We present angular correlations in ‘‘Basel’’ coordinates for α-particle decay in measurements of ${}_{}{}^{12}{}_{}{}^{}[_{}^{12}{}_{}{}^{}$C${,}^{12}$C($3_1^{\mathrm{-}}$)${\to }^8$Be($0_1^{+}$)+ α${]}^{12}$${\mathrm{C}}^{\mathrm{*}}$ scattering at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=32.5 MeV. A semiclassical model of the angular correlation function has been used to describe the observed angular correlations in the various exit channels. We demonstrate that the semiclassical result can be used even in the case where there are two nonzero spins in the exit channel if the decay products from both ejectiles are detected. We apply this new method to the mutual sequential breakup reaction ${}_{}{}^{12}{}_{}{}^{}[_{}^{12}{}_{}{}^{}$C${,}^{12}$C($3_1^{\mathrm{-}}$)${\to }^8$Be($0_1^{+}$)+α${]}^{12}$C($3_1^{\mathrm{-}}$) ${\to }^8$Be($0_1^{+}$)+α. We deduce that the scattering occurs dominantly to a final state with fully aligned spins and orbital angular momentum ${\mathit{L}}^{\prime }$=12 or 14. © 1996 The American Physical Society.

Excitation functions were determined for ${}_{}{}^{58}{}_{}{}^{}\mathrm{Fe}$(p,n${)}^{58}$${\mathrm{Co}}^{\mathit{m}}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Fe}$(d,xn${)}^{58}$${\mathrm{Co}}^{\mathit{m}}$, ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$(α,n${)}^{58}$${\mathrm{Co}}^{\mathit{m}}$, and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$(n,2n${)}^{58}$${\mathrm{Co}}^{\mathit{m}}$ reactions from the respective thresholds to 14.12 MeV in work with protons, 12.97 MeV with deuterons, 13 MeV with neutrons, and 25.52 MeV with alpha particles. The radioactivity of the activation product ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}_{}^{\mathit{m}}{}_{}{}^{}$(${\mathit{T}}_{1/2}$=9.15 h) was determined by high resolution γ-ray and x-ray spectrometry. Using the present ${\mathrm{\sigma }}_{\mathit{m}}$ results and the (${\mathrm{\sigma }}_{\mathit{m}}$+${\mathrm{\sigma }}_{\mathit{g}}$) data reported earlier, the isomeric cross-section ratio ${\mathrm{\sigma }}_{\mathit{m}}$/(${\mathrm{\sigma }}_{\mathit{m}}$+${\mathrm{\sigma }}_{\mathit{g}}$) was determined for each reaction. Statistical model calculations taking into account the precompound effects were performed for the above-mentioned four reactions as well as for the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$(n,p${)}^{58}$${\mathrm{Co}}^{\mathit{m},\mathit{g}}$ process. A consistent set of model parameters was used. The isomeric cross-section ratio for the pair ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}_{}^{\mathit{m},\mathit{g}}{}_{}{}^{}$ strongly depends on the level scheme and branching ratios of the known levels of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$. Different reactions produced different angular momentum distributions of the compound nucleus, resulting in different isomeric cross-section ratio at the same excitation of the compound nucleus. The ratio was found to be relatively high for target nuclei with high spin values. © 1996 The American Physical Society.

