YRAST spectroscopy and g-factor measurements in ¹⁹⁹Pb, ²⁰¹Pb and ²⁰³Pb

Abstract

The half-lives and g-factors of high-spin states in ^199,201,203pb were studied using ^199,200,202Hg(α, 3n) reactions at E_α =41 and 53 MeV. In-beam γ-ray spectroscopy including γγt-coincidence measurements were performed in order to interpret the level schemes. The measured half-lives are $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 7.5 (3)}\text{ns}\text{, 10.0 (2) μ}\text{s and}\text{55 (5)}\text{ns}$ for the previously known $\text{25}\text{2}{}^{\mathrm{-}}\text{,}\text{29}\text{2}{}^{\mathrm{-}}\text{and}\text{33}\text{2}{}^{\mathrm{+}}$ states, respectively, in ${}^{199}\text{Pb}\text{and}\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 508 (5)}\text{ns and}\text{63 (3)}\text{ns for the}\text{29}\text{2}{}^{\mathrm{-}}\text{and the}\text{25}\text{2}{}^{\mathrm{-}}$ states, respectively, in ²⁰¹Pb. A new isomer at 4559.2 + ° keV excitation energy with $\text{T}\text{1}\text{2}\text{= 43 (3)}\text{ns and J}{}^{\mathrm{\pi }}\text{=}\text{41}\text{2}{}^{\mathrm{+}}$ is observed in ²⁰¹Pb and a $\text{33}\text{2}{}^{\mathrm{-}}$ isomer at 2922.7 + Δ keV exitation energy with $\text{T}\text{1}\text{2}\text{= 122 (4)}\text{ns in}{}^{203}\text{Pb}$. The g-factors of the isomeric states were determined using the time differential perturbed angular distribution technique and the results are $\text{g(}\text{29}\text{2}{}^{\mathrm{-}}\text{) = −0.0742 (2)}\text{and}\text{g(}\text{29}\text{2}{}^{\mathrm{-}}\text{) = −0.0697 (4)}\text{for the}\text{29}\text{2}{}^{\mathrm{-}}$ states in ¹⁹⁹Pb and ²⁰¹Pb, respectively, indicating a predominantly three-neutron-hole configuration $\text{i}{}^{\mathrm{-2}}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}\text{f}{}^{\mathrm{-1}}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ for these states. The g-factor of the $\text{33}\text{2}{}^{\mathrm{+}}$ state in ¹⁹ as g= −0.145(9) which agrees with a ν($\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}{}^{\mathrm{-3}}$) configuration. The g-factor of the $\text{41}\text{2}{}^{\mathrm{+}}$ sta $\text{g(}\text{41}\text{2}{}^{\mathrm{+}}\text{) = −0.18 (4)}$ indicates a five-quasiparticle configuration. The probable configuration for the $\text{25}\text{2}{}^{\mathrm{-}}$ isomer has also been suggested on the basis of the measured value of the g-factor$\text{g(}\text{25}\text{2}{}^{\mathrm{-}}\text{) = −0.063 (3)}$ in ²⁰¹Pb and $\text{g(}\text{25}\text{2}{}^{\mathrm{-}}\text{) = −0.059 (3)}$ in ²⁰³Pb and the B(E2) values for t $\text{25}\text{2}{}^{\mathrm{-}}\text{→}\text{21}\text{2}{}^{\mathrm{-}}$ transitions in the odd Pb isotopes.