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Nuclear reactions of interest for astrophysics and applications often rely on statistical model calculations for nuclear reaction rates, particularly for nuclei far from $\beta$-stability. However, statistical model parameters are often poorly constrained, where experimental constraints are particularly sparse for exotic nuclides. For example, our understanding of the breakout from the NiCu cycle in the astrophysical rp-process is currently limited by uncertainties in the statistical properties of the proton-rich nucleus $^{60}$Zn. We have determined the nuclear level density of $^{60}$Zn using neutron evaporation spectra from $^{58}$Ni($^3$He, n) measured at the Edwards Accelerator Laboratory. We compare our results to a number of theoretical predictions, including phenomenological, microscopic, and shell model based approaches. Notably, we find the $^{60}$Zn level density is somewhat lower than expected for excitation energies populated in the $^{59}$Cu(p,$\gamma$)$^{60}$Zn reaction under rp-process conditions. This includes a level density plateau from roughly 5-6 MeV excitation energy, which is counter to the usual expectation of exponential growth and all theoretical predictions that we explore. A determination of the spin-distribution at the relevant excitation energies in $^{60}$Zn is needed to confirm that the Hauser-Feshbach formalism is appropriate for the $^{59}$Cu(p,$\gamma$)$^{60}$Zn reaction rate at X-ray burst temperatures., Comment: 10 pages, 8 figures

Results of ab initio no-core, shell model calculations for the photonuclear cross section of 10B are presented using realistic two-nucleon (NN) chiral forces up to next-to-next-to-next-order (N3LO) softened by the similarity renormalization group method (SRG) with \( \lambda= 2.02\) fm-1. The electric-dipole response function is calculated using the Lanczos method, with the effects of the continuum included via neutron escape widths derived from R-matrix theory and using the Lorentz integral transform method. The calculated cross section agrees well with experimental data in terms of structure as well as in absolute peak height, \( \sigma_{\max}=4.85\) mb at photon energy \( \omega= 23.61\) MeV, and integrated cross section 85.36 MeV. mb. We also test the Brink hypothesis by calculating the electric-dipole response for the first nine positive-parity states with \( J \ne 0\) in 10B and verify that dipole excitations built upon the ground and excited states have similar characteristics.

We present calculations for the $c$ coefficients of the isobaric mass multiplet equation for nuclei from $A=42$ to $A=54$ based on input from three realistic nucleon-nucleon interactions. We demonstrate that there is a clear dependence on the short-range charge-symmetry-breaking (CSB) part of the strong interaction and that there is significant disagreement in the CSB part between the commonly used CD-Bonn, chiral effective field theory at next-to-next-to-next-to-leading-order, and Argonne V18 nucleon-nucleon interactions. In addition, we show that all three interactions give a CSB contribution to the $c$ coefficient that is too large when compared to experiment.

The configuration interaction (CI) approach to solving the nuclear many-body problem, also known as the interacting shell model, has proven to be powerful tool in understanding the structure of nuclei. The principal criticism of past applications of the shell model is the reliance on empirical tuning to interaction matrix elements. If an accurate description of nuclei far from the valley of stability, where little or no data is available, a more fundamental approach is needed. This starts with recent ab initio approaches with effective interactions in the no-core shell model (NCSM). Using effective-field theory for guidance, fully ab initio descriptions of nuclei up to 16O with QCD based NN, NNN, and NNNN interactions will be possible within the next five years. An important task is then to determine how to use these NCSM results to develop effective interactions to describe heavier nuclei without the need to resort to an empirical retuning with every model space. Thus, it is likely that more traditional CI applications utilizing direct diagonalization and more fundamental interactions will be applicable to nuclei with perhaps up to one hundred constituents. But, these direct diagonalization CI applications will always be computationally limited due to the rapid increase in the number of configurations with particle number. Very recently, the shifted-contour method has been applied to the Auxiliary-field Monte Carlo approach to the Shell Model (AFMCSM), and preliminary applications exhibit a remarkable taming of the notorious sign problem. If the mitigation of the sign problem holds true, the AFMCSM will offer a method to compute quantum correlations to mean-field applications for just about all nuclei; giving exact results for CI model spaces that can approach 1020-25. In these lectures, I will discuss modern applications of CI to the nuclear many-body problem that have the potential to guide nuclear structure theory into the next decade.

