Search

We present a brief overview of recent developments in ab initio calculations of nuclear scattering and reactions with a focus on applications of the no-core shell model with continuum method., Comment: 9 pages, 7 figures (one more figure than in the published version)

This is a collection of perspective pieces contributed by the participants of the Institute of Nuclear Theory's Program on Nuclear Physics for Precision Nuclear Physics which was held virtually from April 19 to May 7, 2021. The collection represents the reflections of a vibrant and engaged community of researchers on the status of theoretical research in low-energy nuclear physics, the challenges ahead, and new ideas and strategies to make progress in nuclear structure and reaction physics, effective field theory, lattice QCD, quantum information, and quantum computing. The contributed pieces solely reflect the perspectives of the respective authors and do not represent the viewpoints of the Institute for Nuclear theory or the organizers of the program., Perspective pieces of the virtual INT program 21-1b "Nuclear Forces for Precision Nuclear Physics", 107 pages

We use coupled-cluster theory and nuclear interactions from chiral effective field theory to compute the nuclear matrix element for the neutrinoless double-$\ensuremath{\beta}$ decay of $^{48}\mathrm{Ca}$. Benchmarks with the no-core shell model in several light nuclei inform us about the accuracy of our approach. For $^{48}\mathrm{Ca}$ we find a relatively small matrix element. We also compute the nuclear matrix element for the two-neutrino double-$\ensuremath{\beta}$ decay of $^{48}\mathrm{Ca}$ with a quenching factor deduced from two-body currents in recent ab initio calculation of the Ikeda sum rule in $^{48}\mathrm{Ca}$ [Gysbers et al., Nat. Phys. 15, 428 (2019)].

In any finite system, the presence of a non-zero permanent electric dipole moment (EDM) would indicate CP violation beyond the small violation predicted in the Standard Model. Here, we use the ab initio no-core shell model (NCSM) framework to theoretically investigate the magnitude of the nuclear EDM. We calculate EDMs of several light nuclei using chiral two- and three-body interactions and a PT-violating Hamiltonian based on a one-meson-exchange model. We present a benchmark calculation for $^3$He, as well as results for the more complex nuclei $^{6,7}$Li, $^9$Be, $^{10,11}$B, $^{13}$C, $^{14,15}$N, and $^{19}$F. Our results suggest that different nuclei can be used to probe different terms of the PT violating interaction. These calculations allow us to suggest which nuclei may be good candidates in the search for a measurable permanent electric dipole moment., 6 pages, 3 figures, matches published version

Background: The $^{8}\mathrm{Li}(n,\ensuremath{\gamma})^{9}\mathrm{Li}$ reaction plays an important role in several astrophysics scenarios. It cannot be measured directly and indirect experiments have so far provided only cross section limits. Theoretical predictions differ by an order of magnitude.Purpose: In this work we study the properties of $^{9}\mathrm{Li}$ bound states and low-lying resonances and calculate the $^{8}\mathrm{Li}(n,\ensuremath{\gamma})^{9}\mathrm{Li}$ cross section within the no-core shell model with continuum (NCSMC) with chiral nucleon-nucleon and three-nucleon interactions as input.Methods: The NCSMC is an ab initio method applicable to light nuclei that provides a unified description of bound and scattering states well suited to calculate low-energy nuclear scattering and reactions. For the capture cross section calculation, we adjust calculated thresholds to experimental values.Results: Our calculations reproduce the experimentally known bound states as well as the lowest $5/{2}^{\ensuremath{-}}$ resonance of $^{9}\mathrm{Li}$. We predict a $3/{2}^{\ensuremath{-}}$ spin-parity assignment for the resonance observed at 5.38 MeV. In addition to the very narrow $7/{2}^{\ensuremath{-}}$ resonance corresponding presumably to the experimental 6.43 MeV state, we find several other broad low-lying resonances.Conclusions: Our calculated $^{8}\mathrm{Li}(n,\ensuremath{\gamma})^{9}\mathrm{Li}$ cross section is within the limits derived from the 1998 National Superconducting Cyclotron Laboratory Coulomb-dissociation experiment [Phys. Rev. C 57, 959 (1998)]. However, it is higher than cross sections obtained in recent phenomenological studies. It is dominated by a direct E1 capture to the ground state with a resonant contribution at $\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}0.2$ MeV due to E2/M1 radiation enhanced by the $5/{2}^{\ensuremath{-}}$ resonance.

Precision measurements of $\beta$-decay observables offer the possibility to search for deviations from the Standard Model. A possible discovery of such deviations requires accompanying first-principles calculations. Here we compute the nuclear structure corrections for the $\beta$-decay of $^6$He which is of central interest in several experimental efforts. We employ the impulse approximation together with wave functions calculated using the ab initio no-core shell model with potentials based on chiral effective field theory. We use these state-of-the-art calculations to give a novel and comprehensive analysis of theoretical uncertainties. We find that nuclear corrections, which we compute within the sensitivity of future experiments, create significant deviation from the naive Gamow-Teller predictions, making their accurate assessment essential in searches for physics beyond the Standard Model., Comment: Published version

