2.10. Neutron activation of paintings

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

Requires neutron irradiation of the entire painting using homogenous neutron flux followed by subsequent point by point raster activation measurement. Technical approach with reactors

Neutron guide line is needed for providing sufficient neutron flux (~1014 neutrons/cm2/s) for activation of bulky materials outside the reactor core!

4,7 m shielding door shielding

neutrons painting

2.5 m Activation with subsequent X-ray and γ-ray detection

63Cu(n,γ)64Cu, Cu(x) 202Hg(n,γ)203Hg, Hg(x)

X-ray data provides pigment position γ-ray data provides pigment characteristics Timescale and Radiation Sensitivity Anthony van Dyck, Saint Rosalie praying for the Plague stricken of Palermo 1624

radiograph Pigment identification by analysis of time dependence for characteristic activity 3rd run Pigment identification by analysis of time dependence for characteristic activity 6th run Pigment identification by analysis of time dependence for characteristic activity 8th run Young man in the background

Maryan Wynn Ainsworth et al. Art and Autoradiography; Metropolitan Museum of Art, New York; (1987) 12-18 Van Dyck Self-Portrait

Head also visible in X-ray radiograph Self-Portrait of van Dyck 1622 St. Sebastian ca 1649

Painting in the Gemäldegalerie Berlin original by Georges de la Tour (1593-1652) 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 109 n/cm2s

Neutron induced γ activity is recorded in different time steps: e.g. 64 1 days for Cu (T1/2=12.8h), 203 5 days for Hg (T1/2=46.6d) 32 and P (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 is Neutron activation (lead is not main absorber for x-rays → visible) activated → invisible) Azurite distribution (64Cu)

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

Gemäldegalerie, Berlin, Germany Analysis Results

paint stroke analysis showed that this very famous Rembrandt painting was not painted by Rembrandt ⇒ Rembrandt school? Napoleon’s Death The circumstances of Napoleon’s demise on 5 May 1821 have been shrouded by suspicion. The generally held belief was that he fell victim to carcinoma of the stomach – the supposed cause of his father’s death in 1785. But an analysis of five samples of Napoleon’s hair taken after his death showed a largely enhanced level of arsenic. Was he poisoned?

Napoleon has declared in his will that ‘I die before my time, murdered by the English oligarchy and its hired assassin’. http://www.sciencedaily.com- /releases/2008/02/080211131357.htm Neutron activation of Napoleon’s hair 75As is the only stable isotope of Arsenic

Several hair samples taken from Napoleon at different stages of his life as well as from other persons living at this period (The King of Rome, Empress Josephine) were placed in capsules near the core of the reactor at the University of Pavia, Italy for neutron activation. The Arsenic concentration was 75 76 As(n,γ) As; T1/2 = 26.4 h determined from the 559 and 563 keV γ activity from the activation product 76As. Arsenic levels

The average Arsenic level was high but comparable with the typical level at that time. Modern persons show lower levels of Arsenic contamination.

(King of Rome, Napoleon’s son) 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.