1,004 research outputs found

### Probing the isoscalar excitations of 12C with inelastic alpha scattering

The robust (spin and isospin zero) $\alpha$-particle remains one of the best
projectiles to probe the nuclear isoscalar excitations. In the present work, a
microscopic folding model analysis of the \ac inelastic scattering to the 2$^+$
(4.44 MeV), 0$^+$ (7.65 MeV), 3$^-$ (9.64 MeV), 0$^+$ (10.3 MeV) and 1$^-$
(10.84 MeV) states in $^{12}$C has been performed using the 3-$\alpha$
resonating group method wave functions. The isoscalar transition strengths of
these states were carefully studied based on the coupled-channel analysis using
the microscopic folded form factors. A correlation between the weak binding
and/or short lifetime of the excited state and absorption in the exit channel
of inelastic scattering has been established.Comment: Talk given at SOTANCP Workshop, Strasbourg, May 2008; to appear in
International Journal of Modern Physics

### DWBA analysis of the 13C(6Li,d)17O reaction at 10 MeV/nucleon and its astrophysical implications

The value of the alpha spectroscopic factor (S_alpha) of the 6.356 MeV 1/2+
state of 17O is believed to have significant astrophysical implications due to
the importance of the 13C(alpha,n)16O reaction as a possible source of neutron
production for the s process. To further study this effect, an accurate
measurement of the 13C(6Li,d)17O reaction at E_lab = 60 MeV has been performed
recently by Kubono et al., who found a new value for the spectroscopic factor
of the 6.356 MeV 1/2+ state of 17O based on a distorted wave Born approximation
(DWBA) analysis of these data. This new value, S_alpha approximately = 0.011,
is surprisingly much smaller than those used previously in astrophysical
calculations (S_alpha approximately = 0.3-0.7) and thus poses a serious
question as to the role of the 13C(alpha,n)16O reaction as a source of neutron
production. In this work we perform a detailed analysis of the same
13C(6Li,d)17O data within the DWBA as well as the coupled reaction channel
(CRC) formalism. Our analysis yields an S_alpha value of over an order of
magnitude larger than that of Kubono et al. for the 6.356 MeV 1/2+ state of
17O.Comment: 17 pages, 4 figures, minor changes, accepted by Nuclear Physics

### Evidence for <i>L</i>-dependence generated by channel coupling: <sup>16</sup>O scattering from <sup>12</sup>C at 115.9 MeV

Background: In earlier work, inversion of S matrix for 330 MeV 16O on 12C resulted in highly undulatory potentials; the S matrix resulted from the inclusion of strong coupling to states of projectile and target nuclei. L-independent S-matrix equivalent potentials for other explicitly L-dependent potentials have been found to be undulatory.
Purpose: To investigate the possible implications of the undulatory dynamic polarization potential for an underlying L dependence of the 16O on 12C optical potential.
Methods: S matrix to potential, SL
â V (r), inversion which yields local potentials that reproduce the elastic channel S matrix of coupled channel (CC) calculations, will be applied to the S matrix for 115.9 MeV 16O on 12C. Further, SL for explicitly L-dependent potentials are inverted and the resulting L-independent potentials are characterized and compared with the undulatory potentials found for 16O on 12C.
Results: Some of the undulatory features exhibited by the potentials modified by channel coupling for 115.9 MeV 16O on 12C can be simulated by simple parameterized L-dependent potentials.
Conclusions: The elastic scattering of 16O by 12C is a particularly favorable case for revealing the effective L dependence of the potential modified by channel coupling. Nevertheless, there is no reason to suppose that
undularity is not a generic property leading in many cases to the choice: nucleus-nucleus potentials are (i) smooth and L-dependent, (ii) L-independent and undulatory, or (iii) both

### Theoretical photo-disintegration of $^{16}$O

The photodisintegration of $^{16}$O is predicted to be dominated by $E$2
excitation in the vicinity of the $\alpha$-particle threshold.
The reaction rates of $^{12}$C($\alpha$,$\gamma$)$^{16}$O are expected to be
determined from this reaction.Comment: 3 pages, 2 figures, Proceedings of Nuclei in the Cosmos (NIC-XIV).
19-24 June 2016, Niigata, Japa

### Emergence of a secondary rainbow and the dynamical polarization potential for <sup>16</sup>O on <sup>12</sup>C at 330 MeV

