arXiv subjects

C. A. Bertulani

Publications and source records attributed to C. A. Bertulani.

At least 145 records · Page 8Linked to original sources

arXiv2009

Nuclear astrophysics from direct reactions

Accurate nuclear reaction rates are needed for primordial nucleosynthesis and hydrostatic burning in stars. The relevant reactions are extremely difficult to measure directly in the laboratory at the small astrophysical energies. In recent years direct reactions have been developed and applied to extract low-energy astrophysical S-factors. These methods require a combination of new experimental techniques and theoretical efforts, which are the subject of this presentation.

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arXiv2008

Odd-even mass differences from self-consistent mean-field theory

We survey odd-even nuclear binding energy staggering using density functional theory with several treatments of the pairing interaction including the BCS, Hartree-Fock-Bogoliubov, and the Hartree-Fock-Bogoliubov with the Lipkin-Nogami approximation. We calculate the second difference of binding energies and compare with 443 measured neutron energy differences in isotope chains and 418 measured proton energy differences in isotone chains. The particle-hole part of the energy functional is taken as the SLy4 Skyrme parametrization and the pairing part of the functional is based on a contact interaction with possible density dependence. An important feature of the data, reproduced by the theory, is the sharp gap quenching at magic numbers. With the strength of the interaction as a free parameter, the theory can reproduce the data to an rms accuracy of about 0.25 MeV. This is slightly better than a single-parameter phenomenological description but slightly poorer than the usual two-parameter phenomenological form C/A^alpha . The following conclusions can be made about the performance of common parametrization of the pairing interaction: (i) there is a weak preference for a surface-peaked neutron-neutron pairing, which might be attributable to many-body effects; (ii) a larger strength is required in the proton pairing channel than in the neutron pairing channel; (iii) pairing strengths adjusted to the well-known spherical isotope chains are too weak to give a good overall fit to the mass differences.

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arXiv2008

Neutrino/antineutrino-$^{12}$C charged cross sections in the projected QRPA formalism

The $ν/\barν-^{12}$C cross sections are evaluated in the projected quasiparticle random phase approximation (PQRPA). The cross section for $ν_e$ as a function of the incident neutrino energy is compared with recent theoretical calculations of more sophisticated models. The $\barν-^{12}$C cross section is calculated for the first time with the PQRPA. The distribution of cross sections averaged with the Michel spectrum as well as with other estimated fluxes for future experiments is compared for both $ν_e$ and $\barν_e$. Some astrophysical implications are addressed.

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arXiv2008

Detection of supernovae neutrinos with neutrino-iron scattering

The $ν_e-^{56}$Fe cross section is evaluated in the projected quasiparticle random phase approximation (PQRPA). This model solves the puzzle observed in RPA for nuclei with mass around $^{12}$C, because it is the only RPA model that treats the Pauli principle correctly. The cross sections as a function of the incident neutrino energy are compared with recent theoretical calculations of similar models. The average cross section weighted with the flux spectrum yields a good agreement with the experimental data. The expected number of events in the detection of supernova neutrinos is calculated for the LVD detector leading to an upper limit for the electron neutrino energy of particular importance in this experiment

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arXiv2008

Blurred femtoscopy in two-proton decay

We study the effects of final state interactions in two-proton emission by nuclei. Our approach is based on the solution the time-dependent Schrödinger equation. We show that the final relative energy between the protons is substantially influenced by the final state interactions. We also show that alternative correlation functions can be constructed showing large sensitivity to the spin of the diproton system.

