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A high-count-rate ionization chamber design with position-sensitivity has been developed and deployed at several accelerator facilities. Counting rates of ≥ 500 kHz with good Z -separation (up to 5% energy resolution) for particle identification have been demonstrated in a series of commissioning experiments. A position-sensitive capability, with a resolution of 3 mm, has been implemented for the first time to record position information and suppress pileup. The design and performance of the detectors are described.

Results are presented from the first neutron-transfer measurement on $^{80}\mathrm{Ge}$ using an exotic beam from the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Newly measured spins and spectroscopic factors of low-lying states of $^{81}\mathrm{Ge}$ are determined, and the neutron capture cross section on $^{80}\mathrm{Ge}$ was calculated in a direct-semidirect model to provide a more realistic ($n,\ensuremath{\gamma}$) reaction rate for $r$-process simulations. Furthermore, a region of shape coexistence around $N\ensuremath{\approx}50$ is confirmed and implications for the magic nature of $^{78}\mathrm{Ni}$ are discussed.

The $^{15}$O($\alpha$,$\gamma$)$^{19}$Ne reaction is responsible for breakout from the hot CNO cycle in Type I x-ray bursts. Understanding the properties of resonances between $E_x = 4$ and 5 MeV in $^{19}$Ne is crucial in the calculation of this reaction rate. The spins and parities of these states are well known, with the exception of the 4.14- and 4.20-MeV states, which have adopted spin-parities of 9/2$^-$ and 7/2$^-$, respectively. Gamma-ray transitions from these states were studied using triton-$\gamma$-$\gamma$ coincidences from the $^{19}$F($^{3}$He,$t\gamma$)$^{19}$Ne reaction measured with GODDESS (Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies) at Argonne National Laboratory. The observed transitions from the 4.14- and 4.20-MeV states provide strong evidence that the $J^\pi$ values are actually 7/2$^-$ and 9/2$^-$, respectively. These assignments are consistent with the values in the $^{19}$F mirror nucleus and in contrast to previously accepted assignments.

GODDESS is a coupling of the charged-particle detection system ORRUBA to the gamma-ray detector array Gammasphere. This coupling has been developed in order to facilitate the high-resolution measurement of direct reactions in normal and inverse kinematics with stable and radioactive beams. GODDESS has been commissioned using a beam of 134 Xe at 10 MeV/A, in a campaign of stable beam measurements. The measurement demonstrates the capabilities of GODDESS under radioactive beam conditions, and provides the first data on the single-neutron states in 135 Xe, including previously unobserved states based on the orbitals above the N=82 shell closure.

The design and performance of the Modular Total Absorption Spectrometer built and commissioned at the Oak Ridge National Laboratory is presented. The active volume of the detector is approximately one ton of NaI(Tl), which results in very high full γ energy peak efficiency of 71% at 6 MeV and nearly flat efficiency of around 81.5% for low energy γ -rays between 300 keV and 1 MeV. In addition to the high peak efficiency, the modular construction of the detector permits the use of a γ -coincidence technique in data analysis as well as β -delayed neutron observation.

Spectroscopic data, such as precise γ-ray branching and E2/M1 multipole-mixing ratios, provide vital constraints when performing multi-dimensional Coulomb-excitation analyses. Consequently, as part of our new Coulomb-excitation campaign aimed at investigating the role of exotic non-axial (triaxial) deformations in the unstable refractory Ru-Mo isotopes, additional beta-decay data was obtained. These measurements make use of ANL’s CARIBU facility, which provides intense beams of radioactive refractory isotopes along with the excellent efficiency and angular resolution of the GRETINA γ-ray tracking array. In this article, we report on the analysis of the A = 110 decay chain, focussing on the identification of previously unreported states in 110Ru following the decay of 110Tc.

