Showing papers in "Physical Review C in 1982"
TL;DR: In this article, an analysis of the continuum spectra of light-ion reactions, in terms of multistep direct reaction methods, is discussed, followed by several examples which show that this method works rather well in a variety of cases.
Abstract: Analyses of continuum spectra of light-ion reactions, in terms of multistep direct reaction methods are discussed. The formulation used in the calculations is presented first, and is followed by several examples which show that this method works rather well in a variety of cases. Comparison with related theories is also made.NUCLEAR REACTIONS Multistep direct reaction method, calculations of cross sections, and polarizations of continuum spectra of reactions induced by light ions.
155 citations
TL;DR: In this paper, a model for the preequilibrium emission of light composite particles in the framework of the exciton model is proposed, and the model contains two new points: one is the calculation of the formation factor F/sub l/,m(epsilon) which stands for the probability that the composite particle of an energy epsilon is composed of l particles above the Fermi level and m particles below.
Abstract: A model is proposed for the preequilibrium emission of light composite particles in the framework of the exciton model. The model contains two new points: One is the calculation of the formation factor F/sub l/,m(epsilon) which stands for the probability that the composite particle of an energy epsilon is composed of l particles above the Fermi level and m particles below. Information of the intrinsic wave function of the composite particle is incorporated in the F/sub l/,m(epsilon). Another new point is the inclusion of the pickup type contribution in the particle emission mechanism. We allow some nucleons which constitute the emitted composite particle to come from levels below the Fermi energy. This model is applied to six kinds of (p,..cap alpha..) reactions of incident energies of several tens of MeV on /sup 54/Fe, /sup 118/Sn, and /sup 120/Sn targets. Calculated results reproduce nicely the high energy part of the experimental energy spectra and indicate that its main component is the ''three-particle pickup'' reaction coming from 2p-1h and 3p-2h, but ''two-particle pickup'' also contributes substantially.
148 citations
TL;DR: In this paper, the authors compared the time-dependent Hartree-Fock approximation with a purely classical pseudoparticle simulation and showed that it is approximately equivalent to a pure classical simulation.
Abstract: In order to facilitate the comparison of the time-dependent Hartree-Fock approximation with other classical theories and to help guide our intuition in understanding the underlying physics, we study the time-dependent Hartree-Fock approximation from a classical viewpoint. We show that the time-dependent Hartree-Fock approximation is approximately equivalent to a purely classical pseudoparticle simulation. In this simulation, a collection of pseudoparticles are introduced to discretize the phase space of spatial and momentum coordinates. The dynamics is completely determined by following the pseudoparticle trajectories which are the same as the trajectories of real particles moving in the self-consistent field. As an application of the concept of the pseudoparticle simulation, we study the origin of the nonfusion events in nearly-head-on heavy-ion collisions as obtained in the time-dependent Hartree-Fock approximation. It is argued that for these nearly-head-on collisions, the emergence of the most energetic pseudonucleons of one nucleus outside the far surface of the other nucleus initiates a coherent flow-through motion because of self-consistency and leads to the breakup of the composite system. Based on this picture, we obtain quantitative estimates of the threshold energies and the low-l fusion window which agree quite well with the time-dependent Hartree-Fock results.
142 citations
TL;DR: In this paper, the Bethe-Salpeter equation does not satisfy the requirement that a two-body relativistic equation should approach a one-body equation when one of the masses becomes very large.
Abstract: This paper begins with an explanation of the implications of the requirement that a two-body relativistic equation should approach a one-body equation when one of the masses becomes very large. It is found that the Bethe-Salpeter equation does not satisfy this requirement. An infinite family of three-dimensional equations depending on a parameter $\ensuremath{-}1\ensuremath{\le}\ensuremath{
u}\ensuremath{\le}1$ is constructed, all of which do satisfy this limit. When $|\ensuremath{
u}|=1$ one of the particles is on its mass shell; when $\ensuremath{
u}=0$ both particles are equally off mass shell. The fourth order irreducible kernel for this family is studied in the expanded static limit for all $\ensuremath{
u}$. It is found, both for scalar theories and for a realistic chiral theory of spin \textonehalf{} nucleons interacting with isovector pions, that the leading order terms in the static limit cancel for any $\ensuremath{
u}$, and that the nonleading terms are independent of energy only for the $|\ensuremath{
u}|=1$ equation. Other criteria for the selection of a relativistic two-body equation and implications for the form of the two-pion exchange potential are briefly discussed.
