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

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 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 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

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

Neutron-hole states in 131Sn and spin-orbit splitting in neutron-rich nuclei

In atomic nuclei, the spin-orbit interaction originates from the coupling of the orbital motion of a nucleon with its intrinsic spin. Recent experimental and theoretical works have suggested a weakening of the spin-orbit interaction in neutron-rich nuclei far from stability. To study this phenomenon, we have investigated the spin-orbit energy splittings of single-hole and single-particle valence neutron orbits of 132Sn. The spectroscopic strength of single-hole states in 131Sn was determined from the measured differential cross sections of the tritons from the neutron-removing 132Sn(d,t)131Sn reaction, which was studied in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spectroscopic factors of the lowest 3=2+, 1=2+ and 5=2+states were found to be (2 j+1), confirming the robust N = 82 shell closure at 132Sn. We compared the spin-orbit splitting of neutron single-hole states in 131Sn to those of single-particle states in 133Sn determined in a recent measurement of the 132Sn(d,p)133Sn reaction. We found a significant reduction of the energy splitting of the weakly bound 3p orbits compared to the well-bound 2d orbits, and that all the observed energy splittings can be reproduced remarkably well by calculations using a onebody spin-orbit interaction and a Woods-Saxon potential of standard radius and diffuseness. The observed reduction of spin-orbit splitting can be explained by the extended radial wavefunctions of the weakly bound orbits, without invoking a weakening of the spin-orbit strength

The F-17(p, gamma)Ne-18 direct capture cross section

The F-17(p, gamma) Ne-18 direct capture cross section is important for understanding nucleosynthesis in novae. We have measured cross sections for the proton-transfer reaction N-14 (F-17, Ne-18) C-13 in order to determine asymptotic normalization coefficients for the F-17 + p system and hence the F-17(p, gamma) Ne-18 direct capture cross section. The technique and preliminary results are presented