K. Jensen

A Study of the Beam-Foil Excitation Mechanism Using 4He+, 6Li+ and 7Li+ Projectiles

Beams of 4He+, 6Li+ and 7Li+ ions accelerated to energies between 10 keV and 75 keV have been sent through thin foils of beryllium, carbon, aluminium or gold, or into a helium gas target. The photon emission immediately after the foil has been measured in the wavelength range 200 nm to 600 nm. Excitation functions have been measured for 11 Li Ia spectral lines, 8 Li Ib lines and 10 Li IIa lines. It was found that the excitation functions within one level scheme have similar slopes, whereas differences exist between excitation functions of different level schemes. From the excitation functions relative population functions have been constructed and it is found that the populations of Li Ia levels are proportional to the probability of getting neutral Li, whereas the He I, He II, Li Ib and the Li IIa population functions differ from the charge state distribution curves. Comparisons between the population of corresponding levels in 6Li and 7Li indicate that the collision time is a more relevant parameter than the projectile energy. The statistical weights related to the orbital angular momentum and to the total spin of the electronic structure are found to influence the beam-foil interaction, whereas the statistical weight related to the nuclear spin is not apparent. The foil excitation is compared to single atomic collisions, and it is concluded that the beam-foil excitation is the result of a multi-collision atomic interaction. Sputtered excited atoms of beryllium and aluminium have been observed.

Multi-colisional molecular oribital model for the beam-foil interaction process

Abstract Excitation functions for helium levels excited with a carbon foil are compared with those excited by a single collision ion-atom interaction. A model for the beam foil interaction process is proposed which applies theoretical and experimental results from ion- atom collisions to beam-foil collision data. It is shown that in many respects, the ion-atom and beam-foil interactions are similar. The significant difference is the complication introduced by the high density foil material which effectively causes effects such as excitation functions, sputtering and spectra to appear as gross features averaged over many unrelated collisions.

A study of relative level populations in foil excited He and Li

A set of relative level population measurements has been done for 40 keV beamfoil excited He and Li. The relative populations are discussed as functions of the principal quantum number, the azimuthal quantum number, the spin and the excitation energy.

A beam-foil study of LiI

Abstract Beam-foil excitation functions have been measured for various LiI, LiI ∗∗ , and LiII levels. The slopes are identical for levels within one level scheme, but differ from scheme to scheme. Two new lines are tentatively assigned to the LiI ∗∗ spectrum.

Excitation of projectile Rydberg states in the collisions Be+-He and Mg+-He, 10–75 keV

The collisions Be+-He and Mg+-He have been studied from 10 to 75 keV by means of optical spectrometry. Relative excitation cross sections and polarizations have been measured at 40 keV forS throughG terms with principal quantum numbern up to 10. Within a Rydberg series the excitation cross sections are found to decrease monotonically withn, and the excited terms have in general a negative alignment.

An experimental study of beam-gas collisions, I

Abstract Collisions of 20Ne+ and 22Ne+ with a natural composite neon gas target have been studied with energies ranging from 10 keV to 75 keV. Photons emitted from the collision area have been analysed in the spectral range 200 nm to 600 nm. Lines from NeI through NeV have been observed. Excitation functions for the 4 p [1 1 2 ]J=1 level and the 4 p [1 1 2 ]J=2 level in NeI have been measured, and small but distinct differences have been found in the slopes of these two excitation functions. Also a similar study of the 4 p [2 1 2 ]J=2 level and the 4 p [2 1 2 ]J=3 level showed no constant ratio between the population of level pairs. Differences between the excitation functions of the 4 p [ 1 2 ]J=1 level and the 4 p [1 1 2 ]J=1 level were found, indicating that the excitation mechanism may depend on the coupling between the orbital angular momentum of the running electron and the inner quantum number of the core. The excitation function of the 4 p [1 1 2 ]J=1 level is found to differ from that of the 4 p ′[1 1 2 ]J=1 level. The excitation of the 4 p [1 1 2 ]J=2 level has been studied both using 20Ne+ and 22Ne+ ions. The 22Ne+ induced radiation is found to be slightly more intense than (up to approximately 10%) or equal to that induced by 20Ne+ projectiles. The intensities of the transitions from the 4 p [2 1 2]J = 2 level to the 3 s [1 1 2 ]°J = 1 level and the 3 s [1 1 2 ]°J=2 level was measured for various projectile energies. The branching ratio was found to be constant within 3% giving a good check of the equipment and measuring procedure. The same satisfyingly good result was obtained for the transitions from the 4 p [1 1 2 ]J=1 level to the 3 s [1 1 2 ]°J=1 level and the 3 s [1 1 2 ]°J=2 level. The results are compared to the theory of molecular orbital level crossings.

Sputtered CH observed in beam-foil spectroscopy

Abstract The A 2 Δ-X 2 ∞ spectral system of CH has been observed in beam-foil spectroscopy using 40 keV He + ions and foils of different materials.

A study of isotopical effects in atomic collisions

Gas targets of He, Ne, and Ar have been bombarded with6Li+,7Li+,20Ne+ and22Ne+ ions with energies ranging from 20 to 70keV in the laboratory frame. Excitation functions have been measured. Photon yields using different isotope projectiles have been compared both at the same center of mass energy and at the same relative velocity.It is found that the collision time is a more descriptive parameter than the energy available for excitation. Furthermore it is found that the multiplicity caused by the coupling of the electron spin to the orbital angular momentum plays a more important role than the multiplicity caused by the coupling of nuclear spin to the total angular momentum of the electronic system.

An optical study of the Li+-He collision from 2 to 75 keV

Optical Spectrometry has been used to study inelastic channels of the Li+ -He collision. A number of spectral lines has been observed and relative yields have been measured from 2 to 75 keV projectile energy. The results are discussed in terms of the MO model.

Outer shell excitations of He and Ne using projectiles of C+, N+, O+, F+,20Ne+,22Ne+, Na+ and Mg+

He and Ne have been bombarded with singly charged ions of elements from carbon to magnesium, in the energy range 10–75 keV, and photons emitted from the target atoms have been detected. The results are discussed in terms of molecular orbital level correlation diagrams in which account has been taken of conservation of the total electronic spin. Comparisons are drawn with inner shell excitations and electronic stopping power measurements.