Example 1: Neutron Activation Analysis of Medieval Silver Coins

Matapan / GrossoVenedig

Matapan / GrossoVenedig

TurnosgroschenTours

TurnosgroschenTours

SterlingJülich

SterlingJülich

Denar, AachenDenar, Aachen

DenarSoest

DenarSoest

GroßpfennigBonn

GroßpfennigBonn

DenarOsnabrück

DenarOsnabrück

BrakteatStralsund

BrakteatStralsund

BrakteatDemmin

BrakteatDemmin

DenarBrabant

DenarBrabant

DenarHeinsberg

DenarHeinsbergDenar, LodzDenar, Lodz

Origin of silver coins

Accelerator based neutron source

Neutrons can be produced by charged particle nuclear reactions:(p,n), (α,n), (γ,n) at a wide range of energies (white neutron source)

Reaction 7Li(p,n) produces non-thermal neutron distribution

7Li

p-beamn-cone

Activation MethodActivation Method109Ag(n,γ)110Ag

activity measurement: 110Ag(β-) 110Cd

(t1/2=250 d)

Lithium

CopperProton beam Neutron-

cone

109Ag

Au

Determination of neutron flux by 197Au(n,γ)198Au

Neutron source: 7Li(p,n)7Be

Neutron spectrumNeutron spectrum

neutron energy (keV)

inte

nsity

measurement

calc.neutronspectrum atkT = 25 keV

Comparison: therm. Neutrons kT=26 meV

Quasi-Maxwell-Distribution:

kT = 25 keV Emax = 110 keV

γ-detection

2 Ge-Clover-detectors,with irridiated probe wedged in between70 mm

Probe

Detection efficiency at 1115 keV:

single crystal:ηtot = 11 %ηpeak = 1.1 %

detector array:ηpeak = 15 %

198Au412 keV

110Ag658 keV

64Cu1346 keV

Characteristic γ spectrum after neutron activation

Activity of Au and Ag contents109Ag(n,γ)110Ag T1/2(110Ag)=250 d;

λΑg=1.16·10-4 1/hEγ=658 keV

197Au(n,γ)198Ag T1/2(198Ag)=2.7 d; λΑu=1.07·10-2 1/hEγ=412 keV

Activity after 2 hours of irradiation with 1010 n/cm2s withσAu=3mb and σAg=2mb

A tA t

P eP e

N eN e

I tI t

keV A tkeV A t

Au

Ag

Aut

Agt

Au Aut

Ag Agt

Au

Ag

Au

Ag

Au

Ag

Au

Ag

( )( )

( )( )

( )( )

( )( )

( ) ( )( ) ( )

=⋅ −⋅ −

=⋅ ⋅ −⋅ ⋅ −

=⋅⋅

− ⋅

− ⋅

− ⋅

− ⋅

11

11

412658

λ

λ

λ

λ

σσ

ηη

Efficiency and Count Rate

Effic

ienc

y η

[%]

200 800600400 1000

10

1.0

0.1

Energy [keV]

ηAu=0.5%=0.005

ηAg=0.2%=0.002Iag = 6·105

Iau = 1·105

NN

e Ie I

Ag

Au

Aut

Ag Au

Agt

Au Ag

Au

Ag=

⋅ − ⋅ ⋅

⋅ − ⋅ ⋅=

⋅⋅

≈ ⋅− ⋅

− ⋅

−

−

σ ησ η

λ

λ

( )( )

.

.11

191 109 28 10

2 1025

293

Copper

Silver

Goldmas

s fra

ctio

n %

Coin

#12 shows mintdeviations in Co,Ag, & Au content

Großpfennig,Bonn

Results for single coin measurements

1.part 16.centuryweight 1,30gAg content 889/1000A weight 1,16g

2.part 16.centuryweight 1,33gAg content 972/1000Ag weight 1,14g

weight 0,92gAg content 977/1000Ag weight 0,90g

Previous ResultsPrevious Results present Resultspresent Results

Großpfennig,Bonn

Großpfennig,Bonn

Comparison with official mint statements

Example 2: Qumran Pottery Provenance

All clay sources on earth have a unique geochemical history, but show a slightly different impuritycomposition. Based on the analysis of these impurities the pottery can be traced to the site where it has been manufactured. Similarly, other artifacts made from pumice, obsidian glass, amber, basalt and sporadically flint can be traced to a distinctivesource.

Analysis of Qumran Pottery should establish the origin of the dead sea scroll containers and yield information on the culturalconnection with other groups and villages

The Qumran Scrolls

Qumran site and samplesAnalysis of Qumran Pottery should establish the origin

of dead sea scroll containers and yield information onthe cultural connection with other groups and villages.