Background: In a previous series of papers we investigated the domain of applicability of chiral potentials to the construction of a microscopic optical potential (OP) for elastic nucleon-nucleus scattering. The OP was derived at the first order of the spectator expansion of the Watson multiple scattering theory and its final expression was a folding integral between the nucleon-nucleon ($NN$) $t$ matrix and the nuclear density of the target. In the calculations $NN$ and three-nucleon ($3N$) chiral interactions were used for the target density and only the $NN$ interaction for the $NN t$ matrix.Purpose: The purpose of this work is to achieve another step towards the calculation of a more consistent OP introducing the $3N$ force also in the dynamic part of the OP.Methods: The full treatment of the $3N$ interaction is beyond our present capabilities. Thus, in the present work it is approximated with a density dependent $NN$ interaction obtained after the averaging over the Fermi sphere. In practice, in our model the $3N$ force acts as a medium correction of the bare $NN$ interaction used to calculate the $t$ matrix. Even if the $3N$ force is treated in an approximate way, this method naturally extends our previous model of the OP and allows a direct comparison of our present and previous results.Results: We consider as case studies the elastic scattering of nucleons off $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$. We present results for the differential cross section and the spin observables for different values of the projectile energy. From the comparison with the experimental data and with the results of our previous model we assess the importance of the $3N$ interaction in the dynamic part of the OP.Conclusions: Our analysis indicates that the contribution of the $3N$ force in the $t$ matrix is small for the differential cross section and it is sizable for the spin observables, in particular, for the analyzing power. We find that the two-pion exchange term is the major contributor to the $3N$ force. A chiral expansion order-by-order analysis of the scattering observables confirms the convergence of our results at the next-to-next-to-next-to-leading-order, as already established in our previous work.

Background: In recent years, we constructed a microscopic optical potential (OP) for elastic nucleon-nucleus (NA) scattering using modern approaches based on chiral theories for the nucleon-nucleon (NN) interaction. The OP was derived at first order of the spectator expansion in Watson multiple scattering theory and its final expression was a folding integral between the NN t matrix and the nuclear density of the target. Two- and three-body forces are consistently included both in the target and in the projectile description. Purpose: The purpose of this work is to apply our microscopic OP to nuclei characterized by a ground state of spin-parity quantum numbers Jπ≠0+. Methods: We extended our formalism to include the spin of the target nucleus. The full amplitudes of the NN reaction matrix are retained in the calculations starting from two- and three-body chiral forces. Results: The microscopic OP can be applied in the energy range 100≤E≤350 MeV. We show a remarkable agreement with experimental data for the available observables and, simultaneously, provide reliable estimates for the theoretical uncertainties. Conclusions: This work paves the way toward a full microscopic approach to inelastic NA scattering, showing that the derivation of optical potentials between states with Jπ≠0+ is completely under control.

Measurements of nuclear spin-dependent parity-violating (NSD-PV) effects provide an excellent opportunity to test nuclear models and to search for physics beyond the Standard Model. Molecules possess closely-spaced states with opposite parity which may be easily tuned to degeneracy to greatly enhance the observed parity-violating effects. A high-sensitivity measurement of NSD-PV effects using light triatomic molecules is in preparation [E. B. Norrgard, et al., Commun. Phys. 2, 77 (2019)]. Importantly, by comparing these measurements in light nuclei with prior and ongoing measurements in heavier systems, the contribution to NSD-PV from $Z^0$-boson exchange between the electrons and the nuclei may be separated from the contribution of the nuclear anapole moment. Furthermore, light triatomic molecules offer the possibility to search for new particles, such as the postulated $Z^{\prime}$ boson. In this work, we detail a sensitive measurement scheme and present high-accuracy molecular and nuclear calculations needed for interpretation of NSD-PV experiments on triatomic molecules composed of light elements Be, Mg, N, and C. The ab initio nuclear structure calculations, performed within the No-Core Shell Model (NCSM) provide a reliable prediction of the magnitude of different contributions to the NSD-PV effects in the four nuclei. These results differ significantly from the predictions of the standard single-particle model and highlight the importance of including many-body effects in such calculations. In order to extract the NSD-PV contributions from measurements, a parity-violating interaction parameter $W_{\text{PV}}$, which depends on molecular structure, needs to be known with high accuracy. We have calculated these parameters for the triatomic molecules of interest using the relativistic coupled-cluster approach., Comment: 16 pages, 4 figures, and 6 tables

We report a comprehensive study of $^{10--14}\mathrm{B}$ isotopes within the ab initio no-core shell model (NCSM) using realistic nucleon-nucleon ($\mathit{NN}$) interactions. In particular, we have applied the inside nonlocal outside Yukawa (INOY) interaction to study energy spectra, electromagnetic properties, and point-proton radii of the boron isotopes. The NCSM results with the charge-dependent Bonn 2000 (CDB2K), the chiral next-to-next-to-next-to-leading order (${\mathrm{N}}^{3}\mathrm{LO}$), and optimized next-to-next-to-leading order (${\mathrm{N}}^{2}{\mathrm{LO}}_{opt}$) interactions are also reported. We have reached basis sizes up to ${N}_{\mathrm{max}}=10$ for $^{10}\mathrm{B}, {N}_{\mathrm{max}}=8$ for $^{11,12,13}\mathrm{B}$, and ${N}_{\mathrm{max}}=6$ for $^{14}\mathrm{B}$ with $m$-scheme dimensions up to $1.7\ifmmode\times\else\texttimes\fi{}{10}^{9}$. We also compare the NCSM calculations with the phenomenological YSOX interaction using the shell model to test the predictive power of the ab initio nuclear theory. Overall, our NCSM results are consistent with the available experimental data. The experimental ground state spin ${3}^{+}$ of $^{10}\mathrm{B}$ has been reproduced using the INOY $\mathit{NN}$ interaction. Typically, the $3N$ interaction is required to correctly reproduce the aforementioned state.

