Target effect on fragmentation reaction at E = 290A MeV

The longitudinal and transverse momentum (P_L and PYen_T) distributions of projectile-like fragments, which were produced with an Ar beam and various targets (C, Al, Nb, Tb, Au), were measured at E=290A MeV. No significant target effects are found in P _L distribution. The width of P_T distribution increases with target mass. It is plausible that this result is explained by the deflection of orbit arising from Coulomb repulsion. The nuclear structural effects are observed in isotopic and isotonic distributions of production cross-sections of fragments, which are derived from observed momentum distributions.     

Contribution of electric quadrupole and dipole-quadrupole interference terms in Coulomb breakup of 15C

The effects of electric quadrupole (E2) and dipole-quadrupole interference (E1–E2) terms in the Coulomb breakup of ¹⁵C have been investigated within the framework of eikonal approximation. The sensitivity of Coulomb breakup cross section, differential in relative energy and Longitudinal Momentum Distribution (LMD) of core fragments, towards these terms have been examined. A very small (1% of E1) contribution of E2 transition has been predicted in integrated Coulomb breakup cross section. Further it is also found that the inclusion of E2 and E1–E2 terms introduces a small asymmetry in the peak of relative energy spectrum and also increases the peak height of the spectrum. The contribution of dipole-quadrupole interference terms is clearly shown in LMD, as it introduces an asymmetry in the shape of LMD and enhances the matching between the data and predictions.     

Dynamic polarization in the Coulomb breakup of loosely bound F

Angular distributions of the Coulomb breakup of radioactive ¹⁷F were measured by impinging a 10 MeV/nucleon beam on ²⁰⁸Pb and on ⁵⁸Ni to study the dynamic polarization effects. The breakup products, oxygen and a proton, were detected in coincidence. First-order perturbation theory significantly overpredicts the breakup cross section for the ²⁰⁸Pb target. Dynamical calculations with a dynamic polarization as the leading order correction were performed. The calculations reproduce the data for ¹⁷F on ⁵⁸Ni but overpredict the breakup of ¹⁷F on ²⁰⁸Pb by a factor of two at forward angles.     

Breakup Reactions of Drip-Line Nuclei Near N = 20, 28

The one-neutron removal cross section from ²⁹Ne, ^33,35,37Mg, and ^39,41Si on a Pb target have been measured at around 240 MeV/nucleon at the RIBF (RI-Beam Factory) at RIKEN. This main goal of the experiment was to extract the inclusive Coulomb breakup cross sections in order to probe possible halo structures through their enhanced low-energy E1 strengths - so-called soft E1 excitations. The results showed significant enhancement of the one-neutron removal Coulomb breakup cross section for ³⁷Mg. This in turn provides evidence for the existence of halo structure in ³⁷Mg.     

Elastic scattering for the system 11Be + 209Bi at Coulomb barrier energies

The elastic scattering process for ¹¹Be ions impinging on a ²⁰⁹Bi target was studied in the energy range around the Coulomb barrier. The angular distributions of the ¹¹Be scattered particles were analyzed within the optical model framework in order to evaluate the reaction cross section, which turned out to be much larger than the fusion one, especially in the sub-barrier region. The comparison with the system ⁹Be + ²⁰⁹Bi showed that the reaction cross section is larger for the reaction ¹¹Be + ²⁰⁹Bi in the energy range around the Coulomb barrier, while they are rather similar at higher bombarding energies. This result suggests that direct processes related to the ¹¹Be halo structure and lower binding energy are more relevant at near-barrier energies.     

0+ states and E0 and E2 transition rates in even Sn nuclei

0⁺ states and their depopulating E0 and E2 transitions have been studied in ^112–124Sn. Several methods of γ-ray and electron spectrometry have been employed, including special coincidence techniques for lifetime, conversion electron and double Coulomb excitation measurements. For ^114–118Sn the E2 transition probabilities from the first excited 0⁺states (0₂⁺) are about 20 W.u., which is compatible with a vibrational two-phonon character. Also the E0 transition probabilities from these states are within a factor of two from the vibrational values. For the second excited 0⁺ states (0₃⁺) the corresponding E2 and E0 transition probabilities are considerably smaller. A total of 12 E0 transitions have been observed. The 0₃⁺ → 0₂⁺ transition is observed in ^114–120Sn and has in ¹¹⁶Sn a reduced transition probability 1–2 orders of magnitude larger than those of the groundstate E0 transitions, which indicates that the 0₃⁺ and 0₂⁺ states are strong mixtures of components with different 〈r²〉. The 0⁺ states in ¹¹⁶Sn are discussed as possible rotational band heads associated with a deformation β₂ ≈ 0.2. The Coulomb excitation cross section of the 0₂⁺ state is found to be sensitive to an interference term including matrix elements with the 2₂⁺ state. The relative sign of this term has been determined.     

