Search

This Letter reports the first measurement of the ^{235}U ν[over ¯]_{e} energy spectrum by PROSPECT, the Precision Reactor Oscillation and Spectrum experiment, operating 7.9 m from the 85 MW_{th} highly enriched uranium (HEU) High Flux Isotope Reactor. With a surface-based, segmented detector, PROSPECT has observed 31678±304(stat) ν[over ¯]_{e}-induced inverse beta decays, the largest sample from HEU fission to date, 99% of which are attributed to ^{235}U. Despite broad agreement, comparison of the Huber ^{235}U model to the measured spectrum produces a χ^{2}/ndf=51.4/31, driven primarily by deviations in two localized energy regions. The measured ^{235}U spectrum shape is consistent with a deviation relative to prediction equal in size to that observed at low-enriched uranium power reactors in the ν[over ¯]_{e} energy region of 5-7 MeV.

The Precision Reactor Oscillation and Spectrum (PROSPECT) Experiment is a reactor neutrino experiment designed to search for sterile neutrinos with a mass on the order of 1 eV/c$^2$ and to measure the spectrum of electron antineutrinos from a highly-enriched $^{235}$U nuclear reactor. The PROSPECT detector consists of an 11 by 14 array of optical segments in $^{6}$Li-loaded liquid scintillator at the High Flux Isotope Reactor in Oak Ridge National Laboratory. Antineutrino events are identified via inverse beta decay and read out by photomultiplier tubes located at the ends of each segment. The detector response is characterized using a radioactive source calibration system. This paper describes the design, operation, and performance of the PROSPECT source calibration system.

The search for new decay chains of oganesson isotopes is presented. The experiment utilized the Dubna Gas Filled Recoil Separator and a highly segmented recoil-decay detection system. The signals from all detectors were analyzed in parallel by digital and analog data acquisition systems. For the first time, a target of mixed californium (51% Cf249, 13% Cf250, and 36% Cf251) recovered from decayed Cf252 sources was produced and irradiated with an intense Ca48 beam. The observation of a new decay chain of Og294 is reported. The prospects for reaching new isotopes Og295,296 are discussed.

We report a quantum simulation of the deuteron binding energy on quantum processors accessed via cloud servers. We use a Hamiltonian from pionless effective field theory at leading order. We design a low-depth version of the unitary coupled-cluster ansatz, use the variational quantum eigensolver algorithm, and compute the binding energy to within a few percent. Our work is the first step towards scalable nuclear structure computations on a quantum processor via the cloud, and it sheds light on how to map scientific computing applications onto nascent quantum devices.

This Letter reports the first scientific results from the observation of antineutrinos emitted by fission products of $^{235}$U at the High Flux Isotope Reactor. PROSPECT, the Precision Reactor Oscillation and Spectrum Experiment, consists of a segmented 4 ton $^6$Li-doped liquid scintillator detector covering a baseline range of 7-9 m from the reactor and operating under less than 1 meter water equivalent overburden. Data collected during 33 live-days of reactor operation at a nominal power of 85 MW yields a detection of 25461 $\pm$ 283 (stat.) inverse beta decays. Observation of reactor antineutrinos can be achieved in PROSPECT at 5$\sigma$ statistical significance within two hours of on-surface reactor-on data-taking. A reactor-model independent analysis of the inverse beta decay prompt energy spectrum as a function of baseline constrains significant portions of the previously allowed sterile neutrino oscillation parameter space at 95% confidence level and disfavors the best fit of the Reactor Antineutrino Anomaly at 2.2$\sigma$ confidence level., Comment: 7 pages, 5 figures; v3: Added additional supplemental files