Ab initio calculations of bulk nuclear properties (ground-state energies, root mean square charge radii and charge density distributions) are presented for seven complete isotopic chains around calcium, from argon to chromium. Calculations are performed within the Gorkov self-consistent Green's function approach at second order and make use of two state-of-the-art two- plus three-nucleon Hamiltonians, $NN$+$3N\text{(lnl)}$ and NNLO$_{\text{sat}}$. An overall good agreement with available experimental data is found, in particular for differential energies (charge radii) when the former (latter) interaction is employed. Remarkably, neutron magic numbers $N=28,32,34$ emerge and evolve following experimental trends. In contrast, pairing gaps are systematically underestimated. General features of the isotopic dependence of charge radii are also reproduced, as well as charge density distributions. A deterioration of the theoretical description is observed for certain nuclei and ascribed to the inefficient account of (static) quadrupole correlation in the present many-body truncation scheme. In order to resolve these limitations, we advocate the extension of the formalism towards incorporating breaking of rotational symmetry or, alternatively, performing a stochastic sampling of the self-energy., 17 pages, 14 figures

The strength of the $N=28$ magic number in neutron-rich argon isotopes is examined through high-precision mass measurements of $^{46\text{--}48}\mathrm{Ar}$, performed with the ISOLTRAP mass spectrometer at ISOLDE/CERN. The new mass values are up to 90 times more precise than previous measurements. While they suggest the persistence of the $N=28$ shell closure for argon, we show that this conclusion has to be nuanced in light of the wealth of spectroscopic data and theoretical investigations performed with the SDPF-U phenomenological shell model interaction. Our results are also compared with ab initio calculations using the valence space in-medium similarity renormalization group and the self-consistent Green's function approaches. Both calculations provide a very good account of mass systematics at and around $Z=18$ and, generally, a consistent description of the physics in this region. This combined analysis indicates that $^{46}\mathrm{Ar}$ is the transition between the closed-shell $^{48}\mathrm{Ca}$ and collective $^{44}\mathrm{S}$.

A recently modified method to enable low-energy nuclear scattering results to be extracted from the discrete energy levels of the target-projectile clusters confined by harmonic potential traps is tested. We report encouraging results for neutron--$\alpha$ and neutron--$^{24}\mathrm{O}$ elastic scattering from analyzing the trapped levels computed using two different ab initio nuclear structure methods. The $n$--$\alpha$ results have also been checked against a direct ab initio reaction calculation. The $n$--$^{24}\mathrm{O}$ results demonstrate the approach's applicability for a large range of systems provided their spectra in traps can be computed by ab initio methods. A key ingredient is a rigorous understanding of the errors in the calculated energy levels caused by inevitable Hilbert-space truncations in the ab initio methods., Comment: Close to the published version; ancillary files attached; modifications: (1) the naming of the method is changed in the title and text, (2) a concentrated discussion of error sources is included in the main text, and (3) comparisons with existing methods are included in the supplemental material

Elastic scattering of antiprotons off $^{4}\mathrm{He}$, $^{12}\mathrm{C}$, and $^{16,18}\mathrm{O}$ is described for the first time with a consistent microscopic approach based on the calculation of an optical potential (OP) describing the antiproton-target interaction. The OP is derived using the recent antiproton-nucleon ($\overline{p}N$) chiral interaction to calculate the $\overline{p}N$ $t$ matrix, while the target densities are computed with the ab initio no-core shell model using chiral interactions as well. Our results are in good agreement with the existing experimental data and the results computed at different chiral orders of the $\overline{p}N$ interaction display a well-defined convergence pattern.

Background: Modern ab initio theory combined with high-quality nucleon-nucleon (NN) and three-nucleon (3N) interactions from chiral effective field theory (EFT) can provide a predictive description of low-energy light-nuclei reactions relevant for astrophysics and fusion-energy applications. However, the high cost of computations has so far impeded a complete analysis of the uncertainty budget of such calculations. Purpose: Starting from NN potentials up to fifth order (N4LO) combined with leading-order 3N forces, we study how the order-by-order convergence of the chiral expansion and confidence intervals for the 3N contact and contact-plus-one-pion-exchange low-energy constants (cE and cD) contribute to the overall uncertainty budget of many-body calculations of neutron-He elastic scattering. Methods: We compute structure and reaction observables for three-, four- and five-nucleon systems within the ab initio frameworks of the no-core shell model an no-core shell model with continuum. Using a small set of design runs, we construct a Gaussian process model (GPM) that acts as a statistical emulator for the theory. With this, we gain insight into how uncertainties in the 3N low-energy constants propagate throughout the calculation and determine the Bayesian posterior distribution of these parameters with Markov-Chain Monte-Carlo., 12 pages, 11 figures