A direct test of nova explosion models comes from the observation of γ rays created in the decay of radioactive isotopes produced in the nova. One such isotope, 18F, is believed to be the main source of observable γ rays at and below 511 keV. The main destruction mechanism of 18F is thought to be the 18F(p,α)15O reaction, and uncertainties in the reaction rate arise from uncertainties in the energies, spins, and parities of the nuclear levels in 19Ne above the 18F+p threshold. To measure the properties of these levels, the 19F(3He,t)19Ne∗(γ) reaction was studied at Argonne National Laboratory and the Nuclear Science Laboratory at the University of Notre Dame.A direct test of nova explosion models comes from the observation of γ rays created in the decay of radioactive isotopes produced in the nova. One such isotope, 18F, is believed to be the main source of observable γ rays at and below 511 keV. The main destruction mechanism of 18F is thought to be the 18F(p,α)15O reaction, and uncertainties in the reaction rate arise from uncertainties in the energies, spins, and parities of the nuclear levels in 19Ne above the 18F+p threshold. To measure the properties of these levels, the 19F(3He,t)19Ne∗(γ) reaction was studied at Argonne National Laboratory and the Nuclear Science Laboratory at the University of Notre Dame.

A new detector array, the Modular Total Absorption Spectrometer (MTAS), was commissioned at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL). Total absorption gamma spectra measured with MTAS are expected to improve beta-feeding patterns and beta strength functions in fission products. MTAS is constructed out of hexagonal NaI(Tl) detectors with a unique central module surrounded by 18 identical crystals assembled in three rings. The total NaI(Tl) mass of MTAS is over 1000 kg. The response of the central and other 18 MTAS modules to γ-radiation was simulated using the GEANT4 toolkit modified to analyze the nonlinear light output of NaI(Tl). A detailed description of the GEANT4 modifications made is discussed. Simulated energy resolution of MTAS modules is found to agree well with the measurements for single γ transitions of 662 keV (137Cs) with 8.2% full width half maximum (FWHM), 835 keV (54Mn) with FWHM of 7.5% FWHM, and 1115 keV (65Zn) with FWHM of 6.5%. Simulations of single and multiple γ-rays from 60Co are also discussed.

A new detection system has been installed at the RIKEN Nishina Center (Japan) to investigate decay properties of very neutron-rich nuclei. The setup consists of three main parts: a moderated neutron counter , a detection system sensitive to the implantation and decay of radioactive ions, and γ -ray detectors. We describe here the setup, the commissioning experiment and some selected results demonstrating its performance for the measurement of half-lives and β -delayed neutron emission probabilities. The methodology followed in the analysis of the data is described in detail. Particular emphasis is placed on the correction of the accidental neutron background.

Background: The $^{31}\mathrm{S}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction becomes important for sulfur production in novae if the $^{31}\mathrm{P}(p,\ensuremath{\alpha})^{28}\mathrm{Si}$ reaction rate is somewhat greater than currently accepted. The rate of the $^{31}\mathrm{S}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction is uncertain, primarily due to the properties of resonances at ${E}_{\mathrm{c}.\mathrm{m}.}=156$ and 549 keV.Purpose: We precisely determined the excitation energies of states in $^{32}\mathrm{Cl}$ through high-resolution $\ensuremath{\gamma}$ spectroscopy including the two states most important for the $^{31}\mathrm{S}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction at nova temperatures.Method: Excited states in $^{32}\mathrm{Cl}$ were populated using the $^{10}\mathrm{B}(^{24}\mathrm{Mg},2n)\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction with a $^{24}\mathrm{Mg}$ beam from the ATLAS facility at Argonne National Laboratory. The reaction channel of interest was selected using recoils in the Fragment Mass Analyzer, and precise level energies were determined by detecting $\ensuremath{\gamma}$ rays with Gammasphere.Results: We observed $\ensuremath{\gamma}$ rays from the decay of six excited states in $^{32}\mathrm{Cl}$. The excitation energies for two unbound levels at ${E}_{x}=1738.1$ (6) keV and 2130.5 (10) keV were determined and found to be in agreement with a previous high-precision measurement of the $^{32}\mathrm{S}(^{3}\mathrm{He},t)^{32}\mathrm{Cl}$ reaction [1].Conclusions: An updated $^{31}\mathrm{S}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{Cl}$ reaction rate is presented. With the excitation energies of important levels firmly established, the dominant uncertainty in the reaction rate at nova temperatures is due to the strength of the resonance corresponding to the 2131-keV state in $^{32}\mathrm{Cl}$.