The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, is designed to make both a precise measurement of the antineutrino spectrum from a highly-enriched uranium reactor and to probe eV-scale sterile neutrinos by searching for neutrino oscillations over meter-long baselines. PROSPECT utilizes a segmented $^6$Li-doped liquid scintillator detector for both efficient detection of reactor antineutrinos through the inverse beta decay reaction and excellent background discrimination. PROSPECT is a movable 4-ton antineutrino detector covering distances of 7m to 13m from the High Flux Isotope Reactor core. It will probe the best-fit point of the $\bar\nu_e$ disappearance experiments at 4$\sigma$ in 1 year and the favored regions of the sterile neutrino parameter space at more than 3$\sigma$ in 3 years. PROSPECT will test the origin of spectral deviations observed in recent $\theta_{13}$ experiments, search for sterile neutrinos, and address the hypothesis of sterile neutrinos as an explanation of the reactor anomaly. This paper describes the design, construction, and commissioning of PROSPECT and reports first data characterizing the performance of the PROSPECT antineutrino detector., Comment: 30 pages, 33 figures; updated with journal revision and reference

Detecting neutrinos—elementary particles that barely interact with other matter—usually requires detectors of enormous size. A particular interaction of neutrinos with atomic nuclei, called the coherent elastic neutrino-nucleus scattering (CEνNS), is predicted to occur with relatively high probability, and it could be used to drastically reduce the size of neutrino detectors. However, observing this interaction requires a source of low-energy neutrinos and detectors that contain nuclei of optimal mass. Akimov et al. observed CEνNS with a 6.7σ confidence by using a comparatively tiny, 14.6-kg sodium-doped CsI scintillator exposed to neutrinos from a spallation neutron facility (see the Perspective by Link). The discovery places tighter bounds on exotic, beyond-the-standard-model interactions involving neutrinos. Science , this issue p. [1123][1]; see also p. [1098][2] [1]: /lookup/doi/10.1126/science.aao0990 [2]: /lookup/doi/10.1126/science.aao4050

PROSPECT, the Precision Reactor Oscillation and SPECTrum experiment, is a short-baseline reactor antineutrino experiment designed to provide precision measurements of the $^{235}$U product $\overline{\nu}_e$ spectrum of utilizing an optically segmented 4-ton liquid scintillator detector. PROSPECT's segmentation system, the optical grid, plays a central role in reconstructing the position and energy of $\overline{\nu}_e$ interactions in the detector. This paper is the technical reference for this PROSPECT subsystem, describing its design, fabrication, quality assurance, transportation and assembly in detail. In addition, the dimensional, optical and mechanical characterizations of optical grid components and the assembled PROSPECT target are also presented. The technical information and characterizations detailed here will inform geometry-related inputs for PROSPECT physics analysis, and can guide a variety of future particle detection development efforts, such as those using optically reflecting materials or filament-based 3D printing., Comment: 31 pages, 28 figures

This work reports the production and characterization of lithium-loaded liquid scintillator (LiLS) for the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT). Fifty-nine 90 liter batches of LiLS (${}^6{\rm Li}$ mass fraction 0.082%$\pm$0.001%) were produced and samples from all batches were characterized by measuring their optical absorbance relative to air, light yield relative to a pure liquid scintillator reference, and pulse shape discrimination capability. Fifty-seven batches passed the quality assurance criteria and were used for the PROSPECT experiment., 16 pages, 15 figures

A wide range of energy technologies appears to be needed for the United States to meet its energy goals. A method is developed that relates the uncertainty of technological progress in eleven technology areas to the achievement of CO2 mitigation and reduced oil dependence. We conclude that to be confident of meeting both energy goals, each technology area must have a much better than 50/50 probability of success, that carbon capture and sequestration, biomass, battery electric or fuel cell vehicles, advanced fossil liquids, and energy efficiency technologies for buildings appear to be almost essential, and that the success of each one of the 11 technologies is important. These inferences are robust to moderate variations in assumptions.

International collaborations fill today's research landscape, facilitate scientific progress, and lead to a stronger scientific community through tackling mutually beneficial research problems. Furthermore, international research collaborations result in a cultural understanding among the community of scientists. For these general reasons, the Japan U.S. Theory Institute for Physics with Exotic Nuclei (JUSTIPEN) was established two years ago. JUSTIPEN enables travel of U.S. scientists to Japan to collaborate with their Japanese counterparts as the community pursues a basic understanding of exotic nuclei and their role in astrophysics and other areas. In this brief report, I will describe the activities of JUSTIPEN during the last two years.

