Intruder bands and configuration mixing in the lead isotopes

A three-configuration mixing calculation is performed in the context of the interacting boson model with the aim to describe recently observed collective bands built on low-lying $0^+$ states in neutron-deficient lead isotopes. The configurations that are included correspond to the regular, spherical states as well as two-particle two-hole and four-particle four-hole excitations across the Z=82 shell gap.Comment: 20 pages, 4 figures, accepted by PRC, reference added for section 1 in this revised versio

Collectivity and Configuration Mixing in \u3csup\u3e186,188\u3c/sup\u3ePb and \u3csup\u3e194\u3c/sup\u3ePo

Lifetimes of prolate intruder states in 186Pb and oblate intruder states in 194Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in 188Pb up to the 8+state were carried out using the recoil-gating method. The B(E2) values have been deduced from which deformation parameters lβ2l = 0.29(5) and lβ2l = 0.17(3) for the prolate and the oblate bands, respectively, have been extracted. The results also shed new light on the mixing between different shapes

Collectivity and configuration mixing in 186,188Pb and 194Po

Lifetimes of prolate intruder states in 186Pb and oblate intruder states in 194Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in 188Pb up to the 8+ state were carried out using the recoil-gating method. The B(E2) values have been deduced from which deformation parameters |β2|=0.29(5) and |β2|=0.17(3) for the prolate and the oblate bands, respectively, have been extracted. The results also shed new light on the mixing between different shapes

Lifetimes of intruder states in 186 Pb, 188 Pb and 194 Po

Lifetimes of prolate intruder states in 186Pb and 188Pb and oblate intruder states in 194Po have been determined through recoil distance Doppler-shift lifetime measurements. Deformation parameters of | β2 | = 0.29 (5) and | β2 | = 0.17(3) have been ext

Identification of yrast states in 187Pb

g -ray spectroscopy of the high-spin states of the neutron-deficient nucleus 187Pb has been conducted with the 155Gd(36Ar,4n) reaction. A cascade of three transitions was deduced from g -g coincidence data gated by detection of recoiling evaporation residues in a gas-filled recoil separator. In an earlier, separate experiment, two of these g rays were positively identified with 187Pb by recoil-g coincidence measurements with a high-resolution, recoil mass spectrometer. From comparison with similar sequences in heavier odd-A lead isotopes, the cascade in 187Pb is associated with the sequence of three E2 transitions from the yrast 25/2 + level to a low-lying 13/2 + isomer. The variation of excitation energy with mass number of the levels concerned suggests that their structure can be associated with weak coupling of an odd i13/2 neutron to states in the spherical well. However, the possibility that they are influenced by mixing with states in the prolate-deformed well cannot be discounted

Structure of the Odd-A, Shell-stabilized nucleus No102253

In-beam γ-ray spectroscopic measurements have been made on No102253. A single rotational band was identified up to a probable spin of 39/2, which is assigned to the 7/2+[624] Nilsson configuration. The bandhead energy and the moment of inertia provide discriminating tests of contemporary models of the heaviest nuclei. Novel methods were required to interprete the sparse data set associated with cross sections of around 50nb. These methods included comparisons of experimental and simulated spectra, as well as testing for evidence of a rotational band in the γγ matrix

Investigations into the alpha-decay of \chem{^{195}At}

The low-energy nuclear structure and decay properties of the neutron-deficient isotopes $^{195}$At and $^{191}$Bi have been studied. $^{195}$At was produced in the reaction $^{142}$Nd($^{56}$Fe,p2n)$^{195}$At and $^{191}$Bi as the daughter activity of $^{195}$At. The activities were implanted in a position-sensitive silicon detector after being separated from the primary beam by a gas-filled recoil separator. The 1/2$^+$ intruder state was determined to be the ground state in $^{195}$At with an alpha-decay energy of $E_{\alpha}=6953(3)$ keV and a half-life $T_{1/2}=328(20)$ ms. Another state with an alpha-decay energy $E_{\alpha}=7075(4)$ keV and a half-life $T_{1/2}=147(5)$ ms was found to decay to a 148.7(5) keV excited state in $^{191}$Bi for which a spin and parity of 7/2$^-$ were deduced. Consequently, the same 7/2$^-$ character was assigned to the initial state at 32(7) keV in $^{195}$At on the basis of unhindered alpha-decay. The 9/2$^-$ state, being the ground state in heavier odd-mass astatine isotopes, was not observed