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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

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.

[email protected]

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



Volume


Journal of Research

of

th e National


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



Volume


Journal of Research

of

th e National


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

1 87



Volume


Journal of Research

of

th e National


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)



Volume


Journal of Research

of

th e National


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.

).

1 89



Volume


Journal of Research

of

th e National


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].

1 90



Volume


Journal of Research

of

th e National


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

19 1



Volume


Journal of Research

of

th e National


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

192



Volume


Journal of Research

of

th e National


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].

19 3



Volume


Journal of Research

of

th e National


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

1 94



Volume


Journal of Research

of

th e National


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

19 5



Volume


Journal of Research

of

th e National


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.

1 96



Volume


Journal of Research

of

th e National


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) .

1 97



Volume


Journal of Research

of

th e National


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.

198



Volume


Journal of Research

of

th e National


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].

1 99



Volume


Journal of Research

of

th e National


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

—

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n

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' 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.

20 0



Volume


Journal of Research

of

th e National


(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].

2 01



Volume


Journal of Research

of

th e National


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

202



Volume


Journal of Research

of

th e National


*

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].

203



Volume


Journal of Research

of

th e National


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 .

).

20 4



Volume


Journal of Research

of

th e National


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].

205



Volume


Journal of Research

of

th e National


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].

2 0 6



Volume


Journal of Research

of

th e National


207



Volume


Journal of Research

of

th e National


̂

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



Volume


Journal of Research

of

th e National


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].

2 0 9



Volume


Journal of Research

of

th e National


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



Volume


Journal of Research

of

th e National


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.

211



Volume


Journal of Research

of

th e National


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



Volume


Journal of Research

of

th e National


\

'-

% 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].

2 1 3



Volume


Journal of Research

of

th e National


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

merican

Association or th e Advancement of Science.

Fig.

b

(bottom), ro m

th e

climate igure p. 1 5, ast

eg-

ment

only,

labeled

"Past

1000

years ) in:

Mathews,

S.:

What's

appening o ur limate, ational

Geographic 50

1976)

76-615;

opyright 976 he

National

Geographic

Society.

Fig. an d

Fig. ,

rom:

Toggweiler, .R.,

ixon,

.

nd

ryan,

.:

"Simulations of Radiocarbon n Coarse-Resolution

W or ld

cean

Model,

.

istributions

f bomb-pro-

duced

" 'C,"

J

Geophys

Res

9 4

[C6]

1 9 8 9 ) 8243 - 8264

(figures nd 7,

espectively);

opyright

9 89

American Geophysical

Union.

igures nd

0

re

adapted from Currie, L.A., et

al.,

Authentication an d

Dating ofBiomass

Components

of

Industrial

Materials:

Links

to

Sustainable

Technology," Nuclear

Instruments

an d

Methods

n Physics

Research

B172

pp

8 1 -28 7 ,

copyright 2000), with ermission rom lsevier

Science.

ig .

2:

hotos

re

ourtesy

f Robert

K.

Stevens.

Fig.

3, from

Fig. in: W olfli , W: "Advances

in

accelerator

mass

spectrometry,"

Nuclear

Instruments

an d

Methods

in

Physics

Research

B2 9

numbers

,

2]

pp -13,

opyright

1 9 8 7 ),

it h

ermission

ro m

Elsevier Science.

Fig.

4,

ro m Fig. 6. 2

n:

Taylor,

R.E., Long,

A., nd

Kra, R. , Eds.:

Radiocarbon

fter

Four

Decades: n

Interdisciplinary

Perspective; opy-

right Springer-Verlag, N ew

York,

992.

Fig.

5c

inset

(negative

ma ge )

nd

5d

microphotograph),

rom:

British

roadcasting

orporation

ocumentary,

"Shreds

of

Evidence"

Timewatch

Series),

opyright

1988.

ig . 5b ,

ourtesy

f

ouglas . onahue,

University of

Arizona.

Figures

5a

(reprint cover), 6,

an d

17 ,

from D a mon,

P.,

et

al.:

Radiocarbon

dating

of

th e

hroud

f Turin,"

ature

37

1 9 8 9 )

11- 615;

copyright Macmillan Magazines

td , 989. ig.

8,

from:

a)

Currie,

L.A., t

al.:

The pursuit of

isotopic

an d

molecular

fire

tracers

in

th e polar atmosphere an d

cryosphere," adiocarbon

40 1 9 9 8 ) 81- 3 90, 16f;

copyright

9 98

Arizona

Board

of

Regents on

behalf of

th e

niversity

f

Arizona; nd b)

Mark

wickler,

Univ. N ew

Hampshire.

Fig.

9

center,

backtrajecto-

ries), ro m Dibb, J.E., et

al.,

Biomass burning signa-

tures

n

he

tmosphere

nd now t ummit,

Greenland:

n

event

on

5

August

994,"

Atmospheric

Environment

0

p

53-561

opyright

1996),

with

ermission

ro m

lsevier

cience.

igures 9,

2 0 dapted ro m Currie, L.A., t l. , The pursuit of

isotopic

an d

molecular

fire

tracers

in

th e

polar

atmos-

2 1 4



Volume


Journal of Research

of

th e National


phere

nd

ryosphere,"

Radiocarbon 40

1 9 9 8 )

381-

390,416f; copyright

1998

Arizona Board

of

Regents

on

behalf

of

he

niversity

f

Arizona.

ig.

3,

ro m

Fig.

n: Stafford, T .W ., r., Hare, RE., Currie, L.A.,

Jull, .J.T., nd

onahue,

.:

Accuracy f North

American

uman

keleton ges ,

uarternary

Research,

4,

p 11-120, opyright

1 9 9 0 ) ,

ith

permission

ro m

lsevier

cience.

ig.

4,

dapted

from

ig . n urrie, .A., Evolution

nd

Multidisciplinary

rontiers

f *€

Aerosol

cience,"

Radiocarbon 2

2000) 15- 126,

opyright 0 0 0

Arizona

Board

of

Regents on behalf

of

th e University

of Arizona.

ig.

5,

ro m

ig.

n: urrie,

.A.,

Klouda,

.A.,

enner,

r.,

.A.,

arrity,

.,

nd

Eglinton, T.I.,

"Isotopic

an d Molecular

Fractionation

in

Combustion;

hree

Routes

o Molecular Marker

Validation,

ncluding irect olecular

Dating'

(GC/AMS)," Atm. Environ. 33 ( 1 9 9 9 )

27 8 9 -28 0 6;

pub-

lished by Elsevier

Science

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9. References

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2002) .

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n

002,

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urrie

w as

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arci

medal,

he

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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

history of radiocarbon

Documents