The problem of the damping of the Giant Dipole Resonance (GDR) at finite temperature at T>2 MeV is discussed here. The experimental results are based on fusion evaporation reactions. The most recent results on the mass region A = 132 ( Ce isotopes) obtained in exclusive measurements are compared with the existing results on the A = 110–120 region ( Sn isotopes). The comparison with the theoretical predictions based on thermal shape fluctuations is also discussed. The GDR width is found to increase also in the region T>2 MeV and this is accounted by the combined effect of the increase of the compound nucleus width (smaller lifetime) and to the increase of the average deformation of the nucleus.

Nuclear Theory research under the auspices of the Department of Energy (DOE) Office of Nuclear Physics (NP) is conducted within several funding sources and projects. These include base funding, and early career award, and a collaborative SciDAC-­3 award that is jointly funded by DOE/NP and the Advanced Simulations and Computations (ASC) effort within the National Nuclear Security Agency (NNSA). Therefore, this annual report is organized within the three primary sections covering these projects.

We review recent developments in the ab initio no-core shell model, such as the influence of 3NFs on the binding energies and excitation spectra of light nuclei. Our calculations permit us to compare the effect of different choices for the theoretical 3NF on the properties of light nuclei. This is of particular interest in determining the best choice of the values for the contact terms in 3NFs derived from Chiral Perturbation Theory. Other recent developments in the NCSM include an investigation of the renormalization properties of physical operators, besides the nuclear Hamiltonian, as well as the Lorentz integral transform approach to the description of select reaction observables in light nuclei.

We report on applications of the ab initio, no-core shell model with the primary goal of achieving an accurate description of nuclear structure and reactions from the fundamental inter-nucleon interactions. We show that realistic two-nucleon interactions are inadequate to describe the low-lying structure of 10B, and that realistic three-nucleon interactions are essential. We report preliminary attempts to compute astrophysical S-factors

The ab initio No-Core Shell Model (NCSM) adopts an intrinsic Hamiltonian for all nucleons in the nucleus. Realistic two-nucleon and tri-nucleon interactions are incorporated. From this Hamiltonian, an Hermitian effective Hamiltonian is derived for a finite basis space conserving all the symmetries of the initial Hamiltonian. The resulting finite sparse matrix problem is solved by diagonalization on parallel computers. Applications range from light nuclei to multiquark systems and, recently, to similar problems in quantum field theory. We present this approach with a sample of recent results.

The ab initio No-Core Shell Model (NCSM) begins with an intrinsic Hamiltonian for all nucleons in the nucleus. Realistic two-nucleon and tri-nucleon interactions are incorporated such as those recently developed from effective-field theory and chiral perturbation theory. We then derive a finite basis-space dependent Hermitian effective Hamiltonian that conserves all the symmetries of the initial Hamiltonian. The resulting finite Hamiltonian matrix problem is solved by diagonalization on parallel computers. Applications range from light nuclei to multiquark systems and, recently, to quantum-field theory including systems with bosons. We present this approach with a sample of recent results.

We develop and apply an ab-initio approach to nuclear structure. Starting with the NN interaction, that fits two-body scattering and bound state data, and adding a theoretical NNN potential, we evaluate nuclear properties in a no-core approach. For presently feasible no-core model spaces, we evaluate an effective Hamiltonian in a cluster approach which is guaranteed to provide exact answers for sufficiently large model spaces and/or sufficiently large clusters. A number of recent applications are surveyed including an initial application to exotic multiquark systems.

The ab initio No-Core Shell Model (NCSM) has recently been expanded to include nucleon-nucleon (NN) and three-nucleon (3N) interactions at the three-body cluster level. Here it is used to predict binding energies and spectra of p -shell nuclei based on realistic NN and 3N interactions. First results show that NN plus 3N interactions based on chiral perturbation theory lead to a realistic description of 6 Li.

Absolute partial γ-ray cross sections for discrete γ-ray production in the 239Pu(n,2nγi)238Pu reaction have been measured. The experiments were performed at LANSCE/WNR on the 60R neutron flight path. Reaction γ-rays were measured using the large-scale Compton-suppressed array of Ge detectors, GEANIE. The motivation for this experiment, an overview of the partial γ-ray cross-section measurement, and an introduction to the main experimental issues will be presented. The energy resolution of the Ge detectors allowed identification of reaction γ rays above the background of sample radioactivity and fission γ rays. The use of planar Ge detectors with their reduced sensitivity to neutron interactions and improved line shape was also important to the success of this experiment. Absolute partial γ-ray cross sections are presented for the 61+ → 41+ member of the ground state rotational band in 238Pu, together with miscellaneous other γ-ray partial cross sections. The n,2n reaction cross section shape and magnitude...

