Ground State Of 16O Research Articles

Astrophysical S-factor and reaction rate for 15N(p,γ)16O within the modified potential cluster model* *Supported by the Ministry of Science and Higher Education of the Republic of Kazakhstan (AP09259174)

We study radiative capture on the ground state of 16O at stellar energies within the framework of a modified potential cluster model (MPCM) with forbidden states, including low-lying resonances. The investigation of the 15N( )16O reaction includes the consideration of resonances due to transitions and the contribution of the scattering wave in the p + 15N channel due to the transition. We calculated the astrophysical low-energy S-factor, and the extrapolated turned out to be within 34.7−40.4 keV·b. The important role of the asymptotic constant (AC) for the 15N( )16O process with interfering (312) and (962) resonances is elucidated. A comparison of our calculation for the S-factor with existing experimental and theoretical data is addressed, and a reasonable agreement is found. The reaction rate is calculated and compared with the existing rates. It has negligible dependence on the variation of AC but shows a strong impact of the interference of (312) and (962) resonances in reference to the CNO Gamow windows, especially at low temperatures. We estimate the contribution of cascade transitions to the reaction rate based on the exclusive experimental data from Phys. Rev. C. 85, 065810 (2012). The reaction rate enhancement due to the cascade transitions is observed from and reaches the maximum factor ~ 1.3 at . We present the Gamow energy window and a comparison of rates for radiative proton capture reactions 12N( )13O, 13N( ) 14O, 14N( )15O, and 15N( )16O obtained in the framework of the MPCM and provide the temperature windows, prevalence, and significance of each process.

New Determination of the 12C(α, γ)16O Reaction Rate and Its Impact on the Black-hole Mass Gap

We present a precise measurement of the asymptotic normalization coefficient (ANC) for the 16O ground state (GS) through the 12C(11B, 7Li)16O transfer reaction using the Quadrupole‐3‐Dipole (Q3D) magnetic spectrograph. The present work sheds light on the existing discrepancy of more than 2 orders of magnitude between the previously reported GS ANC values. This ANC is believed to have a strong effect on the 12C(α, γ)16O reaction rate by constraining the external capture to the 16O ground state, which can interfere with the high-energy tail of the 2+ subthreshold state. Based on the new ANC, we determine the astrophysical S-factor and the stellar rate of the 12C(α, γ)16O reaction. An increase of up to 21% in the total reaction rate is found within the temperature range of astrophysical relevance compared with the previous recommendation of a recent review. Finally, we evaluate the impact of our new rate on the pair-instability mass gap for black holes (BH) by evolving massive helium core stars using the MESA stellar evolution code. The updated 12C(α, γ)16O reaction rate decreases the lower and upper edges of the BH gap about 12% and 5%, respectively.

Tetrahedral symmetry in the ground state of 16O

Based on the Skyrme energy density functional, the self-consistent HF calculations have been performed for 16O, and the results show that the double point group tetrahedral symmetry TdD may play an important role in the configuration of many-body fermion system in the ground state of 16O. The corresponding total density distribution in the ground state, calculated by using the HF wave functions, presents the distinct 4α cluster-like tetrahedral structure with the Td symmetry. Among others, the necessary restoration of the rotational and parity symmetry, plays a crucial role for the occurrence of the tetrahedral symmetry in 16O.

Dominance of Tensor Correlations in High-Momentum Nucleon Pairs Studied by (p,pd) Reaction.

The isospin character of p-n pairs at large relative momentum has been observed for the first time in the ^{16}O ground state. A strong population of the J,T=1,0 state and a very weak population of the J,T=0,1 state were observed in the neutron pickup domain of ^{16}O(p,pd) at 392MeV. This strong isospin dependence at large momentum transfer is not reproduced by the distorted-wave impulse approximation calculations with known spectroscopic amplitudes. The results indicate the presence of high-momentum protons and neutrons induced by the tensor interactions in the ground state of ^{16}O.

Elastic α-12C Scattering with the Ground State of 16O at Low Energies in Effective Field Theory

Inclusion of the ground state of 16O is investigated for a study of elastic α-12C scattering for the l = 0 channel at low energies in effective field theory. We employ a Markov chain Monte Carlo method for the parameter fitting and find that the uncertainties of the fitted parameters are significantly improved compared to those of our previous study. We then calculate the asymptotic normalization constants of the 0+ states of 16O and compare them with the experimental data and the previous theoretical estimates. We discuss implications of the results of the present work.

