Example 1: Neutron Activation Analysis of Medieval Silver Coins

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1 Example 1: Neutron Activation Analysis of Medieval Silver Coins Turnosgroschen Tours Tours Matapan // Grosso Grosso Venedig Großpfennig Bonn Bonn Denar Denar Soest Soest Denar Denar Brabant Brabant Brakteat Stralsund Denar, Aachen Denar, Aachen Denar, Lodz Denar, Lodz Brakteat Demmin Sterling Sterling Jülich Jülich Denar Denar Osnabrück Denar Denar Heinsberg

2 Origin of silver coins

3 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 7 Li(p,n) produces non-thermal neutron distribution p-beam n-cone 7 Li

4 Activation Method Activation Method 109 Ag(n,γ) 110 Ag activity measurement: 110 Ag(β - ) 110 Cd (t 1/2 =250 d) Determination of neutron flux by 197 Au(n,γ) 198 Au Copper Proton beam Lithium Au Neutroncone 109 Ag Neutron source: 7 Li(p,n) 7 Be

5 Neutron spectrum Neutron spectrum measurement Quasi-Maxwell- Distribution: kt = 25 kev E max = 110 kev intensity calc.neutron spectrum at kt = 25 kev Comparison: therm. Neutrons kt=26 mev neutron energy (kev)

6 γ-detection 70 mm 2 Ge-Clover-detectors, with irridiated probe wedged in between Detection efficiency at 1115 kev: Probe single crystal: η tot = 11 % η peak = 1.1 % detector array: η peak = 15 %

7 Characteristic γ spectrum after neutron activation 198 Au 412 kev 110 Ag 658 kev 64 Cu 1346 kev

Activity of Au and Ag contents 109 Ag(n,γ) 110 Ag T 1/2 ( 110 Ag)=250 d; λ Αg =1.

07 10-2 1/h E γ =412 kev Activity after 2 hours of irradiation with 10 10 n/cm 2 s with σ Au =3mb and σ Ag =2mb

8 Activity of Au and Ag contents 109 Ag(n,γ) 110 Ag T 1/2 ( 110 Ag)=250 d; λ Αg = /h E γ =658 kev 197 Au(n,γ) 198 Ag T 1/2 ( 198 Ag)=2.7 d; λ Αu = /h E γ =412 kev Activity after 2 hours of irradiation with n/cm 2 s with σ Au =3mb and σ Ag =2mb A A Au Ag () t () t = I I Au Ag P P Au Ag () t () t λ Au t ( 1 e ) t Ag ( 1 e ) = λ = σ σ Au Ag η( 412keV ) AAu( t) η( 658keV ) A ( t) Ag λ Au t N ( 1 e ) Au Ag N ( 1 e ) Ag λ t

9 Efficiency and Count Rate Efficiency η [%] η Au =0.5%=0.005 η Ag =0.2%=0.002 I ag = I au = Energy [kev] N N Ag Au = σ σ Au Ag λ Au t ( 1 e ) I η λ t Ag Ag ( 1 e ) I η Au Au Ag =

$measurements mass fraction % Silver$ Copper #12 shows mint deviations in

10 Results for single coin measurements mass fraction % Silver Copper #12 shows mint deviations in Co, Ag, & Au content Gold Großpfennig, Bonn Coin

century weight 1,30g Ag content 889/1000 A weight 1,16g present

11 Comparison with official mint statements Großpfennig, Bonn Bonn Previous Results 1.part 16.century weight 1,30g Ag content 889/1000 A weight 1,16g present Results weight 0,92g Ag content 977/1000 Ag weight 0,90g 2.part 16.century weight 1,33g Ag content 972/1000 Ag weight 1,14g

Example 2: Qumran Pottery Provenance All clay sources on earth have a unique geochemical history, but show a slightly different impurity composition.

12 Example 2: Qumran Pottery Provenance All clay sources on earth have a unique geochemical history, but show a slightly different impurity composition. 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 distinctive source. Analysis of Qumran Pottery should establish the origin of the dead sea scroll containers and yield information on the cultural connection with other groups and villages

13 The Qumran Scrolls

14 Qumran site and samples Analysis of Qumran Pottery should establish the origin of dead sea scroll containers and yield information on the 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?

15 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 a pellet of uniform size and thickness. The pellets--representing sherds or complete vessels--are wrapped in pure aluminum and set on edge into an aluminum capsule which 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.

16 Neutron Activation Techniques

17 Activation procedure with thermal neutrons in reactor Cherenkov light Probe is positioned into neutron line

18 Activity measurements with a Gedetector 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.

19 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.

20 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.

21 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

22 NAA of paintings Possible applications: Pigment analysis by activation techniques Neutron radiography by neutron absorption neutrons

23 St. Sebastian ca 1649 Painting in the Gemäldegalerie Berlin original by Georges de la Tour ( ) French Court Painter Original in Louvre, question about authorship of copy, George de la Tour himself or by his son Entienne de la Tour? Neutron radiated 10 9 n/cm 2 s Neutron induced γ activity is recorded in different time steps: e.g. 1 days for 64 Cu (T 1/2 =12.8h), 5 days for 203 Hg (T 1/2 =46.6d) and 32 P (T 1/2 =14.2d)

24 X-ray radiograph Painter used white lead for brightly lit areas. (white lead was the only medieval white paint available.)

25 Comparison to x-ray radiograph X-ray radiograph (white lead paint is main absorber for x-rays visible) Neutron activation (lead is not Activated invisible)

26 Azurite distribution ( 64 Cu) Azurite (2CuCO 3 Cu(OH) 2 ) is mainly visible in mourners veil. Contour of body is reinforced with ivory black C+Ca 3 (PO 4 ) 2 ( 32 P)

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

28 The Depiction of St. Sebastian Analysis 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

29 Rembrandt: The Man with the Gold Helmet Gemäldegalerie, Berlin, Germany

30 Analysis Results paint and pigment analysis showed that this most famous Rembrandt painting was not painted by Rembrandt Rembrandt school?

31 Summary neutron activation Neutron 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 approach to X-ray radiography because it offers the possibility to 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.

Activation Analysis. Characteristic decay mechanisms, α, β, γ Activity A reveals the abundance N:

Activation Analysis. Characteristic decay mechanisms, α, β, γ Activity A reveals the abundance N: 2.5. Isotope analysis and neutron activation techniques The previously discussed techniques of material analysis are mainly based on the characteristic atomic structure of the elements and the associated