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

Mean lifetimes of 20 out of 31 bound levels in ${}^{32}\mathrm{S}$ below an excitation energy of 8.0 MeV are deduced from the Doppler-broadened $\ensuremath{\gamma}$-ray line shapes produced in the reactions ${}^{2}\mathrm{H}{(}^{31}\mathrm{P},n\ensuremath{\gamma}{)}^{32}\mathrm{S}, { }^{28}\mathrm{Si}{(}^{6}\mathrm{Li},pn\ensuremath{\gamma}{)}^{32}\mathrm{S},$ and ${}^{31}\mathrm{P}(p,\ensuremath{\gamma}{)}^{32}\mathrm{S}.$ Of the 20 levels, lifetimes for 4 are reported here for the first time. For the remaining 16 levels, the lifetime values obtained in this work are considered to be more reliable and accurate than those reported in the literature. Compared to lifetime measurements reported in the literature, significant procedural improvements have been made by (i) using the entire line shape in the data analysis, (ii) making measurements with targets implanted in high-stopping-power media, and (iii) simulating with the Monte-Carlo method the slowing-down process, experimental conditions, and the delayed feeding from higher levels to the level being analyzed. The low-lying portion of the level scheme, level lifetimes, $\ensuremath{\gamma}$-ray branchings, $E2/M1$ mixing ratios, and reduced transition probabilities are compared with shell-model calculations. The reduced $B(E2)$ values for 16 out of 18 transitions and $B(M1)$ values for 5 out of 10 transitions are reproduced to within a factor of 5. A one-to-one correspondence between 33 experimental and predicted states is established up to 8.2 MeV for both positive- and negative-parity states.

An exact, number-conserving solution to the generalized, orbit-dependent pairing problem is derived by introducing an infinite-dimensional algebra. A method for obtaining eigenvalues and eigenvectors of the corresponding Hamiltonian is also given. The relevance of the orbit-dependent pairing solution is demonstrated by comparing predictions of the model with shell-model calculations., 12 pages, LaTeX (uses RevTex macros), one postscript figure. Submitted to Physical Review Letters

We use a 4ħΩ shell-model calculation with a two-body effective interaction derived microscopically from the Reid93 potential to calculate the isospin-mixing correction for the10C→10B superallowed Fermi transition. The effective interaction takes into account the Coulomb potential as well as the charge dependence ofT=1 partial waves. Our results suggest the isospin-mixing correctionδ c ≈ 0.1%, which is compatible with previous calculations obtained by other methods. The obtainedδ C correction is about a factor of four too small to obtain unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present experimental data.

We use a 4{h_bar}{Omega} shell-model calculation with a two-body effective interaction derived microscopically from the Reid93 potential to calculate the isospin-mixing correction for the {sup 10}C{r_arrow}{sup 10}B superallowed Fermi transition. The effective interaction takes into account the Coulomb potential as well as the charge dependence of T=1 partial waves. Our results suggest the isospin-mixing correction {delta}{sub C}{approx}0.1{percent}, which is compatible with previous calculations. The correction obtained in those calculations, performed in a 0{h_bar}{Omega} space, was dominated by deviation from unity of the radial overlap between the converted proton and the corresponding neutron. In the present calculation this effect is accommodated by the large model space. The obtained {delta}{sub C} correction is about a factor of 4 too small to obtain unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present experimental data. {copyright} {ital 1997} {ital The American Physical Society}

Coulomb energy differences between mirror nuclei with $A \le 70$ are calculated within the framework of the nuclear shell model using an effective Coulomb plus isovector and isotensor interaction. Absolute binding energies for proton-rich nuclei are predicted by adding the calculated Coulomb shifts to experimentally measured binding energies for the neutron-rich mirror. The location of the proton drip-line is investigated, as well as candidates for the exotic decay mode known as di-proton emission. Taking into account the lifetimes of competing decay modes and limits imposed by experimental setups, it is concluded that the best candidates for the observation of correlated di-proton emission are $^{45}$Fe, $^{48}$Ni, and $^{63}$Se., 30 pages, 3 postscript figures, uses RevTex