Background: An assessment done under the auspices of the Nuclear Energy Agency in 2007 suggested that the $\ensuremath{\beta}$ decays of abundant fission products in nuclear reactors may be incomplete. Many of the nuclei are potentially affected by the so called pandemonium effect and their $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ decay heat should be restudied using the total absorption technique. The fission products $^{137}\mathrm{I}$ and $^{137}\mathrm{Xe}$ were assigned highest priority for restudy due to their large cumulative fission branching fractions. In addition, measuring $\ensuremath{\beta}$-delayed neutron emission probabilities is challenging and any new technique for measuring the $\ensuremath{\beta}$-neutron spectrum and the $\ensuremath{\beta}$-delayed neutron emission probabilities is an important addition to nuclear physics experimental techniques.Purpose: To obtain the complete $\ensuremath{\beta}$-decay pattern of $^{137}\mathrm{I}$ and $^{137}\mathrm{Xe}$ and determine their consequences for reactor decay heat and ${\overline{\ensuremath{\nu}}}_{e}$ emission. Complete $\ensuremath{\beta}$-decay feeding includes ground state to ground state $\ensuremath{\beta}$ feeding with no associated $\ensuremath{\gamma}$ rays, ground state to excited states $\ensuremath{\beta}$ transitions followed by $\ensuremath{\gamma}$ transitions to the daughter nucleus ground state, and $\ensuremath{\beta}$-delayed neutron emission from the daughter nucleus in the case of $^{137}\mathrm{I}$.Method: We measured the complete $\ensuremath{\beta}$-decay intensities of $^{137}\mathrm{I}$ and $^{137}\mathrm{Xe}$ with the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory. We describe a technique for measuring the $\ensuremath{\beta}$-delayed neutron energy spectrum, which also provides a measurement of the $\ensuremath{\beta}$-neutron branching ratio, ${P}_{n}$.Results: We validate the current Evaluated Nuclear Structure Data File (ENSDF) evaluation of $^{137}\mathrm{Xe}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decay. We find that major changes to the current ENSDF assessment of $^{137}\mathrm{I}\ensuremath{\beta}$-decay intensity are required. The average $\ensuremath{\gamma}$ energy per $\ensuremath{\beta}$ decay for $^{137}\mathrm{I}\ensuremath{\beta}$ decay ($\ensuremath{\gamma}$ decay heat) increases by 19%, from 1050--1250 keV, which increases the average $\ensuremath{\gamma}$ energy per $^{235}\mathrm{U}$ fission by $0.11%$. We measure a $\ensuremath{\beta}$-delayed neutron branching fraction for $^{137}\mathrm{I}\ensuremath{\beta}$ decay of $7.9\ifmmode\pm\else\textpm\fi{}0.2(\mathrm{fit})\ifmmode\pm\else\textpm\fi{}0.4(\mathrm{sys})%$ and we provide a $\ensuremath{\beta}$-neutron energy spectrum.Conclusions: The Modular Total Absorption Spectrometer measurements of $^{137}\mathrm{I}$ and $^{137}\mathrm{Xe}$ demonstrate the importance of revisiting and remeasuring complex $\ensuremath{\beta}$-decaying fission products with total absorption spectroscopy. We demonstrate the ability of the Modular Total Absorption Spectrometer to measure $\ensuremath{\beta}$-delayed neutron energy spectra.

The Modular Total Absorption Spectrometer (MTAS) array has been designed, constructed, characterized, and applied to the decay studies of {sup 238}U fission products at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. A MTAS commissioning run was performed in January 2012 at the mass separator on-line to the HRIBF Tandem accelerator. Preliminary results of MTAS data confirm known decay patterns of {sup 142}Ba and {sup 142}La deduced from an earlier study using a total absorption spectrometer technique.