The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, is designed to make a precise measurement of the antineutrino spectrum from a highly-enriched uranium reactor and probe eV-scale sterile neutrinos by searching for neutrino oscillations over meter-long distances. PROSPECT is conceived as a 2-phase experiment utilizing segmented $^6$Li-doped liquid scintillator detectors for both efficient detection of reactor antineutrinos through the inverse beta decay reaction and excellent background discrimination. PROSPECT Phase I consists of a movable 3-ton antineutrino detector at distances of 7 - 12 m from the reactor core. It will probe the best-fit point of the $\nu_e$ disappearance experiments at 4$\sigma$ in 1 year and the favored region of the sterile neutrino parameter space at $>$3$\sigma$ in 3 years. With a second antineutrino detector at 15 - 19 m from the reactor, Phase II of PROSPECT can probe the entire allowed parameter space below 10 eV$^{2}$ at 5$\sigma$ in 3 additional years. The measurement of the reactor antineutrino spectrum and the search for short-baseline oscillations with PROSPECT will test the origin of the spectral deviations observed in recent $\theta_{13}$ experiments, search for sterile neutrinos, and conclusively address the hypothesis of sterile neutrinos as an explanation of the reactor anomaly., Comment: 21 pages, 21 figures

A meter-long, 23-liter EJ-309 liquid scintillator detector has been constructed to study the light collection and pulse-shape discrimination performance of elongated scintillator cells for the PROSPECT reactor antineutrino experiment. The magnitude and uniformity of light collection and neutron/gamma discrimination power in the energy range of antineutrino inverse beta decay products have been studied using gamma and spontaneous fission calibration sources deployed along the cell long axis. We also study neutron-gamma discrimination and light collection abilities for differing PMT and reflector configurations. Key design features for optimizing MeV-scale response and background rejection capabilities are identified., Comment: 20 pages, 11 figures

Research reactors host a wide range of activities that make use of the intense neutron fluxes generated at these facilities. Recent interest in performing measurements with relatively low event rates, e.g. reactor antineutrino detection, at these facilities necessitates a detailed understanding of background radiation fields. Both reactor-correlated and naturally occurring background sources are potentially important, even at levels well below those of importance for typical activities. Here we describe a comprehensive series of background assessments at three high-power research reactors, including $\gamma$-ray, neutron, and muon measurements. For each facility we describe the characteristics and identify the sources of the background fields encountered. The general understanding gained of background production mechanisms and their relationship to facility features will prove valuable for the planning of any sensitive measurement conducted therein., Comment: 26 pages, 28 figures. Accepted for publication in Nuclear Instruments and Methods A. v2 incorporates minor revisions requested by NIMA

This presentation focuses on some of the recent developments in low-energy nuclear structure theory, with emphasis on applications of coupled-cluster theory. We report on results for ground and excited states in 4 He and 16 O , and about extensions of coupled-cluster theory to treat three-body forces.

The long-term vision of the Nuclear Structure and Low-Energy Reactions (NSLER) col- laboration is to arrive at a comprehensive and unified description of nuclei and their reactions that is grounded in the interactions between the constituent nucleons. For this purpose, we will develop a uni- versal energy density functional for nuclei and replace current phenomenological models of nuclear structure and reactions with a well-founded microscopic theory that will deliver maximum predictive power with minimal uncertainties that are well quantified. Nuclear structure and reactions play an es- sential role in the science to be investigated at rare isotope facilities, and in nuclear physics applica- tions to the Science-Based Stockpile Stewardship Program, next-generation reactors, and threat reduc- tion. We anticipate an expansion of the computational techniques and methods we currently employ, and developments of new treatments, to take advantage of petascale architectures and demonstrate the capability of the leadership class machines to deliver new science heretofore impossible. 1. The physics of nuclei: NSLER vision and background Our long-term vision is to arrive at a comprehensive and unified description of nuclei and their reac- tions that is grounded in the fundamental interactions between the constituent nucleons. We seek to replace current phenomenological models of nuclear structure and reactions with a well-founded mi- croscopic theory that delivers maximum predictive power with uncertainties that are well quantified. Six years from now, new nuclear facilities will be churning out experimental data on short-lived nuclei. RIBF at RIKEN in Japan, SPIRAL-II, and GSI-FAIR will all be well on the way to either completion or full schedules of runs. The U.S. will also have an enhanced program established to con- tinue research associated with the physics of nuclei. These facilities are trying to answer the basic questions concerning how protons and neutrons make stable nuclei and rare isotopes, and how simple patterns arise in complex nuclei. Today's experimental facilities are paving the way with exciting re- sults concerning the nature of nuclear closed shells when the neutron-to-proton ratio is high, the be- havior of light nuclei near the drip lines where neutron skins can develop and binding becomes very weak, and the masses and lifetimes of very neutron-rich and unstable nuclei. Such results also impact our understanding of element production in the Universe, and also impact application-oriented needs in national security and energy production. Nuclear theory, during the same time frame, faces the continuing challenges of developments that enable answers to the question(s): "Given a lump of nuclear material, what are its properties, where did it come from, and how does it interact?" We seek a unified framework for the description of nuclei and nuclear reaction processes that allows for accurate predictions and quantifiable error estimates for those predictions. Important in this pursuit is the understanding that we will not be able to measure every nuclear property that may be important even with the most sophisticated future experimental

