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

Abstract

The anisotropies of the MO-2p a-radiation have been measured for five symmetric systems with a united atom number Z u between 52 and 94 at beam energies in the range from 7 up to 66 MeV. A comparison with the available theoretical data suggests that the anisotropic part of the 2pa-radiation is mainly due to transitions from near continuum initial states into the minimum of the molecular 2pa-orbital.

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.…”

“…To obtain a more accurate value of Epeak , the lscr intensity should be subtracted from the total intensity before Epeak is found. Second, our calculations imply that the peak position should depend slightly on the projectile velocity or q. Stoller et al [4] show that the peak position changes from approximately 9.5 +0.5 KeV to 10.3_+0.5 KeV in 7-to 70-MeV Fe+Fe collisions where q changes from 2.52 to 0.83. However, in deriving the relationship Epeak/U K = 1.5, they compare Fe + Fe data with q =1.55 with Ag+Ag data with q=3.0.…”

“…Stoller et al [4] measured the anisotropy of the 2p a +lsa MO X-ray continua in symmetric collisions with Fe, Ge, Br, Nb, and Ag projectiles, and found that the position of the anisotropy peak Epeak is always 1.5+_0.04 times the projectile or target Kbinding energy OK, independent of the atomic number of the collision partners. They conclude that the dominant mechanism responsible for the MO X-ray anisotropy must be the radiative-capture-to-MOs (RECMO) process [7].…”

“…One does not have to invoke the RECMO process to explain the anisotropy peak position. The work of Stoller et al [4,23] implies the possibility of deducing 2pa binding or transition energies in superheavy quasi-molecules from measurements of the position of the 2pa MO X-ray anisotropy peak. Our theoretical calculations support this, as long as the scaling relations [Eq.…”

“…Because of the very fine 2pa MO X-ray cross-section and anisotropy data taken by Vincent and Greenberg [5], we concen-trated in this paper on Nb + Nb collisions. Section III compares the calculated MO X-ray cross sections with experiment; Section IV compares the calculated anisotropies with experiment, and comments on the proposed spectroscopy of superheavy quasi-molecules [4]. Finally, in Appendix B we discuss theoretical calculations of 3da-~z-6 rotational coupling which were made as a by-product of this work.…”