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Precise mass measurements of nuclei along the N = Z line are important input parameters for simulations of the rp-process. Of particular interest is the mass of the 6834Se34 rp-process waiting point nucleus for determining the possibility of a two-proton capture branch bypassing its slow β-decay. The mass of 68Se was measured via the β-decay endpoint. 68Se was produced by the 12C(58Ni, 2n)68Se reaction and subsequently implanted onto a moving tape system using the fragment mass analyzer at the ATLAS facility of Argonne National Laboratory. A mass excess value of ( − 54189 ± 240 ) keV was determined from the β-endpoint measurement of Q EC = 4710 ( 200 ) keV . Evaluations of proton separation energies based on the measured mass were used in a one zone type I X-ray burst model. It is concluded that the N = Z = 34 isotope 68Se is a waiting point for the rp-process.

The fusion–evaporation reaction 10 B( 12 C, 2 n ) was used to make the first observation of in-beam γ decays from the astrophysically important nucleus 20 Na, lying adjacent to the proton drip-line. All states below the proton threshold in 20 Na were populated and identified in the experiment. These include new levels, previously unresolved levels, and states located with improved energy precision. The level structure of 20 Na, and its γ transitions, are compared to the mirror partner 20 F measured simultaneously in this experiment. In particular, a high degree of energy stability is found for all negative parity states. These results are discussed in the context of the nuclear shell model.

A Gas–Si–CsI hybrid detector telescope is described and its performance assessed in measuring breakup reactions leading to particle unbound states. The telescope consists of an ionisation chamber, a silicon strip detector and a CsI(Tl) scintillator-photodiode detector. The segmentation of the strip detector allows the simultaneous detection, identification and reconstruction of heavy and light ions within a single hybrid telescope. For double hits in the strip detector, crosstalk between the two active strips modifies the measured energies requiring a correction to the energy calibrations. The technique has been extended to the detection of energetic α-particles from the decay of 8 Be gs fragments. Using two telescopes, a measurement of the 12 C ( 24 Mg , 16 O 12 C α ) α reaction at 170 MeV has identified final states where the 12 C ion and α-particle originate from unbound states in 16 O. The sensitivity to small relative energies between the fragments makes the telescope particularly suitable for the study of near-threshold states of astrophysical interest.

The p(11Be,10Be)d reaction has been studied using a radioactive 11Be beam of 35.3 MeV/nucleon. Differential cross sections have been compared with Distorted Wave Born Approximation calculations, using bound state form factors determined by solving the particle-vibration coupling equations. Calculated cross sections corresponding to a 16% core excitation admixture in the 11Begs wave function are in good agreement with the present data.

The population and decay of excited states in ${}^{24}\mathrm{Mg}$ has been investigated through the ${}^{12}{\mathrm{C}(}^{16}{\mathrm{O},}^{12}{\mathrm{C}}^{12}\mathrm{C})\ensuremath{\alpha}$ and ${}^{12}{\mathrm{C}(}^{16}{\mathrm{O},}^{8}{\mathrm{Be}}^{16}\mathrm{O})\mathrm{\ensuremath{\alpha}}$ reactions, at beam energies of 75, 85, and 115 MeV. The fragments from the breakup of the ${}^{24}\mathrm{Mg}$ nucleus were detected in coincidence, permitting a study of both the excitation energies and the spins of the fissioning states. These measurements indicate a series of states in ${}^{24}\mathrm{Mg}$ between 20 and 40 MeV with spins ranging from $J=4$ to 14 $\ensuremath{\Elzxh}$. The results are discussed in the context of the ${}^{12}{\mathrm{C}+}^{12}\mathrm{C}$ quasimolecular scattering resonances and other ${}^{24}\mathrm{Mg}$ breakup reactions.

We have performed the Be reaction in inverse kinematics. The were detected in the SPEG spectrometer and the deuterons detected in a silicon array in coincidence. The yield to the first excited state of is greater than that to the ground state, and increases with angle. Strong population of the two-alpha plus two-neutron states near 6 MeV (in the two-centre shell-model description) is observed. The ultimate goal is to study the microscopic structure of from the extracted spectroscopic factors.