135 citations
Abstract: A perturbative calculation is reported for the mixing of Gamow-Teller strength with two-particle two-hole configurations at high excitation energies. We find that roughly 50% of the Gamow-Teller strength is shifted into the region of 10--45 MeV excitation for the nucleus /sup 90/Zr. This would explain a substantial part of the continuum background seen in the 200 MeV (p,n) reaction.
131 citations
TL;DR: In this article, the authors analyzed the energy and target mass dependence of the cross section and analyzed power angular distribution of polarized protons in a conventional optical potential model, and the behavior of the potential parameters as a function of energy was investigated.
Abstract: Elastic scattering of polarized protons of 80-180 MeV from a number of target nuclei ($24lAl208$) has been measured. The systematic energy and target mass dependence of the cross section and analyzing power angular distributions is discussed. The data have been analyzed within the framework of a conventional optical potential model, and the behavior of the potential parameters as a function of energy is investigated. Comparisons are made with results obtained at energies greater than 180 MeV and with predictions obtained from microscopic models.NUCLEAR REACTIONS $^{24}\mathrm{Mg}(\stackrel{\ensuremath{\rightarrow}}{p}, p)$, ${E}_{p}=134.7$ MeV; $^{28}\mathrm{Si}(\stackrel{\ensuremath{\rightarrow}}{p}, p)$, ${E}_{p}=134.5$ MeV; $^{40}\mathrm{Ca}(\stackrel{\ensuremath{\rightarrow}}{p}, p)$, ${E}_{p}=80.2, 181.5$ MeV; $^{90}\mathrm{Zr}(\stackrel{\ensuremath{\rightarrow}}{p}, p)$, ${E}_{p}=79.6, 98.7, 134.8, 160$ MeV; $^{92}\mathrm{Zr}(\stackrel{\ensuremath{\rightarrow}}{p}, p)$, ${E}_{p}=104$ MeV; $^{120}\mathrm{Sn}(\stackrel{\ensuremath{\rightarrow}}{p}, p)$, ${E}_{p}=104$ MeV; $^{208}\mathrm{Pb}(\stackrel{\ensuremath{\rightarrow}}{p}, p)$, ${E}_{p}=79.8, 98, 182$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$, ${A}_{y}(\ensuremath{\theta})$; optical-model analysis, deduced energy dependence, comparison with microscopic models.
111 citations
TL;DR: A detailed study of the transition between the SU(5) and O(6) limit of the interacting boson model (IBA-1) has been performed in a schematic way as mentioned in this paper.
Abstract: A detailed study of the transition between the SU(5) and O(6) limit of the interacting boson model (IBA-1) has been performed in a schematic way A comparison of the experimental excitation energies and E2 transition probabilities for neutron-rich Ru and Pd isotopes with this calculation show that this mass region is well described in terms of this phase transition
96 citations
TL;DR: In this article, the mean square radius of the real central part of the optical potential was found to obey the relation of the binding energy curve for the target mass number, and the dependence of the mass number and energy on the optical capacity was analyzed.
Abstract: Elastic scattering of 65 MeV polarized protons from 25 nuclei ($^{16}\mathrm{O}$---$^{209}\mathrm{Bi}$) has been measured. The volume integral of the real central part of the optical potential (${J}_{R}$) shows a behavior similar to the binding energy curve for the target mass number. The mean square radius of the real central part of the optical potential is found to obey the relation ${〈{r}^{2}〉}_{\mathrm{pot}}=(0.937\ifmmode\pm\else\textpm\fi{}0.012){A}^{\frac{2}{3}}+(6.42\ifmmode\pm\else\textpm\fi{}0.21)$ ${\mathrm{fm}}^{2}$. By comparing with the systematics of the charge distributions obtained from electron scattering data, it is found that the effective two-body interaction range between an incident proton and a nucleon in the target has a target mass number dependence given by ${〈{r}^{2}〉}_{\mathrm{int}}=(0.132\ifmmode\pm\else\textpm\fi{}0.013){A}^{\frac{2}{3}}+(4.24\ifmmode\pm\else\textpm\fi{}0.24)$ ${\mathrm{fm}}^{2}$. Assuming this relation, root mean square radii of the point nucleon distributions are obtained. The dependences of the ${J}_{R}$ value and the ${〈{r}^{2}〉}_{\mathrm{pot}}$ value on the mass number and energy obtained here are compared critically with recent microscopic optical potential calculations.NUCLEAR REACTIONS $^{16}\mathrm{O}$, $^{24}\mathrm{Mg}$, $^{28}\mathrm{Si}$, $^{40}\mathrm{Ar}$, $^{40,44,48}\mathrm{Ca}$, $^{46,48,50}\mathrm{Ti}$, $^{54,56}\mathrm{Fe}$, $^{58,60,62,64}\mathrm{Ni}$, $^{89}\mathrm{Y}$, $^{90}\mathrm{Zr}$, $^{98,100}\mathrm{Mo}$, $^{144}\mathrm{Sm}$, $^{208}\mathrm{Pb}$, $^{209}\mathrm{Bi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}, p)$, $E=65$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$, $A(\ensuremath{\theta})$; deduced optical-model parameters, mean-square nuclear radii, and volume integrals for the real central potential.
