Level structure of 68 149 Er81 and high-spin isomerism in proton-richN=81, 82, 83 nuclei

Abstract

The level structure of the N = 81 nucleus 149Er has been studied by y-ray spectroscopy following the reaction 92Mo+255 MeV 6~Yrast levels in 149Er are established up to ~3.

Isomeric decay studies using a recoil mass separator

“…Instead, through an A/q ambiguity with A= 149, 150 recoils in the q=21 + charge state, this gate showed ),-rays following 4.8 #s ~49Er and 2.55 ~ts 15~ isomers, which had been studied in detail previously [7,19]. The N= 83 species 15SHf may still have a long-lived yrast isomer, but the cross section for its production here by 1 n evaporation is likely to have been prohibitively small.…”

Conversion electron spectroscopy at the fragment mass analyzer focal plane: Studies of isomeric decays near the proton drip line

“…This result removes any remaining uncertainty about the Z assignment of the transitions reported in Ref. [9].…”

“…In the original y-ray study [9] of the 4.8 p, s ' 9Er iso-meric decay, total conversion coefficients, and multipolarities for several key low-energy transitions were inferred from intensity balance requirements. The present measurements confirm the previous results, establishing E2 character for the 69 and 132 keV transitions, M1 multipolarity for the 63 keV transition, and El character for the 167 keV transition.…”

“…The first test experiment was performed with the reaction "Mo + 250 MeV Ni 52Yb* and resulted in good yields for the 2 55 &s &soEr and 4.8 p, s ' Er isomers, the products of 2p and 2pn evaporation. Isomeric decay schemes for these two nuclei were already well known from y-ray measurements [3,4,6,9] and the present work has focused on establishing definite multipolarities for all the strong transitions below 500 keV. In the second experiment, isomeric decays were studied in Yb nuclei produced in the reaction Ru + 250 MeV Ni~' Hf*.…”

Yrast isomers in exoticN=81 nucleusYb151studied using a fragment mass analyzer

“…However, both the 203 and 601 keV y rays decayed significantly faster than the transitions de-exciting the ' Yb isomer, and they exhibited much steeper excitation function behavior, typical of a three-nucleon (rather than a two-nucleon) evaporation product. Consequently, the 26 (5) ps isomer was tentatively assigned to the X =81 nucleus ' 'Yb, although no *Permanent address: Institute of Nuclear Physics, PL-31342 Cracow, Poland. ~Present address: Vanderbilt University, Nashville, TN 37235& direct evidence for either the A or Z assignment could be deduced.…”