Using the shell-model Monte Carlo method, we study the thermal properties of four N = 40 medium-mass nuclei: 68 Ni, a substantially spherical and weakly paired nucleus; 70 Zn, a superfluid spherical nucleus; 72 Ge, a superfluid deformed nucleus which exhibits shape-coexistence; and the well-deformed, weakly-paired nucleus 80 Zr. We investigate the competition between shape deformations and pairing correlations as a function of temperature. We find that shape and pairing changes contribute to the specific heat of the nucleus in a different way. While the superfluid-to-normal transition manifests itself as a pronounced peak in the specific heat around T = 0.6 – 0.7 MeV , the deformed-to-spherical transition is more gradual.

We discuss large-scale ah initio calculations of ground and excited states of 16 O and preliminary calculations for 15 O and 17 O using coupled-cluster methods and algorithms developed in quantum chemistry. By using realistic two-body interactions and the renormalized form of the Hamiltonian obtained with a no-core G-matrix approach, we are able to obtain the virtually converged results for 16 O and promising results for 15 O and 17 O at the level of two-body interactions. The calculated properties other than binding and excitation energies include charge radius and charge form factor. The relatively low costs of coupled-cluster calculations, which are characterized by the low-order polynomial scaling with the system size, enable us to probe large model spaces with up to seven or eight major oscillator shells, for which nontruncated shell-model calculations fornuclei with A = 15-17 active particles are presently not possible.

The dynamics of stellar core collapse are strongly dependent on nuclear electron capture, primarily on nuclei with masses larger than 60. In prior simulations of core collapse, electron capture on these nuclei has been treated in a highly parameterized fashion, if not ignored. Recent advances in nuclear structure theory have allowed a more realistic treatment to be developed. With this new treatment of electron capture on heavy nuclei come significant changes in the hydrodynamics of core collapse and bounce. We discuss these as well as the sensitivity of these results to the strength of nuclear electron capture.

We report preliminary large scale ab initio calculations of ground and excited states of 16O using quantum chemistry inspired coupled cluster methods and realistic two-body interactions. By using the renormalized Hamiltonians obtained with a no-core G-matrix approach, we obtain the virtually converged results at the level of two-body interactions. Due to the polynomial scaling with the system size that characterizes coupled cluster methods, we can probe large model spaces with up to seven major oscillator shells, for which standard non-truncated shell-model calculations are not possible.

We study neutral-current neutrino–nucleus reaction cross sections for Mn, Fe, Co and Ni isotopes. An earlier study for a few selected nuclei has shown that in the supernova environment the cross sections are increased for low energy neutrinos due to finite-temperature effects. Our work supports this finding for a much larger set of nuclei. Furthermore we extend previous work to higher neutrino energies considering allowed and forbidden multipole contributions to the cross sections. The allowed contributions are derived from large-scale shell model calculations of the Gamow–Teller strength, while the other multipole contributions are calculated within the random phase approximation. We present the cross sections as functions of initial and final neutrino energies and for a range of supernova-relevant temperatures. These cross sections will allow improved estimates of inelastic neutrino reactions on nuclei in supernova simulations.