86 citations
TL;DR: The isospin reaction cross sections for single pion production are extracted from data for the processes of NN-nucleon scattering and single particle production in this article, and they are shown to be essentially zero below 1000 MeV.
Abstract: The isospin reaction cross sections for $\mathrm{NN}$ single pion production are extracted from data for the processes $\mathrm{NN}\ensuremath{\rightarrow}\ensuremath{\pi}d$ and $\mathrm{NN}\ensuremath{\rightarrow}\mathrm{NN}\ensuremath{\pi}$. New data in conjunction with older existing data have precisely determined the components of the cross sections for the isospin one ($\mathrm{pp}$) initial state. Other new data for the $\mathrm{np}$ initial state and correct treatment of some older data indicate that the isospin zero reaction cross section is essentially zero below 1000 MeV, which indicates against the presence of inelastic isospin zero $\mathrm{NN}$ resonances.NUCLEAR REACTIONS Nucleon-nucleon scattering, $\ensuremath{\pi}$ production reaction cross sections, isospin decomposition, isospin cross sections deduced from data.
81 citations
TL;DR: In this article, a phenomenological analysis was performed using the WKB method, constructed a simple interaction potential and introduced a radially-dependent effective mass, which led to a meaningful description of the above-barrier data.
Abstract: Differential cross sections for evaporation residue formation following complete fusion of /sup 64/Ni and /sup 74/Ge with 171 to 215 MeV /sup 58/Ni and /sup 64/Ni ions were measured with high precision using a velocity selector together with a counter telescope. The resulting excitation functions for complete fusion ranged in magnitude from 10 ..mu..b to 300 mb. The excitation functions exhibited a strong response, at subbarrier energies, to changes in the underlying nuclear structure. We interpreted these variations as evidence that the fusion proceeds through dynamic single-particle/softness-related processes. A phenomenological analysis was performed. In the analysis, we employed the WKB method, constructed a simple interaction potential and introduced a radially-dependent effective mass. The use of the variable effective mass led to a meaningful description of our above-barrier data and to improvements towards describing our subbarrier data.
78 citations
TL;DR: In this paper, the authors used the double differential cross-sections of the triple differential distributions to obtain the azimuthal dependence of triple differential distribution, which can yield deeper insight into the collision process.
Abstract: The fluid dynamical model is used to study the reactions $^{20}\mathrm{Ne}$+$^{238}\mathrm{U}$ and $^{40}\mathrm{Ar}$+$^{40}\mathrm{Ca}$ at ${E}_{\mathrm{lab}}=390$ MeV/nucleon. The calculated double differential cross sections ${d}^{2}\frac{\ensuremath{\sigma}}{d\ensuremath{\Omega}}\mathrm{dE}$ exhibit sidewards maxima in agreement with recent experimental data. The azimuthal dependence of the triple differential distributions, to be obtained from an event-by-event analysis of $4\ensuremath{\pi}$ exclusive experiments, can yield deeper insight into the collision process: Jets of nuclear matter are predicted with a strongly impact-parameter-dependent thrust angle ${\ensuremath{\theta}}_{\mathrm{jet}}(b)$.NUCLEAR REACTIONS Ar+Ca, Ne+U, ${E}_{\mathrm{lab}}=393$ MeV/nucleon, fluid dynamics with thermal breakup, double differential cross sections, azimuthal dependence of triple differential cross sections, event-by-event thrust analysis of $4\ensuremath{\pi}$ exclusive experiments.