Due to the limitations of present-day quantum hardware, it is especially critical to design algorithms that make the best possible use of available resources. When simulating quantum many-body systems on a quantum computer, straightforward encodings that transform many-body Hamiltonians into qubit Hamiltonians use $N$ of the available basis states of an $N$-qubit system, whereas $2^N$ are in theory available. We explore an efficient encoding that uses the entire set of basis states, where terms in the Hamiltonian are mapped to qubit operators with a Hamiltonian that acts on the basis states in Gray code order. This encoding is applied to the commonly-studied problem of finding the ground state energy of a deuteron with a simulated variational quantum eigensolver (VQE). It is compared to a standard "one-hot" encoding, and various trade-offs that arise are analyzed. The energy distribution of VQE solutions has smaller variance than the one obtained by the one-hot encoding even in the presence of simulated hardware noise, despite an increase in the number of measurements. The reduced number of qubits and a shorter-depth variational ansatz enables the encoding of larger problems on current-generation machines. This encoding also demonstrates improvements for simulating time evolution of the same system, producing circuits for the evolution operators with reduced depth and roughly half the number of gates compared to a one-hot encoding., Comment: 22 pages, 15 figures

A novel parameterisation of a Hamiltonian based on chiral effective field theory is introduced. Specifically, three-nucleon operators at next-to-next-to-leading order are combined with an existing (and successful) two-body interaction containing terms up to next-to-next-to-next-to-leading order. The resulting potential is labelled $N\!N\!$+$3N\text{(lnl)}$. The objective of the present work is to investigate the performance of this new Hamiltonian across light and medium-mass nuclei. Binding energies, nuclear radii and excitation spectra are computed using no-core shell model and self-consistent Green's function approaches. Calculations with $N\!N\!$+$3N\text{(lnl)}$ are compared to two other representative Hamiltonians currently in use, namely NNLO$_{\text{sat}}$ and the older $N\!N\!$+$3N(400)$. Overall, the performance of the novel interaction is very encouraging. In light nuclei, total energies are generally in good agreement with experimental data. Known spectra are also well reproduced with a few notable exceptions. The good description of ground-state energies carries on to heavier nuclei, all the way from oxygen to nickel isotopes. Except for those involving excitation processes across the $N=20$ gap, which is overestimated by the new interaction, spectra are of very good quality, in general superior to those obtained with NNLO$_{\text{sat}}$. Although largely improving on $N\!N\!$+$3N(400)$ results, charge radii calculated with $N\!N\!$+$3N\text{(lnl)}$ still underestimate experimental values, as opposed to the ones computed with NNLO$_{\text{sat}}$ that successfully reproduce available data on nickel. On the whole, the new two- plus three-nucleon Hamiltonian introduced in the present work represents a promising alternative to existing nuclear interactions., 21 pages, 22 figures, matches published version

Exclusive cross sections and momentum distributions have been measured for quasifree one-neutron knockout reactions from a ^{54}Ca beam striking on a liquid hydrogen target at ∼200 MeV/u. A significantly larger cross section to the p_{3/2} state compared to the f_{5/2} state observed in the excitation of ^{53}Ca provides direct evidence for the nature of the N=34 shell closure. This finding corroborates the arising of a new shell closure in neutron-rich calcium isotopes. The distorted-wave impulse approximation reaction formalism with shell model calculations using the effective GXPF1Bs interaction and ab initio calculations concur our experimental findings. Obtained transverse and parallel momentum distributions demonstrate the sensitivity of quasifree one-neutron knockout in inverse kinematics on a thick liquid hydrogen target with the reaction vertex reconstructed to final state spin-parity assignments.

Recently, the bound and continuum spectrum of $^{11}\mathrm{Be}$ has been calculated within the ab initio no-core shell model with continuum (NCSMC) method, with the parity inversion in the ground state successfully reproduced. The continuum spectrum obtained is in agreement with known experimental levels. The S matrix contained in the NCSMC continuum wave functions of the $\mathrm{n}+^{10}\mathrm{Be}$ system is used in this work for the first time in a transfer-to-the-continuum (TC) reaction calculation. The TC approach is applied to study the excitation energy spectrum of $^{11}\mathrm{Be}$ measured in the $^{9}\mathrm{Be}(^{18}\mathrm{O},^{16}\mathrm{O})^{11}\mathrm{Be}$ reaction at 84 MeV. Previously known levels are confirmed and theoretical and experimental evidence for a 9/${2}^{+}$ state at ${E}_{x}=5.8$ MeV is given, whose configuration is thought to be $^{10}\mathrm{Be}({2}^{+})+\mathrm{n}({d}_{5/2})$.