Mean lifetimes of 20 out of 31 bound levels in {sup 32}S below an excitation energy of 8.0 MeV are deduced from the Doppler-broadened {gamma}-ray line shapes produced in the reactions {sup 2}H({sup 31}P,n{gamma}){sup 32}S, {sup 28}Si({sup 6}Li,pn{gamma}){sup 32}S, and {sup 31}P(p,{gamma}){sup 32}S. Of the 20 levels, lifetimes for 4 are reported here for the first time. For the remaining 16 levels, the lifetime values obtained in this work are considered to be more reliable and accurate than those reported in the literature. Compared to lifetime measurements reported in the literature, significant procedural improvements have been made by (i) using the entire line shape in the data analysis, (ii) making measurements with targets implanted in high-stopping-power media, and (iii) simulating with the Monte-Carlo method the slowing-down process, experimental conditions, and the delayed feeding from higher levels to the level being analyzed. The low-lying portion of the level scheme, level lifetimes, {gamma}-ray branchings, E2/M1 mixing ratios, and reduced transition probabilities are compared with shell-model calculations. The reduced B(E2) values for 16 out of 18 transitions and B(M1) values for 5 out of 10 transitions are reproduced to within a factor of 5. A one-to-one correspondence between 33 experimental and predicted statesmore » is established up to 8.2 MeV for both positive- and negative-parity states. thinsp {copyright} {ital 1998} {ital The American Physical Society}« less

The similarity renormalization group (SRG) is used to soften interactions for ab initio nuclear structure calculations by decoupling low- and high-energy Hamiltonian matrix elements. The substantial contribution of both initial and SRG-induced three-nucleon forces requires their consistent evolution in a three-particle basis space before applying them to larger nuclei. While, in principle, the evolved Hamiltonians are unitarily equivalent, in practice the need for basis truncation introduces deviations, which must be monitored. Here we present benchmark no-core full configuration calculations with SRG-evolved interactions in $p$-shell nuclei over a wide range of softening. These calculations are used to assess convergence properties, extrapolation techniques, and the dependence of energies, including four-body contributions, on the SRG resolution scale.

We report on Li-6 calculations performed with the IT-NCSM and compare them to full NCSM calculations. We employ the Entem and Machleidt chiral two-body N3LO interaction (regulated at 500 MeV/c), which has been modified to a phase-shift equivalent potential by the similarity renormalization group (SRG) procedure. We investigate the dependence of the procedure on the technique employed to extrapolate to the complete Nmax space, the harmonic oscillator energy, and investigate the dependence on the momentum-decoupling scale (\lambda) used in the SRG. We also investigate the use of one or several reference states from which the truncated basis is constructed. We find that the uncertainties generated from various extrapolating functions used to extrapolate to the complete Nmax space increase as Nmax increases. The extrapolation uncertainties range from a few keV for the smallest Nmax spaces to about 50 keV for the largest Nmax spaces. We note that the difference between extrapolated IT-NCSM and NCSM ground-state energies, however, can be as large as a 100-250 keV depending on the chosen harmonic oscillator energy. We also present the extrapolation of IT-NCSM results to Nmax infinity and compare these to similarly extrapolated full NCSM results., Comment: 22 pages, 12 figures

The giant-dipole resonance (GDR) in ${}^{120}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ is studied as a function of excitation energy, angular momentum, and intrinsic width. Theoretical evaluations of the full width at half maximum (FWHM) for the GDR strength function are compared with recent experimental data and are found to be in overall agreement. Differences observed between ${}^{120}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ are attributed to strong shell corrections in ${}^{208}\mathrm{Pb}$ favoring spherical shapes at low temperatures. At high temperature, the FWHM in ${}^{120}\mathrm{Sn}$ exhibits effects due to the evaporation width of the compound nucleus.

The formalism for the auxiliary-field Monte Carlo approach to the nuclear shell model is presented. The method is based on a linearization of the two-body part of the Hamiltonian in an imaginary-time propagator using the Hubbard-Stratonovich transformation. The foundation of the method, as applied to the nuclear many-body problem, is discussed. Topics presented in detail include: (1) the density-density formulation of the method, (2) computation of the overlaps, (3) the sign of the Monte Carlo weight function, (4) techniques for performing Monte Carlo sampling, and (5) the reconstruction of response functions from an imaginary-time auto-correlation function using MaxEnt techniques. Results obtained using schematic interactions, which have no sign problem, are presented to demonstrate the feasibility of the method, while an extrapolation method for realistic Hamiltonians is presented. In addition, applications at finite temperature are outlined.

