Refractive effects in the scattering of loosely bound nuclei

A study of the interaction of loosely bound nuclei 6,7Li at 9 and 19 AMeV with light targets has been undertaken. With the determination of unambiguous optical potentials in mind, elastic data for four projectile-target combinations and one neutron transfer reaction 13C(7Li,8Li)12C have been measured on a large angular range. The kinematical regime encompasses a region where the mean field (optical potential) has a marked variation with mass and energy, but turns out to be sufficiently surface transparent to allow strong refractive effects to be manifested in elastic scattering data at intermediate angles. The identified exotic feature, a "plateau" in the angular distributions at intermediate angles, is fully confirmed in four reaction channels and interpreted as a pre-rainbow oscillation resulting from the interference of the barrier and internal barrier farside scattering subamplitudes.Comment: 19 pages, 14 figures, 3 tables to submit to Phys. Rev.

Connection between asymptotic normalization coefficients, subthreshold bound states, and resonances

Journals published by the American Physical Society can be found at http://publish.aps.org/We present here useful relations showing the connection between the asymptotic normalization coefficient (ANC) and the fitting parameters in K- and R-matrix theory methods which are often used when analyzing low energy experimental data. It is shown that the ANC of a subthreshold bound state defines thr normalization of both direct radiative capture leading to this state and resonance capture in which the start: behaves like a subthreshold resonance. A determination of the appropriate ANC(s) thus offers an alternative method for finding the strength of these types of capture reactions, both of which are important in nuclear astrophysics. [S0556-2813(99)01006-7]

Fragmentation Barriers of Toroidal and Bubble Nuclei

Journals published by the American Physical Society can be found at http://publish.aps.org/With an improved Boltzmann-Uehling-Uhlenbeck model, the deformation energy surfaces in reactions leading to the formation of toroidal and bubble nuclei are examined for central Mo-92+Mo-92 collisions. We found that the potential maximum, or the fragmentation barrier, occurs at times close to the times when these exotic shapes are formed. However, due to the dynamics of large amplitude compression and expansion, the fragmentation barriers are significantly higher than those estimated from the liquid-drop models

Asymptotic normalization coefficients, spectroscopic factors, and direct radiative capture rates

Journals published by the American Physical Society can be found at http://publish.aps.org/We compare the use of asymptotic normalization coefficients (ANC's) and spectroscopic factors determined from peripheral transfer reactions for determining the overall normalization of peripheral direct radiative capture reaction processes. We demonstrate that ANC's provide a natural way to parametrize the rates of both peripheral transfer and direct capture reactions. Furthermore, ANC's inferred from one reaction may be used in the analysis of a second reaction without further knowledge regarding their origin, and independent measurements of a given ANC may be combined to give an overall "best value" in a straightforward manner. In contrast, a spectroscopic factor derived from analysis of a peripheral transfer reaction can only be used in subsequent calculations if one has detailed knowledge of the single-particle bound state orbital that was assumed when the spectroscopic factor was obtained

Breakup of B-8 and the S-17 astrophysical factor reexamined

Journals published by the American Physical Society can be found at http://publish.aps.org/Existing experimental data for the breakup of B-8 at energies from 30 to 1000 MeV/nucleon on light through heavy targets are analyzed in detail in terms of an extended Glauber model. The predictions of the model are in excellent agreement with independent reaction data (reaction cross sections and parallel momentum distributions for corelike fragments). Final-state interactions have been included in the Coulomb dissociation component. We extract asymptotic normalization coefficients (ANC) from which the astrophysical factor S-17(0) for the key reaction for solar neutrino production, Be-7(p,gamma)B-8, can be evaluated. Glauber model calculations using different effective interactions give consistent, though slightly different results. The differences give a measure of the precision one can expect from the method. The unweighted average of all ANCs extracted leads to S-17(0)=18.7+/-1.9 eV b. The results of this new analysis are compared with the earlier one. They are consistent with the values from most direct measurements and other indirect methods

Radius of B-8 halo from the asymptotic normalization coefficient

Journals published by the American Physical Society can be found at http://publish.aps.org/The experimental asymptotic normalization coefficient determined from peripheral transfer reactions is used to obtain the root-mean-square radius of the wave function for the loosely bound proton in SB. It is shown that the asymptotic region contributes most and that matching of the interior wave function with the asymptotic part yields a nearly model-independent radius. We obtain [r(2)] (1/2) = 4.20 +/- 0.22 fm for the root-mean-square (rms) radius of the last proton, much larger than the rms radius of the Be-7 core. This large value and the fact that the asymptotic part of the proton wave function contributes 85% to the rms radius are good sign that B-8 is a halo nucleus

Formation and Decay of Toroidal and Bubble Nuclei and the Nuclear-Equation of State

Journals published by the American Physical Society can be found at http://publish.aps.org/Multifragmentation, following the formation of toroidal and bubble nuclei, is observed with an improved Boltzmann-Uehling-Uhlenbeck model for central Mo-92 + Mo-92 collisions. With a stiff equation of state, simultaneous explosion into several nearly equal fragments in a ringlike manner occurs due to the formation of metastable toroidal nuclei. In contrast, with a soft equation of state, simultaneous explosion into several nearly equal fragments in a volumelike manner occurs due to the formation of metastable bubble nuclei. Experimental signatures for the formation of these exotic shapes are discussed

Deuteron Elastic-Scattering at 110 and 120 Mev

Journals published by the American Physical Society can be found at http://publish.aps.org/Deuteron elastic scattering cross sections have been measured at 110 and 120 MeV on C, Ni-58, and Pb-208. Optical model potentials have been extracted and compared to deuteron global optical model potentials

Low-lying levels in F-15 and the shell model potential for drip-line nuclei

Journals published by the American Physical Society can be found at http://publish.aps.org/The ground and first excited states in F-15 were studied in resonant elastic scattering using the thick (CH4) gas target method in inverse kinematics with a separated O-14 beam. An analysis of the excitation functions of the elastic scattering was carried out with the potential model. The quantum numbers 1/2(+) (ground state) and 5/2(+) (first excited state) were assigned to the lowest two states in F-15. Also, the widths and the proton decay energies of the unbound levels were obtained. The analysis of the data indicates that a large diffuseness is needed in the Woods-Saxon potential in order to describe single-particle features in drip-line nuclei

Asymptotic normalization coefficients from the (20)Ne((3)He, d)(21)Na reaction and astrophysical factor for (20)Ne(p,gamma)(21)Na

Journals published by the American Physical Society can be found at http://publish.aps.org/The (20)Ne(p,gamma)(21)Na reaction rate at stellar energies is dominated by capture to the ground state through the tail of a subthreshold resonance state at an excitation energy of 2425 keV in (21)Na. Both resonant and direct capture contribute to the reaction rate while direct captures to other bound states are negligible. The overall normalization of direct capture to the subthreshold state is determined by the asymptotic normalization coefficient (ANC). Simultaneously this ANC determines the proton partial width of the subthreshold resonance state. To determine the ANC, the (20)Ne((3)He,d)(21)Na proton transfer reaction has been measured, at an incident energy of 25.83 MeV. Angular distributions for proton transfer to the ground and first three excited states were measured, and ANCs were then extracted from comparison with distorted-wave Born approximation calculations. Using these ANCs, we calculated the astrophysical factor for (20)Ne(p,gamma)(21)Na. Our total astrophysical factor is S(0)=5900 +/- 1200 keV b. Our analysis confirms that only nonresonant and resonant captures through the subthreshold state are important