TL;DR: In this paper, the low-lying quadrupole vibrational configurations of two-particle two-hole excitations were derived from a simplified model, treating proton twoparticle excitations in interaction with lowlying quadrachromatic configurations.
Abstract: Starting from a simplified model, treating proton two-particle two-hole excitations in interaction with low-lying quadrupole vibrational configurations, we calculate the low-lying levels in even-even $^{112,114}\mathrm{Cd}$. We also present configuration mixing calculations within the framework of the interacting boson model. Both approaches give a good description of the quintuplet of levels occurring below ${E}_{x}\ensuremath{\cong}1.5$ MeV in $^{112,114}\mathrm{Cd}$ (energy spectra and a detailed account of $E2$ and $E0$ decay properties). Finally, we point out some similarities between both approaches and try to interpret the interacting boson model mixing parameters in terms of shell-model quantities (two-body matrix elements and single-particle energies).
TL;DR: In this paper, a quantitatively adequate form of the deformed proximity potential suitable for use with a coupled channels reaction code in the analysis of inelastic scattering data above the Coulomb barrier is described.
Abstract: The usual treatment of the deformed optical model for analysis of heavy ion induced inelastic scattering data involves a deformed (target) radius, a spherical (projectile) radius and a potential strength dependent on the surface separation along the line between the two centers. Several authors using various approaches have shown that this center line potential is geometrically inadequate especially for description of higher L deformation parameters probed in heavy ion induced inelastic scattering experiments. A quantitatively adequate form of the deformed proximity potential suitable for use with a coupled channels reaction code in the analysis of inelastic scattering data above the Coulomb barrier is described. A major objective is to be able to extract reliably higher deformed multipole moments from such data. The deformed potential calculated in the folding model will serve as a geometrically exact benchmark to evaluate the accuracy of the proximity potential prescriptions. (WHK)
TL;DR: In this article, double differential cross sections have been measured for energetic $p, $d, $t, and $\ensuremath{\alpha}$ particles emitted in O-induced reactions on targets of A1, Zr and Au at incident energies of 140, 215, and 310 MeV.
Abstract: Double differential cross sections have been measured for energetic $p$, $d$, $t$, and $\ensuremath{\alpha}$ particles emitted in $^{16}\mathrm{O}$-induced reactions on targets of A1, Zr, and Au at incident energies of 140, 215, and 310 MeV. The energy and angular distributions are well described by isotropic emission from a moving thermal source. The extracted temperature and velocity parameters are found to vary systematically with the incident energy per nucleon above the Coulomb barrier. The observed trends cannot be explained by compound nucleus emission but instead suggest emission from a source which consists of comparable contributions from target and projectile. Alternatively, the proton energy spectra are compared with a precompound model and with a simple knockout model. The $d$, $t$, and $\ensuremath{\alpha}$-particle cross sections are also described in terms of a generalized coalescence relation which takes into account Coulomb repulsion from the target nucleus.
TL;DR: In this paper, a model-independent way with a Fourier-Bessel parametrization of the charge distribution was analyzed in a model independent way, and the behavior of the form factor in the diffraction minimum was investigated.
Abstract: Elastic electron scattering cross sections for the nucleus $^{12}\mathrm{C}$ have been measured in a momentum transfer range from 0.25 to 2.75 ${\mathrm{fm}}^{\ensuremath{-}1}$. The data were analyzed in a model independent way with a Fourier-Bessel parametrization of the charge distribution. For the rms radius, the value ${〈{r}^{2}〉}^{\frac{1}{2}}=(2.464\ifmmode\pm\else\textpm\fi{}0.012)$ fm (no dispersion corrections applied) has been obtained, and agrees with those of other electron scattering experiments and with muonic atom experiments, but disagrees with data obtained from measurements of muonic x-ray transitions with a crystal spectrometer which show a larger rms radius. The extracted distribution disagrees with Hartree-Fock calculations in both the radial dependence and the rms radius. The behavior of the form factor in the diffraction minimum was investigated in detail. The experimentally determined cross sections in the minimum are always larger than those obtained from the Fourier-Bessel analysis. These deviations amounted to 5% for a primary energy of 320 MeV and to 2% for 240 MeV and may be interpreted as an indication of dispersion effects.NUCLEAR REACTIONS $^{12}\mathrm{C}$; absolute ($e, e$) cross sections measured. Charge distribution and rms radius deduced. Discussion of dispersion effects, comparison with HF calculations.