Background: The production of $^{7}\mathrm{Be}$ and $^{7}\mathrm{Li}$ nuclei plays an important role in primordial nucleosynthesis, nuclear astrophysics, and fusion energy generation. The $^{3}\mathrm{He}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Be}$ and $^{3}\mathrm{H}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Li}$ radiative-capture processes are important to determine the $^{7}\mathrm{Li}$ abundance in the early universe and to predict the correct fraction of $pp$-chain branches resulting in $^{7}\mathrm{Be}$ versus $^{8}\mathrm{B}$ neutrinos. The $^{6}\mathrm{Li}(p,\ensuremath{\gamma})^{7}\mathrm{Be}$ has been investigated recently hinting at a possible cross section enhacement near the thershold. The $^{6}\mathrm{Li}(n,^{3}\mathrm{H})^{4}\mathrm{He}$ process can be utilized for tritium breeding in machines dedicated to fusion energy generation through the deuteron-tritium reaction, and is a neutron cross section standard used in the measurement and evaluation of fission cross sections.Purpose: In this work we study the properties of $^{7}\mathrm{Be}$ and $^{7}\mathrm{Li}$ within the no-core shell model with continuum (NCSMC) method, using chiral nucleon-nucleon interactions as the only input, and analyze all the binary mass partitions involved in the formation of these systems.Methods: The NCSMC is an ab initio method applicable to light nuclei that provides a unified description of bound and scattering states and thus is well suited to investigate systems with many resonances and pronounced clustering like $^{7}\mathrm{Be}$ and $^{7}\mathrm{Li}$.Results: Our calculations reproduce all the experimentally known states of the two systems and provide predictions for several new resonances of both parities. Some of these new possible resonances are built on the ground states of $^{6}\mathrm{Li}$ and $^{6}\mathrm{He}$, and thus represent a robust prediction. We do not find any resonance in the $p+^{6}\mathrm{Li}$ mass partition near the threshold. On the other hand, in the $p+^{6}\mathrm{He}$ mass partition of $^{7}\mathrm{Li}$ we observe an $S$-wave resonance near the threshold producing a very pronounced peak in the calculated $S$ factor of the $^{6}\mathrm{He}(p,\ensuremath{\gamma})^{7}\mathrm{Li}$ radiative-capture reaction.Conclusions: While we do not find a resonance near the thershold in the $p+^{6}\mathrm{Li}$ channel, in the case of $^{6}\mathrm{He}+p$ reaction a resonant $S$-wave state is predicted at a very low energy above the reaction threshold, which could be relevant for astrophysics and its implications should be investigated. We note though that this state lies above the three-body breakup threshold not included in our method and may be influenced by three-body continuum correlations.

We show the first results for the elastic scattering of neutrons off oxygen and calcium isotopes obtained from ab initio optical potentials. The potential is derived using self consistent Green's function theory (SCGF) with the saturating chiral interaction NNLO$_{\textrm{sat}}$. Our calculations are compared to available scattering data and show that it is possible to reproduce low energy scattering observables in medium mass nuclei from first principles., 6 pages, 4 figures, Zakopane conference on nuclear physics

$\beta$-decay, a process that changes a neutron into a proton (and vice versa), is the dominant decay mode of atomic nuclei. This decay offers a unique window to physics beyond the standard model, and is at the heart of microphysical processes in stellar explosions and the synthesis of the elements in the Universe. For 50 years, a central puzzle has been that observed $\beta$-decay rates are systematically smaller than theoretical predictions. This was attributed to an apparent quenching of the fundamental coupling constant $g_A \simeq $ 1.27 in the nucleus by a factor of about 0.75 compared to the $\beta$-decay of a free neutron. The origin of this quenching is controversial and has so far eluded a first-principles theoretical understanding. Here we address this puzzle and show that this quenching arises to a large extent from the coupling of the weak force to two nucleons as well as from strong correlations in the nucleus. We present state-of-the-art computations of $\beta$-decays from light to heavy nuclei. Our results are consistent with experimental data, including the pioneering measurement for $^{100}$Sn. These theoretical advances are enabled by systematic effective field theories of the strong and weak interactions combined with powerful quantum many-body techniques. This work paves the way for systematic theoretical predictions for fundamental physics problems. These include the synthesis of heavy elements in neutron star mergers and the search for neutrino-less double-$\beta$-decay, where an analogous quenching puzzle is a major source of uncertainty in extracting the neutrino mass scale., Comment: 20 pages, 18 figures

The exotic Borromean nucleus $^{20}$Mg with $N$ = 8, located at the proton drip-line provides a unique testing ground for nuclear forces and the evolution of shell structure in the neutron-deficient region. We report on the first observation of proton unbound resonances together with bound states in $^{20}$Mg from the $^{20}$Mg($d$,$d'$) reaction performed at TRIUMF. Phenomenological shell-model calculations offer a reasonable description. However, our experimental results present a challenge for current first-principles nuclear structure approaches and point to the need for improved chiral forces and {\it ab initio} calculations. Furthermore, the differential cross section of the first excited state is compared with distorted-wave Born approximation calculations to deduce a neutron quadrupole deformation parameter of $\beta_n$=0.46$\pm$0.21. This provides the first indication of a possible weakening of the $N$ = 8 shell closure at the proton drip-line.

To better understand response or fracture conditions of the ceramic foam materials to the mechanical loading, a finite element (FE) analysis of these structures has to be employed. The cellular structure of foams can be modelled either using a detailed realistic FE model based on the computer tomography scans or by using of simplified, beam element based, models. Nevertheless a main drawback of the realistic foam modelling consists in its high demandingness on computational resources. Therefore, simplified models are welcome substitutions (at least for analysis of the global mechanical foam response). The regular foam structure, based e.g. on Kelvin cells, is simple from the modelling point of view, but it doesn´t exactly capture the fully random character of the real foam structures and corresponding response to the external load. Definition of the random beam foam structure (respecting the real cell shapes and their distribution within volume), can thus improve this deficiency. The main aim of this work is thus to compare these different modelling approaches and quantify the influence of the foam irregularity on the response of ceramic foams to external (tensile) loading for various model sizes.

The 3He(α,γα,γ)7Be and 3H(α,γα,γ)7Li astrophysical S factors are calculated within the no-core shell model with continuum using a renormalized chiral nucleon–nucleon interaction. The 3He(α,γα,γ)7Be astrophysical S factors agree reasonably well with the experimental data while the 3H(α,γα,γ)7Li ones are overestimated. The seven-nucleon bound and resonance states and the α + 3He/3H elastic scattering are also studied and compared with experiment. The low-lying resonance properties are rather well reproduced by our approach. At low energies, the s-wave phase shift, which is non-resonant, is overestimated.