A study of high energy (43--68 MeV/nucleon) one-neutron removal reactions on a range of neutron-rich psd-shell nuclei (Z = 5--9, A = 12--25) has been undertaken. The inclusive longitudinal and transverse momentum distributions for the core fragments, together with the cross sections have been measured for breakup on a carbon target. Momentum distributions for reactions on tantalum were also measured for a subset of nuclei. An extended version of the Glauber model incorporating second order noneikonal corrections to the JLM parametrisation of the optical potential has been used to describe the nuclear breakup, whilst the Coulomb dissociation is treated within first order perturbation theory. The projectile structure has been taken into account via shell model calculations employing the psd-interaction of Warburton and Brown. Both the longitudinal and transverse momentum distributions, together with the integrated cross sections were well reproduced by these calculations and spin-parity assignments are thus proposed for $^{15}$B, $^{17}$C, $^{19-21}$N, $^{21,23}$O, $^{23-25}$F. In addition to the large spectroscopic amplitudes for the $\nu2$s$_{1/2}$ intruder configuration in the N=9 isotones,$^{14}$B and $^{15}$C, significant $\nu2$s$_{1/2}^2$ admixtures appear to occur in the ground state of the neighbouring N=10 nuclei $^{15}$B and $^{16}$C. Similarly, crossing the N=14 subshell, the occupation of the $\nu2$s$_{1/2}$ orbital is observed for $^{23}$O, $^{24,25}$F. Analysis of the longitudinal and transverse momentum distributions reveals that both carry spectroscopic information, often of a complementary nature. The general utility of high energy nucleon removal reactions as a spectroscopic tool is also examined., 50 pages, 19 figures, submitted to Phys. Rev. C

Lifetimes of the first ${4}^{+}$ and ${6}^{+}$ states in ${}^{104}\mathrm{Mo}$ and ${}^{106}\mathrm{Mo}$ have been measured using the recoil distance method following spontaneous fission of ${}^{252}\mathrm{Cf}.$ The experiment was performed at the 88-inch cyclotron of the Lawrence Berkeley National Laboratory employing the Gammasphere array and the New Yale Plunger Device. Reduced transition probabilities in the ground state band of ${}^{104}\mathrm{Mo}$ are compared with predictions of the critical point symmetry X(5) for phase transitional nuclei between rotational and vibrational shape. While known level energies of ${}^{104}\mathrm{Mo}$ are in good agreement with the X(5) predictions, the analysis of the measured $B(E2)$ values favors a rotor interpretation.

The Qec value for 80Y has been measured by beta-gamma coincidence spectroscopy. Combining this result with the adopted mass excess of the daughter 80Sr gives a mass excess of >-61376(83) keV. Results are compared with other measurements and predictions of mass formulas. Implications of this measurement are considered for the rp-process.

In order to search for a proposed α:2n:α:2n:α molecular structure in 16C its break-up into 10Be + 6He, 12Be + α, 8He + 2α and 6He + 6He + α has been studied using a 560 MeV 16C beam inelastically excited on a 12C target. States in 16C appear to be only weakly populated in this reaction.

A measurement of the ${}^{12}\mathrm{C}{+}^{16}\mathrm{O}$ breakup of ${}^{28}\mathrm{Si}$ following ${}^{24}\mathrm{Mg}$ scattering from targets of carbon, lithium oxide, and beryllium has been performed. A study of the relative energy of the correlated ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ fragments has allowed the excitation energy of states in ${}^{28}\mathrm{Si}$ to be determined. A comparison of the excitation energy spectra in ${}^{28}\mathrm{Si}$ obtained from the three targets indicates that the same states are populated in the ${}^{12}\mathrm{C}{(}^{24}\mathrm{Mg}{,}^{12}{\mathrm{C}}^{16}\mathrm{O}{)}^{8}\mathrm{Be},$ ${}^{7}\mathrm{Li}{(}^{24}\mathrm{Mg}{,}^{12}{\mathrm{C}}^{16}\mathrm{O})t,$ and ${}^{9}\mathrm{Be}{(}^{24}\mathrm{Mg}{,}^{12}{\mathrm{C}}^{16}\mathrm{O}{)}^{5}\mathrm{He}$ reactions. The data support the hypothesis that the reaction mechanism populating the ${}^{12}\mathrm{C}{+}^{16}\mathrm{O}$ breakup states observed in these channels is $\ensuremath{\alpha}$ transfer, and rule out an alternative involving resonant, or ``doorway,'' states in the ${}^{12}\mathrm{C}{+}^{24}\mathrm{Mg}$ compound system.

A systematic study of high energy, one-neutron removal reactions on 23 neutron-rich, psd--shell nuclei (Z=5-9, A=12-25) has been carried out. The longitudinal momentum distributions of the core fragments and corresponding single-neutron removal cross sections are reported for reactions on a carbon target. Extended Glauber model calculations, weighted by the spectroscopic factors obtained from shell model calculations, are compared to the experimental results. Conclusions are drawn regarding the use of such reactions as a spectroscopic tool and spin-parity assignments are proposed for 15B, 17C, 19-21N, 21,23O, 23-25F. The nature of the weakly bound systems 14B and 15,17C is discussed., Comment: 11 pages + 2 figures

The reaction 11Be(p,d)10Be has been studied for the first time, using a secondary 11Be beam of 35.3 MeV/nucleon. Angular distributions up to about 15cmo were measured by detecting 10Be in a spectrometer and coincident deuterons in a position sensitive silicon detector array. Preliminary analysis provides evidence for a large core excitation component in the structure of 11BeGS.