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Elastic $$^{16}\hbox {O}+^{12}\hbox {C}$$ scattering is known to exhibit the nuclear rainbow pattern at incident energies $$E_\text {lab} > rsim 200$$ MeV, with the Airy structure of the far-side scattering cross section clearly seen at medium and large angles. Such a rainbow pattern is well described by the deep real optical potential (OP) given by the double-folding model (DFM). At lower energies, the extensive elastic $$^{16}\hbox {O}+^{12}\hbox {C}$$ scattering data show consistently that the nuclear rainbow pattern at backward angles is deteriorated by an oscillating enhancement of elastic cross section that is difficult to describe in the conventional optical model (OM). Given a significant $$\alpha $$ spectroscopic factor predicted for the dissociation $$^{16}$$ O $$\rightarrow \alpha +^{12}$$ C by the shell model and $$\alpha $$ -cluster models, the contribution of the elastic $$\alpha $$ transfer (or the core-core exchange) to the elastic $$^{16}\hbox {O}+^{12}\hbox {C}$$ scattering should not be negligible and is expected to account for the enhanced elastic cross section at backward angles. To reveal the impact of the elastic $$\alpha $$ transfer, a systematic coupled reaction channels analysis of the elastic $$^{16}\hbox {O}+^{12}\hbox {C}$$ scattering has been performed, with the coupling between the elastic scattering and elastic $$\alpha $$ transfer channels treated explicitly, using the real OP given by the DFM. We found that the elastic $$\alpha $$ transfer enhances the near-side scattering significantly at backward angles, giving rise to an oscillating distortion of the smooth Airy structure. The dynamic polarization of the OP by the coupling between the elastic scattering and elastic $$\alpha $$ transfer channels can be effectively taken into account in the OM calculation by an angular-momentum (or parity) dependent potential added to the imaginary OP, as suggested by Frahn and Hussein 40 years ago.

We develop a formalism to calculate electromagnetic (EM) transition rates for rotational-vibrational models of nuclei. The formalism is applied to recently proposed models of ¹²C and ¹⁶O which are inspired by nuclear dynamics in the Skyrme model. We compare the results to experimental data as well as other nuclear models. The results for ¹²C are in good agreement with the data across all models, making it difficult to differentiate the models. More experimental data is needed to do this, and we suggest which transitions would be most interesting to measure. The models of ¹⁶O are less successful in describing the data, and we suggest some possible improvements to our approximations which may help.

The root-mean-square radii of short-lived 0+-states in 16O were obtained for the first time from an analysis of α+16O diffraction scattering. Data on elastic and inelastic α+16O scattering were analyzed on the basis of the modified diffraction model in the range of projectile energies between a few tens of MeV units to 400 MeV. No case of a significant enhancement of the radius with respect to its ground-state value was observed. In particular, this concerns the 15.1-MeV 0 6 + state, which lies near the threshold for breakup to four alpha particles and for which we did not confirm a giant radius predicted by the alpha-particle-condensate model. This result disproves the hypothesis that the 16O nucleus in the 0 6 + state has a rarefied structure and appears to be an analog of the known Hoyle state at 7.65 MeV (0 2 + ) in 12C.

A study of multiplicity distribution of singly charged, doubly charged, multi charged projectile fragments and shower particles have been carried out for the peripheral collisions in 16O-emulsion,22Ne-emulsion and 28Si-emulsion interactions at an incident momentum of (4.1-4.5) AGeV/c. Events having no target fragments have been designated as peripheral collision events. Percentage of peripheral events has been found to increase with the increase of projectile mass. Dispersion of the multiplicity distribution and its dependence on projectile mass for projectile fragments and shower particles has also been investigated. Dependence of average multiplicity of projectile fragments and shower particles on the mass of the projectile beam has been studied. Study of different fragmentation mode during the emission of multi charged projectile fragments has also been carried out., arXiv admin note: text overlap with arXiv:nucl-ex/0604007 by other authors

A model for vibrational and rotational excitations of an intrinsic tetrahedral structure of the Oxygen-16 nucleus has been investigated, building on classic work of Wheeler, Dennison and Robson. Tetrahedral A- and F-phonons are treated harmonically, but the E-phonon dynamics is extended to dynamics on an E-manifold of configurations of four α-particles. This allows for tunnelling between the tetrahedral configuration and its dual, through a square configuration, and lifts the parity doubling that would otherwise occur. Unlike in earlier models, including the algebraic cluster model, the E-phonon frequency is taken to be about half the F-phonon frequency, which in turn is about half the A-phonon frequency. As a result, the first-excited 0+ state is a 2-phonon, E-manifold excitation, whereas the lowest 2+ and 2− states are 1-phonon, E-manifold excitations. Coriolis contributions to the rotational energy of states with F-phonons are significant. Altogether, rotational bands are constructed based on vibrational states with up to four phonons, and with spin/parity up to 9−. Nearly all the observed states of Oxygen-16 are accommodated, up to 20 MeV and partly beyond. Predictions for some so far unobserved states, especially those of unnatural parity, are made.

