The neutron-rich nucleus 144 Ba (t 1/2 =11.5 s) is expected to exhibit some of the strongest octupole correlations among nuclei with mass numbers A less than 200. Until now, indirect evidence for such strong correlations has been inferred from observations such as enhanced E1 transitions and interleaving positive-and negative-parity levels in the ground-state band. In this experiment, the octupole strength was measured directly by sub-barrier, multi-step Coulomb excitation of a postaccelerated 650-MeV 144 Ba beam on a 1.0-mg/cm 2 208 Pb target. The measured value of the matrix element, 3 − 1 M(E3) 0 + 1 = 0.65( +17 −23 ) eb 3/2 , corresponds to a reduced B(E3) transition probability of 48( +25 −34 ) W.u. This result represents an unambiguous determination of the octupole collectivity, is larger than any available theoretical prediction, and is consistent with octupole deformation.

The 22 Ne(α, n) reaction is expected to provide the dominant neutron source for the weak s process in massive stars and intermediate-mass (IM) Asymptotic Giant Branch (AGB) stars. However, the production of neutrons in such environments is hindered by the competing 22 Ne(α, γ) 26 Mg reaction. Here, the 11 B(16 O,p) fusion-evaporation reaction was used to identify γ-decay transitions from 22 Ne + α resonant states in 26 Mg. Spin-parity restrictions have been placed on a number of α-unbound excited states in 26 Mg and their role in the 22 Ne(α, γ) 26 Mg reaction has been investigated. In particular, a suspected natural-parity resonance at E c.m. = 557(3) keV, that lies above the neutron threshold in 26 Mg, and is known to exhibit a strong α-cluster character, was observed to γ decay. Furthermore, a known resonance at E c.m. = 466(4) keV has been definitively assigned 2 + spin and parity. Consequently, uncertainties in the 22 Ne(α, γ) stellar reaction rate have been reduced by a factor of ∼ 20 for temperatures ∼ 0.2 GK.

Despite the more than one order of magnitude difference between the measured dipole moments in 144 Ba and 146 Ba, the strength of the octupole correlations in 146 Ba are found to be as strong as those in 144 Ba with a similarly large value of B(E3; 3 − → 0 + ) determined as 48( +21 −29 ) W.u. The new results not only establish unambiguously the presence of a region of octupole deformation centered on these neutron-rich Ba isotopes, but also manifest the dependence of the electric dipole moments on the occupancy of different neutron orbitals in nuclei with enhanced octupole strength, as revealed by fully microscopic calculations.

Superheavy elements are formed in fusion reactions which are hindered by fast nonequilibrium processes. To quantify these, mass-angle distributions and cross sections have been measured, at beam energies from below-barrier to 25% above, for the reactions of 48 Ca, 50 Ti, and 54 Cr with 208 Pb. Moving from 48 Ca to 54 Cr leads to a drastic fall in the symmetric fission yield, which is reflected in the measured massangle distribution by the presence of competing fast nonequilibrium deep inelastic and quasifission processes. These are responsible for reduction of the compound nucleus formation probablity P CN (as measured by the symmetric-peaked fission cross section), by a factor of 2.5 for 50 Ti and 15 for 54 Cr in comparison to 48 Ca. The energy dependence of P CN indicates that cold fusion reactions (involving 208 Pb) are not driven by a diffusion process.

We report the first observation of the 108 Xe → 104 Te → 100 Sn α-decay chain. The α emitters, 108 Xe [Eα = 4.4(2) MeV, T1 /2 = 58 +106 −23 µs] and 104 Te [Eα = 4.9(2) MeV, T1 /2 <18 ns], decaying into doubly magic 100 Sn were produced using a fusion-evaporation reaction 54 Fe(58 Ni,4n) 108 Xe, and identified with a recoil mass separator and an implantation-decay correlation technique. This is the first time α radioactivity has been observed to a heavy self-conjugate nucleus. A previous benchmark for study of this fundamental decay mode has been the decay of 212 Po into doubly magic 208 Pb. Enhanced proton-neutron interactions in the N = Z parent nuclei may result in superallowed α decays with reduced α-decay widths significantly greater than that for 212 Po. From the decay chain, we deduce that the α-reduced width for 108 Xe or 104 Te is more than a factor of 5 larger than that for 212 Po.