Paul-Dominique Dumont

Thickness Variations and Lifetimes of Carbon Foils under Nitrogen-ion Bombardment

The deposition of carbon upon carbon foils and the lifetimes of foils during bombardment by nitrogen ions have been investigated under various experimental conditions. The rate of carbon deposition depends upon the energy and current density of the bombarding ions, as well as upon the condition of vacuum. For ion energies of 0.125-1.5 MeV/atom and current densities of 0.25-13.0 μA/cm2, increases in areal density of up to 40% for 10 μg/cm2 foils have been observed under conditions typically employed in nuclear physics and beam-foil spectroscopy. The source of the deposited carbon appears to be carbon-containing molecules in the residual gas of the vacuum system. Elimination of carbon deposition has been achieved by surrounding the foil with a cooled baffle. The lifetime of the foil (time until breakage) is found to be, at a given energy per atom, the time required for a constant number of atoms to have bombarded the foil.

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.

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.

Transition probabilities for vacuum ultraviolet lines of N I through N IV

Abstract New beam-foil lifetime measurements of excited levels have been made for N I-N IV using lines in the vacuum ultraviolet spectral range. These values are compared with other experimental results and theoretical data. ‘Best’ values of absolute transition probabilities are proposed.

Analysis of charge-state distributions of heavy ions in carbon foils and gases

The charge-state distributions of heavy ions after passing through carbon foils with an energy per nucleon E/M or approximately=20 keV amu-1 follow the Gaussian law surprisingly well. Charge-state distributions in carbon foils calculated using either the chi-squared model or the Gaussian model are in better agreement with experimental data than those calculated from the independent-electron model (binomial model).

Secondary electron emission from thin foils under fast ion bombardment

Abstract The total yield of secondary electrons emitted when fast ions pass through a thin carbon foil has been measured as a function of the ion beam current and of the tilt angle of the target. We have shown that the dependence on the beam current can be interpreted as a temperature effect and that the dependence on the incidence angle is partly explained by geometrical considerations.

Beam-foil Study of Nitrogen in the Vacuum Ultraviolet

Beam-foil spectra of nitrogen have been studied in the wavelength region 280-1 230 A, employing linewidths of about 0.7 A. Lifetime measurements have been performed for 28 terms in N II-N VI and new classifications have been proposed in N II, III, and V. Where comparison with previous results is possible, good agreement is generally found with the most recent beam-foil determinations or with configuration-interaction calculations. For seven terms there exist no previous experimental or theoretical results.

Identification of new lines in the beam-foil spectrum of nitrogen

Many unidentified lines appearing in the VUV beam-foil spectra of nitrogen (40-180 nm) have been classified in N III-V. The observation of eight new lines in the quartet states of N V confirm the recent theoretical results of K. T. Chung. Energies have been determined for two new levels in N III and five new levels in N IV.

Yield of secondary electrons emitted by heavy ions passing through carbon foils

Abstract Using a new technique the total yield of secondary electrons emitted when heavy projectiles (He, N, O, Ar and Kr) pass through a carbon foil has been measured as a function of the ion energy [0.2 E (MeV)

Effect of the Spatial Resolution Function of the Spectrometer on the Analysis of Multi-exponential Beam-foil Decay Curves

The effect of the spatial resolution function of the spectrometer on beamfoil lifetime measurements is studied. Intensity curves obtained by convolution of the measured spatial resolution function and a sum of exponentials are compared with measured decay curves. Optimum spatial resolution functions are discussed and results of the analysis of decay curves obtained using different beam lengths viewed by the spectrometer are given, for two transitions presenting strong cascading: 3s3d3 D-3s4f3F0 in SV (568 A) and 3d2D-4f2F0 in S VI (465 A).