We have measured the mass and kinetic-energy distributions of fragments from the spontaneous fission (SF) of ${}_{104}{}^{262}{}_{}{}^{}\mathrm{Rf}$. The ${}_{104}{}^{262}{}_{}{}^{}\mathrm{Rf}$ was produced via the ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}$${(}^{22}$Ne,4n) reaction with a production cross section of ∼0.7 nb using 114.4-MeV projectiles. The kinetic energies and times of the coincident fission fragments were measured using our rotating wheel system. From these data the half-life, mass, and kinetic-energy distributions were derived. The total kinetic-energy (TKE) distribution appears to consist of a single component with a most probable pre-neutron-emission TKE of 215±2 MeV. The mass distribution is symmetric with a full width at half maximum of about 22 mass numbers. These results are consistent with trends observed for other trans-berkelium spontaneously fissioning isotopes. We determined the half-life to be 2.1±0.2 s by measuring its spontaneous fission decay. We also attempted to observe the alpha decay of ${}_{104}{}^{262}{}_{}{}^{}\mathrm{Rf}$ by searching for alpha decay correlated in time with SF from the alpha daughter, 1.2-ms ${}_{}{}^{258}{}_{}{}^{}\mathrm{No}$. We observed no such decays and have set an upper limit of 0.8% (68% confidence level) on the alpha decay branch of ${}_{104}{}^{262}{}_{}{}^{}\mathrm{Rf}$. © 1996 The American Physical Society.

Measurements of few-nucleon transfer reaction probabilities and Q-value distributions have been made with a kinematic-coincidence detector system at sub-barrier energies in ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{162}{}_{}{}^{}\mathrm{Dy}$. Both the one-neutron pickup and one-proton stripping reaction probabilities fall off as a function of the distance of closest approach as expected from semiclassical models; the measured two-neutron pickup probabilities fall off less steeply than expected, consistent with previous measurements. The origin of this ‘‘slope anomaly’’ is discussed. The measured transfer Q-value distributions are consistent with semiclassical expectations, both in terms of the optimum Q values (${\mathit{Q}}_{\mathrm{opt}}$) and the widths of the Q-value distributions, except for the one-proton stripping channel ${\mathit{Q}}_{\mathrm{opt}}$, which is more negative than expected by approximately 3 MeV. ‘‘Cold’’ two-neutron transfer has been observed, and the probability of the cold portion of the two-neutron transfer is in agreement with the previous γ-ray measurements and calculations. No enhanced quasielastic multipair transfer is observed, in contrast to some previous measurements. An upper limit of ${\mathit{P}}_{\mathrm{tr}}$<${10}^4$ is placed on the quasielastic four-neutron pickup channel. © 1996 The American Physical Society.

Measurements of neutron-induced fission cross sections for ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$, and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ have been performed in the 70–160 MeV energy region at the neutron beam facility at the The Svedberg Laboratory in Uppsala using the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,n) reaction as neutron source. The fission fragments were detected by thin-film breakdown counters. The neutron flux was measured relative to the n-p scattering cross section with a proton-recoil spectrometer. The results are compared with calculations and with earlier reported experimental data. © 1996 The American Physical Society.

Reaction cross sections for deuterons have been measured for ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{40,48}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{58,60}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{112,116,120,124}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ at 37.9, 65.5, and 97.4 MeV. © 1996 The American Physical Society.

The binary decay into strongly damped fragments and the quasielastic reactions of the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$+ ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ system were measured at $E_{\mathrm{lab}}=107.5\mathrm{} \mathrm{and} 139.0$ MeV in the angular range of $30°<~{\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~150°$ using kinematic coincidence. The loss in the binary decay cross section due to light particle evaporation by the highly excited fragments was evaluated. The $Q$-value-integrated angular distributions of the primary decay exhibit the $\frac{1}{{sin\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}}$ behavior at backward angles, indicating a long lifetime. Mass distributions and the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$/${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ratio suggest a noncompound process for the reaction mechanism. Coupled-channels calculations, including a great number of channels populated in the reactions, yield good agreement with the experimental angular distributions.

We derive the self-consistent relativistic Boltzmann-Uehling-Uhlenbeck (RBUU) equation for the delta distribution function within the framework which we have done for nucleon's. In our approach, the $\Delta$ isobars are treated in essentially the same way as nucleons. Both mean field and collision terms of $\Delta \text{'}\mathrm{s}$ RBUU equation are derived from the same effective Lagrangian and presented analytically. We calculate the in-medium $N\Delta$ elastic and inelastic scattering cross sections up to twice nuclear matter density and the results show that the in-medium cross sections deviate substantially from Cugnon's parametrization that is commonly used in the transport model.

