In this communication we show that two nuclear methods permit a non-destructive determination of major, minor and trace elements
in three important “archaeological” metals: gold, silver, copper and alloys. With the first one, neutron activation analysis
with a252Cf neutron source, we can perform a fast and accurate determination of three important elements of the coin's composition,
viz. gold, silver and copper. With the second one, proton activation analysis, we can determine trace elements at ppm level
in gold, silver and copper metals. Using these two techniques of activation analysis two important numismatic problems can
be studied: the evolution of the fineness; characterization or differentiation by the trace elements the metal used to mint
the coin. One example of each numismatic problem is also given.
Nous montrons que l'activation par les protons de 11 MeV permet le dosage non destructif de traces d'impuretés dans des échantillons
d'Argent, d'Aluminium et de Cobalt. Nous avons pour le moment étudié le dosage de 30 éléments dans Al et Co et de 24 dans
Ag. Nous avons choisi les protons car ces particules sont les seules qui permettent d'effectuer un dosage non destructif dans
Ag et Co, au niveau des traces sans interférence, et ceci pour de nombreux éléments. Le cas de l'aluminium a été étudié, bien
que les neutrons puissent ici être utilisés pour l'analyse non destructive car l'activation dans les protons permet de doser
facilement des éléments autres que ceux dosés en irradiant dans les neutrons. Ces premiers résultats nous conduisent à penser
que l'activation dans les protons sera très employée dans les cas où l'activation neutronique est en difficulté (exemple de
Ag, Co, Ir, HgTe, AsGa, terres rares, etc.).
The excitation functions for nuclear reactions induced by tritons are determined up to about 3.5 MeV for some light and medium
elements: fluorine, sodium, magnesium, aluminium, silicon, titanium and vanadium. Because of large cross-sections the activation
technique was used with thin targets. Then the possibilities of using these reactions to analytical purposes are discussed.
We have irradiated 30 elements with 11 MeV protons and we present here: (1) The specific activities for the main radioisotopes
produced by (p, n) or (p, α) reactions (on main γ rays except the 511 keV). (2) The main γ energies of these radioisotopes
(at ±0.3 keV) when they have not been accurately measured previously. (3) The limits of detection or the lowest amounts measured
in samples of Al, Ag or Co. From these preliminary results it can be deduced that 11 MeV protons offer new possibilities in
the field of activation analysis.
The sensitivities for the determination of 25 elements from Z=4 to Z=33, using 3.5 MeV triton activation, were calculated
from experimentally measured yields for 50 radioisotopes obtained via (t, n), (t, d), (t, 2n) or (t, α) reactions. For an
irradiation of 1 hour at 1 μA, the calculated detection limits are better than 100 ppb for B, N, O, F, Na, Mg, Al, Si an S.
Because of the Coulomb barrier, triton activation is of considerable interest for non destructive analysis of low Z elements
in medium and high Z matrices. Finally integrated activation curves of high sensitivity elements were determined.
Authors:B. Borderie, M. Basutcu, J. Barrandon, and J. Pinault
A method is described for analyzing some light elements with high accuracy. Prompt gamma-ray spectrometry with 3.5 MeV alpha-particles
from a Van de Graaff accelerator was used: this technique is non-destructive, rapid and experimentally simple. Sensitivities
are indicated and factors affecting the accuracy of analysis are considered. A range of different materials has been analyzed
and analytical results are presented.
Authors:J. Barrandon, L. Quaglia, J. Debrun, M. Cuypers, and G. Robaye
The oxygen and carbon concentrations on metal surfaces were determined by two methods. The first method was based on the detection
of the emitted particles in the12C(d,p)13C and16O(d, p)17O reactions, the second one on the measurement of the induced radioactivities in the12C(d,n)13N and16O(t,n)18F reactions, respectively. The results, obtained by the two different methods for high purity metals, were in agreement. A
type of error which exists in the determination of trace amounts of carbon and oxygen in pure metals by combustion and reductive
fusion was quantitatively demonstrated. This error exists also in the determination of oxygen by 14 MeV neutron bombardment.
Authors:B. Gratuze, M. Blet-Lemarquand, and J.-N. Barrandon
Interest in mass spectrometry with an inductively coupled plasma as an ion source and its association with laser ablation as a sample introduction technique (LA-ICP-MS) has steadily increased during the past few years. After a description of the analytical procedure and the calculation method, we show the potential of this technique to characterize non destructively archaeological artefacts. A comparison is made between the results obtained with LA-ICP-MS and those obtained on the same objects with other analytical methods. A large variety of archaeological materials such as obsidians, glasses, glazes and flints are studied.