Shell-model calculations of solar neutrino absorption cross sections for $^{40}$Ar, the proposed component of the ICARUS detector, are presented. It is found that low-lying Gamow-Teller transitions lead to a significant enhancement of the absorption rate over that expected from the Fermi transition between the isobaric analog states, leading to an overall absorption rate of 6.7 SNU. We also note that the pertinent Gamow-Teller transitions in $^{\sss 40}$Ar are experimentally accessible from the $\beta$-decay of the mirror nucleus $^{\sss 40}$Ti. Predictions for the branching ratios to states in $^{\sss 40}$Sc are presented, and the theoretical halflife of 53~ms is found to be in good agreement with the experimental value of $56^{+18}_{-12}$~ms.

Earlier studies of 239Pu(n, f) have been extended to incident neutron energies up to 20 MeV within the framework of the event-by-event fission model FREYA, into which we have incorporated multichance fission and pre-equilibrium neutron emission. The main parameters controlling prompt fission neutron evaporation have been identified and the prompt fission neutron spectrum has been analyzed by fitting those parameters to the average neutron multiplicity nubar from ENDF-B/VII.0, including the energy-energy correlations in nubar(E) obtained by fitting to the experimental nubar data used in the ENDF-B/VII.0 evaluation. We present our results, discuss relevant tests of this new evaluation, and describe possible further improvements., 20 pages, 26 figures

We report the microscopic origins of the anomalously suppressed beta decay of $^{14}\mathrm{C}$ to $^{14}\mathrm{N}$ using the ab initio no-core shell model with the Hamiltonian from the chiral effective field theory including three-nucleon force terms. The three-nucleon force induces unexpectedly large cancellations within the $p$ shell between contributions to beta decay, which reduce the traditionally large contributions from the nucleon-nucleon interactions by an order of magnitude, leading to the long lifetime of $^{14}\mathrm{C}$.

The main goal for year 2010 was to improve parallelization of the configuration interaction code BIGSTICK, co-written by W. Erich Ormand (LLNL) and Calvin W. Johnson (SDSU), with the parallelization carried out primarily by Plamen Krastev, a postdoc at SDSU and funded in part by this grant. The central computational algorithm is the Lanczos algorithm, which consists of a matrix-vector multiplication (matvec), followed by a Gram-Schmidt reorthogonalization.

We report the microscopic origins of the anomalously suppressed beta decay of ¹⁴C to ¹⁴N using the ab initio no-core shell model with the Hamiltonian from the chiral effective field theory including three-nucleon force terms. The three-nucleon force induces unexpectedly large cancellations within the p shell between contributions to beta decay, which reduce the traditionally large contributions from the nucleon-nucleon interactions by an order of magnitude, leading to the long lifetime of ¹⁴C.

We present the first auxiliary field Monte Carlo calculations for a rare earth nucleus, 170Dy. We calculate various static Hamiltonian is used to demonstrate the physical properties that can be studied in this region. We calculate various static observables for both uncranked and crancked systems and show how the shape distribution evolves with temperature. We also introduce a discretization of the path integral that allows a more efficient Monte Carlo sampling.

A coincidence (electron, γ-ray) experiment designed to identify one or more components of the solar neutrino spectrum has been proposed based on a large array of NaBr detectors. In support of the design of this detector, we calculate the solar neutrino absorption rate for v + 23 Na → 23 Mg + e − within the Standard Solar Model making use of both experimental and theoretical data for the structure of the two nuclei involved. It is found that the inclusion of excited states in 23Mg enhances the absorption cross section by ≈30%, with approximately one third of this enhancement coming from excited states for which experimental data does not exist. The solar neutrino absorption rate is calculated to be 3.5 ± 1.3 SNU, which amounts to about one count every six days for the proposed detector.

A model accounting for the time dependence of shape fluctuations in metal microclusters and their effect on the damping width of the plasmon resonance is discussed. An estimate of the relaxation time of the quadrupole shape is given, and calculations demonstrating the effects of time-dependent thermal fluctuations on the plasmon in K9+ are presented.

