The 3He(4He,gamma) 7Be reaction plays an important role in determining the high energy solar neutrino flux and in understanding the abundances of primordial 7Li. This Letter reports a new precision measurement of the cross sections of this direct capture reaction, determined by measuring the ensuing 7Be activity in the region of Ec.m.=420 to 950 keV. Various recent theoretical fits to our data result in a consistent extrapolated value of S34(0)=0.53(2)(1) keV b.

We report on the g-factor measurement of the first isomeric state in (16)43S27 [Ex=320.5(5) keV, T1/2=415(5) ns, and g=0.317(4)]. The 7/2- spin-parity of the isomer and the intruder nature of the ground state of the nucleus are experimentally established for the first time, providing direct and unambiguous evidence of the collapse of the N=28 shell closure in neutron-rich nuclei. The shell model, beyond the mean-field and semiempirical calculations, provides a very consistent description of this nucleus showing that a well deformed prolate and quasispherical states coexist at low energy.

3The general phenomenon of shell structure in atomic nuclei has been understood since the pioneering work of Goeppert-Mayer, Haxel, Jensen and Suess [1].They realized that the experimental evidence for nuclear magic numbers could be explained by introducing a strong spin-orbit interaction in the nuclear shell model potential.However, our detailed knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), the unique nature of the atomic nucleus as an object composed of two distinct types of fermions can be expressed as enhanced correlations arising between neutrons and protons occupying orbitals with the same quantum numbers. Such correlations have been predicted to favor a new type of nuclear superfluidity; isoscalar neutron-proton pairing [2][3][4][5][6], in addition to normal isovector pairing (see Fig. 1). Despite many experimental efforts these predictions have not been confirmed. Here, we report on the first observation of excited states in N = Z = 46 nucleus 92 Pd. Gamma rays emitted following the 58 Ni( 36 Ar,2n) 92 Pd fusionevaporation reaction were identified using a combination of state-of-the-art highresolution -ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutronproton coupling scheme, different from the previous prediction [2][3][4][5][6]. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling [7,8]) in the ground and low-lying excited states of the heaviest N = Z nuclei. The strong isoscalar neutron-proton correlations in these N = Z nuclei are predicted to have a considerable impact on their level structures, and to influence the dynamics of the stellar rapid proton capture nucleosynthesis process.For all known nuclei, including those residing along the N = Z line up to around mass 80, a detailed analysis of their properties such as binding energies [9] and the spectroscopy of the excited states [10] strongly suggests that normal isovector (T = 1) pairing is dominant at low excitation energies. On the other hand, there are long standing predictions for a change in the heavier N = Z nuclei from a nuclear superfluid dominated by isovector pairing to a structure where isoscalar (T = 0) neutron-proton (np) pairing has a major influence as the mass number increases towards the exotic doubly magic nucleus 100 Sn [2-6], the heaviest N = Z nucleus to be bound. N = Z nuclei with mass number > 90 can only be produced in the laboratory with very low The two-neutron (2n) evaporation reaction channel following formation of the 94 Pd compound nucleus, leading to 92 Pd, was very weakly populated with a relative yield of less than 10 −5 of the total fusion cross section. Gamma rays from decays of excited states in 92 Pd were identified by comparing γ-ray spectra in coincidence with two emitted neutrons and no charged particles with γ-ray spectra in coincidence with oth...

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...

Excited states in 96 Ag were populated in fragmentation of an 850-MeV/u 124 Xe beam on a 4-g/cm 2 Be target. Three new high-spin isomers were identified and the structure of the populated states was investigated. The level scheme of 96 Ag was established, and a spin parity of (13 − ), (15 + ), and (19 + ) was assigned to the new isomeric states. Shell-model calculations were performed in various model spaces, including πν(p 1/2 , g 9/2 , f 5/2 , p 3/2 ) and the large-scale shell-model space πν(gds), to account for the observed parity changing M2 and E3 transitions from the (13 − ) isomer and the E2 and E4 transitions from the (19 + ) core-excited isomer, respectively. The calculated level schemes and reduced transition strengths are found to be in very good agreement with the experiment.