Henri-Pierre Garnir

Use of PIXE-PIGE under variable incident angle for ancient glass corrosion measurements

Abstract Although glass is usually considered as a very stable archaeological material, it can undergo severe degradation. Soda-lime glass, the most common glass throughout ancient times, is particularly sensitive to this problem. The glass surface absorbs moisture from its environment and the contact with CO 2 causes Na 2 O and NaOH to convert to Na 2 CO 3 , which is extremely hygroscopic. The subsequent unstable glass layer can be leached out and causes decomposition of the glass. The non-destructive PIGE–PIXE method of investigation allows detection of this phenomenon even if no visible effect appears. The variable incident angle method is able to discern the depth of the degradation. One aim of such studies is the possible dating or at least fake detecting of archaeological materials. Furthermore, even objects of large size can be investigated with the atmospheric PIGE–PIXE set-up. Some examples of measurements on ancient glass are given.

Comparison of the photoreduction of protochlorophyllide to chlorophyllide in leaves and cotyledons from dark-grown bean as a function of age

Abstract77 K fluorescence spectra of bean (Phaseolus vulgaris cv Commodore) leaves and cotyledons show the presence of active and inactive protochlorophyllides. The first detected product of the protochlorophyllide photoreduction is the chlorophyllide emitting fluorescence at 690 nm (C690) which is observed one day (leaves) and three days (cotyledons) after sowing. In cotyledons, C690 undergoes the ‘rapid’ and ‘Shibata’ shifts; in leaves, these spectral changes are age-dependent. In order to characterize the formation of C690, we have recorded 298 K fluorescence kinetics at 690 nm and the corresponding absorbance kinetics at 440 nm. The amplitude of the variations of both kinetics increases with the sample age. The absorbance and fluorescence kinetics can be modelized as a monoexponential law. The rate constant of the absorbance and fluorescence kinetics does not significantly change during the studied period (except for old cotyledons). The results presented in this paper give evidences for a low energy transfer between pigments during the photoreduction of protochlorophyllide at room temperature.

Time-resolved laser-induced fluorescence lifetime measurements and relativistic Hartree–Fock calculations of transition probabilities in Sm II

Radiative lifetime measurements were performed with time-resolved laserinduced fluorescence techniques for 47 levels of the astrophysically important ion Sm 1+ over the energy range 21 000–36 000 cm −1 .T henew results have been compared with previous measurements but also with theoretical calculations taking configuration interactions and core-polarization effects into account, and as atisfying agreement has been found for many levels of this complex ion. New calculated transition probabilities are deduced from the experimental lifetimes and from the theoretical branching fractions for 162 transitions of astrophysical interest. These results will help astrophysicists in the quantitative investigation of the chemical composition of CP stars.

Experimental and theoretical energy levels, transition probabilities and radiative lifetimes in Yb III

The analysis of the spectrum of Yb III has been extended allowing us to establish 11 new energy level values. In addition, radiative lifetimes of two excited states of Yb III have been measured for the first time using time-resolved laser-induced fluorescence following two-photon excitation. The good agreement between experimental results and semi-empirical calculations performed with the relativistic Hartree-Fock method including core-polarization effects allows the determination of transition probabilities for 15 lines.

Study of color centers induced by PIXE irradiation

The particle induced X-ray emission method is perfectly adapted to the study, by external beam, of art objects (like paintings) and allows non-destructive analysis of the atomic composition of the target. However, a strange phenomenon occurs during irradiation on some pigments: dark brownish stains appear, and this could be due to the formation of color centers. In fact, these darkening spots progressively fade out and disappear after a few weeks. Heat and UV light accelerate the decreasing process. The aim of this study is to understand the physical processes of the stain creation and to find a way to make stains disappear, avoiding any damage for the painting.

Beam-foil study of sulfur between 500 and 1200 Å

Beam-foil spectra of sulfur have been studied between 500 and 1200 A. Lifetime measurements have been performed for 33 levels in S iii – S vi (first measurements for 14 levels.) Our lifetime results are compared with other experimental and theoretical values where possible. Three new classifications are proposed in S vi.

Radiative lifetime measurements in Tm III with time-resolved laser spectroscopy and comparisons with HFR calculations

Natural radiative lifetimes of eight levels in Tm m were measured with the time-resolved laser-induced fluorescence (LIF) technique. Free doubly ionized thulium ions were obtained in a laser-produced plasma. Three even-parity levels were excited from the ground state with one-photon excitation, using a laser system generating pulses of 1 ns duration. Five odd-parity levels were excited from the ground state with two-photon excitation, where a picosecond laser system was employed. In both cases, the lifetimes were evaluated from transient LIF signals detected with a fast-detection system. The experimental lifetime results were compared with Hartree-Fock calculations including relativistic corrections. Good agreement was achieved for the 4f(12)6p levels while larger discrepancies are noted for some 4f(12)5d levels. (Less)

Study of S VII in the Vacuum Ultraviolet

The spectrum of S VII has been observed between 500 and 1200 A using the beam-foil excitation and the triggered-spark source. Twelve new lines have been observed and classified as transitions between 2p5 3s, 3p and 3d configurations. Energies and designations are given for 12 new levels of these configurations. Lifetimes have been measured for 7 levels.

Is the external beam PIXE method suitable for determining ancient silver artifact fineness

Abstract In archeometry, the non-destructive characteristic of an analytical method is always very attractive. For most of techniques, besides the need of sampling, difficulties can originate from the shape and the size of the silver artifacts to be analyzed. The external PIXE method should be an answer to this problem but several questions are arising from the implementation of the technique to such a material. The aim of this paper is to specify the experimental procedure as to take into account several parameters, which could induce dramatic errors. Among them it can be pointed out the superficial enrichment in silver, arising from the dissolution of copper and copper oxide, the surface roughness effects, the great importance of the stability of the geometric conditions. The accuracy and the precision of the method are considered within the scope of the results obtained in ancient times by the cupellation with ashbone cupels. In addition, the process involved to obtain silver alloys has been studied in order to define its influence on the real fineness of the objects.

Lifetimes and Oscillator Strengths for Ultraviolet Transitions in Neutral Sulfur

A consistent set of f-values for vacuum ultraviolet lines of S I is deduced from a combination of laser lifetime measurements and theoretical branching ratios. The new results are compared with results deduced from absorption by interstellar gas toward zeta Ophiuchi, and good agreement is observed for most transitions.