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.

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.

The 62Ni(n,gamma)63Ni(t(1/2)=100+/-2 yr) reaction plays an important role in the control of the flow path of the slow neutron-capture (s) nucleosynthesis process. We have measured for the first time the total cross section of this reaction for a quasi-Maxwellian (kT=25 keV) neutron flux. The measurement was performed by fast-neutron activation, combined with accelerator mass spectrometry to detect directly the 63Ni product nuclei. The experimental value of 28.4+/-2.8 mb, fairly consistent with a recent calculation, affects the calculated net yield of 62Ni itself and the whole distribution of nuclei with 62

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The 44 Ti(t 1/2 = 59 y) nuclide, an important signature of supernova nucleosynthesis, has recently been observed as live radioactivity by γ-ray astronomy from the Cas A remnant. We investigate in the laboratory the major 44 Ti production reaction, 40 Ca(α, γ) 44 Ti (Ecm ∼ 0.6-1.2 MeV/u), by direct off-line counting of 44 Ti nuclei. The yield, significantly higher than inferred from previous experiments, is analyzed in terms of a statistical model using microscopic nuclear inputs. The associated stellar rate has important astrophysical consequences, increasing the calculated supernova 44 Ti yield by a factor ∼ 2 over previous estimates and bringing it closer to Cas A observations. PACS numbers: 26.30.+k,97.60.Bw,95.85.Pw,24.60Dr The radionuclide 44 Ti(t 1/2 = 59 y) is considered an important signature of explosive nucleosynthesis in corecollapse supernovae (SN) [1], where multiple α capture is the path for SN nucleosynthesis from 28 Si to 56 Ni(Fe). 44 Ti is mainly produced during an α-rich freeze-out phase, the ratio 44 Ti/ 56 Ni being sensitive to the explosion conditions. Stellar production of 44 Ti determines the abundance of stable 44 Ca and contributes to that of 48 Ti (fed by 48 Cr on the α-chain). Live 44 Ti has been directly observed from a point source identified as Cassiopeia A (Cas A) by γ-and X-ray telescopes (CGRO, RXTE, BeppoSAX) and very recently by the INTEGRAL mission (see [2,3]). Cas A is believed to be the remnant of a core-collapse SN whose progenitor mass was in the range 22-25 M ⊙ (M ⊙ denotes a solar mass) [4]. Using known values of the distance and age of the remnant, half-life of 44 Ti and the combined γ flux from all observations, an initial 44 Ti yield of 160± 60 µM ⊙ is implied [3]. This value is larger by a factor of 2-10 than 44 Ti yields calculated in current models (e.g. [5,6]) and various explanations have been proposed [4,7,8,9]. 44 Ti γ-ray emission from SN1987A in the near Large Magellanic Cloud galaxy, the closest known SN remnant in the last two centuries, is below detection limits. But its present lightcurve is believed to be powered by 44 Ti radioactivity and the inferred initial 44 Ti yield is estimated to be 100-200 µM ⊙ (see [2]), similar to that of Cas A. Using the 56 Ni yield of SN1987A directly measured by γ-ray astronomy, the implied 44 Ti/ 56 Ni ratio is larger by * To whom correspondence should be addressed, email address: paul@vms.huji.ac.il a factor ∼3 than estimated by stellar calculations [2]. No other source of 44 Ti activity has been confirmed so far, despite a number of candidates and the improved sensitivity of the INTEGRAL γ-ray telescope [2]. Although many nuclear reactions play roles in determining the SN yield of 44 Ti [9, 10], the major production reaction is 40 Ca(α, γ) 44 Ti and its importance has been emphasized [11]. Experimental information about this reaction is incomplete and theoretical estimates are made less reliable by the suppression of dipolar T = 0 → 0 transitions in selfconjugate (N =Z) nuclei. The reaction was studied in the 70's b...