TL;DR: The accuracy of the uncoupled adiabatic approximation for bound trinucleon systems was investigated in this article, and the quality of this approximation was related to the strength of the repulsive core of the nuclear potential.
Abstract: The accuracy of the uncoupled adiabatic approximation is investigated for bound trinucleon systems. The quality of this approximation is related to the strength of the repulsive core of the nuclear potential.
TL;DR: On-line high-resolution laser spectroscopy has been performed on radioactive /sup 20 -31/Na as discussed by the authors, where the spectroscopic quadrupole moments of /sup 21,25-29/Na have been determined using a double resonance method.
Abstract: On-line high resolution laser spectroscopy has been performed on radioactive /sup 20 -31/Na. New values for the isotope shift of the D/sub 1/ line of /sup 20-24,31/Na relative to /sup 23/Na have been obtained. The spectroscopic quadrupole moments of /sup 21,25-29/Na have been determined using a double resonance method. The D/sub 2/ line hyperfine structure of /sup 21,25-27/Na has also been studied by laser optical spectroscopy. Results are in agreement with those obtained by rf double resonance. No evidence of the sudden onset of a deformation expected at N = 20 has been found. A strong shell effect in the change in the mean-square charge radius is exhibited at N = 14.
TL;DR: In this article, the thermal neutron capture cross section of deuterium was measured by direct observation of the prompt gamma ray, and the results showed that the cross section was positively correlated with the thermal neutrons.
Abstract: We have measured the thermal neutron capture cross section of deuterium by direct observation of the prompt gamma ray.
TL;DR: In this paper, a group of 40 neutron-deficient nulcides with atomic numbers ranging from 65 to 68 were measured to an accuracy of 2 to 5 keV.
Abstract: Alpha particle energies were redetermined to an accuracy of 2 to 5 keV for a group of 40 neutron-deficient nulcides with atomic numbers ranging from 65 to 68. Improved half-life values were measured for 10 of these nuclides. Weightless samples containing mixtures of these activities were prepared by use of the helium jet transport technique to remove spallation and fragmentation products recoiling from targets of U, Th, Au, and Ta bombarded with 5 GeV protons. Experimental and calibration techniques are discussed in detail. Implications of the results for the mechanism of reaction of 5 GeV protons with complex targets are briefly discussed.
TL;DR: In this article, the excitation functions of fission products for 22 fragment masses and neutron-evaporation products, ($p$,$n$), ($p),$2n$) and ($p,$3n) were measured in detail for the system of $^{232}mathrm{Th}$+$p$ in the proton energy range of 8 to 22 MeV.
Abstract: Excitation functions of fission products for 22 fragment masses and neutron-evaporation products, ($p$,$n$), ($p$,$2n$) and ($p$,$3n$) were measured in detail for the system of $^{232}\mathrm{Th}$+$p$ in the proton energy range of 8 to 22 MeV. It was found that the excitation functions of symmetrically divided fission fragments were apparently different from those of asymmetrically divided ones. For the interpretation of the experimental results, a statistical evaporation-and-fission calculation was performed by taking into consideration symmetric and asymmetric fission barriers. The experimental data could be reproduced by this statistical calculation, with fission barrier heights that were in accord with the reported experimental ones for the asymmetric fragments and the theoretically predicted one for the symmetric mass division. The level density parameter at the symmetric saddle had to be about 13% larger than that for the asymmetric saddle in order to reproduce the energy dependence of the cross section ratios of asymmetric to symmetric product yields.NUCLEAR REACTIONS, FISSION $^{232}\mathrm{Th}$($p$,$f$), ${E}_{p}=8\ensuremath{-}22$ MeV, stacked-foil method, excitation functions of fission products and neutron-evaporation products, statistical calculation, symmetric and asymmetric fission barriers.
TL;DR: In this paper, a set of relativistic three-body Faddeev equations from ladder and crossed ladder exchanges is studied, where two of the three particles are restricted to their mass shell.
