H.H. Bukow

Lifetimes and initial populations of foil-excited hydrogen and lithium states

Abstract Ion beams of hydrogen and lithium are accelerated to energies of 50–400 keV and sent through a thin carbon foil. The decay of hydrogen states is observed by recording light intensities as a function of distance behind the foil. Two detectors are used simultaneously to measure Lyman-α and Balmer lines. They consist of an interference filter with cooled multiplier and an MgF 2 filter with channeltron, respectively. A correlated fit of both decay curves allows satisfactory elimination of cascade effects and yields an experimental lifetime for Ly-α of (1.592± ±0.025)ns. The main error results from uncertainties in the beam velocity. The initial state populations obtained using H 2 + and proton beams show significant differences which may be of interest concerning the ion-foil interaction problem. The lithium spectrum is measured between 400 and 1500 A using a 6 Li + beam viewed by a 0.5 m Seya-Namioka VUV monochromator with a channeltron detector. In this range, all known Li II transitions are found and most of them are investigated for lifetimes, cascades, and initial state populations. Also lines in the hydrogen-like Li III spectrum are observed, equivalent to H α through H σ . Their decay curves reveal the existence of a long-lived cascades which is believed to originate from an autoionizing state of Li + .

Correlation of energy loss and crystallographic transformation in ion-irradiated carbon foils

Abstract Fast ions in the energy range 100–400 keV traversing carbon foils of typically 5–15 μg / cm 2 surface density suffer a specific energy loss of 1–1.7 keV / μg cm −2 per ion. The energy deposited in the foil causes a continuous crystallographic transformation (graphitization) leading to an increase of the mass density and also of the energy loss per ion (at constant surface density). The rate of the energy loss variation is investigated as a function of the atomic nuumber of the projectile, the current density, and the projeċtile energy. It is shown that the increase of energy loss is a consequence of the crystallographic transformation and may be interpreted in terms of the Lindhard-Scharff theory.

Ionenstrahlspektroskopie mit Wasserstoffionen als Primärteilchen

Relative initial populations of foil-excited hydrogen atoms in the2p, 3s, 3p, and3d states are determined by measuring the Balmer-α and Lyman-α emissions simultaneously. The data are analyzed by a computer program which takes into account the correlation of both emissions. The results show a dependence on the kind of incident ions: molecular ions give more light and lead to more pronounced excitation of higher angular momentum states than do atomic ions. A possible mechanism to explain this “molecule effect” is discussed qualitatively.

Relative Anfangsbesetzungszahlen der Zustände 2p und 3d folienangeregter Wasserstoffatome

The Lyman-α radiation of fast moving hydrogen atoms excited by a thin carbon foil is measured using a channel electron multiplier with a Mg F2 filter. The photonintensity-versus-distance curve exhibits the 2p (1.596 ns) decay followed by a cascade tail originating mainly from the 3d level (15.47 ns). The data is analyzed by a computer program using the known mean lives of the 2p, 3d, and 3s states and yields the relative initial state populationY=N2p0N3 d0 which depends on the kind of incident ions (H+ or H2+). For H2+ ions, excited with a single foil, there might be a slight dependence ofY on the beam velocity, but for H+ ions incident on the foil, no such dependence is found.

Messung von Lebensdauern und relativen Besetzungszahlen angeregter Zustände des Wasserstoffatoms mit der Methode der Ionenstrahlspektroskopie

H2+ ions or protons, accelerated to energies between 80 and 300 keV, are sent through a thin carbon target. Light emitted by the excited atoms moving out of the foil with a definite velocity is analyzed using interference filters and a cooled photomultiplier. Intensities of theHα,Hβ, andHγ lines are measured as functions of the distance from the foil. The data is analyzed with a computer program, which yields (in agreement with theory) mean lives of the hydrogen atom excited states involved, and the relative initial state populations of states belonging to the same principal quantum number. There is no indication of cascading.

A high-transmission triple-reflection polarizer for lyman-α radiation

Abstract A polarizer for the vacuum ultraviolet has been constructed consisting of three double-layer mirrors ( Al + MgF 2 ). Interference effects at these double layers yield high polarization and transmission.

Behavior of carbon foils under ion irradiation

Abstract The microscopic transformations of originally amorphous thin carbon foils under the effect of laser-induced heat and of ion irradiation are described. The increase of crystallographic order by heat and the disordering effect of low energy (100–800 keV) heavy ion irradiation are shown.

Crystallographic transformation and lifetime of thin carbon foils under ion and laser irradiation

Abstract The energy loss of ions of 100–400 keV energy when traversing thin carbon foils causes a temperature rise of the foils up to 1300 K. At such a temperature the foil experiences a continuous crystallographic transformation which ultimately leads to foil breakage. Heating the foil using the light of a CO 2 -laser to a temperature of 2000 K prior to ion irradiation has the effect of increasing the foil lifetime by a factor 7±1. Differences between laser and ion beam induced graphitization of the foils are discussed.

Einbeziehung von Kaskaden bei der Ionenstrahlspektroskopie des Wasserstoffs durch korrelierte Analyse zweier Linien

Ion beams of hydrogen are accelerated to energies of 50–400 keV and sent through a thin carbon foil. The decay of excited states of principal quantum numbersn=2 and 3 is observed by recording light intensities as a function of distance behind the foil. Two detectors are used to measure Lyman-α and Balmer-α-lines simultaneously. A correlated fit of both decay curves allows satisfactory elimination of cascade effects and yields an experimental lifetime for Ly-α of (1.592±0.025) ns. The main error results from uncertainties in the beam velocity. Furthermore, the relative initial populations of the 2p, 3s, 3p, and 3d states are determined.

Alignment ofH(2P) after beam-foil excitation

The alignment of foil-excited hydrogen was determined by measuring the polarization of Ly-α radiation in the particle energy region 23≦E≦190 keV. A change of sign at 45 keV is observed.