Branching ratios for de-excitation processes of daughter nuclei following invisible dinucleon decays in 16O

Various theories beyond the standard model of particle physics predict the existence of baryon number violating processes resulting in nucleon decay. When occurring within an atomic nucleus, such a decay will be followed by secondary decays of the daughter nucleus unless its ground state is directly populated. In this paper, we estimate branching ratios for processes associated with dinucleon decays of the 16O nucleus. To this end, we use a simple shell model for the ground state of 16O. For decays from the configuration, which result in highly excited states in the daughter nucleus, we employ a statistical model with the Hauser–Feshbach theory. Our analysis indicates that the branching ratio for gamma-ray emission in the energy range between 5 and 9 MeV, which is relevant to low-threshold water Cherenkov experiments such as SNO+, is 4.53%, 35.7%, and 20.2% for the nn, pp, and pn decays in 16O, respectively. In particular, emission of 6.09 and 7.01 MeV gamma-rays from 14C, and 6.45 and 7.03 MeV gamma-rays from 14N, have branching ratios of as large as 10.9%, 20.1%, 7.73% and 8.90%, respectively.

Ground-state properties of 4He and 16O extrapolated from lattice QCD with pionless EFT

We extend the prediction range of Pionless Effective Field Theory with an analysis of the ground state of 16O in leading order. To renormalize the theory, we use as input both experimental data and lattice QCD predictions of nuclear observables, which probe the sensitivity of nuclei to increased quark masses. The nuclear many-body Schrödinger equation is solved with the Auxiliary Field Diffusion Monte Carlo method. For the first time in a nuclear quantum Monte Carlo calculation, a linear optimization procedure, which allows us to devise an accurate trial wave function with a large number of variational parameters, is adopted. The method yields a binding energy of 4He which is in good agreement with experiment at physical pion mass and with lattice calculations at larger pion masses. At leading order we do not find any evidence of a 16O state which is stable against breakup into four 4He, although higher-order terms could bind 16O.

Alpha Cluster Structures and Isoscalar Monopole Excitations in Light Nuclei

Isoscalar monopole excitations to cluster states in light nuclei are in general strong as to be comparable with the single particle strength. Their experimental strengths share about 20 % of the sum rule value in the case of 4He, 11B, 12C, and 16O etc. We discuss the isoscalar monopole strength function in 16O, which is typical in light nuclei, is discussed up to Ex ~ 40 MeV. It is found that 1) two different types of monopole excitations exist in 16O; one is the monopole excitation to cluster states which is dominant in the lower energy part, and the other is the monopole excitation of the mean-field type such as one-particle one-hole (1p1h) which is attributed mainly to the higher energy part, and 2) this character of the monopole excitations originates from the fact that the ground state of 16O with the dominant doubly closed shell structure has a duality of the mean-field-type as well as alpha-clustering character.

Isoscalar Monopole Excitations and Cluster Structures in Light Nuclei

Isoscalar monopole excitation to cluster states in light nuclei is in general strong as to be comparable with the single particle strength and shares about 20 % of the sum rule value. The isoscalar monopole strength function in 16O is discussed up to \({E_x \lesssim 40 \, {\rm MeV}.}\) We found that (1) two different types of monopole excitations exist in 16O; one is the monopole excitation to cluster states which is dominant in the lower energy part, and the other is the monopole excitation of the mean-field type such as one-particle one-hole (1p1h) which is attributed mainly to the higher energy part, and (2) this character of the monopole excitations originates from the fact that the ground state of 16O with the dominant doubly closed shell structure has a duality of the mean-field-type as well as alpha-clustering character.

Cluster structure and isoscalar monopole excitation in light nuclei

Isoscalar monopole excitation to cluster states in light nuclei is in general strong as to be comparable with the single particle strength and shares about 20 % of the sum rule value. In the present paper, the isoscalar monopole strength function in 16O is discussed up to Ex ≲ 40 MeV as a typical example. We found that 1) two different types of monopole excitations exist in 16O; one is the monopole excitation of cluster states which is dominant in the lower energy part, and the other is the monopole excitation of the mean-field type such as one-particle one-hole (1p1h) which is attributed mainly to the higher energy part, 2) this character of the monopole excitations originates from the fact that the ground state of 16O with the dominant doubly closed shell structure has a duality of the mean-field-type as well as alpha-clustering character, and 3) the monopole strength is much enhanced by the α-type ground state correlation.

A new cluster model interpretation of the anomalous lifetime of 14C

A new cluster model solution to the long-standing nuclear structure problem of describing the anomalously long lifetime of 14C is presented. Related beta-decay data for 14O to states in 14N, gamma-decay data between low-lying positive parity states in 14N and the elastic and inelastic magnetic dipole electron scattering from 14N data are all shown to be very accurately described by the model. The shapes of the beta spectra for the A = 14 system are also well reproduced by the model. The model invokes four-nucleon tetrahedral symmetric spatial correlations arising from three- and four-nucleon interactions, which yields a high degree of SU(4) singlet structure for the clusters and a tetrahedral intrinsic shape for the doubly magic 16O ground state. The large quadrupole moment of the 14N ground state is obtained here for the first time and arises because of the almost 100% d-wave deuteron-like-hole cluster structure inherent in the model.