The (p,${\mathit{d}}^{\mathrm{*}}$) pickup reaction, leading to spin-singlet and spin-triplet continuum final states of the np system, is treated within the adiabatic approximation. Calculations are carried out for the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(p,${\mathit{d}}^{\mathrm{*}}$) and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(p,d) reactions at 35 MeV, leading to the ground and 4.44 MeV states of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, for which new data have recently been reported. The np relative energy dependence of the (p,${\mathit{d}}^{\mathrm{*}}$) cross sections and the contributions from triplet and singlet configurations are clarified. We show that, within the adiabatic model, theoretical expectations for the magnitude of the singlet state cross section and of the relative magnitudes of the cross sections for the (p,d) and singlet and triplet (p,${\mathit{d}}^{\mathrm{*}}$) channels are particularly transparent. The calculated adiabatic model cross sections differ by an order of magnitude from recently published calculations and data. We show that vector analyzing power data for the ground state transition could be very valuable in clarifying this disagreement. © 1996 The American Physical Society.

On the basis of the antisymmetrized molecular dynamics (AMD) of wave packets for the quantum system, a novel model (called AMD-V) is constructed by the stochastic incorporation of the diffusion and the deformation of wave packets which is calculated by the Vlasov equation without any restriction on the one-body distribution. In other words, the stochastic branching process in molecular dynamics is formulated so that the instantaneous time evolution of the averaged one-body distribution is essentially equivalent to the solution of the Vlasov equation. Furthermore, as usual molecular dynamics, AMD-V keeps the many-body correlation and can naturally describe the fluctuation among many channels of the reaction. It is demonstrated that the newly introduced process of AMD-V has drastic effects in heavy ion collisions of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${+}^{40}$Ca at 35 MeV/nucleon, especially on the fragmentation mechanism, and AMD-V reproduces the fragmentation data very well. Discussions are given on the interrelation among the frameworks of AMD, AMD-V, and other microscopic models developed for the nuclear dynamics. © 1996 The American Physical Society.

In the light of the recent discovery that different forms of the S matrix produce equally good fits to heavy-ion scattering data, we use the simple Ericson parametrization of the phase shifts to analyze the experimental data and apply the Glauber approximation to evaluate the corresponding optical potential. © 1996 The American Physical Society.

Calculations have been performed for inelastic electron scattering from ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ within the framework of the recoil-corrected continuum shell model. Comparisons are made to data ranging from q near zero to q=650 MeV/c. Both inclusive and exclusive processes have been investigated. The effect of meson exchange currents, spin-channel coupling, p-n channel coupling, relativistic corrections, and final state interactions are investigated. Agreement with data is generally good; however, the calculated inclusive transverse response is too small in the region of low energy transfer. This reduced strength is related to the lack of current conservation in the model. © 1996 The American Physical Society.

The reactions ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ + ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ + ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}$ at $\frac{E}{A}=45\mathrm{}$ MeV have been modeled by combining a Boltzmann-Nordheim-Vlasov dynamical model calculation with a statistical sequential binary decay model code. For the reaction ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ + ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, the major features of the experimental data are adequately described by the model calculations. These features include the inclusive fragment cross sections and the total charge and source velocity distributions of multiple fragment events. Other finer features, such as charge-Dalitz plots and the branching ratios between events of different multiplicity, are not reproduced by the calculation. The failure of the calculations is even greater for the reaction ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ + ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}$, in which only the source velocity distributions of multiple fragment events are reproduced. Because the source velocity can be a measure of how much of the target is incorporated into the projectile in inverse kinematics reactions, this suggests that the earliest stages of the reaction, described by the dynamical calculation, are adequately characterized by the model. It is the later stages of the reaction, when fragments are emitted, where the model calculation appears to fail. However, there are some indications that statistical decay in the reaction ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ + ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}$ has occurred, whether by sequential binary decays or some type of prompt multifragmentation.

