The Doppler shift and anisotropy of quasimolecular X-rays emitted in Nb+Nb collisions at 67 MeV

Abstract

The quasimolecular KX-ray spectrum obtained by bombarding Nb with 67 MeV Nb ions has been found to undergo a Doppler shift with an effective Doppler velocity equal to the mean center-of-mass velocity of the intermediate Nb + Nb molecule, corresponding to the projectile velocity. By applying Doppler shift corrections the intrinsic anisotropy of the quasimolecular KX-radiation is found.We have first shown in our previous experiments with Ge, Nb and ga ions [1][2][3] that the x-ray continuum lying above the intensive characteristic KX-lines of the ions and the target material consists of a lowenergy and high-energy component, denoted by us as (C1) and (C2), respectively. The high-energy part (C2) of the continuum has been interpreted as quasimolecular KX-radiation. Besides the properties of the (C2) component, the physical nature of the low energy component (

Anisotropy and angular distribution of quasimolecularK X-radiation emitted in Ge+Ge collisions

“…This structure manifests itself in the form of the ~7(E~)-function. Both components of the quasimolecular spectrum have a characteristic energy-dependent anisotropy with maxima in the energy regions, which nearly correspond to the accepted maximum energies of transitions to the 2pcr and 1 sa states in the Gc + Gesystem, l'he same result was obtained by us already in the Nb+ Nb investigations [9]. The results described in the present paper and covering our earlier findings on the Ni and Nb systems [8,9] lead to the following statements: i) The quasimolccular K X-ray spectra emitted by symmetric collision systems with atomic numbers Z = Z 1 -~ Z 2 > 56 display a two-component structure caused by superposition of the quasimolecular transitions to the 2pa-and 1 sa states at small internuclear distances.…”

“…This structure has been indentified by systematic theoretical and experimental investigations as superposition of quasimolecular radiation emitted by transitions to the 2pa-MO level (low-energy component) and 1 s a-MO level (high-energy component) [1 l, 12]. Moreover, in the case of the Nb + Nb system it was possible to show convincingly that this double structure of the K-MO-spectra manifests itself in the form of the t/(Ex)-function [9]. A logical step in the direction of the anisotropy studies of the MO-KX-rays is the investigation of the Ge + Ge system, whose atomic number lies between the atomic numbers of the Ni+Ni and Nb+Nb systems.…”

Theory of the angular distribution of 2p? molecular orbital X-rays

“…Calculations of the 1 sa and 2pa MO X-ray production cross sections are in good agreement with experiment [2,3]. Recently, Stoller et al [4] (and others [5,6]) measured the angular distribution of 2pa MO X-rays. (1) where da(O, Ex)/dE x is the MO X-ray production cross section measured at an angle 0 from the beam direction at an X-ray energy Ex, is sharply peaked at E~ =Epeak =(1.5 +0.04) UK, where U K is the separatedatom K-shell binding energy.…”

The anisotropy of the MO-2p?-radiation observed in symmetric heavy ion collisions

“…Our finding is therefore at variance with the results of Frank et al [41 who found that the observed peak energies can be explained by MO-M to L transitions. From the energies given in this paper [4] we conclude that a scaled relativistic HI-calculation was used for their comparison [12]. Therefore the transition energies and the binding energies are expected to be considerably larger than in neutral or almost neutral molecules.…”

“…It should be noted that the minimum of the 2pa-orbital is reached at a rather large internuclear separation and that it is considerably lower than the united atom limit [3]. The suggestion that the C1 continuum is due to transitions into the minimum of the 2pa-level is strongly supported by the investigations of Frank et al on the respective anisotropies [4]. These authors showed that the anisotropies reach a maximum at an X-ray energy which can only be explained by transitions into the 2p a-minimum.…”