Abstract: Examination of the sum of all ladder and crossed ladder exchanges between three particles leads to a set of relativistic three-body equations of the Faddeev type in which two of the three particles are restricted to their mass shell. The choice of which two particles are on shell at a given instant is uniquely determined by the requirement that they be spectators either before or after the interaction. It is shown that these equations satisfy the cluster property, and the two-body amplitudes which drive the equations are known in principle. Three-body unitarity is proved. Three-body forces which arise from the underlying dynamics are discussed, classified, and estimated numerically for a spinless example. It is found that the three-body forces tend to cancel to some extent, are sensitive to the details of the dynamics, and that contributions to such forces, primarily of relativistic origin, can be important.NUCLEAR STRUCTURE Relativistic Faddeev equations from ladder and crossed ladder exchanges. Unitarity, cluster property, and three-body forces.
TL;DR: In this paper, the Woods-Saxon potential is employed to interpret the properties of single particle and high spin spectra of a single particle, and spin-orbit potential parameters are found which simultaneously reproduce the experimental yrast and yrare states up to $I\ensuremath{\sim}18$ and generate the proton single particle energy gap = 2.0$ MeV.
Abstract: The Woods-Saxon potential is employed to interpret the properties of single particle and high spin spectra of $^{146}\mathrm{Gd}$. Spin orbit potential parameters are found which simultaneously reproduce the experimental yrast and yrare states up to $I\ensuremath{\sim}18$ and generate the proton single particle energy gap ${\ensuremath{\delta}}_{p}=2.0$ MeV. The spin-orbit potential parameters obtained are nearly identical for neutrons and protons and are close to the parameter values obtained previously by optimizing the potential to high spin spectra in the vicinity of $^{208}\mathrm{Pb}$. Properties of the pairing correction method, the Bardeen-Cooper-Schrieffer approximation with blocking, and the particle number projection are discussed and illustrated. It is demonstrated that including the particle number projection term in the total energy formula improves considerably the average slope of the calculated yrast line. The possibility of the collective quadrupole vibrational states becoming yrast states is studied for $I\ensuremath{\gtrsim}7\ensuremath{\hbar}$ using the random phase approximation but only a rather weak effect of collectivity is found in the spin-range studied.NUCLEAR STRUCTURE $^{146}\mathrm{Gd}$; Woods-Saxon single-particle levels, high spin excitations. Collectivity in the high spin states, RPA.
TL;DR: The shape and absolute values of complete fusion excitation functions are compared to macroscopic models and to the predictions of a coupled-channels approach of the reaction, which gives a more satisfactory account of experimental results.
Abstract: Complete fusion or residue distributions have been measured with several experimental techniques for the following systems: $^{24}\mathrm{Mg}$, $^{28}\mathrm{Si}$+ $^{12}\mathrm{C}$, $^{24}\mathrm{Mg}$+ $^{24,26}\mathrm{Mg}$, $^{28}\mathrm{Si}$+ $^{24}\mathrm{Mg}$, $^{28,29,30}\mathrm{Si}$. The range of energies spreads from 1 to 3 times the Coulomb barrier. None of these systems presents structures in its fusion excitation function as pronounced as the ones observed for lighter entrance channels. The intensities of the residue distribution are generally in agreement with the predictions of a multiple deexcitation code. The shape and absolute values of complete fusion excitation functions are compared to macroscopic models and to the predictions of a coupled-channels approach of the reaction, which gives a more satisfactory account of experimental data.NUCLEAR REACTIONS Fusion, measured ${\ensuremath{\sigma}}_{\mathrm{fusion}}(E,\ensuremath{\theta})$, ${\ensuremath{\sigma}}_{\mathrm{residue}}(E,\ensuremath{\theta})$; $^{24}\mathrm{Mg}$+ $^{12}\mathrm{C}$, $16.4l{E}_{\mathrm{c}.\mathrm{m}.}l29.8$ MeV; $^{28}\mathrm{Si}$+ $^{12}\mathrm{C}$, $15.1l{E}_{\mathrm{c}.\mathrm{m}.}l24.6$ MeV; $^{24}\mathrm{Mg}$+ $^{24}\mathrm{Mg}$, $21l{E}_{\mathrm{c}.\mathrm{m}.}l41.6$ MeV; $^{24}\mathrm{Mg}$+ $^{26}\mathrm{Mg}$, $20.3l{E}_{\mathrm{c}.\mathrm{m}.}l32.9$ MeV; $^{28}\mathrm{Si}$+ $^{24}\mathrm{Mg}$, $24.2l{E}_{\mathrm{c}.\mathrm{m}.}l38.1$ MeV; $^{28}\mathrm{Si}$+ $^{28}\mathrm{Si}$, $27.9l{E}_{\mathrm{c}.\mathrm{m}.}l41.4$ MeV; $^{28}\mathrm{Si}$+ $^{29}\mathrm{Si}$, $27.4l{E}_{\mathrm{c}.\mathrm{m}.}l42.1$ MeV; $^{28}\mathrm{Si}$+ $^{30}\mathrm{Si}$, $27.3l{E}_{\mathrm{c}.\mathrm{m}.}l42.8$ MeV; comparison with evaporation calculation; barrier parameters deduced from ${\ensuremath{\sigma}}_{\mathrm{CF}}(E)$. Comparison of ${\ensuremath{\sigma}}_{\mathrm{CF}}(E)$ with macroscopic models; coupled-channels approach of the fusion strength.