Energy dependence of11Li dissociation cross section

The Coulomb breakup cross section of¹¹Li is calculated as a function of its bombarding energy. Comparison is made to cross sections at 790 MeV/nucleon and 30 MeV/nucleon. Low energy reactions on a high-Z target show a greatly enhanced Coulomb breakup cross section that is more sensitive to the distribution of dipole response strength than high energy reactions thus providing more structure information.     

Transfer, breakup, and fusion reactions of 6He with 209Bi near the Coulomb barrier

The fusion of ⁶He with a ²⁰⁹Bi target displays a large enhancement at energies near to and below the Coulomb barrier. Recently, a ⁴He group of remarkable intensity, which dominates the total reaction cross-section, has also been observed in the near-barrier interaction of the same system. It is argued that this transfer/breakup channel acts as a doorway state to fusion. Received: 1 May 2001 / Accepted: 4 December 2001     

Influence of breakup on elastic and α-production channels in the ~6Li+~(116)Sn reaction

The effects of breakup reactions on elastic and α-production channels for the ~6Li+~(116)Sn system have been investigated at energies below and near the Coulomb barrier. The angular distributions of α-particle production differential cross sections have been obtained at several projectile energies between 22 and 40 MeV. The measured breakup α-particle differential cross sections and elastic scattering angular distributions have been compared with the predictions of continuum-discretized coupled channels(CDCC) calculations. The influence of breakup coupling has also been investigated by extracting dynamic polarization potentials(DPP) from the CDCC calculations. From the predictions of CDCC calculations the relative importance of the nuclear, Coulomb, and total breakup contributions have also been investigated. The nuclear breakup couplings are observed to play an important role in comparison to the Coulomb breakup for the direct breakup mechanisms associated in the reaction of ~6Li projectile with ~(116)Sn target nuclei. The influence of strong nuclear breakup coupling exhibits suppression in the Coulomb-nuclear interference peak. The direct breakup cross sections from the CDCC calculations under-predict the measured α-particle differential cross sections at all energies. This suggests that the measured α particles may also have contributions from other possible breakup reaction channels.     

E2 component in subcoulomb breakup of 8B

We calculate the angular distribution and total cross section of the ⁷Be fragment emitted in the break up reaction of ⁸B on ⁵⁸Ni and ²⁰⁸Pb targets at the subcoulomb beam energy of 25.8 MeV, within the non-relativistic theory of Coulomb excitation with proper three-body kinematics. The relative contributions of the E1, E2 and M1 multipolarities to the cross sections are determined. The E2 component makes up about 65% and 40% of the ⁷Be total cross section for the ⁵⁸Ni and ²⁰⁸Pb targets respectively. We find that the extraction of the astrophysical S-factor, S₁₇(0), for the ⁷Be(p,γ)⁸B reaction at solar energies from the measurements of the cross sections of the ⁷Be fragment in the Coulomb dissociation of ⁸B at sub-Coulomb energies is still not free from the uncertainties of the E2 component.     

Second-order breakup corrections to elastic deuteron-nickel scattering between 13 and 80 MeV

Breakup corrections to the elastic scattering matrix elements are calculated in the second-order distorted-wave Born approximation at deuteron incident energies of 45 and 85 MeV. The effects of spin are included. The size of the corrections are found to be generally as large as those obtained in a previous study at 13 and 21.6 MeV. The breakup cross section is calculated to first order in the breakup matrix elements by a distorted-wave Born treatment. Comparison with fully coupled calculations shows that the DWBA method overestimates the breakup cross section by a factor of about three.The continuum of breakup states up to a n-p relative momentum 1 fm^?1 is included in the calculations. This continuum is discretized by subdividing it first into two bins, and then into four bins. The finer discretization does not make a large difference in either the elastic cross section or the breakup cross sections. The higher bins give only a small contribution to either quantity.     

7 Be(p, γ) 8 B cross section from indirect breakup experiments

The amplification of the E2 and M1 electromagnetic transitions in the radiative capture reaction⁷ Be(p, γ)⁸ B is investigated. This amplification occurs in Coulomb dissociation experiments. Interference between the excitation amplitudes of E1, E2 and M1 multipolarities leads to anisotropy effects in the angular distribution of the fragments. Dynamical coupling which could affect the direct correspondence between the Coulomb breakup and the radiative capture cross sections are studied by means of a coupled-channels approach.     

