Electron-impact-ionization measurements using hyperfine-assisted state preparation of ground-state berylliumlike sulfur

Abstract

We have measured electron impact ionization (EII) of the beryllium-like ion S¹²⁺. The use of an isotopically pure A=33 beam of S¹²⁺ ions is established as a method to eliminate all metastable levels, including the extremely long-lived metastable level 2s2p³ P₀, which, for this isotope, decays by hyperfine-induced radiative transitions. The energy dependence and absolute size of the EII cross section were measured from the resulting pure ground-state population at energies from below the threshold at ≈ 652.2 eV up to 3000 eV. These data provide an experimental benchmark for theory

STORAGE RING CROSS SECTION MEASUREMENTS FOR ELECTRON IMPACT IONIZATION OF Fe7+

“…Our cross section measurements were performed using the TSR heavy ion storage ring [11,12] located at the Max-Planck-Institut für Kernphysik in Heidelberg, Germany. The procedures used here are basically the same as those we have described for previous EII measurements and are described in detail in [13][14][15][16][17][18][19][20][21]. Recombination measurements for Fe 8+ were previously performed at TSR by [22], who used similar methods.…”

“…As a result, it has an essentially infinite lifetime. In previous work, such metastables were removed using hyperfine-induced transitions [17,39], but no hyperfine splitting exists for 56 Fe, as the nuclear spin is zero. The next important metastable level is the 3p 3d F 5 3…”

Theoretical electron-impact-ionization cross section for Fe11+forming Fe12+

“…Linkemann et al [11], Kenntner et al [12], and more recently Hahn et al [13][14][15][16] have carried out a sequence of EII measurements using the TSR heavy ion storage ring combined with a merged electron-ion beams arrangement. The storage ring geometry allows one to store the ions long enough for essentially all of the metastable levels to radiatively decay to their ground state.…”

“…The resulting EII measurements provide unambiguous benchmark data for theory. The isoelectronic sequences studied to date include Li-like Si 11+ and Cl 14+ [12], Be-like S 12+ [16], B-like Mg 7+ [13], Na-like Fe 15+ [11], Si-like Fe 12+ [14], P-like Fe 11+ [15], and S-like Fe 10+ and Cl-like Fe 9+ [Hahn et al (in preparation)]. …”

Absolute rate coefficients for photorecombination and electron-impact ionization of magnesiumlike iron ions from measurements at a heavy-ion storage ring

“…Beam storage and beam cooling allow the preparation of ion beams with well characterized mass, charge, and velocity distribution. An advantage of the storage-ring technique over conventional single-pass experiments is that long-lived excited states, that often contaminate ion beams, have sufficient time to decay while the ion beam coasts in the storage ring before a cross-section measurement is started (see, e.g., [9,10]). We exploit this feature to reduce the fraction of metastable Fe 14+ ([Ne] 3s 3p 3 P ) ions in the stored ion beam.…”