The magic nature of 132Sn explored through the single-particle states of 133Sn

Atomic nuclei have a shell structure where nuclei with 'magic numbers' of neutrons and protons are analogous to the noble gases in atomic physics. Only ten nuclei with the standard magic numbers of both neutrons and protons have so far been observed. The nuclear shell model is founded on the precept that neutrons and protons can move as independent particles in orbitals with discrete quantum numbers, subject to a mean field generated by all the other nucleons. Knowledge of the properties of single-particle states outside nuclear shell closures in exotic nuclei is important for a fundamental understanding of nuclear structure and nucleosynthesis (for example the r-process, which is responsible for the production of about half of the heavy elements). However, as a result of their short lifetimes, there is a paucity of knowledge about the nature of single-particle states outside exotic doubly magic nuclei. Here we measure the single-particle character of the levels in 133Sn that lie outside the double shell closure present at the short-lived nucleus 132Sn. We use an inverse kinematics technique that involves the transfer of a single nucleon to the nucleus. The purity of the measured single-particle states clearly illustrates the magic nature of 132Sn.Comment: 19 pages, 5 figures and 4 table

Elastic scattering of the proton drip-line nucleus F-17

Journals published by the American Physical Society can be found at http://publish.aps.org/Precision data have been obtained for the elastic scattering of F-17 on C-12 and N-14 at 10 MeV/nucleon to clarify the reaction mechanism for loosely bound nuclei at low energies and to assess the validity of a double-folding procedure to predict optical model potentials for use in indirect methods for nuclear astrophysics. The double-folding procedure incorporates density and energy-dependent effective nucleon-nucleon interactions with realistic densities consistent with experimentally determined asymptotic normalization coefficients. The derived potentials provide an excellent description of the data and point to a complete dominance of absorption at the barrier. A semiclassical analysis in terms of multireflection barrier-internal barrier series expansion of the scattering amplitude shows that only the barrier component survives in the scattering process, pointing to the peripheral character of the reactions

New Ne-19 resonance observed using an exotic F-18 beam

The rates of the F-18(p, alpha)O-15 and F-18(p, gamma) Ne-19 reactions in astrophysical environments depend on the properties of Ne-19 levels above the F-18 + p threshold. There are at least 8 levels in the mirror nucleus F-19 for which analogs have not been observed in Ne-19 in the excitation energy range E-x = 6.4-7.6 MeV. We have made a search for these levels by measuring the H-1(F-18, p)F-18 excitation function over the energy range Ec.m. = 0.3-1.3 MeV. We have identified and measured the properties of a newly observed level at E, = 7.420 +/- 0.014 MeV, which is most likely the mirror to the J(pi) = 7/2(+) F-19 level at 7.56 MeV. This new level is found to increase the calculated F-18(p,alpha)O-15 reaction rate by 16%, 63%, and 106% at T = 1,2, and 3 GK, respectively

Search for astrophysically important Ne-19 levels with a thick-target F-18(p,p)F-18 measurement

The rates of the F-18(p, alpha) O-15 and F-18(p, gamma) Ne-19 reactions in astrophysical environments depend on the properties of Ne-19 levels above the F-18+p threshold. There are at least eight levels in the mirror nucleus F-19 for which analogs have not been observed in Ne-19 in the excitation energy range E-x=6.4-7.6 MeV. These levels may significantly enhance the F-18+p reaction rates, and thus we have made a search for these levels by measuring the H-1(F-18,p) F-18 excitation function over the energy range E-c.m.=0.3-1.3 MeV. We have identified and measured the properties of a newly observed level at E-x=7.420 +/- 0.014 MeV, which is most likely the mirror to the J(pi) = 7/2 + F-19 level at 7.56 MeV. We have additionally found a significant discrepancy with a recent compilation for the properties of a Ne-19 state at E-x=7.5 MeV and set upper limits on the proton widths of missing levels

New Ne-19 level observed with a thick target F-18(p,p)F-18 measurement

The rates of the F-18 (p, alpha)O-15 and F-18(p, gamma)Ne-19 reactions in astrophysical environments depend on the properties of Ne-19 levels above the F-18 + p threshold. There are at least 8 levels in the mirror nucleus F-19 for which analogs have not been observed in Ne-19 in the excitation energy range E-x = 6.4 - 7.6 MeV. These levels may significantly enhance the F-18 + p reaction rates, and thus we have made a search for these levels by measuring the H-1(F-18,p)F-18 excitation function over the energy range E-c.m. = 0.3 - 1.3 MeV. We have identified and measured the properties of a newly observed level at E-x = 7.420 +/- 0.014 MeV. which is most likely the mirror to the J(pi) = (7)/(+)(2) F-19 level at 7.56 MeV. We have additionally found a significant discrepancy with a recent compilation for the properties of a Ne-19 state at E-x = 7.5 MeV and set upper limits on the proton widths of missing levels

New constraints on the F-18(p, alpha)O-15 rate in novae from the (d, p) reaction

The degree to which the (p, gamma) and (p, alpha) reactions destroy F-18 at temperatures (1-4) x 10(8) K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide F-18, a target of gamma-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the F-18+p threshold (E-x = 6.411 MeV in Ne-19). To gain further information about these resonances, we used a radioactive F-18 beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in F-19 via the inverse H-2((18)p)F-19 neutron transfer reaction. Neutron spectroscopic factors were measured for states in F-19 in the excitation energy range 0-9 MeV. Widths for corresponding proton resonances in Ne-19 were calculated using a Woods-Saxon potential. The results imply significantly lower F-18(p, gamma)Ne-19 and F-18(p, alpha)O-15 reaction rates than reported previously, thereby increasing the prospect of observing the 511 keV annihilation radiation associated with the decay of F-18 in the ashes ejected from novae

New limits for the F-18(p,alpha)O-15 rate in Novae

The degree to which the (p, gamma) and (p, alpha) reactions destroy F-18 at temperatures similar to 14x10(8) K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide F-18, a target of gamma ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the F-18+p threshold (E-x=6.411 MeV in Ne-19). To gain further information about these resonances, we have used the d (F-18,p)F-19 neutron transfer reaction to selectively populate corresponding mirror states in F-19. The results would suggest F-18(p, gamma)Ne-19 and F-18(p, alpha)O-15 reaction rates that are 2-3 times lower than reported previously

Resonances in C-11 observed in the He-4(Be-7, alpha)Be-7 and He-4(Be-7, p)B-10 reactions

Measurements of the He-4(Be-7, alpha)Be-7 and He-4(Be-7, p)B-10 reactions were performed using Be-7 beam energies of 7.1 and 23 MeV and a helium-4 target, employing the thick target technique. Resonances were observed between E-x(C-11) = 8.6 to 13.8 MeV. An R-matrix analysis was performed to characterize the spins and partial widths. This analysis showed that the observed sequence of states was consistent with that found for Li-7 + alpha resonant scattering populating resonances in B-11. A comparison of the proposed partial widths for decay with the Wigner limit indicates that several of the states are associated with cluster-like structures.status: publishe