7Be(p, γ)8 B cross section from indirect breakup experiments

The amplification of the E2 and M1 electromagnetic transitions in the radiative capture reaction ⁷Be(p, γ)⁸ B is investigated. This amplification occurs in Coulomb dissociation experiments. Interference between the excitation amplitudes of E1, E2 and M1 multipolarities leads to anisotropy effects in the angular distribution of the fragments. Dynamical coupling which could affect the direct correspondence between the Coulomb breakup and the radiative capture cross sections are studied by means of a coupled-channels approach.     

Reaction functions for weakly bound systems

We propose a new technique to analyze total reaction cross sections. In this technique, which has been previously applied to fusion reactions, the experimental data are used to build a dimensionless reaction function, which does not depend on the system size or details of the optical potential. In this way, total reaction cross sections for different systems can be directly compared. We employ this technique to perform a systematic study of reaction cross sections of weakly bound systems in different mass ranges, and compare their reaction functions with the ones of tightly bound systems with similar masses. We show that breakup reactions and neutron transfers in halo systems lead to large reaction functions, well above the ones of typical tightly or weakly bound stable systems.     

Final state three-body Coulomb effects in the 208Pb(8B,7Bep)208Pb Coulomb breakup reaction

We present results of the first calculation of the double differential cross section for the 208Pb(8B,(7)Bep)208Pb Coulomb breakup reaction which treats the postdecay acceleration of the ejectiles within a genuine three-body approach. From this we conclude that, in order to minimize postdecay Coulomb acceleration effects, experiments should be performed at as small as possible scattering angles, not too low 7Be-p relative energies, and high incident energy.     

Momentum distribution of 15B fragments from the breakup of 17B

The two-neutron removal cross section (sigma(-2n)) and the longitudinal momentum distribution of 15B fragments from the breakup of 17B on 9Be were measured at 70A MeV. The distribution in the projectile rest frame is characterized by a FWHM of 80+/-10 MeV/c for 15B. The sigma(-2n) is found to be 0.22+/-0.05 b. A Glauber-type analysis of the data provides clear evidence of a two-neutron halo structure in 17B.     

Why breakup of photons and pions into forward dijets is so different: Predictions from nonlinear nuclear <Emphasis Type="Italic">k</Emphasis><Subscript>⊥</Subscript> factorization

Based on an approach to non-Abelian propagation of color dipoles in a nuclear medium, we formulate a nonlinear k_⊥ factorization for the breakup of photons and pions into forward hard dijets in terms of the collective Weizsäcker-Williams glue of nuclei. We find quite distinct practical consequences of nonlinear nuclear k_⊥ factorization for interactions of pointlike photons and nonpointlike pions. In the former case, the large transverse momentum p_⊥ of jets comes from the intrinsic momentum of quarks and antiquarks in the photon, and nuclear effects manifest themselves as an azimuthal decorrelation with an acoplanarity momentum of the order of the nuclear saturation momentum Q _A . In the breakup of pions off free nucleons to the leading order in pQCD, the spectator parton has a small transverse momentum and the hard dijet cross section is suppressed. In the breakup of pions off heavy nuclei, the forward hard jets are predicted to be entirely decorrelated. We comment on the sensitivity of the pionic dijet cross section to the pion distribution amplitude. The predicted distinction between the breakup of photons and pions can be tested by the sphericity and thrust analysis of the forward hadronic system in the COMPASS experiment at CERN.     

Measurement of mutual coulomb dissociation in sqrt[s(NN)] = 130 GeV Au + Au collisions

We report on the first measurement of mutual Coulomb dissociation in heavy-ion collisions. We employ forward calorimeters to measure neutron multiplicity at beam rapidity. The cross section for simultaneous electromagnetic breakup of Au nuclei at a nucleon-nucleon center of mass energy sqrt[s(NN)] = 130 GeV is sigma(MCD) = 3.67+/-0.26 barns, which is comparable to the geometrical cross section. The ratio of the electromagnetic to the total cross section is in good agreement with calculations, as is the neutron multiplicity distribution.     

Calculation of Interaction Potentials between Spherical and Deformed Nuclei

The interaction potential for spherical-deformed reaction partners is calculated. The shape, separation and orientation dependence of the interaction potential and fusion cross section of the system ^32S＋^154Sm are investigated within the double-folding model of the deformed nuclei. The effective nucleon-nucleon interaction is taken to be the M3Y-Reid potential. The density is considered for three terms of the expansion using the truncated multipole expansion method, which is a deformed Fermi shape With quadrupole and hexadecapole for the density distribution of ^154Sm. It is found for the interaction potential that the height and the position of barrier strongly depend on the deformations, the orientation angle of the deformed nucleus, and hence produce great effects on fusion cross section. The integrated fusion cross section is in good agreement with the experimental data.