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arXiv2007

Geometry of Borromean Halo Nuclei

We discuss the geometry of the highly quantal nuclear three-body systems composed of a core plus two loosely bound particles. These Borromean nuclei have no single bound two-body subsystem. Correlation plays a prominent role. From consideration of the $B(E1)$ value extracted from electromagnetic dissociation, in conjunction with HBT-type analysis of the two valence-halo particles correlation, we show that an estimate of the over-all geometry can be deduced. In particular we find that the opening angle between the two neutrons in $^{6}$He and $^{11}$Li are, respectively, $θ_{nn} = {83^{\circ}}^{+20}_{-10}$ and ${66^{\circ}}^{+22}_{-18}$. These angles are reduced by about 12% to $θ_{nn} = {78^{\circ}}^{+13}_{-18}$ and ${58^{\circ}}^{+10}_{-14}$ if the laser spectroscopy values of the rms charge radii are used to obtain the rms distance between the cores and the center of mass of the two neutrons. The opening angle in the case of $^{11}$Li is more than 20% larger than recently reported by Nakamura \cite{Nak06}. The analysis is extended to $^{14}$Be and the two-proton Borromean nucleus $^{17}% $Ne where complete data is still not available. Using available experimental data and recent theoretical calculations we find, $θ_{nn} = {64^{0}}^{+9}_{-10}$ and $θ_{pp} = 110^{0}$, respectively.

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arXiv2007

Tunneling of a composite particle: Effects of intrinsic structure

We consider simple models of tunneling of an object with intrinsic degrees of freedom. This important problem was not extensively studied until now, in spite of numerous applications in various areas of physics and astrophysics. We show possibilities of enhancement for the probability of tunneling due to the presence of intrinsic degrees of freedom split by weak external fields or by polarizability of the slow composite object.

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arXiv2007

Coulomb excitation of unstable nuclei at intermediate energies

We investigate the Coulomb excitation of low-lying states of unstable nuclei in intermediate energy collisions ($E_{lab}\sim10-500$ MeV/nucleon). It is shown that the cross sections for the $E1$ and $E2$ transitions are larger at lower energies, much less than 10 MeV/nucleon. Retardation effects and Coulomb distortion are found to be both relevant for energies as low as 10 MeV/nucleon and as high as 500 MeV/nucleon. Implications for studies at radioactive beam facilities are discussed.

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arXiv2007

Electro-disintegration following beta-decay

I show that the disintegration of weakly-bound nuclei and the ionization of weakly-bound atomic electrons due to their interaction with leptons from beta decay is a negligible effect.

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arXiv2007

Pygmy resonances probed with electron scattering

Pygmy resonances in light nuclei excited in electron scattering are discussed. These collective modes will be explored in future electron-ion colliders such as ELISe/FAIR (spokesperson: Haik Simon - GSI). Response functions for direct breakup are explored with few-body and hydrodynamical models, including the dependence upon final state interactions.

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arXiv2007

Excitation of soft dipole modes in electron scattering

The excitation of soft dipole modes in light nuclei via inelastic electron scattering is investigated. I show that, under the proposed conditions of the forthcoming electron-ion colliders, the scattering cross sections have a direct relation to the scattering by real photons. The advantages of electron scattering over other electromagnetic probes is explored. The response functions for direct breakup are studied with few-body models. The dependence upon final state interactions is discussed. A comparison between direct breakup and collective models is performed. The results of this investigation are important for the planned electron-ion colliders at the GSI and RIKEN facilities.

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arXiv2006

Probing nuclear skins and halos with elastic electron scattering

I investigate the elastic electron scattering off nuclei far from the stability line. The effects of the neutron and proton skins and halos on the differential cross sections are explored. Examples are given for the charge distribution in Sn isotopes and its relation to the neutron skin. The neutron halo in $^{11}$Li and the proton halo in $^{8}$B are also investigated. Particular interest is paid to the inverse scattering problem and its dependence on the experimental precision. These studies are of particular interest for the upcoming electron ion colliders at the GSI and RIKEN facilities.

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arXiv2006

Direct reactions in/for astrophysics

Precise nuclear reaction rates are needed for a detailed description of the production of elements in primordial nucleosynthesis and during the hydrostatic burning of stars to constrain the astrophysical models. The relevant reactions are extremely difficult to measure directly in the laboratory at the small astrophysical energies. In recent years direct reactions methods have been developed and applied to extract low-energy astrophysical S factors. The application of these methods requires a combination of experimental and theoretical efforts. This contribution focuses on the underlying reaction theories that have to be well understood in order to assess the precision and limitations of the various approaches.