Core Collapse supernovae are among the most energetic explosions in the Universe and the predominant source of chemical elements heavier than carbon. They drive matter to extremes of density and temperature that cannot be produced on Earth and serve as laboratories for fundamental physics. Understanding these events requires the partnership of nuclear and particle physicists with astrophysicists and computational scientists. A case in point is the study of the role that captures of electrons and neutrinos on atomic nuclei play during the collapse of the core of a massive star as it reaches the end of its life. In addition to the astrophysical modeling, the required understanding of the structure of the atomic nucleus is itself a terascale application. We will discuss recent work which shows that a realistic treatment of electron capture on these nuclei causes significant changes in the hydrodynamics of core collapse and bounce, which set the stage for the subsequent evolution of the supernova.

I discuss an interesting method for approaching the quantum many-body problem that will be useful for investigating neutron-rich nuclei that will be produced at next-generation nuclear facilities such as the Rare Isotope Accelerator (RIA).

This review aims at a critical discussion of the interplay between effective interactions derived from various many-body approaches and spectroscopic data extracted from large scale shell-model studies. To achieve this, our many-body scheme starts with the free nucleon-nucleon (NN) interaction, typically modelled on various meson exchanges. The NN interaction is in turn renormalized in order to derive an effective medium dependent interaction. The latter is in turn used in shell-model calculations of selected nuclei. We also describe how to sum up the parquet class of diagrams and present initial uses of the effective interactions in coupled cluster many-body theory., 61 pages, submitted to Prog. Part. Nucl. Phys

We discuss several pairing-related phenomena in nuclear systems, ranging from superfluidity in neutron stars to the gradual breaking of pairs in finite nuclei. We describe recent experimental evidence that points to a relation between pairing and phase transitions (or transformations) in finite nuclear systems. A simple pairing interaction model is used in order to study and classify an eventual pairing phase transition in finite fermionic systems such as nuclei. We show that systems with as few as 10-16 fermions can exhibit clear features reminiscent of a phase transition., Proceedings of COMEX1, Sorbonne, Paris, june 10-13 2003. To appear in Nuclear Physics A

Practice effects in memory testing complicate the interpretation of score changes over repeated testings, particularly in clinical applications. Consequently, several alternative forms of the Auditory Verbal Learning Test (AVLT) have been developed. Studies of these typically indicate that the forms examined are equivalent. However, the implication that the forms in the literature are interchangeable must be tempered by several caveats. Few studies of equivalence have been undertaken; most are restricted to the comparison of single pairs of forms, and the pairings vary across studies. These limitations are exacerbated by the minimal overlapping across studies in variables reported, or in the analyses of equivalence undertaken. The data generated by these studies are nonetheless valuable, as significant practice effects result from serial use of the same form. The available data on alternative AVLT forms are summarized, and recommendations regarding form development and the determination of form equivalence are offered.

I discuss the current state of low-energy nuclear theory and the scientific questions that will be addressed over the next ten years as we move to the description of increasingly unstable nuclei. Much of our understanding of unstable nuclei will directly benefit astrophysics, particularly in the areas of supernova-core deleptonization, neutrino interactions with nuclei in stellar environments, the nuclear equation of state at high temperatures and densities, and nucleosynthesis. I will discuss the current status of our understanding of one of these overlaps, namely electron capture on nuclei. I will then turn to a description of coupled-cluster theory, which is a technique of solving the nuclear many-body problem that may be useful for calculating selected nuclear properties relevant to astrophysics.

We perform shell model Monte Carlo calculations for proton-rich Kr, Sr, and Zr isotopes in the mass range A =72–84. We employ a complete 1 p 0 f –0 g 1 d 2 s configuration space and an effective quadrupole-plus-pairing residual interaction. Our calculation reproduces the large B ( E 2) values observed in these nuclei. We relate these values to the gain in correlation energy obtained by moving nucleons across the N =40 subshell closure into g 9/2 orbitals.

I will describe the behaviour of two different quantum-mechanical systems as a function of increasing temperature. While these systems are somewhat different, the questions addressed are very similar, namely, how does one describe transitions in phase of a finite many-body system; how does one recognise these transitions in practical calculations; and how may one obtain the order of the transition.

