# Optical Radiation during Sputtering of Lithium into a Noble Gas Using a Nanosecond Electron Beam
###### Abstract  
The optical radiation in a gaseous medium upon the irradiation of a lithium layer with a fast electron beam of a 5 ns duration has been studied. The irradiation chamber was filled with argon, krypton, or xenon at a pressure of 10 kPa up to 60 kPa. The lines of lithium atoms appear in the emission spectrum at a lithium layer temperature of 650-680 K, and the intensity of these lines sharply increases with the increasing temperature of the lithium layer. The optical radiation arises from both the transitions of noble gas atoms and the transition of the lithium atom in a time of about 20-30 ns. The duration of the radiation pulses at half maximum at temperatures above 800 K was 60-100 ns at a wavelength of 610.4 nm and 140-220 ns at 670.8 nm in krypton and argon. The various mechanisms for the population of lithium levels during the radiation pulse are discussed. sputtering; lithium; noble gases; electron accelerator; luminescence +
Footnote †: journal: Physics Letters [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]. +++ ==WARNING: Truncated because of repetitions==
. Optical Radiation during Sputtering of Lithium into a Noble Gas Using a Nanosecond Electron Beam  
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situ irradiation ions with an energy of 4.8 MeV/u of \({}^{197}\)Au and \({}^{48}\)Ca was investigated using time-of-flight mass spectrometry in combination with laser post-ionization. In previous studies [6], catcher foils were used to collect the ejected material. It has been shown that most of the material sputtered from a solid surface under irradiation with fast heavy ions are emitted in a neutral state. In [5], a mass-resolved comparison of secondary ions and neutral particles was created for the first time for separately determining the composition of the sputtered flux and the ion fractions of different emitted species. In most cases, most of the sputtered material is emitted in the neutral state, with the flux of sputtered particles mainly consisting of single atoms and small (mostly diatomic) clusters [5]. In [1; 7], a different mechanism from [2] was proposed for the appearance of lithium lines upon the irradiation of a lithium layer in a gaseous medium by products of the \({}^{6}\)Li(n,\(\alpha\))\({}^{3}\)H nuclear reaction. From the analysis of the dependence of the intensity of noble gas and lithium atoms lines on the temperature of the lithium layer, it is concluded that the main channel leading to the population of the lithium levels is the Penning process with noble gas atoms (R) in the 1s-state:  
\[\mathrm{R^{*}(1s)+Li\to Li^{+}+R+e} \tag{1}\]  
Further plasma-chemical-reaction molecular ions of Li\({}_{2}\)+ are formed. During the process of the dissociative recombination of ion:  
\[\mathrm{Li_{2}}^{+}+\mathrm{e}+R\to Li+Li^{*}+R, \tag{2}\]  
excited lithium atoms are formed. The rapid increase in the luminescence intensity is well approximated by [1]:  
\[\mathrm{I}\ \sim\ \exp\ (-\frac{A}{kT}) \tag{3}\]  
where \(A\) is the activation energy of this process. The \(A\) values obtained for 610.4 nm lithium lines are 1.67 eV in argon, 1.63 eV in neon, and 1.61 eV in xenon. These values are in good agreement with the evaporation energy of lithium, which is equal to 1.63 eV (156.9 kJ/mol [8]). It can be assumed that the sputtering of lithium is due to the evaporation in the nuclear particle channel [1]. For the ion energies in the MeV range, the electronic sputtering processes contribute to the surface sputtering [6; 9]. A major part of the energy of the heavy ions is transferred to electrons along the ion track. A coupling between the electrons and phonons causes large local heating in the cylindrical volume. The surface atoms may be removed through evaporation in a jet from the heated volume [6].