Coulomb Dissociation Cross Section Research Articles

Calculation of Coulomb breakup cross sections using a new Coulomb dynamical polarization potential

A new method for calculating the Coulomb breakup of unstable neutron-rich isotopes at high energies is presented. The calculations employ the eikonal approximation and use a new Coulomb dynamical polarization potential (CDPP), calculated by solving the Schr\"odinger equation for the entire motion of the exotic projectile as a two-body cluster structure using the adiabatic approximation and incorporating excitations to the continuum. Calculations for some exotic isotopes are compared with Coulomb dissociation cross section data and found to be in good agreement.

Direct experimental evidence for a multiparticle-hole ground state configuration of deformedMg33

The first direct experimental evidence of a multiparticle-hole ground state configuration of the neutron-rich Mg-33 isotope has been obtained via intermediate energy (400 A MeV) Coulomb dissociation measurement. The major part similar to(70 +/- 13)% of the cross section is observed to populate the excited states of Mg-32 after the Coulomb breakup of Mg-33. The shapes of the differential Coulomb dissociation cross sections in coincidence with different core excited states favor that the valence neutron occupies both the s(1/2) and p(3/2) orbitals. These experimental findings suggest a significant reduction and merging of sd-pf shell gaps at N similar to 20 and 28. The ground state configuration of Mg-33 is predominantly a combination of Mg-32(3.0,3.5MeV; 2(-), 1(-)) circle times nu(s1/2), Mg-32(2.5MeV; 2(+)) circle times nu(p3/2), and Mg-32(0; 0(+)) circle times nu(p3/2). The experimentally obtained quantitative spectroscopic information for the valence neutron occupation of the s and p orbitals, coupled with different core states, is in agreement with Monte Carlo shell model (MCSM) calculation using 3 MeV as the shell gap at N = 20.

Coulomb dissociation ofN20,21

Neutron-rich light nuclei and their reactions play an important role for the creation of chemical elements. Here, data from a Coulomb dissociation experiment on $^{20,21}$N are reported. Relativistic $^{20,21}$N ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the $^{19}\mathrm{N}(\mathrm{n},\gamma)^{20}\mathrm{N}$ and $^{20}\mathrm{N}(\mathrm{n},\gamma)^{21}\mathrm{N}$ excitation functions and thermonuclear reaction rates have been determined. The $^{19}\mathrm{N}(\mathrm{n},\gamma)^{20}\mathrm{N}$ rate is up to a factor of 5 higher at $T<1$\,GK with respect to previous theoretical calculations, leading to a 10\,\% decrease in the predicted fluorine abundance.

Measurement of the 92,93,94,100Mo(γ,n) reactions by Coulomb Dissociation

The Coulomb Dissociation (CD) cross sections of the stable isotopes 92,94,100Mo and of the unstable isotope 93Mo were measured at the LAND/R3B setup at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Experimental data on these isotopes may help to explain the problem of the underproduction of 92,94Mo and 96,98Ru in the models of p-process nucleosynthesis. The CD cross sections obtained for the stable Mo isotopes are in good agreement with experiments performed with real photons, thus validating the method of Coulomb Dissociation. The result for the reaction 93Mo(γ,n) is especially important since the corresponding cross section has not been measured before. A preliminary integral Coulomb Dissociation cross section of the 94Mo(γ,n) reaction is presented. Further analysis will complete the experimental database for the (γ,n) production chain of the p-isotopes of molybdenum.

Experimental study of the 15O(2p, γ)17Ne cross section by Coulomb Dissociation for the rp process

The time-reversed reaction 15O(2p, γ)17Ne has been studied by the Coulomb dissociation technique. Secondary 17Ne ion beams at 500 AMeV have been produced by fragmentation reactions of 20Ne in a beryllium production target and dissociated on a secondary Pb target. The incoming beam and the reaction products have been identified with the kinematically complete LAND-R3B experimental setup at GSI. The excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb Dissociation cross sections (σCoul) have been calculated, which provide a photoabsorption (σphoto) and a radiative capture cross section (σcap). Additionally, important information about the nuclear structure of the 17Ne nucleus will be obtained. The analysis is in progress.

Coulomb Dissociation Experiment of $^{27}$P

The 26Si(p; γ)27P reaction, which might play an important role in the rp process, was studied by the Coulomb Dissociation method. The experiment was performed at GSI, Darmstadt. A secondary 27P ion beam of 500 MeV/nucleon was directed onto a Pb target. From this experiment, the Coulomb Dissociation cross section, σ Coulex , will be deduced and then converted to the photoabsorption cross section, σ photo , and the radiativecapture cross section, σ cap . Also information on the structure of 27P will be obtained. The analysis is in progress.

