Search

The low-lying level structure of the unbound neutron-rich nucleus $^{13}$Be has been investigated via breakup on a carbon target of secondary beams of $^{14,15}$B at 35 MeV/nucleon. The coincident detection of the beam velocity $^{12}$Be fragments and neutrons permitted the invariant mass of the $^{12}$Be+$n$ and $^{12}$Be+$n$+$n$ systems to be reconstructed. In the case of the breakup of $^{15}$B, a very narrow structure at threshold was observed in the $^{12}$Be+$n$ channel. Contrary to earlier stable beam fragmentation studies which identified this as a strongly interacting $s$-wave virtual state in $^{13}$Be, analysis here of the $^{12}$Be+$n$+$n$ events demonstrated that this was an artifact resulting from the sequential-decay of the $^{14}$Be(2$^+$) state. Single-proton removal from $^{14}$B was found to populate a broad low-lying structure some 0.70 MeV above the neutron-decay threshold in addition to a less prominent feature at around 2.4 MeV. Based on the selectivity of the reaction and a comparison with (0-3)$\hbar\omega$ shell-model calculations, the low-lying structure is concluded to most probably arise from closely spaced J$^\pi$=1/2$^+$ and 5/2$^+$ resonances (E$_r$=0.40$\pm$0.03 and 0.85$^{+0.15}_{-0.11}$ MeV), whilst the broad higher-lying feature is a second 5/2$^+$ level (E$_r$=2.35$\pm$0.14 MeV). Taken in conjunction with earlier studies, it would appear that the lowest 1/2$^+$ and 1/2$^-$ levels lie relatively close together below 1 MeV., Comment: 14 pages, 13 figures, 2 tables. Accepted for publication in Physical Review C

The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of 132Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the cross section. The magnitude of the nuclear effects was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p1/2 state expected above the N=82 shell closure. The data were analyzed using finite range adiabatic wave calculations and the results compared with the previous analysis using the distorted wave Born approximation. Angular distributions for the ground and first excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one neutron states beyond the benchmark doubly-magic nucleus 208Pb., Comment: 22 pages, 7 figures

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., 19 pages, 5 figures and 4 tables

A measurement of the α(12C, α) 12C reaction has been performed using resonant scattering with a gas target. Beam energies of 46, 52, 56 and 63 MeV were used to populate resonances in the excitation energy range of 11.6–22.9 MeV in 16O. The angular distributions of the elastic scattering were measured at zero degrees, using an array of segmented silicon strip detectors with a minimum range of 0°–30° in the centre-of-mass. The spins of 8 resonances between 14.1 and 18.5 MeV were obtained, confirming spin assignments made using elastic scattering in normal kinematics. An R-matrix analysis of the data was performed which indicates that the present understanding of 16O in this region is good, but not complete.

The $^{12}\mathrm{C}$($^{16}\mathrm{O}$,$^{14}\mathrm{O}$)$^{14}\mathrm{C}$ reaction was studied at a beam energy of 234 MeV. The $^{14}\mathrm{O}$ ejectile was detected by a Q3D spectrometer at forward angles. The energies and angles of the excited $^{14}\mathrm{C}$ recoil break-up fragments were measured in coincidence with the $^{14}\mathrm{O}$ ejectile using a double sided silicon strip detector array at backward angles. A complete kinematic reconstruction of the reaction was performed to reconstruct the ${}^{14}{\mathrm{C}}^{*}\ensuremath{\rightarrow}{}^{10}\mathrm{Be}+\ensuremath{\alpha}$ and ${}^{14}{\mathrm{C}}^{*}\ensuremath{\rightarrow}{}^{13}\mathrm{C}+n$ decay channels and the branching ratios and widths of these decays were calculated. Theoretical decay branches were calculated using barrier penetrability factors and were compared to the measured ratios to provide information on the spins, parities, and configurations of the states. Neutron emission was found to be favored for the 11.73, 12.96, 14.87, 16.72, and 18.6 MeV states. The 14.87, 18.6, and 21.4 MeV states were found to have a considerable width for $\ensuremath{\alpha}$-decay and are candidates for the three bodied molecular cluster structure of $^{14}\mathrm{C}$.

A search has been made for the $^{6}\mathrm{He}+^{6}\mathrm{He}$ and \ensuremath{\alpha} + $^{8}\mathrm{He}$ decay of the molecular rotational band in $^{12}\mathrm{Be}$ using the $^{10}\mathrm{Be}$($^{14}\mathrm{C}$,$^{12}\mathrm{Be}$${}^{*}$)$^{12}\mathrm{C}$ reaction at 88.5 MeV. Although the \ensuremath{\alpha} + $^{6}\mathrm{He}$ decay of $^{10}\mathrm{Be}$ was observed in the data set there is no evidence for the breakup of $^{12}\mathrm{Be}$. The cross-section upper limits for the $^{10}\mathrm{Be}$($^{14}\mathrm{C}$,$^{6}\mathrm{He}$ $^{6}\mathrm{He}$)$^{12}\mathrm{C}$ and $^{10}\mathrm{Be}$($^{14}\mathrm{C}$,\ensuremath{\alpha} $^{8}\mathrm{He}$)$^{12}\mathrm{C}$ reactions are 50 and 300 nb respectively.

International audience; A search for the 2 + excitation of the Hoyle state in 12 C has been performed using the 12 C(12 C, 3α) 12 C reaction at a beam energy of 101.5 MeV. An angular correlation analysis was used to suppress known contributions to the excitation energy spectrum, enhancing the experimental sensitivity. No strong evidence was found for new states in 12 C between 9 and 11 MeV ; rather upper limits for their excitation in the 12 C+ 12 C inelastic scattering reaction are determined.

Various excited states in 14C, above the α-decay threshold, are believed to possess a geometric arrangement of three α-particles covalently bound by the two delocalised valence neutrons. The 12C(16O, 14O)14C* reaction was studied at a beam energy of 234 MeV, at the ISL facility at the Hahn-Meitner-Institut (HMI), Berlin. The 14O ejectile was detected by a Q3D spectrometer at forward angles. The energies and angles of the excited 14C recoil break-up fragments were measured in coincidence using a double sided silicon strip detector array comprised of four detectors at backwards angles. A complete kinematic reconstruction of the reaction was performed to reconstruct the 14C* → 10Be + α and 14C* → 13C + n decay channels and the branching ratios of these decays were calculated. Neutron emission was found to be favoured for the 12.96, 14.87, 16.72 and 18.6 MeV states. Evidence for α-decay was found for the 14.87, 18.6 and 21.4 MeV states; which are candidates for the three bodied molecular cluster structure of 14C.

A group of multifunctional surfactants was synthesized in order to arrive at materials which might function well in hard water. The salts of alkylaryl sulfopropionates, ; alkylaryl sulfonamides of taurine R-C6H4-SO2NHCH2CH2SO3Na; and the alkylaryl sulfonamide of aminoethylsulfuric acid R-C6H4-SO2NHCH2CH2OSO3Na were found to be quite effective. These compounds were synthesized via conventional routes and their biodegradability was established. These materials were formulated into the detergents with the aid of various organic and inorganic builders other than condensed phosphates. The detergency of these materials was evaluated with the aid of standard test cloths. Analogously formulated detergents based upon linear alkylbenzenesulfonate were also included for comparison in this evaluation study. It was found that a number of fairly satisfactory phosphate-free heavy duty detergent formulations could be developed.