Is there a difference between pottery found in the caves and at the Qumran site?Was the pottery made locally or was it imported?

Taking & Preparing a Sample

A pottery sample is taken by grinding off 100 mg of ceramic resulting into a powder. This is then mixed with pure cellulose (50 mg) (as a binder) and pressed into apellet of uniform size and thickness. The pellets--representing sherds or complete vessels--are wrapped in pure aluminum and set on edge into an aluminum capsulewhich is sent to a nuclear reactor where it is submitted to a neutron flux. Two or more samples of a standard of known chemical composition are added to the rest of the pellets.

Neutron Activation Techniques

Activation procedure with thermal neutrons in reactor

Cherenkov light

Probe is positioned into neutron line

Activity measurements with a Ge-detector

Gamma-ray spectrum showing several short-lived elements measured in a sample of pottery irradiated for 5 seconds, decayed for 25 minutes, and counted for 12 minutes with an HPGe detector.

Long-lived Isotopes

Gamma-ray spectrum from 0 to 800 keV showing medium- and long-lived elements measured in a sample of pottery irradiated for 24 hours, decayed for 9 days, and counted for 30 minutes on a HPGe detector.

High Energy γ-radiation

Gamma-ray spectrum from 800 to 1600 keV showing medium- and long-lived elements measured in a sample of pottery irradiated for 24 hours, decayed for 9 days, and counted for 30 minutes on a HPGe dectector.

Gamma-ray Counts to Calculate Element Concentration

To calculate the concentration (i.e., ppm of element) in the unknown sample it is irradiated together with a comparator standard containing a known amount of the element of interest. If the unknown sample and the comparator standard are both measured on the same detector, one usually corrects the measured counts (or activity) for both samples back to the end of irradiation using the half-life of the measured isotope. The equation used to calculate the mass of an element in the unknown sample relative to the comparator standard is

where A= activity of the sample (sam) and standard (std), m= mass of the element, λ= decay constant for the isotope and t= decay time. For short irradiations, the irradiation, decay and counting times are the same for all samples and standards such that the time dependent factors cancel. Thus the above equation simplifies into

where c= concentration of the element and W= weight of the sample and standard

Possible applications: • Pigment analysis by activation techniques• Neutron radiography by neutron absorption

neutrons

NAA of paintings

St. Sebastian ca 1649Painting in the Gemäldegalerie Berlinoriginal by Georges de la Tour (1593-1652)French Court Painter

Original in Louvre, question about authorshipof copy, George de la Tour himself or by his son Entienne de la Tour?

Neutron radiated 109 n/cm2s

Neutron induced γ activity is recorded in different time steps:e.g.1 days for 64Cu (T1/2=12.8h), 5 days for 203Hg (T1/2=46.6d)

and 32P (T1/2=14.2d)

X-ray radiograph

Painter used white lead for brightly lit areas.(white lead was the only medieval white paint available.)

Comparison to x-ray radiograph

X-ray radiograph (white lead paint ismain absorber for x-rays → visible)

Neutron activation (lead is not Activated → invisible)

Azurite distribution (64Cu)

Azurite (2CuCO3·Cu(OH)2) is mainly visible in mourners veil.Contour of body is reinforced with ivory black C+Ca3(PO4)2 (32P)

The long-lived component 203Hg

The long-lived activity of 203Hg (vermilion HgS) is clearly recognizable in the red dress and the lighter flesh colors. Also the body contour shows as 32P decay.

The Depiction of St. SebastianAnalysis gives evidence that painting is original copy by Georges de la Tour himself!

• Paint stroke similar to the one used in other paintings

• Clear outline and lack of overlap between painted areas indicates the use of cartoons which is also typical for Georges de la Tour

Rembrandt: The Man with the Gold Helmet

Gemäldegalerie, Berlin, Germany

Analysis Results

paint and pigment analysis showed that this most famous Rembrandt paintingwas not painted by Rembrandt ⇒ Rembrandt school?

Summary neutron activationNeutron activation is one of the standard techniques in the analysis of art and archaeological samples. Typically it is done in reactors which provide a large flux of thermal neutrons which have a large activation cross section. Neutron activation offers the possibility of isotope analysis – something that is not possible with X-ray studies. Isotope analysis is a powerful tool for provenance studies – the Identification of the origin and manufacture of artifacts. Neutron activation also offers a complementary approachto X-ray radiography because it offers the possibilityto create a two-dimensional image of pigment distribution In paintings and other art samples. Neutron activation has Its limitations since it can only be applied when neutron capture produces radioactive isotopes with appreciable life time and characteristic β or γ decay signals.