13,14B(n, γ) via Coulomb Dissociation for Nucleosynthesis towards the r-Process

Radioactive beams of 14,15B produced by fragmentation of a primary 40Ar beam were directed onto a Pb target to investigate the neutron breakup within the Coulomb field. The experiment was performed at the LAND/R3B setup. Preliminary results for the Coulomb dissociation cross sections as well as for the astrophysically interesting inverse reactions, 13,14B(n,γ), are presented.

Study of the $^{15}$O$(2p,\gamma )^{17}$Ne Cross Section by Coulomb Dissociation of $^{17}$Ne for the $rp$ Process of Nucleosynthesis

The O-15(2p, gamma)Ne-17 cross section has been studied by the inverse reaction, the Coulomb dissociation of Ne-17. The experiment has been performed at the GSI. The Ne-17 excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb dissociation cross sections (sigma(Coul)) have been extracted, which provide a photoabsorption (sigma(photo)) and a radiative capture cross section (sigma(cap)). Additionally, important information about the Ne-17 nuclear structure will be obtained. The analysis is in progress.

Investigation of the CNO-break-out reaction: 15O(2p,γ)17Ne by the Coulomb dissociation of 17Ne

By the Coulomb dissociation of 17Ne, the time-reversed reaction 15O(2p, γ)17Ne has been investigated. This reaction might play an important role in the rp process, as a bypass of the 15O waiting point. The secondary 17Ne ion beam of 500 AMeV has been dissociated on a Pb target, and the reaction products have been recorded with the LAND-R3B experimental setup (GSI). This experiment allows to determine the Coulomb dissociation cross section σCoul, which can be converted into a photo-absorption cross section σphoto, and a radiative-capture cross section σcap for the 15O(2p,γ) 17Ne reaction. Additionally, informations about the structure of the 17Ne nucleus, a possible two-proton halo, may be obtained. The analysis is still in progress.

Dissociation of deuteron, 6He and 11Be from Coulomb dissociation reaction cross-section

The fragmentation of deuteron, 6He and 11Be have been studied during interaction with the 208Pb nucleus at various projectile energies. The Coulomb dissociation cross-sections and the momentum distribution of the break-up fragments have been analysed within the framework of the direct fragmentation model. The post-acceleration effect of deuteron during break-up and the halo structures of both the 6He and 11Be have been investigated.

The process of coulomb dissociation of weakly bound relativistic nuclei and hypernuclei within the two-cluster model

Using the analogy with the problem of ionization and excitation of atoms in the propagation of relativistic charged particles through a bulk of matter, the process of Coulomb dissociation of weakly bound relativistic nuclei and hypernuclei is theoretically investigated in the framework of the two-cluster deuteron-like model. Explicit expressions for the total cross section of Coulomb disintegration of weakly bound systems are derived taking into account the corrections due to the finite size of a target nucleus. Numerical estimations for the Coulomb dissociation of relativistic hypernuclei {sup 3}H{sub {lambda}} and {sup 6}He{sub {lambda}} are performed. It is shown that, owing to a sharp dependence of the Coulomb dissociation cross section on the binding energy, experimental measurements of the cross section allow one to determine the values of binding energy for these systems.

Scaling and interference in the dissociation of halo nuclei

The dissociation of halo nuclei through their collision with light and heavy targets is considered within the Continuum Discretized Coupled Channels theory. We study the one-proton halo nucleus $^8$B and the one-neutron halo nucleus $^{11}$Be, as well as the more normal $^7$Be. The procedure previously employed to extract the Coulomb dissociation cross section by subtracting the nuclear one is critically assessed, and the scaling law usually assumed for the target mass dependence of the nuclear breakup cross section is also tested. It is found that the nuclear breakup cross section for these very loosely bound nuclei does indeed behave as $a+bA^{1/3}$. However, it does not have the geometrically inspired form of a circular ring which seems to be the case for normal nuclei such as $^{7}$Be. We find further that we cannot ignore Coulomb-nuclear interference effects, which may be constructive or destructive in nature, and so the errors in previously extracted B(E1) using the subtraction procedure are almost certainly underestimated.

Re-evaluation of the low-energy Coulomb-dissociation cross section of 8B and the astrophysical S17 factor

An exclusive measurement of the Coulomb breakup of 8B into 7Be+p at 254 AMeV was used to infer the low-energy 7Be(p,γ)8B cross section. Particular emphasis was placed on the angular correlations of the breakup particles which demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S17 factors exhibit good agreement with the most recent direct 7Be(p,γ)8B measurements.