The trapping effect is investigated close to the elastic threshold. The nucleus is described as an open quantum mechanical many-body system embedded in the continuum of decay channels. An ensemble of compound nucleus states with states below and above threshold is investigated in an energy-dependent formalism. It is shown that the states below threshold can trap the resonance ones and also that they can directly influence the scattering cross section. © 1996 The American Physical Society.

Measurements of reaction cross sections are routinely used to deduce effective nuclear root mean square (rms) radii by comparison with theoretical model predictions. Cross sections calculated using the optical limit Glauber model depend strongly on the rms radius of the density assumed for the projectile nucleus. We investigate such calculations by assuming a range of projectile density distributions. We show that calculated ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$-target cross sections at fixed rms radii retain a significant sensitivity to higher radial moments of the projectile density which is quite different for light and heavy targets.

For cold (neutronless) fission we consider an analytical model of quantum tunneling with dissipation through a barrier U(q) evaluated with a M3Y nucleon-nucleon force. We calculate the tunneling spectrum, i.e., the fission rate as a function of the total kinetic energy of the fragments. The theoretical results are compared with the experimental data obtained for the fine structure of two cold fission modes of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$: ${}_{}{}^{148}{}_{}{}^{}\mathrm{Ba}$${+}^{104}$Mo and ${}_{}{}^{146}{}_{}{}^{}\mathrm{Ba}$${+}^{106}$Mo. Taking into account the dissipative coupling of the potential function U(q) and of the momentum p with all the other neglected coordinates, we obtain a remarkable agreement with the experimental data. We conclude that the cold fission process is a spontaneous decay with a spectrum determined by the shape of the barrier and an amplitude depending on the strength of the dissipative coupling. © 1996 The American Physical Society.

Corrections to the first order term of the multiple scattering expansion of the nucleon-nucleus optical potential due to the propagation of the projectile nucleon in the target nucleus mean field are estimated. The effects of nonlocalities of the nucleon-nucleon transition amplitude are included. Calculations are performed for nucleon scattering from ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ at 100, 200, and 400 MeV incident energies. We show that the mean field effect is repulsive and reduces the strength of the local representation of the impulse approximation potential by approximately 25% in the nuclear interior. © 1996 The American Physical Society.

We investigate the consequences of the requirements of antisymmetrization upon the optical model description of α-particle scattering on an open-shell target. As an illustrative example, we carry out a global optical model analysis of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ elastic scattering data between 22 and 54 MeV. We demonstrate the coexistence of a conventional optical potential with a ‘‘hybrid,’’ l-dependent potential which admits unphysical bound states whose quantum numbers agree with those of the forbidden states predicted by the resonating group method. We stress the role of the discrete ambiguity in explaining this coexistence, and we investigate the properties of a supersymmetric partner of the deep l-independent potential which agrees with the resonating group prescription. © 1996 The American Physical Society.

The Krakow-Louisiana-Minnesota-Moscow Collaboration (KLMM) has exposed a set of emulsion chambers with lead targets to a 158 GeV/c per nucleon beam of ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ nuclei, and we report the initial analysis of 40 high-multiplicity Pb-Pb collisions. To test the validity of the superposition model of nucleus-nucleus interactions in this new regime, we compare the shapes of the pseudorapidity distributions with FRITIOF Monte Carlo model calculations, and find close agreement for even the most central events. We characterize head-on collisions as having a mean multiplicity of 1550±120 and a peak pseudorapidity density of 390±30. These estimates are significantly lower than our FRITIOF calculations. © 1996 The American Physical Society.

Short-distance QCD is employed to calculate the J/ψ survival probability in an equilibrating parton gas whose evolution is governed by a set of master rate equations. Partons in the early stage of high-energy nuclear collisions may initially not be in equilibrium, but their average transverse momentum is sufficiently high to break up a QQ¯ bound state. Such a breakup during the evolution of the parton gas is shown to cause a substantial J/ψ suppression at both RHIC and LHC energies, using realistic estimates of the initial parton densities. The transverse momentum dependence of the suppression is also shown to be sensitive to the initial conditions and the evolution history of the parton plasma. © 1996 The American Physical Society.