TL;DR: In this article, the energy dependence of the optical model parameters for low energy, 0--50 MeV, pions was determined by a compromise fit to pionic atoms, elastic scattering and absorption mesurements.
Abstract: The energy dependence of the optical model parameters for low energy, 0--50 MeV, pions was determined by a compromise fit to pionic atoms, ..pi../sup +/ elastic scattering and ..pi../sup - +/ absorption mesurements.
TL;DR: In this article, the classical Hamiltonian of the interacting boson model is defined and expressed in terms of the conventional quadrupole variables, which are used in the analyses of the dynamics in the various limits of the model.
Abstract: The classical Hamiltonian of the interacting boson model is defined and expressed in terms of the conventional quadrupole variables. This is used in the analyses of the dynamics in the various limits of the model. The purpose is to determine the range and the features of the collective phenomena which the interacting boson model is capable of describing. In the commonly used version of the interacting boson model with one type of the $s$ and $d$ bosons and quartic interactions, this capability has certain limitations and the model should be used with care. A more sophisticated version of the interacting boson model with neutron and proton bosons is not discussed.
TL;DR: In this paper, the results of fission-fragment angular correlation measurements on uranium target nuclei were analyzed over an energy range which extends well above the interaction barrier, and it was shown that above 10 MeV/nucleon, the experimental definition of complete fusion is complicated by the increasing probability for large, but incomplete, linear momentum transfer collisions.
Abstract: The systematic behavior of linear momentum transfer from projectile to target in nonrelativistic nucleus-nucleus collisions has been studied using the results of fission-fragment angular-correlation measurements on uranium target nuclei. Data for $^{4}\mathrm{He}$, $^{12}\mathrm{C}$, $^{16}\mathrm{O}$, and $^{20}\mathrm{Ne}$ projectiles have been analyzed over an energy range which extends well above the interaction barrier. The data illustrate the division of the total reaction cross section into two primary components: one associated with \ensuremath{\sim} 90 percent or greater linear momentum transfer and the other involving much smaller amounts of linear momentum transfer. The former is attributed to fusionlike collisions and the latter to peripheral collisions. The minimum between these two components corresponds to a linear momentum transfer of about 50 percent. It is observed that the ratio of fusionlike collisions to the total reaction cross section decreases regularly as a function of both increasing bombarding energy and projectile mass. From comparison of the experimental fission-fragment angular correlation functions with the predictions of complete fusion kinematics, it is shown that above 10 MeV/nucleon, the experimental definition of complete fusion is complicated by the increasing probability for large, but incomplete, linear momentum transfer collisions. Estimates of critical angular momenta derived from these data do not show any major disagreement with rotating-liquid-drop predictions.NUCLEAR REACTIONS, FISSION Studied systematics of fission-fragment angular correlation measurements from uranium target nuclei. Deduced linear momentum transfer distributions, fusionlike collision and complete fusion probabilities, and critical angular momenta.
TL;DR: In this article, the model dependence of the spin parameters for low and medium energy antinucleon-nucleon (N-barN) scattering is discussed, and the sensitivity of these effects to changes in the real and imaginary parts of the N-BarN potential is explored.
Abstract: We discuss the model dependence of the spin parameters for low and medium energy antinucleon-nucleon (N-barN) scattering. An N-barN potential model is used, consisting of a t-channel meson exchange part, supplemented by a complex annihilation potential, adjusted to reproduce the observed energy dependence of total elastic, inelastic and charge exchange cross sections. A number of striking spin effects are predicted, particularly in the charge exchange channel. We explore the sensitivity of these effects to changes in the real and imaginary parts of the N-barN potential; in particular, we assess the possibility of extracting the strength of the coherent N-barN tensor potential due to ..pi.., rho, and ..omega.. exchange from future data. Some implications of our results for future experiments are mentioned.