Feature Article:Structure and Reactions of Halo Nuclei

It is a challenge to artificially produce thousands of nuclei that do not exist in nature, to study their properties and to explore their roles in forming nature. Recent techniques with radioactive beams have made it possible to reach the limit of the neutron dripline for relatively light nuclei. At this limit for Z=9, one of the most fascinating discoveries was that of a neutron halo in 11Li. The measurements that led to the discovery showed enhanced interaction cross-sections, narrow momentum distributions of 9Li fragments, and large Coulomb dissociation cross-sections. Subsequently, the neutron halos were confirmed in several other nuclei near the dripline, for example, 6He, 11Be, 14Be, and 19C.

Studies of light neutron-rich nuclei near the drip line

Coulomb breakup of neutron-rich Be, B, C, and O isotopes at relativistic energies (400–600 A MeV) was studied with kinematically complete measurements. The ground-state properties of these nuclei were deduced by comparing experimental data for Coulomb-dissociation cross-sections with directbreakup model calculations. The dominant ground-state configurations of 15C, 11Be, 14B, and 23O were found to be 14Cgs(0+) ⊗ v s, 10Begs(0+) ⊗ v s, 13Bgs(3/2+) ⊗ v s,d, and 22Ogs(0+) ⊗ v s, respectively, and 16C(2+) ⊗ v s,d, for 17C. The capture cross-section for 14C(n,λ) 15C relevant in astrophysical scenarios was measured indirectly through Coulomb dissociation.

Proton Halo of8B within Direct Fragmentation Model

In a recent publication, Phys. Rev. C 63 (2001) 65806, experimental datas on the coulomb dissociation cross sections of 8 B have been reported. In the present research, a theoretical attempt has been made to explain these results that are based on direct fragmentation model when 8 B interacts with 107 Ag and 208 Pb target nuclei. The symmmetric momentum distribution of the ejected 7 Be might be due to outcome of both nuclear and coulomb effect for the dissociation of 8 B.

A kinematically complete measurement of the Coulomb dissociation of 8B

We present preliminary results of a kinematically complete measurement of the Coulomb dissociation of 83 MeV/u 8B on a Pb target. A dipole magnet separated the unreacted beam from the breakup fragments. We measured the Coulomb dissociation cross section at low relative energies in order to extract the astrophysical S factor for the 7Be(p, γ ) 8B reaction.

Dissociation of14B,15,17,19Cin a direct fragmentation model

The fragmentation of ${}^{14}\mathrm{B}$ and ${}^{15,17,19}\mathrm{C}$ have been obtained through the interaction of these nuclei with a tantalum target nucleus at various energies. The Coulomb dissociation cross section has been analyzed within a direct fragmentation model. The theory of diffraction dissociation and diffraction stripping has been incorporated within the framework of the present model to show the nuclear effect in the process of breakup. The theoretical results have been compared with recent experimental works on these neutron-rich drip line nuclei.

Three-body halos. V. Computations of continuum spectra for Borromean nuclei

We solve the coordinate space Faddeev equations in the continuum. We employ hyperspherical coordinates and provide analytical expressions allowing easy computation of the effective potentials at distances much larger than the ranges of the interactions where only s-waves in the different Jacobi coordinates couple. Realistic computations are carried out for the Borromean halo nuclei 6He (n+n+\alpha) for J\pi = 0+-, 1+-, 2+- and 11Li (n+n+9Li) for (1/2)+-, (3/2)+-, (5/2)+-. Ground state properties, strength functions, Coulomb dissociation cross sections, phase shifts, complex S-matrix poles are computed and compared to available experimental data. We find enhancements of the strength functions at low energies and a number of low-lying S-matrix poles.

Structure effects on Coulomb dissociation of

Coulomb dissociation provides an alternative method for determining the radiative capture cross sections at astrophysically relevant low relative energies. For the break-up of on , we calculate the total Coulomb dissociation cross section and the angular distribution for E1, E2 and M1. Our calculations are performed first within the standard first-order semiclassical theory of Coulomb excitation, including the correct three-body kinematics, and later including the projectile-target nuclear interactions. We study the dependence of the Coulomb dissociation cross section on the structure models assumed for the projectile. A range of potential models for are compared: we look at the effect of potential shapes, deformation and inclusion of inelastic channels in the projectile states. We analyse the relative E1 and E2 components and investigate the relation between the measured cross section and the S-factor . Preliminary Coulomb-nuclear interference results are presented.