A Study of the Beam-foil Excitation Mechanism Using 60-360 keV Be⁺Projectiles

Abstract

Beam-foil excitation functions have been measured for a number of optical transitions in Be Ia (configuration 1s 2 2s nl), Be Ib (configuration 1s 2 nl n'l'), Be IIa (configuration 1s 2 nl), Be IIb (configuration 1s nl n'l'), and Be IIIa (configuration 1s nl) in the projectile energy range 60-360 keV. The excitation functions within one level scheme were found to be proportional. They have been converted into relative population functions and the five sets of Be population functions have been linked together by only two empirically determined parameters. Comparisons to results from earlier works, using He and Li projectiles are drawn. Relative level population measurements have been performed in Be Ia, Be Ib, Be IIa and Be IIIa, the results are compared with earlier findings, and systematical trends are found. General conclusions about the beam-foil excitation mechanism are drawn.

A study of relative level populations in beam-foil excited Li, Be, and Mg

“…of the same charge state and with the same core configuration) showed the same relative intensity change with the projectile energy. This result was noted already in [5], and many more lines have been studied here. Population functions (viz.…”

“…The data given in this paper extend the old data for Li [4] and Be [5] to higher lying levels (generally up to levels with principal quantum number n~ 10) and to other pro- In the previous work on Be [5] attention was focussed on excitation functions for only a few low lying levels of Be I-Be III, the relative level population data given in [5] being sparse because of the lack of a quantum efficiency calibrated monochromator. This paper thus supplements [4,5].…”

“…The level population is a quantity of basic interest, and we shall here give some examples of relative level populations as functions of the quantum numbers of the excited states at different projectile energies. The data reported previously for Li [4] and Be [5] were limited in the sense that only levels with low values of the principal quantum number were observed, and also that the observations were done only at one projectile energy. It is, of course, of basic interest to see whether the relative population of levels of the same charge state and with the same core configuration changes with the projectile energy, for a discussion of this see e.g.…”

“…Therefore only relative numbers are given. The relative line intensities, corrected for background, were converted into relative level populations by use of the relation [4,5] Here Nj is the relative population of level j, S(2jf) is the signal per monitor count of the optical transition of wavelength 2jr from level j to level f, K(2jf) is the monochromator quantum efficiency [11] at wavelength 2~f, and A~f is the transition probability for the transition from level j to level f. Repopulation through cascade processes were ignored, since the observation region was immediately behind the foil [4], and no attention was paid to polarization effects.…”

“…However, for estimating cascade contributions, relative level population data are needed, and only very few measurements have been done to obtain such quantities. Data have so far only been reported for H [2], He [3], Li [4], Be [5], C [6], Fe [7], and Zn [8]. Furthermore, in most of these works the data sets are very incomplete, so further experiments are clearly required to establish systematical trends as well as to guide a quantitative theory.…”