Speaker
Description
Complete spectroscopy for a certain nucleus means that up to a given
excitation energy for each state, spin and parity is determined by
experiment and the composition is described by some theoretical model.
Among heavy nuclei the goal to reach complete spectroscopy is
approached only for $^{208}$Pb.
Knowledge of nuclear states in $^{208}$Pb is gained since 1899. Since
the 1990s the sensitivity of the Munich Q3D magnetic spectrograph [1]
improved and several hundred levels in $^{208}$Pb up to 8 MeV were
found. The shell model describes the majority of nuclear states in
$^{208}$Pb with great success [2].
From the very beginning a few low-lying states were recognized to need
other model descriptions. The qualities of the 3- yrast state were
understood to be peculiar already in the 1950s. Its coupling to 1p-1h
configurations revealed a new class of nuclear excitations [3,4]. The
description of collective states as tetrahedral rotations and
vibrations invented 80 years ago was verified by discovering the 2-
member of the predicted 2+- parity doublet in $^{208}$Pb at Ex = 4.1
MeV [5,6].
In 2016 a major step of complete spectroscopy was reached with the
identification of 151 states below 6.2 MeV with spin, parity, and
major composition [3]. Now below 6.2 MeV nearly 160 states are
observed - including 5 states predicted but not yet clearly identified
[3-6]. The shell model predicts, however, only about 125 states.
Sixteen states are described by coupling 1p-1h configurations to the
3- yrast state, four states as pairing vibrations, nine states as
tetrahedral rotations and vibrations, and six states wait for some
model description.
[1] G. Dollinger and T. Faestermann. Nucl. Phys. News 28:5 (2018)
[2] R. Broda et al. PRC 95:064308 (2017)
[3] A. Heusler et al. PRC 93:054321 (2016)
[4] A. Heusler et al. PRC submitted
[5] A. Heusler et al. EPJ A 53:215 (2017)
[6] A. Heusler et al. PRC(R) submitted
