The decay scheme of Pb²¹¹

Abstract

The disintegration scheme of the 36.1 min β^- emitter Pb²¹¹ has been studied by means of a six-gap β-ray spectrometer, scintillation spectrometers, coincidence techniques, directional correlation measurements and lifetime measurements. The β^- spectrum of Pb²¹¹ has four components with endpoint energies: 1355 keV (92.4%), 951 keV (1.4%), 525 keV (5.5%) and 251 keV (0.7%). The following transitions in Bi²¹¹ were observed: 404 keV (55% M1 and 45% E2), 426 keV (M1), 700 keV (M1), 830 keV (M1) and 1104 keV. A decay scheme is proposed with levels in Bi²¹¹ at 0 keV (9/2^-), 404 keV (7/2^-), 830 keV (9/2^-) and 1104 keV. The transition energy between Pb²¹¹ and Bi²¹¹ is 1355 keV. The half life of the 404 keV level is (3.15±0.20)×10^-10 sec. The E2 lifetime of the 404 keV level is compared with theoretical estimates. The half life of the 830 keV level is less than 0.9±10^-10 sec. In addition it was possible to set an upper limit of 0.6±10^-10 sec on the half life of the 351 keV level in Tl²⁰⁷. The levels of Bi²¹¹ are discussed in terms of single-proton states or states involving the single proton and two neutrons outside the doubly closed shell.