A Modular Total Absorption Spectrometer constructed at the Holifield Radioactive Ion Beam Facility has been applied to decay studies of over 20 238 U fission products. The measurements were focused on nuclei identified as important for decay heat analysis during a nuclear fuel cycle. Preliminary results on the average electromagnetic (EM) energy release in the β decay of 89 Kr and 139 Xe isotopes yielded values of 2446 keV and 1126 keV, respectively. It represents an increase of over 35% and 20%, respectively, when compared to the average EM energies deduced using the ENSDF database.

Reactions on certain proton-rich, radioactive nuclei have been shown to have a significant influence on X-ray bursts. We provide an overview of two recent measurements of important X-ray burst reactions using in-flight radioactive ion beams from the RESOLUT facility at the J. D. Fox Superconducting Accelerator Laboratory at Florida State University. The 17 F(d,n) 18 Ne reaction was measured, and Asymptotic Normalization Coefficients were extracted for bound states in 18 Ne that determine the direct-capture cross section dominating the 17 F(p, γ ) 18 Ne reaction rate for T≲ 0.45 GK. Unbound resonant states were also studied, and the single-particle strength for the 4.523-MeV (3 + ) state was found to be consistent with previous results. The 19 Ne(d,n) 20 Na proton transfer reaction was used to study resonances in the 19 Ne(p, γ ) 20 Na reaction. The most important 2.65-MeV state in 20 Na was observed to decay by proton emission to both the ground and first-excited states in 19 Ne, providing strong evidence for a 3 + spin assignment and indicating that proton capture on the thermally-populated first-excited state in 19 Ne is an important contributor to the 19 Ne(p, γ ) 20 Na reaction rate.

The 14O(α,p)17F reaction is important for understanding the αp process that occurs in X-ray bursts, but the rate of this reaction remains uncertain due to the uncertain properties of states in 18Ne. We measured the 17F(p,p)17F and 17F(p,α)14O reactions to study the properties of states in 18Ne that are important for the 14O(α,p)17F reaction using 17F radioactive beams from the RESOLUT facility at Florida State University. Double-sided silicon strip detectors were used to detect light particles, and recoiling heavy ions were detected in coincidence using a gas ionization chamber at forward angles. The performance of the system was first tested using the 17O(p,α)14N reaction. This was the first measurement using the ASIC electronics and recoil detector being developed for the Array for Nuclear Astrophysics Studies with Exotic Nuclei (ANASEN). We report on the performance and preliminary results.

Type I X-ray bursts are the most common explosions in the Galaxy; however, the nucleosynthesis that occurs during the thermonuclear runaway and explosion is poorly understood. In this proceedings we discuss current experimental efforts and techniques that are being used to study X-ray burst nucleosynthesis in the laboratory. Specifically, radioactive ion beam techniques that have recently been developed have allowed the study of some of the most important (α, p) reactions in X-ray bursts for the first time.

Reactions involving radioactive nuclei play an important role in stellar explosions, but those reactions involving short-lived nuclei have only limited experimental information available due to currently limited beam intensities. Several facilities are aiming to provide greater access to these unstable isotopes at higher beam intensities, but more efficient and selective techniques and devices are needed to properly study these important reactions. The Array for Nuclear Astrophysics Studies with Exotic Nuclei (ANASEN), a charged particle detector designed by Louisiana State University (LSU) and Florida State University (FSU), was created for this purpose. ANASEN is used to study the reactions important in the αp- and rp- processes with proton-rich exotic nuclei, providing essentially complete solid angle coverage through an array of 40 silicon-strip detectors backed with CsI scintillators, covering an area of roughly 1300 cm2. ANASEN also includes an active gas target/detector in a position-sensitive annular gas proportional counter, which allows direct measurement of (α,p) reactions in inverse kinematics. The first in-beam measurements with a partial implementation of ANASEN were performed at the RESOLUT radioactive beam facility of FSU during the summer of 2011. They included stable beam experiments and measurements of the 17F(p,p)17F and 17F(p,α)14O reactions which are important to understanding the structure of 18Ne and the 14O(α,p)17F reaction rate. The performance of ANASEN and initial results from the 17F studies will be presented.