We present a synergetic effort of a group of theorists to characterize a molecular electronics device through a multiscale modeling approach. We combine electronic-structure calculations with molecular dynamics and Monte Carlo simulations to predict the structure of self-assembled molecular monolayers on a metal surface. We also develop a novel insight into molecular conductance, with a particular resolution of its fundamental channels, which stresses the importance of a complete molecular structure description of all components of the system, including the leads, the molecule, and their contacts. Both molecular dynamics and electron transport simulations imply that knowledge of detailed molecular structure and system geometry are critical for successful comparison with carefully performed experiments. We illustrate our findings with benzenedithiolate molecules in contact with gold.

In the past decade, coupled-cluster theory has seen a renaissance in nuclear physics, with computations of neutron-rich and medium-mass nuclei. The method is efficient for nuclei with product-state references, and it describes many aspects of weakly bound and unbound nuclei. This report reviews the technical and conceptual developments of this method in nuclear physics, and the results of coupled-cluster calculations for nucleonic matter, and for exotic isotopes of helium, oxygen, calcium, and some of their neighbors.

The Facility for Rare Isotope Beams (FRIB) will be a world-leading laboratory for the study of nuclear structure, reactions and astrophysics. Experiments with intense beams of rare isotopes produced at FRIB will guide us toward a comprehensive description of nuclei, elucidate the origin of the elements in the cosmos, help provide an understanding of matter in neutron stars, and establish the scientific foundation for innovative applications of nuclear science to society. FRIB will be essential for gaining access to key regions of the nuclear chart, where the measured nuclear properties will challenge established concepts, and highlight shortcomings and needed modifications to current theory. Conversely, nuclear theory will play a critical role in providing the intellectual framework for the science at FRIB, and will provide invaluable guidance to FRIB's experimental programs. This article overviews the broad scope of the FRIB theory effort, which reaches beyond the traditional fields of nuclear structure and reactions, and nuclear astrophysics, to explore exciting interdisciplinary boundaries with other areas. \keywords{Nuclear Structure and Reactions. Nuclear Astrophysics. Fundamental Interactions. High Performance Computing. Rare Isotopes. Radioactive Beams., Comment: 20 pages, 7 figures

Excited states of nuclei near the doubly-magic nucleus Sn-100 were studied with the Ni-58+Cr-50 reaction. The experimental setup consisted of the GAMMASPHERE array augmented with light charged-particle and neutron detectors. Excited states were identified for the first time in the proton emitting nucleus Sb-105. Excitations across the N=Z=50 doubly closed shell were observed in Cd-99 and In-101. Some results of large-scale shell-model calculations are discussed.

The dynamical string-parton model for relativistic heavy-ion collisions is generalized to include particle identification of the final-state hadrons by phenomenologically quantizing the masses of the classical strings which result from string breaking. General features of the Nambu-Gotō strings are used to motivate a model that identifies a mass window near the physical mass of a meson, and does not allow the string to decay further if its mass falls within the window. Data from e+e- collisions in the region [Formula: see text] to 30 GeV are well reproduced by this model.

We demonstrate the feasibility of realistic shell-model Monte Carlo (SMMC) calculations spanning multiple major shells, using a realistic interaction whose bad saturation and shell properties have been corrected by a newly developed general prescription. Particular attention is paid to the approximate restoration of translational invariance. The model space consists of the full sd-pf shells. We include in the study some well-known T=0 nuclei and several unstable neutron-rich ones around N=20,28. The results indicate that SMMC calculations can reproduce binding energies, B(E2) transitions, and other observables with an interaction that is practically parameter free. Some interesting insight is gained into the nature of deep correlations. The validity of previous studies is confirmed.

