Description

Energy loss field in bulk of the foil is so large that can blend the fine structure sub levels completely. However, small surface wake field (SWF) [1] induced mixing leads to partial admixture of 2s 2S1/2 and 2p 2P1/2 in H-like ions that quenches the 2s 2S1/2 lifetime to a great extent [2]. In order to study this effect in various ion species, we have used the beam energy above the Coulomb barrier to obtain the spectrum from projectile and projectile-like ions in a single beam-foil experiment as shown in Fig.1. The four peaks observed can be assigned to He-like Ti, Cr, Fe and H-like Co ions [4] as the peak of radiative electron capture disappears from the delayed spectra. Infact, the x-ray lines from projectile-like ions are much weaker than the one from the projectile-ion; a special technique [3] is adopted to record them. Upper level lifetime measurements were carried out using the beam-foil time-of-flight technique with 110 MeV Ti ions with a flight distance of only 0-3 mm for the short lived levels as given in the Table 1. The lifetimes obtained cannot be attributed to a pure metastable state in the corresponding ion. Hence, effect of the Stark mixing of closely spaced 1s2p 3P1 and 1s2s 3S1 in He-like ions and 2p 2P1/2 and 2s 2S1/2 in H-like ions need to be considered. The prescription given elsewhere [2] have been followed to obtain the SWFs, which fall in the order of 107 V/cm. It is thus much smaller than the field required for complete mixing (~1010 V/cm) the above mentioned states. Further, the results show that the SWF decreases linearly with the atomic number of the corresponding ion species. Figure 1: The X-ray spectrum of 110 MeV Ti on 80 g/cm2 C target. The lines from projectile ion and projectile like ions are resolved using 110 m Al absorber before the detector. References [1] T Nandi et. al, Phys. Rev. Lett. 110 163203 (2013). [2] T Nandi and B P Mohanty, J. Phys. B: At. Mol. Opt. Phys. 42 225402 (2009). [3] https://arxiv.org/1512.08399. [4] J. Hata and I.P. Grant, J. Phys. B: At. Mol. Phys. 14 2111 (1981).