Stress/strain concentration around a crack tip in ceramic foam-like structures, where the characteristic size of the foam cell is comparable with a typical length over which field quantities change significantly, is analysed. It is convenient to replace the foam structure by an effective continuum which retains all necessary characteristic features of the foam. To this end a homogenized cracked open cell ceramic foam is analysed using the strain/stress model based upon an implicit dependence of the non-local stress and strain on the local stress and strain in the form of an inhomogeneous Helmholtz equation which is solved together with the equilibrium equations. To preserve the advantage of the uncoupled system of equations, which means that one set of equations is solved prior the other one and that two sets of shape functions can be chosen independently, are current sequence of well posed boundary value problems is constructed which can be solved using a classical 8-nodes isoparametric element for 2D problems. The key idea behind the suggested procedure consists in replacing the scale parameter l by a parameter increment dl chosen arbitrarily small. The given small disturbance causes are distribution of the local stress/displacement field. After the new local stress/displacement field is known, another disturbance is introduced and so on. The procedure is stopped when the solution, exhibiting boundary layer behaviour, leads to the cohesive-like zone with length reaching a value uniquely related to the scale parameter l. V rámci této publikace je analyzována deformačně-napěťová odezva v blízkém okolí čela trhliny, která je situována uprostřed zkušebního vzorku (keramická pěna s otevřenou pórovitostí) kolmo vzhledem k jeho zatížení. K řešení byla použita teorie gradientní elasticity, která zohledňuje charakteristický rozměr dané struktury (zde Kelvinova buňka). Vzhledem k časové a hardwarové náročnosti řešení na diskrétní struktuře byla provedena homogenizace materiálových charakteristik a deformačně-napěťová odezva je řešena, za podmínek rovinné deformace, na 2D modelu kontinua.

The ground-state energies and radii for $^{4}$He, $^{16}$O, and $^{40}$Ca are calculated with the unitary-model-operator approach (UMOA). In the present study, we employ the similarity renormalization group (SRG) evolved nucleon-nucleon ($NN$) and three-nucleon ($3N$) interactions based on the chiral effective field theory. This is the first UMOA calculation with both $NN$ and $3N$ interactions. The calculated ground-state energies and radii are consistent with the recent {\it ab initio} results with the same interaction. We evaluate the expectation values with two- and three-body SRG evolved radius operators, in addition to those with the bare radius operator. With the aid of the higher-body evolution of radius operator, it is seen that the calculated radii tend to be SRG resolution-scale independent. We find that the SRG evolution gives minor modifications for the radius operator., Comment: 11 pages, 7 figures

We report on the first γ-ray spectroscopy of 51,53K produced via the 52,54Ca(p,2p) reactions at ∼250 MeV/nucleon. Unambiguous final-state angular-momentum assignments were achieved for beam intensities down to few particles per second by using a new technique based on reaction vertex tracking combined with a thick liquid-hydrogen target. Through γ-ray spectroscopy and exclusive parallel momentum distribution analysis, 3/2+ ground states and 1/2+ first excited states in 51,53K were established quantifying the natural ordering of the 1 d 3 / 2 and 2 s 1 / 2 proton-hole states that are restored at N = 32 and 34. State-of-the-art ab initio calculations and shell-model calculations with improved phenomenological effective interactions reproduce the present data and predict consistently the increase of the E(1/2 1 + ) - E(3/2 1 + ) energy differences towards N = 40.

Background: The nuclear kinetic density is one of many fundamental quantities in density functional theory (DFT) dependent on the nonlocal nuclear density. Often, approximations may be made when computing the density that may result in spurious contributions in other DFT quantities. With the ability to compute the nonlocal nuclear density from ab initio wave functions, it is now possible to estimate effects of such spurious contributions. Purpose: We derive the kinetic density using ab initio nonlocal scalar one-body nuclear densities computed within the no-core shell model (NCSM) approach, utilizing two- and three-nucleon chiral interactions as the sole input. With the ability to compute translationally invariant nonlocal densities, it is possible to directly gauge the impact of the spurious center-of-mass (COM) contributions in DFT quantities such as the kinetic density. Methods: The nonlocal nuclear densities are derived from the NCSM one-body densities calculated in second quantization. We present a review of COM contaminated and translationally invariant nuclear densities. We then derive an analytic expression for the kinetic density using these nonlocal densities, producing an ab initio kinetic density. Results: The ground state nonlocal densities of \textsuperscript{4,6,8}He, \textsuperscript{12}C, and \textsuperscript{16}O are used to compute the kinetic densities of the aforementioned nuclei. The impact of the COM removal technique in the densities is discussed. The results of this work can be extended to other fundamental quantities in DFT. Conclusions: The use of a general nonlocal density allows for the calculation of fundamental quantities taken as input in theories such as DFT. This allows benchmarking of procedures for COM removal in different many-body techniques., 14 pages, 17 figures. Version accepted for publication

We realize the treatment of bound and continuum nuclear systems in the proximity of a three-body breakup threshold within the ab initio framework of the no-core shell model with continuum. Many-body eigenstates obtained from the diagonalization of the Hamiltonian within the harmonic-oscillator expansion of the no-core shell model are coupled with continuous microscopic three-cluster states to correctly describe the nuclear wave function both in the interior and asymptotic regions. We discuss the formalism in detail and give algebraic expressions for the case of core + $n+n$ systems. Using similarity-renormalization-group evolved nucleon-nucleon interactions, we analyze the role of $\phantom{\rule{0.28em}{0ex}}^{4}\mathrm{He}+n+n$ clustering and many-body correlations in the ground and low-lying continuum states of the Borromean $^{6}\mathrm{He}$ nucleus, and study the dependence of the energy spectrum on the resolution scale of the interaction. We show that $^{6}\mathrm{He}$ small binding energy and extended radii compatible with experiment can be obtained simultaneously, without resorting to extrapolations. We also find that a significant portion of the ground-state energy and the narrow width of the first ${2}^{+}$ resonance stem from many-body correlations that can be interpreted as core-excitation effects.

