Incident ion energy dependence of the secondary photon emission of ion bombarded beryllium

Secondary photon emission due to ion bombardment of Be metal foil by 200--3000 eV Kr+, Ar+, Ne+, O+2, and N+2 was studied and the emission yield from four Be (I) and one Be (II) transitions as a function of incident ion energy was interpreted in terms of relevant excitation processes. A model based on a velocity dependent excitation process, the random linear collision cascade theory of sputtering; and making allowance for nonradiative de-excitation of the excited sputtered atoms and/or ions, accounted for the observed energy dependent emission yields. The results of this model indicate that the secondary photon emission yield, Y/sup ex//sub i/(v/sub m/), of a given emission line, i, can be expressed as Y/sup ex//sub i/ (v/sub m/) α J(μamp/cm2) S(no./ion) exp[-(A/a)/sub i//v/sub m/], where J is the incident ion current density, S the sputtering yield; v/sub m/ is the velocity corresponding to the maximum transferred energy between the incident ion of energy E1, mass M1, and the target atom of mass M2, i.e., v/sub m/=8M1E1/(M1 +M2)2]/sup 1/2/; (A/a)/sub i/ is the effective nonradiative de-excitation parameter for state i. Values for the (A/a)/sub i/ parameters were found to be 1--3 x 107 cm/sec for the Be (I) and Be (II) states; a decrease to 5--7 x 106 cm/sec upon O+2 bombardment was observed for the Be (I) states, while the value for the Be (II) state did not change