Sensitivity of 8B breakup cross section to projectile structure in CDCC calculations

Given the Astrophysical interest of $^7$Be$(p,\gamma)^8$B, there have been several experiments applying the Coulomb dissociation method for extracting the capture rate. Measurements at Michigan State are dominated by $E1$ contributions but have a small $E2$ component. On the other hand, a lower energy measurement at Notre Dame has a much stronger $E2$ contribution. The expectation was that the two measurements would tie down the $E2$ and thus allow for an accurate extraction of the $E1$ relevant for the capture process. The aim of this brief report is to show that the $E2$ factor in breakup reactions does not translate into a scaling of the $E2$ contribution in the corresponding capture reaction. We show that changes to the $^8$B single particle parameters, which are directly related to the $E2$ component in the capture reaction, do not effect the corresponding breakup reactions, using the present reaction theory.Comment: 4 pages, 6 figures, revtex

New treatment of breakup continuum in the method of continuum discretized coupled channels

A new method of pseudo-state discretization is proposed for the method of continuum discretized coupled channels (CDCC) to deal with three-body breakup processes. We propose real- and complex-range Gaussian bases for the pseudo-state wave functions, and show that they form in good approximation a complete set in the configuration space which is important for breakup processes. Continuous S-matrix elements are derived with the approximate completeness from discrete ones calculated by CDCC. Accuracy of the method is tested quantitatively for two realistic examples, d+$^{58}$Ni scattering at 80 MeV and $^{6}$Li+$^{40}$Ca scattering at 156 MeV with the satisfactory results. Possibility of application of the method to four-body breakup processes is also discussed.Comment: 10 pages, 14 Postscript figures, uses REVTeX 4, submitted to Phys. Rev.

Are spectroscopic factors from transfer reactions consistent with asymptotic normalisation coefficients?

It is extremely important to devise a reliable method to extract spectroscopic factors from transfer cross sections. We analyse the standard DWBA procedure and combine it with the asymptotic normalisation coefficient, extracted from an independent data set. We find that the single particle parameters used in the past generate inconsistent asymptotic normalization coefficients. In order to obtain a consistent spectroscopic factor, non-standard parameters for the single particle overlap functions can be used but, as a consequence, often reduced spectroscopic strengths emerge. Different choices of optical potentials and higher order effects in the reaction model are also studied. Our test cases consist of: $^{14}$C(d,p)$^{15}$C(g.s.) at $E_d^{lab}=14$ MeV, $^{16}$O(d,p)$^{17}$O(g.s.) at $E_d^{lab}=15$ MeV and $^{40}$Ca(d,p)$^{41}$Ca(g.s.) at $E_d^{lab}=11$ MeV. We underline the importance of performing experiments specifically designed to extract ANCs for these systems.Comment: 15 pages, 12 figures, Phys. Rev. C (in press

Global optical potential for nucleus-nucleus systems from 50 MeV/u to 400 MeV/u

We present a new global optical potential (GOP) for nucleus-nucleus systems, including neutron-rich and proton-rich isotopes, in the energy range of $50 \sim 400$ MeV/u. The GOP is derived from the microscopic folding model with the complex $G$-matrix interaction CEG07 and the global density presented by S{\~ a}o Paulo group. The folding model well accounts for realistic complex optical potentials of nucleus-nucleus systems and reproduces the existing elastic scattering data for stable heavy-ion projectiles at incident energies above 50 MeV/u. We then calculate the folding-model potentials (FMPs) for projectiles of even-even isotopes, $^{8-22}$C, $^{12-24}$O, $^{16-38}$Ne, $^{20-40}$Mg, $^{22-48}$Si, $^{26-52}$S, $^{30-62}$Ar, and $^{34-70}$Ca, scattered by stable target nuclei of $^{12}$C, $^{16}$O, $^{28}$Si, $^{40}$Ca $^{58}$Ni, $^{90}$Zr, $^{120}$Sn, and $^{208}$Pb at the incident energy of 50, 60, 70, 80, 100, 120, 140, 160, 180, 200, 250, 300, 350, and 400 MeV/u. The calculated FMP is represented, with a sufficient accuracy, by a linear combination of 10-range Gaussian functions. The expansion coefficients depend on the incident energy, the projectile and target mass numbers and the projectile atomic number, while the range parameters are taken to depend only on the projectile and target mass numbers. The adequate mass region of the present GOP by the global density is inspected in comparison with FMP by realistic density. The full set of the range parameters and the coefficients for all the projectile-target combinations at each incident energy are provided on a permanent open-access website together with a Fortran program for calculating the microscopic-basis GOP (MGOP) for a desired projectile nucleus by the spline interpolation over the incident energy and the target mass number.Comment: 25 pages, 13 figure

Continuum-discretized coupled-channels method for four-body nuclear breakup in 6^6He+12^{12}C scattering

We propose a fully quantum-mechanical method of treating four-body nuclear breakup processes in scattering of a projectile consisting of three constituents, by extending the continuum-discretized coupled-channels method. The three-body continuum states of the projectile are discretized by diagonalizing the internal Hamiltonian of the projectile with the Gaussian basis functions. For $^6$He+$^{12}$C scattering at 18 and 229.8 MeV, the validity of the method is tested by convergence of the elastic and breakup cross sections with respect to increasing the number of the basis functions. Effects of the four-body breakup and the Borromean structure of $^6$He on the elastic and total reaction cross sections are discussed.Comment: 5 pages, 6 figures, uses REVTeX 4, submitted to Phys. Rev.