A Coulomb-excitation reorientation-effect measurement using the TIGRESS γ−ray spectrometer at the TRIUMF/ISAC II facility has permitted the determination of the 〈 2 1 + ‖ E 2 ˆ ‖ 2 1 + 〉 diagonal matrix element in 12C from particle−γ coincidence data and state-of-the-art no-core shell model calculations of the nuclear polarizability. The nuclear polarizability for the ground and first-excited (2 1 + ) states in 12C have been calculated using chiral NN N4LO500 and NN+3NF350 interactions, which show convergence and agreement with photo-absorption cross-section data. Predictions show a change in the nuclear polarizability with a substantial increase between the ground state and first excited 2 1 + state at 4.439 MeV. The polarizability of the 2 1 + state is introduced into the current and previous Coulomb-excitation reorientation-effect analyses of 12C. Spectroscopic quadrupole moments of Q S ( 2 1 + ) = + 0.053 ( 44 ) eb and Q S ( 2 1 + ) = + 0.08 ( 3 ) eb are determined, respectively, yielding a weighted average of Q S ( 2 1 + ) = + 0.071 ( 25 ) eb, in agreement with recent ab initio calculations. The present measurement confirms that the 2 1 + state of 12C is oblate and emphasizes the important role played by the nuclear polarizability in Coulomb-excitation studies of light nuclei.

This paper is focused on the detection of the level of destruction of a cylinder lock, opened using the Salinger-Grydilov (SG) method, and on measuring the resonance curve while striking a bump key as well as its influence on overcoming locks using SG method. It also presents an analysis and verification of the laboratory measurements of the level of destruction of a lock which was overcome using the SG method and its differentiation from a lock opened using the appropriate key. Further, attention is paid to measurements of the frequency of individual blows when using the SG method and its influence on overcoming cylinder locks.

This paper is focused on usability of multiestimation scheme approach in the area of identification and control of nonlinear systems. A multiestimation scheme is introduced and subsequently used for the adaptive control of real-time nonlinear system. The multiestimation scheme integrates on-line identification of suitable models of a controlled system and a controller synthesis on base of the identified model. The real-time testing has been carried out by the control of nonlinear laboratory model of interconnected tanks (DTS200 by Amira company).

Background: The exotic $^{9}\mathrm{He}$ nucleus, which presents one of the most extreme neutron-to-proton ratios, belongs to the $N=7$ isotonic chain famous for the phenomenon of ground-state parity inversion with decreasing number of protons. Consequently, it would be expected to have an unnatural (positive) parity ground state similar to $^{11}\mathrm{Be}$ and $^{10}\mathrm{Li}$. Despite many experimental and theoretical investigations, its structure remains uncertain. Apart from the fact that it is unbound, other properties including the spin and parity of its ground state, and the very existence of additional low-lying resonances are still a matter of debate.Purpose: In this work, we study the properties of $^{9}\mathrm{He}$ by analyzing the $n+^{8}\mathrm{He}$ continuum in the context of the ab initio no-core shell model with continuum (NCSMC) formalism with chiral nucleon-nucleon interactions as the only input.Methods: The NCSMC is a state-of-the-art approach for the ab initio description of light nuclei. With its capability to predict properties of bound states, resonances, and scattering states in a unified framework, the method is particularly well suited for the study of unbound nuclei such as $^{9}\mathrm{He}$.Results: Our analysis produces an unbound $^{9}\mathrm{He}$ nucleus. Two resonant states are found at the energies of $\ensuremath{\sim}1$ and $\ensuremath{\sim}3.5$ MeV, respectively, above the $n+^{8}\mathrm{He}$ breakup threshold. The first state has a spin-parity assignment of ${J}^{\ensuremath{\pi}}={1/2}^{\ensuremath{-}}$ and can be associated with the ground state of $^{9}\mathrm{He}$, while the second, broader state has a spin parity of ${3/2}^{\ensuremath{-}}$. No resonance is found in the ${1/2}^{+}$ channel, only a very weak attraction.Conclusions: We find that the $^{9}\mathrm{He}$ ground-state resonance has a negative parity and thus breaks the parity-inversion mechanism found in the $^{11}\mathrm{Be}$ and $^{10}\mathrm{Li}$ nuclei of the same $N=7$ isotonic chain.