Erratum: Constraining theSfactor ofN15(p,γ)O16at astrophysical energies [Phys. Rev. C82, 055804 (2010)

The 15N(p,g)16O reaction represents a break out reaction linking the first and second cycle of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances at Ep = 338 keV and 1028 keV and a Direct Capture contribution to the ground state of 16O. Interference effects between these contributions in both the low energy region (Ep < 338 keV) and in between the two resonances (338 <Ep < 1028 keV) can dramatically effect the extrapolation to energies of astrophysical interest. To facilitate a reliable extrapolation the 15N(p,g)16O reaction has been remeasured covering the energy range from Ep=1800 keV down to 130 keV. The results have been analyzed in the framework of a multi-level R-matrix theory and a S(0) value of 39.6 keV b has been found.

Margenau–Brink alpha model with central Jastrow and linear state-dependent correlations for p-shell nuclei

Wave functions based on the alpha cluster model of Margenau–Brink without effective interactions have been obtained for p-shell nuclei. In this approach the constituent clusters are located at fixed centers which are taken as variational parameters. The trial wave functions have been built up with correct total angular momentum and include central Jastrow and linear state dependent correlations. The ground state and the 2 + and 4 + excited states of 8Be, 12C, and the ground state of 16O are studied. The role of the different correlation mechanisms incorporated by the trial wave function is analyzed and the results are compared with previous calculations. The energies of the different bound states have been calculated by using the Variational Monte Carlo method.

Variational calculation of the ground state of 16O.

We report variational calculations of the ground state of $^{16}\mathrm{O}$ with realistic two- and three-nucleon interactions. The trial wave function is constructed from pair- and triplet-correlation operators acting on a product of single-particle determinants. These operators include central, spin, isospin, tensor, spin-orbit, and three-nucleon potential components. Expectation values are evaluated with a cluster expansion for the noncentral correlations; terms in the expansion are evaluated exactly using Monte Carlo integration. The optimal trial function is obtained by minimizing the energy through the four-body cluster level. Results are reported for the ground-state binding energy, nucleon density and momentum distributions, charge form factor, and longitudinal structure function. They are also compared with the available results for few-body nuclei and nuclear matter with the same interactions.

Effective sd-shell interaction from nuclear multishell configurations

Nuclear many-body states composed of the wave functions of valence nucleons and the correlated 16O ground state determined in a multishell configuration mixing calculation are constructed. These states are used to renormalize the sd-shell interaction derived from a realistic nucleon-nucleon potential. The properties of this interaction are similar to the interaction which reproduces the correlated two-valence-nucleon spectrum. Used in sd-shell model space hamiltonians the renormalized interaction is found to produce spectra similar to the ones found in exact multishell calculations.

Can the boson condensate ground state of 16O be a physical one?

The mean-field boson approach as applied by Kuchta to the description of the structure of 16O is discussed. The ground state wave function in that approach is found to have strange properties.

10 + states in 20Ne

The α-transfer reaction 12C( 16O, 20Ne ∗) 8Be has been studied at a bombarding energy of 150 MeV in a search for high-spin α-cluster resonances in 20Ne. Angular correlations were measured for states in 20Ne which α-decay to the ground state of 16O. A broad 10 + resonance was located at E x ( 20 Ne)∼27.5 MeV , but no definite evidence was found for any 10 + strength at lower excitation energy.

Spins of 12C + 12C resonances via the 12C(12C, αα)16O reaction

We have measured the spins of 12C + 12C resonances which decay to the ground state of 16O via excited states of 20Ne using a novel α-α angular correlation geometry. Between ECM = 19 and 27 MeV we find that spins of 12 and 14 dominate many of the resonant cross sections. We observe qualitatively different results for α-decays via the low lying bands in 20Ne and those which proceed via the 18.54 MeV 8+ state in 20Ne. We interpret our results in terms of Nilsson Strutinsky calculations and recent α-cluster model calculations for 24Mg.

Effective pade Hamiltonian operator and its application for treatment of H 216O rotational spectrum in the ground state

Both microwave and infrared data on frequencies of rotational transitions in the H 2 16O ground state are fitted for the first time within the limits of experimental errors. This fitting is based on a representation of the effective rotational Hamiltonian operator in the form of a Pade operator. New experimental data on frequencies of microwave transitions in the submillimeter wave region are obtained.

Magnetic dipole strength in 16O

The strength of magnetic dipole excitation from the 16O ground state is calculated. One anticipates a relatively large amount of the M1 strength between 16 MeV and 18 MeV which is about one third of that of the 15.1 MeV, 1+ state in 12C.