TL;DR: In this paper, positive energy Weinberg states are defined and numerically calculated in the presence of a general complex Woods-Saxon potential and a set of auxiliary positive energy states are used as basis functions in order to provide a separable approximation of rank to a potential.
Abstract: Positive energy Weinberg states are defined and numerically calculated in the presence of a general complex Woods-Saxon potential. The numerical procedure is checked for the limit of a square well potential for which the Weinberg states and the corresponding eigenvalues are known. A finite number $M$ of these (auxiliary) positive energy Weinberg states are then used as a set of basis functions in order to provide a separable approximation of rank $M$, ${V}_{M}$, to a potential $V$, and also to the scattering matrix element $S$ which obtains as a result of the presence of $V$,${S}_{M}$. Both ${V}_{M}$ and ${S}_{M}$ are obtained by means of algebraic manipulations which involve the matrix elements of $V$ calculated in terms of the auxiliary positive energy Weinberg states. Next, expressions are derived which enable one to iteratively correct for the error in $V\ensuremath{-}{V}_{M}$. These expressions are a modified version of the quasiparticle method of Weinberg. The convergence of ${S}_{M}$ to $S$, as well as the first order iteration of the error in ${S}_{M}$, is examined as a function of $M$ for a numerical example which uses a complex Woods-Saxon potential for $V$ and assumes zero angular momentum. With $M=5$ and one iteration an error of less than 10% in $S$ is achieved; for $M=8$ the error is less than 1%. The method is expected to be useful for the solution of large systems of coupled equations by matrix techniques or when a part of the potential is nonlocal.NUCLEAR REACTIONS Scattering theory, expansions on a basis set of positive energy Weinberg states, removal of truncation error by the quasiparticle method. Normal mode effective scattering channels.
TL;DR: In this paper, the authors measured cross sections for the production of isotopes of Bk through No in bombardments of $ √ √ n √ N with ions at energies near the Coulomb barrier.
Abstract: We have measured cross sections for the production of isotopes of Bk through No in bombardments of $^{248}\mathrm{Cm}$ with $^{16}\mathrm{O}$, $^{18}\mathrm{O}$, $^{20}\mathrm{Ne}$, and $^{22}\mathrm{Ne}$ ions at energies near the Coulomb barrier. In general, the peak of the mass-yield curve for each element is about two mass units larger for $^{18}\mathrm{O}$ and $^{22}\mathrm{Ne}$ than for $^{16}\mathrm{O}$ and $^{20}\mathrm{Ne}$, reflecting the neutron excess of the projectiles. The production cross sections and maxima of the actinide isotopic distributions are at least as favorable for production of neutron-rich actinides as those measured for irradiation of $^{238}\mathrm{U}$ and $^{248}\mathrm{Cm}$ with very heavy ions. The observation of so many neutron-rich products between the masses of the target and compound nucleus suggests a direct transfer reaction in which the product nuclide is formed with relatively low excitation which minimizes depletion from prompt fission.NUCLEAR REACTIONS $^{248}\mathrm{Cm}$($^{16,18}\mathrm{O}$,$X$), ($^{20,22}\mathrm{Ne}$,$X$) $E(^{16,18}\mathrm{O})=98, 97$ MeV, $E(^{20,22}\mathrm{Ne}=115, 116 \mathrm{MeV})$; measured $\ensuremath{\sigma}$ and isotopic distributions for $Z=97\ensuremath{-}102$.
TL;DR: In this article, the convergence of the ground state eigenvalues versus the grand orbital quantum number was analyzed for the case of three nucleons interacting via central spindependent two-body potentials.
Abstract: In the framework of the hyperspherical formalism, we present a study of the coupled adiabatic approximation for the case of three nucleons interacting via central spindependent two-body potentials. We analyze the convergence of the ground state eigenvalues versus the grand orbital quantum number ($2K$) and compare the results to that of the coupled equations. We also compare with two simpler but less accurate approximations: the uncoupled adiabatic approximation and the extreme adiabatic approximation. The former provides an upper and the latter provides a lower bound to the ground state energy.NUCLEAR STRUCTURE Few body bound states, reduction of hyperspherical equations applied to triton, quantum few-body problem.