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, and charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library. Fil: Brown, D.A.. Brookhaven National Laboratory; Estados Unidos Fil: Chadwick, M.B.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Capote, R.. International Atomic Energy Agency, Vienna; Austria Fil: Kahler, A.C.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Trkov, A.. International Atomic Energy Agency, Vienna; Austria Fil: Herman, M.W.. Brookhaven National Laboratory; Estados Unidos Fil: Sonzogni, A.A.. Brookhaven National Laboratory; Estados Unidos Fil: Danon, Y.. Rensselaer Polytechnic Institute; Estados Unidos Fil: Carlson, A.D.. National Institute of Standards and Technology; Estados Unidos Fil: Dunn, M.. Spectra Tech; Estados Unidos Fil: Smith, D.L.. Argonne National Laboratory; Estados Unidos Fil: Hale, G.M.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Arbanas, G.. Oak Ridge National Laboratory; Estados Unidos Fil: Arcilla, R.. Brookhaven National Laboratory; Estados Unidos Fil: Bates, C.R.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Beck, B.. Lawrence Livermore National Laboratory; Fil: Becker, B.. Gesellschaft für Anlagen und Reaktorsicherheit; Alemania Fil: Brown, F.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Casperson, R.J.. Lawrence Livermore National Laboratory; Estados Unidos Fil: Conlin, J.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Cullen, D.E.. Lawrence Livermore National Laboratory; Estados Unidos Fil: Descalle, M.A.. Lawrence Livermore National Laboratory; Estados Unidos Fil: Firestone, R.. Lawrence Berkeley National Laboratory; Estados Unidos Fil: Gaines, T.. AWE plc; Reino Unido Fil: Guber, K.H.. Oak Ridge National Laboratory; Estados Unidos Fil: Hawari, A.I.. University of North Carolina; Estados Unidos Fil: Holmes, J.. Naval Nuclear Laboratory; Estados Unidos Fil: Johnson, T.D.. Brookhaven National Laboratory; Estados Unidos Fil: Kawano, T.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Kiedrowski, B.C.. University of Michigan; Estados Unidos Fil: Koning, A.J.. International Atomic Energy Agency, Vienna; Austria Fil: Kopecky, S.. EC-JRC; Bélgica Fil: Leal, L.. Institut de Radioprotection et de Sûreté Nucléaire; Francia Fil: Lestone, J.P.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Lubitz, C.. Naval Nuclear Laboratory; Estados Unidos Fil: Marquez Damian, Jose Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Mattoon, C.M.. Lawrence Livermore National Laboratory; Estados Unidos Fil: McCutchan, E.A.. Brookhaven National Laboratory; Estados Unidos Fil: Mughabghab, S.. Brookhaven National Laboratory; Estados Unidos Fil: Navratil, P.. TRIUMF; Canadá Fil: Neudecker, D.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Nobre, G.P.A.. Brookhaven National Laboratory; Estados Unidos Fil: Noguere, G.. Commissariat A Energie Atomique; Francia Fil: Paris, M.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Pigni, M.T.. Oak Ridge National Laboratory; Estados Unidos Fil: Plompen, A.J.. EC-JRC; Bélgica Fil: Pritychenko, B.. Brookhaven National Laboratory; Estados Unidos Fil: Pronyaev, V.G.. PI Atomstandart at SC Rosatom; Rusia Fil: Roubtsov, D.. Laboratoires Nucleaires Canadiens; Canadá Fil: Rochman, D.. Paul Scherrer Institut; Suiza Fil: Romano, P.. Argonne National Laboratory; Estados Unidos Fil: Schillebeeckx, P.. EC-JRC; Bélgica Fil: Simakov, S.. Karlsruhe Institute of Technology; Alemania Fil: Sin, M.. University of Bucharest; Rumania Fil: Sirakov, I.. Institute For Nuclear Research And Nuclear Energy Bulgarian Academy Of Sciences; Bulgaria Fil: Sleaford, B.. Lawrence Livermore National Laboratory; Estados Unidos Fil: Sobes, V.. Oak Ridge National Laboratory; Estados Unidos Fil: Soukhovitskii, E.S.. Joint Institute for Energy and Nuclear Research; Bielorrusia Fil: Stetcu, I.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Talou, P.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos. Oak Ridge National Laboratory; Estados Unidos Fil: Thompson, I.. Lawrence Livermore National Laboratory; Estados Unidos Fil: van der Marck, S.. NRG; Países Bajos Fil: Welser-Sherrill, L.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Wiarda, D.. Oak Ridge National Laboratory; Estados Unidos Fil: White, M.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Wormald, J.L.. University of North Carolina; Estados Unidos Fil: Wright, R.Q.. Oak Ridge National Laboratory; Estados Unidos Fil: Zerkle, M.. Naval Nuclear Laboratory; Estados Unidos Fil: Zerovnik, G.. EC-JRC; Bélgica Fil: Zhu, Yan. University of North Carolina; Estados Unidos

The production of biomethane from biogas offers the possibility to obtain chemical resources fuels from combustion engines, gas turbine and fuel cells. However, each biomethane application requires specific treatment. This work is focused on the removal of CO2 from biogas as a fundamental step in biogas treatment. A laboratory scale PSA unit is introduced in this paper. The extruded activated carbon was used to construct the fixed bed adsorption layer. The maximum sorption capacity of CO2 was determined from the adsorption isotherm of pure CO2 carried out in a high pressure thermogravimeter. Breakthrough curves of CO2 and CH4 were determined for different volumetric flows of feed. The results were applied for the optimisation of PSA time in order to maximalize the suppression of CO2 from upgrading CH4. The concentration of CH4 is more than 98 % after the upgrading process. The total efficiency of the process was 77 %.