Th228nuclear states fed inAc

Abstract

The decay of radiochemically-separated Ac sources has been reinvestigated using highresolution coaxial HPGe detectors and y-y coincidence measurements. Energies and intensities of more than 240 photons were accurately measured, 80 of them for the first time. A ' 'Th level scheme, built on the bases of good energy fits and on y-y coincidence data, involves 58 excited states, of which 17 are new, up to 2159 keV with spin 0(I (6. Collective properties of lowenergy states belonging to K =0,2+,2 bands are discussed in the framework of the Bohr-Mottelson model. Decay modes of a K =0+ excited band at 831.82 keV favor strong two octupole phonon K =0 components. The K"=1 band is expected to have I =2 and 3 members at 938.5 and 968.4 keV. Coriolis coupling calculations involving the four K =0, 1, 2, and 3 bands were carried out. Tentative K =2+ two-quasiparticle bands at 1638.23 and 1899.99 keV are discussed in terms of Nilsson orbitals.

0+states and collective bands in228Th studied by the (p,Levon1, Graw2, Hertenberger3 et al. 2013Phys. Rev. C269700View full textAdd to dashboardCite

“…Besides 0 + excitations, where the number of reliable assignments could be increased for five states in comparison with the preliminary analysis in publication [4], information on the spins for many other states was obtained. This information was essentially complementary to what was known from publications [2,7]. Some levels are grouped into rotational bands, thus allowing to derive the moment of inertia for some 0 + , 2 + and 0 − , 1 − , 2 − , 3 − bands.…”

“…The lowest collective bands in 228 Th were studied in the (α, xnγ)-reaction [8]. A total of 58 levels were reported in [2] and 80 levels were observed in [7] below 2.1 MeV, connected by more than 240 γ-rays that were established in these studies. • .…”

“…The most complete information was obtained from the β-decay of 228 Ac reported by Dalmasso et al [2] and from the EC-decay study of 228 Pa by Weber et al [7]. The lowest collective bands in 228 Th were studied in the (α, xnγ)-reaction [8].…”

“…They are listed in Table I. The energies and spins of the levels as derived from this study are compared to known energies and spins, mainly from the published data [2,7]. They are given in the first four columns.…”

“…The strong excitations in the (p,t)-reaction suggest that these states represent a collective excitation different from the β-vibration. Decay modes of the levels of the band on the first excited 0 + state in 228 Th have led to the suggestion that this band might predominantly have an octupole two-phonon structure [2]. One has to expect a complicated picture at higher excitations: residual interactions could mix the one-phonon and multiphonon vibrations of quadrupole and octupole character with each other and with quasiparticle excitations.…”