Lifetimes of two-photon-emitting states in heliumlike and hydrogenlike nickel

Heavy-ion storage-ring quest for atomic lifetimes in Li+ and Be2+

“…This value and its uncertainty of 13% were later improved to (2.32 ± 0.2) ns (8%) [33]. For Ni (Z = 28) an uncertainty of 1% was reached [34,35], for Br (Z = 35) the uncertainty was 0.8% [36], and for Kr (Z = 36) the uncertainty was 1% [37]. Thus the high-Z trend seems well-established, but experiments delivering more accurate data on low-Z ions would be desirable.…”

Branching ratio for theM1 decay of the 22S1/2Cheng1, Berry2, Rw3 et al. 1993Phys. Rev. ASelf Cite18070View full textAdd to dashboardCite

“…The requirement of a coincidence with the proper sum-energy eliminates problems from background and He-like two-photon decays. This technique has produced 1% lifetime measurements of two-photon decays in Hlike and He-like nickel [10,24] using lower-energy beams (11 MeV/amu) from Argonne's ATLAS accelerator. In order to get sufficient two-photon coincidence rates for a viable experiment, the background nuclear emissions encountered in this experiment must be reduced.…”

“…Drake Johnson [3] calculated the Ml matrix element in the Dirac theory and evaluated it in the nonrelativistic limit to obtain =2.496X 10 Z' s (2) 13.45- b"'=0 3643 (4) Fully relativistic calculations [4 -6] give a lifetime of 37.008 ps and a branching ratio 1 The lifetime of the 2 S, &2 level in one-electron ions has been previously measured to a precision of about 1% in He+ [7,8], Ar' + [9], and Ni + [10], and to lower precision in 0 +, F + [11],and S' + [12]. The Ar' + experiment was sensitive to the contribution of the magneticdipole amplitude to the total decay rate, and the Ni measurement was sensitive to the relativistic corrections to the two-photon amplitude.…”

“…A A. Coincidence data The geometry for detectors 1 and 2 was chosen to optimize the detection of coincidence events from H-like two-photon decays. A lifetime measurement based on coincidence detection is desirable because a coincidence with the proper sum-energy provides a means for eliminating background and competition from He-like twophoton decays [10]. But the coincidence method requires high count rates in order to be successful.…”

Two-Photon Decay in Heavy Atoms and Ions

“…The lifetime of the 2 2 S 1=2 level in H-like ions has been measured for a number of ions in the range Z ¼ 1 to Z ¼ 47 [35][36][37][38][39][40][41][42][43][44][45], with results at the level of 1% being reported for Ar 17þ [38] and Ni 27þ [35]. The lifetime of the 2 1 S 0 level in He-like ions has been measured from Z ¼ 2 to Z ¼ 41 [11,35,36,38,[44][45][46][47][48][49]. The most precise measurements have been made in Kr 34þ [46], Br 33þ [49], and Ni 26þ [35] where uncertainties of about 1% have been reported.…”