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Type-I x-ray bursts can reveal the properties of an accreting neutron star system when compared with astrophysics model calculations. However, model results are sensitive to a handful of uncertain nuclear reaction rates, such as ^{22}Mg(α,p). We report the first direct measurement of ^{22}Mg(α,p), performed with the Active Target Time Projection Chamber. The corresponding astrophysical reaction rate is orders of magnitude larger than determined from a previous indirect measurement in a broad temperature range. Our new measurement suggests a less-compact neutron star in the source GS1826-24.

Carbon and oxygen burning reactions, in particular, $^{12}\mathrm{C}+^{12}\mathrm{C}$ fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$\ensuremath{\gamma}$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for $^{12}\mathrm{C}+^{12}\mathrm{C}$ fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed.

Carbon and oxygen burning reactions, in particular, $^{12}$C+$^{12}$C fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$\gamma$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for $^{12}$C+$^{12}$C fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed., Comment: accepted for publication in Phys. Rev. Lett

A cosmic-ray veto shield for the University of Notre Dame neutron wall has been constructed in order to carry out low-rate neutron time-of-flight (TOF) measurements. The veto detector employs plastic scintillator embedded with wavelength-shifting fibers and is read out by a versatile coupling to standard photomultiplier tubes (PMTs). This veto shield is effective at reducing the muon background by about one order of magnitude and therefore increases the sensitivity for experiments with low neutron yields. The 26Mg(3He,n)28Si reaction was used as a testbed for the veto.

We describe the design and operation of a detector system for measuring all-photon decays of mesons photoproduced in a tagged photon beam with energies between 4.3 and 5.4 GeV and a flux of 5×107 tagged photons per second. Photons from meson decays were detected with a lead-glass calorimeter with an energy resolution of 11% at 1 GeV. Various veto and trigger components were also present. Final states with as many as six photons were successfully detected and reconstructed.

A gamma-ray spectroscopy program has been established at the University of Notre Dame using a low-energy radioactive beam of 6 He for fusion–evaporation reactions. There are many experimental difficulties to overcome in the design of any such facility, most notably the large neutron flux associated with producing the secondary beam. Solutions to the problems are discussed and illustrated with the reaction 6 He + 63 Cu .

Many astrophysical events, such as novae and X-ray bursts, are powered by reactions with radioactive nuclei. Studying the properties of these nuclei in the laboratory can therefore further our understanding of these astrophysical explosions. The TwinSol separator at the University of Notre Dame has recently been used to produce intense (~106 pps) beams of 17F. In this article, some of the first measurements with these beams are discussed.

Isobaric analog states of $^{7}\mathrm{He}$ have been investigated by a novel technique involving the observation of the resonant yield of neutrons from the $^{6}\mathrm{He}(p,n)$ reaction in coincidence with $\ensuremath{\gamma}$ rays from the decay of the $({0}^{+},T=1)$ state in $^{6}\mathrm{Li}$. The $\ensuremath{\gamma}$ rays provide a clean signature for the isospin-conserving neutron decay of the low-lying isobaric analog resonances. It is conclusively shown that the analog of the recently observed low-lying spin-orbit partner of the $^{7}\mathrm{He}$ ground state does not exist. Evidence is presented that this state lies at much higher energies, in agreement with microscopic calculations.

The β‐delayed neutron decays of 17B and 19C were studied using radioactive ion beams. The neutron energies, measured via time‐of‐flight, give information on states above the neutron decay threshold in 17C and 19N, respectively. These low lying states are of possible interest for Big Bang nucleosynthesis.

Fusion-evaporation reactions induced by beams of 25--55-MeV /sup 15/N and /sup 18/O on an isotopically enriched /sup 48/Ca target have been used to populate high-spin yrast levels in /sup 59/ /sup 60/Fe and /sup 59/ /sup 60/Co. Measurements consisted of ..gamma..-ray excitation functions, angular distributions, ..gamma..-..gamma.. coincidences, and recoil-distance and Doppler-shift lifetime measurements, from which were deduced the energy levels, ..gamma..-ray branching ratios, most probable spin-parity assignments, and level lifetimes. The results of p-..gamma.. correlation measurements in the /sup 58/Fe(t,p..gamma..)/sup 60/Fe reaction are also reported.

Characteristic ..gamma.. radiation produced in the reaction /sup 7/Li(K/sup -/,..pi../sup -/..gamma..) at a kaon momentum of 1.7 GeV/c has been analyzed with Ge(Li) detectors. A transition at 789 +- 4 keV is a candidate for a new hypernuclear ..gamma..-ray line. The intensity of this transition corresponds to a c.m. forward-angle production cross section of 48 +- 12 ..mu..b for the reaction /sup 7/Li(K/sup -/,..pi../sup -/..gamma..). Several ..gamma..-ray lines observed with /sup 6/Li, Be, B, C, and O targets could be ascribed to ordinary nuclear transitions.

The 6 He+ 209 Bi reaction displays a remarkably large cross section for α -particle emission at energies near the Coulomb barrier. The possible reactions that may produce the observed α particles include two-neutron transfer, one-neutron transfer, and direct projectile breakup. Each of these mechanisms results in a distinctive angular correlation between the α particle and outgoing neutron(s). A neutron- α -particle coincidence experiment was performed to separate these different modes. The neutron data show significant angular correlations. Monte Carlo simulations of one-neutron transfer are compared with the experimental data. It is shown that approximately 20% of the observed α -particle yield is due to this process.

In-beam \ensuremath{\gamma}-rays from excited states of the neutron-rich (${T}_{z}$=3) nucleus $^{40}\mathrm{Cl}$ have been identified in a threefold coincidence experiment in which \ensuremath{\gamma} rays and light charged particles were observed. The resulting decay scheme is presented, and implications for the structure of low-lying levels in $^{40}\mathrm{Cl}$ are discussed in light of recent data from charge-exchange and \ensuremath{\beta}-decay work. The ordering of levels would seem to be quite different from the predictions of recent shell-model calculations.

Previous results for high-spin decay schemes in $^{38}\mathrm{Ar}$ and $^{39}\mathrm{K}$ obtained by the Brook-haven group from heavy-ion fusion-evaporation $\ensuremath{\gamma}$-ray spectroscopy are revised and some new results are given. In particular, guided by recently published particle-$\ensuremath{\gamma}$ coincidence measurements, we find that in both nuclei the time sequences of two $\ensuremath{\gamma}$ transitions in cascade were wrongly ordered. Thus, in $^{38}\mathrm{Ar}$ a 7609-keV level is replaced by a ${J}^{\ensuremath{\pi}}=({7}^{\ensuremath{-}})$ 8972-keV level, while in $^{39}\mathrm{K}$ a 4831-keV level is replaced by a 7142-keV level. In addition, new mean lives of 17 \ifmmode\pm\else\textpm\fi{} 3 and 20 \ifmmode\pm\else\textpm\fi{} 1.5 ps were extracted for the $^{39}\mathrm{K}$ 6476- and 8029-keV levels, respectively.NUCLEAR REACTIONS ($\mathrm{HI},xn,yp,z\ensuremath{\alpha}$) studies for $A\ensuremath{\sim}40$ nuclei, $^{14}\mathrm{N}$ projectile, $^{27}\mathrm{Al}$ target, $E=40$ MeV, measured $\ensuremath{\sigma}({E}_{\ensuremath{\gamma}},\ensuremath{\theta})$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ coin; deduced $^{38}\mathrm{Ar}$ and $^{39}\mathrm{K}$ levels; measured recoil distance; deduced ${\ensuremath{\tau}}_{m}$.