We present novel Monte Carlo methods for treating the interacting shell model that allow exact calculations much larger than those heretofore possible. The two-body interaction is linearized by an auxiliary field; Monte Carlo evaluation of the resulting functional integral gives ground-state or thermal expectation values of few-body operators. The ``sign problem'' generic to quantum Monte Carlo calculations is absent in a number of cases. We discuss the favorable scaling of these methods with nucleon numb er and basis size and their suitability to parallel computation., 13 pages, MAP-148

This is document reports the progress and accomplishments achieved in 2006-2007 with LDRD funding under the proposal 06-LW-013, 'Nuclear Physics the Monte Carlo Way'. The project was a theoretical study to explore a novel approach to dealing with a persistent problem in Monte Carlo approaches to quantum many-body systems. The goal was to implement a solution to the notorious 'sign-problem', which if successful, would permit, for the first time, exact solutions to quantum many-body systems that cannot be addressed with other methods. In this document, we outline the progress and accomplishments achieved during FY2006-2007 with LDRD funding in the proposal 06-LW-013, 'Nuclear Physics the Monte Carlo Way'. This project was funded under the Lab Wide LDRD competition at Lawrence Livermore National Laboratory. The primary objective of this project was to test the feasibility of implementing a novel approach to solving the generic quantum many-body problem, which is one of the most important problems being addressed in theoretical physics today. Instead of traditional methods based matrix diagonalization, this proposal focused a Monte Carlo method. The principal difficulty with Monte Carlo methods, is the so-called 'sign problem'. The sign problem, which will discussed in some detail later, is endemic to Monte Carlomore » approaches to the quantum many-body problem, and is the principal reason that they have not been completely successful in the past. Here, we outline our research in the 'shifted-contour method' applied the Auxiliary Field Monte Carlo (AFMC) method.« less

This document contains a comprehensive literature review in support of the theoretical assessment of the {sup 178m2}Hf de-excitation, as well as a rigorous description of controlled energy release from an isomeric nuclear state.

We outline two complementary approaches based on the no core shell model (NCSM) and present recent results. In the ab initio approach, nuclear properties are evaluated with two-nucleon (NN) and three-nucleon interactions (TNI) derived within effective field theory (EFT) based on chiral perturbation theory (ChPT). Fitting two available parameters of the TNI generates good descriptions of light nuclei. In a second effort, an ab exitu approach, results are obtained with a realistic NN interaction derived by inverse scattering theory with off-shell properties tuned to fit light nuclei. Both approaches produce good results for observables sensitive to spin-orbit properties.

We outline the ab initio no core shell model and present recent results. Nuclear properties are evaluated with two‐nucleon (NN) and three‐nucleon interactions (TNI) derived within effective field theory (EFT) based on chiral perturbation theory (ChPT). Fitting two available parameters of the TNI generates good descriptions of light nuclei. In another effort, referred to as the ab exitu approach, results are obtained with a realistic NN interaction derived by inverse scattering theory with off‐shell properties tuned to fit light nuclei. Both approaches produce good results for observables sensitive to spin‐orbit properties. In a third approach, we supplement the derived realistic effective interaction with phenomenological NN interaction terms with the goal to describe spectra of fp‐shell nuclei in the limited basis spaces currently available.

The stability of nuclei is a balance between the kinetic energy of the nucleons, the Coulomb repulsion and the nuclear attraction, resulting in the fact that no compound nucleus seems to exist at temperatures above 6–8 MeV. Even at lower temperatures, the competition between single-particle and collective channels through which the compound nucleus cools down is such that the variety of collective modes may not exist at all temperatures. Furthermore, even if the coupling of a collective mode to the compound nucleus is adequate to secure its excitation at a given temperature, the width associated from mechanisms different from compound-nucleus decay may be so large that the mode is overdamped and consequently, not directly observable as a independent mode. In the present paper, information about these temperatures for the case of the giant dipole resonance will be discussed. It will be suggested that the first temperature is controlled by the times it takes the vibration and the neutron motion to couple to the compound nucleus, while the second temperature reflects the relaxation time associated with quadrupole surface deformations.

A model accounting for the time dependence of thermal shape fluctuations in hot nuclei and their effects on the giant-dipole resonance (GDR) is presented. The thermal fluctuations are assumed to be governed by a Kubo-Anderson process, while the GDR is modeled by a classical rotating harmonic oscillator, where the photon cross section is obtained by examining the average power absorbed by a harmonic external driving force. Experimental data for Er and Sn isotopes are compared with theoretical calculations, and evidence for the motional narrowing of the GDR is investigated.