Coupled-channels effects in elastic scattering and near-barrier fusion induced by weakly bound nuclei and exotic halo nuclei

The influence on fusion of coupling to the breakup process is investigated for reactions where at least one of the colliding nuclei has a sufficiently low binding energy for breakup to become an important process. Elastic scattering, excitation functions for sub-and near-barrier fusion cross sections, and breakup yields are analyzed for $^{6,7}$Li+$^{59}$Co. Continuum-Discretized Coupled-Channels (CDCC) calculations describe well the data at and above the barrier. Elastic scattering with $^{6}$Li (as compared to $^{7}$Li) indicates the significant role of breakup for weakly bound projectiles. A study of $^{4,6}$He induced fusion reactions with a three-body CDCC method for the $^6$He halo nucleus is presented. The relative importance of breakup and bound-state structure effects on total fusion is discussed.Comment: 29 pages, 9 figure

Application of Absorbing Boundary Condition to Nuclear Breakup Reactions

Absorbing boundary condition approach to nuclear breakup reactions is investigated. A key ingredient of the method is an absorbing potential outside the physical area, which simulates the outgoing boundary condition for scattered waves. After discretizing the radial variables, the problem results in a linear algebraic equation with a sparse coefficient matrix, to which efficient iterative methods can be applicable. No virtual state such as discretized continuum channel needs to be introduced in the method. Basic aspects of the method are discussed by considering a nuclear two-body scattering problem described with an optical potential. We then apply the method to the breakup reactions of deuterons described in a three-body direct reaction model. Results employing the absorbing boundary condition are found to accurately coincide with those of the existing method which utilizes discretized continuum channels.Comment: 21 pages, 5 figures, RevTeX

Transfer/Breakup Modes in the 6He+209Bi Reaction Near and Below the Coulomb Barrier

Reaction products from the interaction of 6He with 209Bi have been measured at energies near the Coulomb barrier. A 4He group of remarkable intensity, which dominates the total reaction cross section, has been observed. The angular distribution of the group suggests that it results primarily from a direct nuclear process. It is likely that this transfer/breakup channel is the doorway state that accounts for the previously observed large sub-barrier fusion enhancement in this system.Comment: 4 pages; 3 figure

Overview of ¹⁴C release from irradiated zircaloys in geological disposal conditions

Carbon-14 (radiocarbon, 14C) is a long-lived radionuclide (5730 yr) of interest regarding the safety for the management of intermediate level wastes (ILW). The present study gives an overview of the release of 14C from irradiated Zircaloy cladding in alkaline media. 14C is found either in the alloy part of Zircaloy cladding due to the neutron activation of 14N impurities by 14N(n,p)14C reaction, or in the oxide layer (ZrO2) formed at the metal surface by the neutron activation of 17O from UO2 or (U-Pu)O2 fuel and water from the primary circuit in the reactor by 17O(n,α)14C reaction. Various irradiated and unirradiated Zircaloys have been studied. The total 14C inventory has been determined both experimentally and by calculations. The results seem to be in good agreement. Leaching experiments were conducted in alkaline media for several time durations. 14C was mainly released as carboxylic acids. Further, corrosion measurements were performed by using both hydrogen measurements and electrochemical measurements. The corrosion rate (CR) ranges from a few nm/yr to 100 nm/yr depending on the surface conditions and the method used for measurement. From a safety assessment point of view, the instant release fraction (IRF) was determined on irradiated Zircaloy-2. The results showed that the 14C inventory in the oxide was significantly below the 20% commonly used in safety case assessments

Effects of finite width of excited states on heavy-ion sub-barrier fusion reactions

We discuss the effects of coupling of the relative motion to nuclear collective excitations which have a finite lifetime on heavy-ion fusion reactions at energies near and below the Coulomb barrier. Both spreading and escape widths are explicitly taken into account in the exit doorway model. The coupled-channels equations are numerically solved to show that the finite resonance width always hinders fusion cross sections at subbarrier energies irrespective of the relative importance between the spreading and the escape widths. We also show that the structure of fusion barrier distribution is smeared due to the spreading of the strength of the doorway state.Comment: 13 pages, 3 figures, Submitted to Physical Review