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arXiv2006

Elastic Electron Scattering off Exotic Nuclei

Electron scattering will provide the most direct information about charge distribution in exotic nuclei. A technical proposal for an electron-heavy-ion collider has been incorporated in the GSI/Germany physics program (spokesperson: Haik Simon - GSI). The main purpose is to study the structure of nuclei far from the stability line. In this work I explore the possibilities to study charge distributions of nuclei far form the stability line with the proposed facility.

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arXiv2006

MOMDIS: a Glauber model computer code for knockout reactions

A computer program is described to calculate momentum distributions in stripping and diffraction dissociation reactions. A Glauber model is used with the scattering wavefunctions calculated in the eikonal approximation. The program is appropriate for knockout reactions at intermediate energy collisions (30 MeV $\leq$ E$_{lab}/$nucleon $\leq 2000$ MeV). It is particularly useful for reactions involving unstable nuclear beams, or exotic nuclei (e.g. neutron-rich nuclei), and studies of single-particle occupancy probabilities (spectroscopic factors) and other related physical observables. Such studies are an essential part of the scientific program of radioactive beam facilities, as in for instance the proposed RIA (Rare Isotope Accelerator) facility in the US.

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arXiv2006

7Be(p,gamma)8B S-factor from ab initio no-core shell model wave functions

Nuclear structure of 7Be, 8B and 7,8Li is studied within the ab initio no-core shell model (NCSM). Starting from high-precision nucleon-nucleon (NN) interactions, wave functions of 7Be and 8B bound states are obtained in basis spaces up to 10 hbar Omega and used to calculate channel cluster form factors (overlap integrals) of the 8B ground state with 7Be+p. Due to the use of the harmonic oscillator (HO) basis, the overlap integrals have incorrect asymptotic properties. We fix this problem in two alternative ways. First, by a Woods-Saxon (WS) potential solution fit to the interior of the NCSM overlap integrals. Second, by a direct matching with the Whittaker function. The corrected overlap integrals are then used for the 7Be(p,gamma)8B S-factor calculation. We study the convergence of the S-factor with respect to the NCSM HO frequency and the model space size. Our S-factor results are in agreement with recent direct measurement data. We also test the spectroscopic factors and the corrected overlap integrals from the NCSM in describing the momentum distributions in knockout reactions with 8B projectiles. A good agreement with the available experimental data is also found, attesting the overall consistency of the calculations.

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arXiv2005

Short-range correlations in two-nucleon knockout reactions

A theory of short-range correlations in two-nucleon removal due to elastic breakup (diffraction dissociation) on a light target is developed. Fingerprints of these correlations will appear in momentum distributions of back-to-back emission of the nucleon pair. Expressions for the momentum distributions are derived and calculations for reactions involving stable and unstable nuclear species are performed. The signature of short-range correlations in other reaction processes is also studied.

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arXiv2005

New $^{32}$Cl(p,$γ$)$^{33}$Ar reaction rate for astrophysical rp-process calculations

The $^{32}$Cl(p,$γ$)$^{33}$Ar reaction rate is of potential importance in the rp-process powering type I X-ray bursts. Recently Clement et al. \cite{CBB04} presented new data on excitation energies for low lying proton unbound states in $^{33}$Ar obtained with a new method developed at the National Superconducting Cyclotron Laboratory. We use their data, together with a direct capture model and a USD shell model calculation to derive a new reaction rate for use in astrophysical model calculations. In particular, we take into account capture on the first excited state in $^{32}$Cl, and also present a realistic estimate of the remaining uncertainties. We find that the $^{32}$Cl(p,$γ$)$^{33}$Ar reaction rate is dominated entirely by capture on the first excited state in $^{32}$Cl over the whole temperature range relevant in X-ray bursts. In the temperature range from 0.2 to 1 GK the rate is up to a factor of 70 larger than the previously recommended rate based on shell model calculations only. The uncertainty is now reduced from up to a factor of 1000 to a factor of 3 at 0.3-0.7 GK and a factor of 6 at 1.5 GK.

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