Properties of finite nuclei are evaluated with two-nucleon (NN) and three-nucleon (NNN) interactions derived within chiral effective field theory (EFT). The nuclear Hamiltonian is fixed by properties of the A = 2 system, except for two low-energy constants (LECs) that parameterize the short range NNN interaction. We constrain those two LECs by a fit to the A = 3 system binding energy and investigate sensitivity of {sup 4}He, {sup 6}Li, {sup 10,11}B and {sup 12,13}C properties to the variation of the constrained LECs. We identify a preferred choice that gives globally the best description. We demonstrate that the NNN interaction terms significantly improve the binding energies and spectra of mid-p-shell nuclei not just with the preferred choice of the LECs but even within a wide range of the constrained LECs. At the same time, we find that a very high quality description of these nuclei requires further improvements to the chiral Hamiltonian.

An experimental study of the lower fp-shell nuclei Sc-42,Sc-43 was performed via alpha pn and alpha p evaporation, respectively, from Ne-20 + Si-28 and Mg-24 + Mg-24 fusion-evaporation reactions. The experiments were conducted with the Gammasphere and Microball detector arrays. The level schemes of both nuclei have been extended considerably. Terminating states associated with the f(7/2)(n) and d(3/2)(-1)f(7/2)(n+1) configurations were identified in each nuclide and incorporated into detailed comparisons with neighboring nuclei and with shell model calculations. The energy differences between the terminating states provide a test of the sd-fp cross-shell interactions in these calculations.

The no-core shell model (NCSM), in which all A nucleons are treated as active, is an ab initio approach for calculating the properties of nuclei microscopically. We first present the basic NCSM formalism, which allows us to exactly determine the effective Hamiltonian as well as any general operator in a model space of arbitrary size for performing shell-model calculations. Good results for binding energies and spectra have been obtained for nuclei up to mass A = 14 using the best available two-nucleon (NN) and theoretical three-nucleon forces (3NF's). We next present three new applications and extensions of the NCSM approach: I) the use of the NCSM in the three-nucleon (3N) cluster approximation as a method for testing the reliability of different 3NF's, and the application of the NCSM to 2) other general operators and 3) inclusive electromagnetic responses.

Report on the progress achieved in 04-ERD-058. The primary goal of the project was to investigate new methods to provide a comprehensive understanding of how reactions between light nuclei proceed in hot, dense environments, such as stellar interiors. The project sought to develop an entirely new theoretical framework to describe the dynamics of nuclear collisions based on the fundamental nuclear interactions. Based on the new theoretical framework, new computational tools were developed to address specific questions in nuclear structure and reactions. A full study of the true nature of the three-nucleon interaction was undertaken within the formalism of effective field theory. We undertook a preliminary theoretical study of the quantum corrections to electron screening in thermal plasmas to resolve a discrepancy exhibited in previous theoretical approaches.

Properties of finite nuclei are evaluated with two-nucleon (NN) and three-nucleon (NNN) interactions derived within chiral effective field theory. The nuclear Hamiltonian is fixed by properties of the A=2 system, except for two low-energy constants (LECs) that parametrize the short range NNN interaction, which we constrain with the A=3 binding energies. We investigate the sensitivity of 4He, 6Li, 10,11B, and 12,13C properties to the variation of the constrained LECs. We identify observables that are sensitive to this variation and find preferred values that give the best overall description. We demonstrate that the NNN interaction terms significantly improve the binding energies and spectra of mid-p-shell nuclei not just with the preferred choice of the LECs but even within a wide range of the constrained LECs. We find that a very high quality description of these nuclei requires further improvements to the chiral Hamiltonian.

Recent developments in nuclear theory allow us to make a connection between quantum chromodynamics (QCD) and low-energy nuclear physics. First, chiral effective field theory (chiEFT) provides a natural hierarchy to define two-nucleon (NN), three-nucleon (NNN), and even four-nucleon interactions. Second, ab initio methods have been developed capable to test these interactions for light nuclei. In this contribution, we discuss ab initio no-core shell model (NCSM) calculations for s-shell and p-shell nuclei with NN and NNN interactions derived within chiEFT., Comment: 6 pages, 6 figures, proceedings of the 20th European Conference on Few-Body Problems in Physics (EFB20)