovered from
th e
aromatic
fraction
of SR M
1 64 9 a
are
2 1 2
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\
'-
% Biomass-C
I ~l
T- —I-
r^
f I
i
'^T
t̂̂ ^̂ ^̂ —̂^̂
3.0
4.7
_L
- 2 .8
\
j
-I——-̂ —
I
j'
u
-<-—- I
3. 1
6.2
6.4
-_L^>_^fc><
\
*vi|
JWW*--̂
±
30 0 0 0
0 0 0
Fig.
5.
as
chromatography/accelerator
mass
pectrometry G C / A M S) : A M S ollowing utomated
prep-scale apillary GO yields
dates
equivalent
biomass arbon mass ractions) or
micromolar
amounts
of individual
polycyclic
aromatic
hydrocarbons
[63-65].
(Results
shown forNIST SR M
649a;
"I.S."
denotes
an
internal
standard;
abscissa
indicates
retention
time
(min).)
shown
in
Fig.
2 5.
Th e critical first
step
w as
th e sequen-
tial isolation
of tens
of
micrograms
of th e
six
PAHs
in
separate
traps
by automated preparative scale capillary
ga s
hromatography
66].
he
ndividually
rapped
PAHs were he n oxidized an d converted
to
AM S
ar -
gets.
These
esults
epresent he
irst
uch
data ver
available
or
n
tmospheric
articulate
RM ,
nd
although such compounds ar e only
trace
constituents
of
atmospheric particles
(=10
ng/g), they ar e of
great con-
sequence du e
to
their mutagenic and carcinogenic prop-
erties.
n
hi s ase, s hown n
Fig. 5,
adiocarbon
dating
of
th e
individual
PAHs
revealed
these
congeners
to
be sotopically heterogeneous, nd
demonstrated
basic flaw
in
th e
conventional
wisdom that th e heavier
PAHs, n
particular, re
mor e
ikely
o
be
produced
strictly
from
fossil
fuel combustion sources.
On-line
G C / A M S
is nearly upon
us.
The linkage of
ga s
or liquid) chromatographic eparation, nd direct
injection
of
microgram
mounts
of
pure
ompounds
into
th e
io n
source of an
accelerator
mass
spectrometer,
is under
active
investigation
in
several
AM S
laborato-
ries;
an d
it
promises a new dimension in th e practice of
radiocarbon
dating at th e
molecular level
that m ay have
an
mpact
n rchaeology
nd sotopic
iogeo-
chemistry comparable
to
that
of
G C / M S
on
analytical,
physical, organic, an d biochemistry
[67].
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8.
Epilogue
Libby's discovery, an d th e remarkable developments
that followed, rose from
scientific
question freely
translated):
W h at il l
ecome
f he
osmic
ay
neutrons? It
is
noteworthy
that
an
"academic
son"
of
this Nobel Laureate
also
posed
a
scientific
question
to
himself.
F.
Sherwood Rowland's question
also
le d
to
an
unexpected discovery having major practical import fo r
mankind: he
possible
destruction of
the
tratospheric
ozone
ayer. Rowland's
query, lso
ulminating
n
N obel
rize
1995) ,
as
I
egan
o
onder
what
w as
oing
o
appen
o
his
man-made
ompound
[trichlorofluoromethane]
ewly
ntroduced
nto
he
atmosphere"
[68].
M ay this historical
journey
into
scientific
discovery,
as
an outgrowth of seemingly simple scientific curiosi-
ty, nd th e onsequent unanticipated cientific-metro-
logical
revolutions,
encourage students
to
examine
th e
original
historical literature documenting
such
discov-
eries, nd
o
ealize
ha t
profound unforeseen devel-
opments m ay be
n
tore or presumably mature
scientific discipline.
Acknowledgment
This article represents an adaptation an d extension of
a
ecent publication
n
he zechoslovak Journal
of
Physics:
The Remarkable Metrological
History
of ' *€
Dating:
ro m
ancient Egyptian artifacts to particles
of
soot
an d
grains of pollen" [Czech. J. Phys. 53, (Suppl.
A )
A1 37 -A1 60 2003)]. Permission of th e Institute of
Physics,
Academy
of Sciences of the Cz e c h
Republic
is
gratefully cknowledged.
Thanks
go
lso
o
Cynthia
Zeissler an d
Ed
M ai fo r assistance in final preparation
of
th e
figures
fo r
publication.
Figures
re
dapted,
it h
ermission,
ro m
he
following
ources. Fig. :
photo by Fabian Bachrach
(AEC-5 4-5 1 23-DOE)
from
page
of
de
Messieres,
N.:
Libby an d th e interdisciplinary aspect of radiocarbon
dating." Radiocarbon 43 2 0 0 1 )
-5;
opyright
0 0 1
Arizona
Board
of
Regents
on
behalf
of
th e
University
of
Arizona.
Fig.
,
ro m
Radiocarbon
Dating
jacket
cover]
Eds.
R.
Berger an d
H.
Suess) Univ. California
Press, Berkeley,
979] .
Fig.
4,
ro m
Fig.
f: Libby,
W illard F.,
Radiocarbon Dating, Univ. Chicago Press,
Chicago,
copyright
1952 (1st edition).
Cov er
an d
Fig.
5
(plot),
ro m
ig.
p.
1 0)
n:
lsson,
.U.,
d.
Radiocarbon Variations an d
Absolute Chronology (12th
N obel Symposium), Almqvist
&
W iksell , Stockholm,
1970;
copyright,
th e
Nobel Foundation.
Fig.
5
(photo).
courtesy
of
Douglas
J.
Donahue,
University
ofArizona.
Fig.
6a
(top), reprinted
with
permission
from Fig.
5a in:
Eddy,
.:
The
Maunder
Minimum,
cience
92
(1976)
1 8 9 - 1 2 0 2 ;
opyright
9 76
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M.
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A. W i se,
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on Total, Elemental,
an d
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(2001), an invited
NIST
Sigma Xi lecture (1998), and a
plenary
ecture
t
he
ourteenth
adiochemical
Conference
2002) .
t
he
onference
n
002,
Dr.
urrie
w as
presented
he .M .
arci
medal,
he
highest award ofthe Czech Spectroscopic Society ofthe
Czech
Academy f Sciences.
he ational
nstitute
of Standards
nd
echnology
s
n gency
f
he
Technology
dministration,
.S.
epartment
f
Commerce.
About
the
author:
Dr L.A. Currie
is
an
NIST
Fellow
Emeritus
n he hemical
cience
nd
echnology
Laboratory.
he
deas behind
his rticle were
first
conceived bout 5 ears go
n
onnection
ith
lectures at
NIH
and the University
of
Maryland,
and
as
n
utgrowth
of
the
author's
esearch
n
nviron-
mental adiocarbon while eader
of
the
Atmospheric
Chemistry Group at
NIST.
Th e concept and scope
of
the
article
were
rystallized in
onnection
with uncheon