Hadronic structure functions are modeled as a distribution of solutions to the classical string model of Nambu and Got{bar o}. In the model, the endpoints of the strings, identified as quarks, carry a finite amount of energy and momentum. The endpoint trajectories are assumed to be polygons and it is shown that the structure function in the scaling limit is directly related to the distribution of lengths of the straight line segments making up the polygons. The relationship is inverted to give an analytic expression for the distribution of straight line segments in terms of the structure function. The results are applied to the measured proton and pion structure functions. {copyright} {ital 1999} {ital The American Physical Society}

We present Gamow-Teller strength distributions from shell model Monte Carlo studies of fp-shell nuclei that may play an important role in the precollapse evolution of supernovas. We then use these strength distributions to calculate the electron-capture cross sections and rates in the zero-momentum transfer limit. We also discuss the thermal behavior of the cross sections. We find large differences in these cross sections and rates when compared to the naive single-particle estimates. These differences need to be taken into account for improved modeling of the early stages of type-II supernova evolution. thinsp {copyright} {ital 1998} {ital The American Physical Society}

We use a cranked shell model Monte Carlo (SMMC) approach to study rotational properties and pair correlationsin the odd-odd N = Z nucleus 74Rb. The calculation is performed in the complete 1p-0ƒ 5 2 -0g 9 2 model space with a residual interaction derived from the Paris potential. The calculated ground state is dominated by isovector J = 0 proton-neutron (pn) pairing. With increasing frequency the J = 0 pn correlations decrease to a constant value at around 〈J〉 = 3 ± 1.5 h while the isoscalar pn correlations (mainly J = 9) increase. Relatedly, the isospin decreases with frequency from its ground state value T = 1 as isoscalar correlations set in. This finding is in agreement with experiement, where at higher rotational frequency a T = 0 band becomes energetically favored over the T = 1 ground state band.

We present Shell Model Monte Carlo calculations for nuclei within the full major shell 50-82 for both protons and neutrons. The interaction is determined solely by self-consistency and odd-even mass differences. The methods are illustrated for ${}^{124}$Sn, ${}^{128}$Te and ${}^{124}$Xe. We calculate shape distributions, moments of inertia and pairing correlations as functions of temperature and angular velocity. Our calculations are the first microscopic evidence of $\gamma$-softness of nuclei in this region., Comment: uuencoded postscript of manuscript with three figures

We perform shell model Monte Carlo calculations for nuclei in the 100 Sn region within the complete 0 g -1 d -2 s oscillator shell using an effective interaction derived from the Paris nucleon-nucleon potential. We find good agreement with empirically calculated masses, and reproduce the observed quenching of the total Gamow-Teller strengths in this mass region. The Gamow-Teller strength in 100 Sn is predicted to be nearly a factor of 3 smaller than the single particle estimate.

We study the gross properties of even-even and $N=Z$ nuclei with $A=48-64$ using shell-model Monte Carlo methods. Our calculations account for all $0 \hbar \omega$ configurations in the $fp$-shell and employ the modified Kuo-Brown interaction KB3. We find good agreement with data for masses and total $B(E2)$ strengths, the latter employing effective charges $e_p=1.35e$ and $e_n=0.35e$. The calculated total Gamow-Teller strengths agree consistently with the $B(GT_+)$-values deduced from $(n,p)$ data if the shell model results are renormalized by $0.64$, as has already been established for $sd$-shell nuclei. The present calculations therefore suggest that this renormalization (i.e., $g_A=1$ in the nuclear medium) is universal., Comment: 20 pages, 7 figures, Caltech Preprint

We study the thermal properties of 54Fe with the Brown-Richter interaction in the complete 1p0f model space. Monte Carlo calculations show a peak in the heat capacity and rapid increases in both the moment of inertia and M1 strength near a temperature of 1.1 MeV that are associated with the vanishing of proton-proton and neutron-neutron monopole pair correlations; neutron-proton correlations persist to higher temperatures. Our results are consistent with a Fermi gas level density whose backshift vanishes with increasing temperature.

Electron capture rates on neutron-rich nuclei (A>65) were calculated within the Random Phase Approximation with partial number formalism, including allowed and forbidden transitions. The partial occupation numbers were provided as a function of temperature by Shell-Model Monte Carlo calculations, including an pairing+quadrupole interaction. Capture rates on relevent nuclei were calculated for density and temperature conditions during the core collapse of a massive star. It was found that electron captures on nuclei can compete with electron captures on free protons. Furthermore, they produce neutrinos with average energies lower than neutrinos emitted from captures on free protons, with possible consequences on the cooling of the core., 3 pages, 4 figures, submitted to the proceedings of Nuclei in the Cosmos XVII