Systematics of isomeric configurations inN=77odd-Zisotones near the proton drip line

Abstract

The systematics of the πh 11/2 ⊗ νh 11/2 and πh 11/2 ⊗ νs 1/2 isomeric configurations was studied for the odd-Z N = 77 isotones near the proton drip line. The isomeric decays in 140 Eu, 142 Tb, 144 Ho, and 146 Tm were measured by means of x-ray, γ -ray, and charged particle spectroscopy at the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility (ORNL). The spin and parity of I π = 8 + and 5 − were deduced for the isomers in 140 Eu and 142 Tb. New decay schemes were established, and the half-lives of the 8 + isomers were measured to be 302(4) ns for 140m2 Eu and 25(1) µs for 142m2 Tb. No evidence for the expected 1 + ground-state was found in the 144 Ho decay data. The proton-emission from 146 Tm was restudied. Five proton transitions were assigned to two proton-emitting states. The half-lives of 198(3) ms and 68(3) ms and the spin and parity values of I π = 10 + and 5 − were established for 146m Tm and 146gs Tm, respectively. For the first time for an odd-odd nucleus, the interpretation of the observed decay properties and structure of the proton-emitting states was made by accounting for deformation and proton and neutron coupling to the core excitations. A complex wave-function structure was obtained, with dominating components of πh 11/2 ⊗ νh 11/2 for the 10 + isomer and πh 11/2 ⊗ νs 1/2 for the 5 − ground state.

Radioactive decays at limits of nuclear stability

“…The 146 Tm, s = 2, proton emitter is the richest proton emitter known. There are 5 proton transition known in this case (Tantawy et al, 2006). Three transitions are coming from the ground state and two were assigned to its isomeric state.…”

“…It is worth noting that the s = 1 141 Ho proton emitter is among the most extensively studied and understood isotopes beyond the proton-drip line. We know proton emission from both ground and isomeric states in 141 Ho to the 0 + ground state as well as first excited 2 + TABLE VI Proton energies Ep and branching ratios I exp p measured for proton emission channels from 146 Tm together with the calculated values based on the particle-core vibration coupling model (Hagino, 2001;Tantawy et al, 2006). E f denote excitation energy of the final state in 145 Er.…”

“…Three transitions are coming from the ground state and two were assigned to its isomeric state. Table VI shows experimental results obtained for these transitions together with the calculated wave functions components, based on the work of Tantawy et al (2006) and Hagino (2001).…”

Identification of isomeric states in theN=73neutron-deficient nuclei132Pr and130La

“…This competition results in soft nuclear shapes for nuclei in this region, which are susceptible to nonaxial deformations. Studies of 144 Ho [2,3], 142 Tb [2,4,5], 140 Eu [6], and 134,136 Pm [7,8] nuclei have unearthed isomers resulting from a change in nuclear shape linked by E1 γ -ray transitions. An interpretation of K isomerism was prohibited in these cases due to the γ softness associated with their shapes.…”

Exotic nuclei far from the stability line

“…A single-proton radioactivity has been found in many odd-Z proton-rich nuclei, and has provided a powerful tool to study the spectroscopy of proton-rich nuclei beyond the proton-drip line. 29,104,[108][109][110] When the single-proton emission is energetically forbidden, proton-rich nuclei beyond the proton drip line decay via emission of two protons. Even though this process had been predicted theoretically in 1960, 111 its first experimental discovery was much later, only in 2002, 112,113 for the 45 Fe nucleus.…”