Isomers from intrinsic excitations in Tl200 and Pb201,202

Abstract

A six-quasiparticle isomer with T 1/2 = 57(2) ns has been established in the doubly-odd isotope 200 Tl and its level scheme is significantly extended. Half-lives of previously reported isomers in 200 Tl and 201,202 Pb have been determined and revised values are reported in a few cases, with T 1/2 = 397(17) ns and 7.0(5) ns for the I π = 5 + and 7 − states in 200 Tl, 52(2) ns for the 41/2 + level in 201 Pb, and 93(4) ns for the 16 + state in 202 Pb. Configurations for the isomers have been assigned and these predominantly involve intrinsic excitations of neutrons from the i 13/2 subshell. The inferred transition rates for the decay of these isomers compare well with single-particle estimates attesting to their intrinsic character.

Metastable states from multinucleon excitations in Tl202 and Pb203

“…With subsequent, high-resolution γray measurements, the excitation energies of these levels in 204,206 Tl were determined to be 2319 and 2643 keV, respectively, and their isomeric character was established with T 1/2 = 2.6 μs and 3.74 min, respectively. However, a similar level has not been identified in 200 Tl [6,23,24]. In 202 Tl, a 12 − state is identified at E x = 2179 keV from the present work, a value within the uncertainty reported from the earlier (d, α) measurement.…”

“…In protonrich isotopes with A 199, prompt structures are known and there is no evidence of metastable states at high spin [4,5]. In contrast, there is comparatively limited information on metastable states in Tl isotopes with A = 200 to 203 [6][7][8]. Isotopes of Pb (Z = 82) with A ≈ 200 have been studied more extensively and a number of isomers at low and intermediate spin identified [9].…”

Nanosecond isomers and the evolution of collectivity in stable, even- A Hg isotopes

“…The 3513-keV level in 202 Hg, which is tentatively assigned I π = (12 + ), may be associated with the breaking of an i 13/2 neutron pair. This is supported by empirical calculations, using 1-quasiparticle energies from neighboring nuclei together with pair-gap energies calculated from odd-even mass differences and residual interactions deduced from isomeric states with the same configuration [7], which compute a i 13/2 broken-pair configuration at an excitation energy E x = 3554 keV; only 41 keV higher than the E x = 3513 keV experimental energy.…”

“…Nuclei in the A ≈ 200 region, just below doubly magic 208 Pb, exhibit diverse structural phenomena. Isotopes with several valence nucleons show evidence for moderate deformation [1][2][3], however, the proximity to both neutron and proton shell closures leads to a substantial contribution of intrinsic degrees of freedom (e.g., particle-hole excitations) to the level structure [4][5][6][7]. Isotopes of Hg, where both proton and neutron shells are almost filled, are characterized by oblate deformation near their ground states.…”

Isomers in 203Tl and core excitations built on a five-nucleon-hole structure

“…In contrast, there was limited knowledge on isomers in 200−203 Tl prior to investigations by this collaboration. Recently, the observation of isomers with half-lives ranging from a few nanoseconds to hundreds of microseconds in 200 Tl [11] and 202 Tl [8] were reported. The existing information on 203 Tl prior to the present work is limited, with levels up to possible spin (17/2) and excitation energy ≈3 MeV established through a deuteron-induced reaction [9], while a microsecond isomer was identified using projectile fragmentation [12].…”