Background: It was shown recently that an anomaly in the elastic scattering of 16O on 12C at around 300 MeV is resolved by including within the scattering model the inelastic excitation of specific collective excitations of both nuclei, leading to a secondary rainbow. There is very little systematic knowledge concerning the contribution of collective excitations to the interaction between nuclei, particularly in the overlap region when neither interacting nuclei are light nuclei.
Purpose: Our goals are to study the dynamic polarization potential (DPP) generated by channel coupling that has been experimentally validated for a case (16O on 12C at around 300 MeV) where scattering is sensitive to the nuclear potential over a wide radial range; to exhibit evidence of the nonlocality due to collective coupling; to validate, or otherwise invalidate, the representation of the DPP by uniform renormalizing folding models or global potentials.
Methods: S-matrix to potential, SL â V (r), inversion yields local potentials that reproduce the elastic channel S matrix of coupled channel calculations. Subtracting the elastic channel uncoupled potential yields a local L-independent representation of the DPP. The dependence of the DPP on the nature of the coupled states and other parameters can be studied.
Results: Local DPPs were found due to the excitation of 12C and the combined excitation of 16O and 12C. The radial forms were different for the two cases, but each were very different from a uniform renormalization of the potential. The full coupling led to a 10% increase in the volume integral of the real potential. Evidence for the nonlocality of the underlying formal DPP and for the effect of direct coupling between the collective states is presented.
Conclusions: The local DPP generating the secondary rainbow has been identified. In general, DPPs have forms that depend on the nature of the specific excitations generating them, but, as in this case, they cannot be represented by a uniform renormalization of a global model or folding model potential. The method employed herein is a useful tool for further exploration of the contribution of collective excitations to internuclear potentials, concerning which there is still remarkably little general information

### Folding model analysis of proton radioactivity of spherical proton emitters

Half lives of the decays of spherical nuclei away from proton drip line by
proton emissions are estimated theoretically. The quantum mechanical tunneling
probability is calculated within the WKB approximation. Microscopic
proton-nucleus interaction potentials are obtained by single folding the
densities of the daughter nuclei with M3Y effective interaction supplemented by
a zero-range pseudo-potential for exchange along with the density dependence.
Strengths of the M3Y interaction are extracted by fitting its matrix elements
in an oscillator basis to those elements of the G-matrix obtained with the
Reid-Elliott soft-core nucleon-nucleon interaction. Parameters of the density
dependence are obtained from the nuclear matter calculations. Spherical charge
distributions are used for calculating the Coulomb interaction potentials.
These calculations provide reasonable estimates for the observed proton
radioactivity lifetimes of proton rich nuclei for proton emissions from 26
ground and isomeric states of spherical proton emitters.Comment: 6 page

### 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.Comment: 18 pages, 26 figure

### Isospin dependence of 6He+p optical potential and the symmetry energy

A consistent folding analysis of the elastic p(6He,6He)p scattering and
charge exchange p(6He,6Li*)n reaction data measured at Elab=41.6A MeV has been
performed within the coupled channels formalism. We have used the isovector
coupling to link the isospin dependence of 6He+p optical potential to the cross
section of p(6He,6Li*)n reaction exciting the 0+ isobaric analog state (IAS) at
3.563 MeV in 6Li. Based on these results and the Hartree-Fock calculation of
asymmetric nuclear matter using the same isospin-dependent effective
nucleon-nucleon interaction, we were able to confirm that the most realistic
value of the symmetry energy Esym is around 31 MeV. Our analysis has also shown
that the measured charge exchange p(6He,6Li*)n data are quite sensitive to the
halo tail of the 6He density used in the folding calculation and the IAS of 6Li
is likely to have a halo structure similar to that established for the ground
state of 6He.Comment: Accepted for publication in Phys. Rev.

### Influence of the Dirac sea on proton electromagnetic knockout

We use the relativistic distorted-wave impulse approximation (RDWIA) to study
the effects of negative-energy components of Dirac wave functions on the
left-right asymmetry for (e,e'p) reactions on 16-O with 0.2 < Q^2 < 0.8 and
12-C with 0.6 < Q^2 < 1.8 (GeV/c)^2. Spinor distortion is more important for
the bound state than for the ejectile and the net effect decreases with Q^2.
Spinor distortion breaks Godon equivalence and the data favor the CC2 operator
with intermediate coupling to the sea. The left-right asymmetry for Q^2 < 1.2
(GeV/c)^2 is described well by RDWIA calcuations, but at Q^2 = 1.8 (GeV/c)^2
the observed variation with missing momentum is flatter than predicted.Comment: 12 pages, 9 figures, to be submitted to PR

### A Computer Program for Relativistic Multiple Coulomb and Nuclear Excitation

A computer program is presented by which one may calculate the multiple
electric dipole, electric quadrupole and magnetic dipole Coulomb excitation
with relativistic heavy ions. The program applies to an arbitrary nucleus,
specified by the spins and energies of the levels and by all E1, E2 and M1
matrix elements. Nuclear excitation is calculated optionally for monopole,
dipole and quadrupole excitations and needs inputs of optical potentials. For
given bombarding conditions, the differential cross sections and statistical
tensors (useful to calculate gamma-ray angular distribution functions) are
computed.Comment: 10 page

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