The nuclear mean-field potential built up during the $${}^{12}\hbox {C}+{}^{12}\hbox {C}$$ and $${}^{16}\hbox {O}+{}^{16}\hbox {O}$$ collisions at low energies relevant for the carbon- and oxygen-burning processes is constructed within the double-folding model (DFM) using the realistic ground-state densities of $$^{12}\hbox {C}$$ and $$^{16}$$ O, and CDM3Yn density-dependent nucleon–nucleon (NN) interaction. The rearrangement term, indicated by the Hugenholtz–van Hove theorem for the single-particle energy in nuclear matter, is properly considered in the DFM calculation. To validate the use of the density-dependent NN interaction at low energies, an adiabatic approximation was suggested for the dinuclear overlap density. The reliability of the nucleus–nucleus potential predicted through this low-energy version of the DFM was tested in the optical model (OM) analysis of the elastic $${}^{12}\hbox {C}+{}^{12}\hbox {C}$$ and $${}^{16}\hbox {O}+{}^{16}\hbox {O}$$ scattering data at energies below 10 MeV/nucleon. These OM results provide a consistently good description of the elastic angular distributions and 90 $$^\circ$$ excitation function. The dinuclear mean-field potential predicted by the DFM is further used to determine the astrophysical S factor of the $${}^{12}\hbox {C}+{}^{12}\hbox {C}$$ and $${}^{16}\hbox {O}+{}^{16}\hbox {O}$$ fusions in the barrier penetration model. Without any adjustment of the potential strength, our results reproduce the non-resonant behavior of the S factor of the $${}^{12}\hbox {C}+{}^{12}\hbox {C}$$ and $${}^{16}\hbox {O}+{}^{16}\hbox {O}$$ fusions very well over a wide range of energies.

Data for the $^{13}\mathrm{C}(^{6}\mathrm{Li},t)^{16}\mathrm{O}$ reaction, obtained in inverse kinematics at a $^{13}\mathrm{C}$ incident energy of 7.72 MeV, are presented. A distorted wave Born approximation (DWBA) analysis was used to extract spectroscopic factors and asymptotic normalization coefficients (ANCs) for the $\ensuremath{\langle}^{16}\mathrm{O}\ensuremath{\mid}^{13}\mathrm{C}+^{3}\mathrm{He}\ensuremath{\rangle}$ overlaps, subject to the assumption of a fixed $\ensuremath{\langle}^{6}\mathrm{Li}\ensuremath{\mid}^{3}\mathrm{He}+^{3}\mathrm{H}\ensuremath{\rangle}$ overlap. The variation of the extracted spectroscopic factors and ANCs as a function of various inputs to the DWBA calculations was explored. The extracted ANCs were found to vary as a cubic function of the radius of the potential well binding the transferred $^{3}\mathrm{He}$ to the $^{13}\mathrm{C}$ core while the spectroscopic factors varied as a quartic function of the radius. The ANC values could be determined to within a factor of two for this system.

Using a theory of large amplitude collective motion, the adiabatic self-consistent collective coordinate method, we derive reaction path for the fusion process at sub-barrier energies. The collective Hamiltonian to describe the fusion process is constructed, based on the obtained reaction path and canonical variables. We study the reaction of N=Z stable nuclei, alpha+16O, 16O+16O, and alpha+12C. The results suggest that, after two nuclei touch, the reaction path is significantly deviated from the simple relative motion, which may affect the deep sub-barrier fusion cross section., Comment: 8 pages, 2 figures, Proceedings of IIRC symposium "Perspectives of the Physics of Nuclear Structure"

Nowadays there is a rising interest towards exploiting new therapeutical beams beyond carbon ions and protons. In particular, [Formula: see text]O ions are being widely discussed due to their increased LET distribution. In this contribution, we report on the first experimental verification of biologically optimized treatment plans, accounting for different biological effects, generated with the TRiP98 planning system with [Formula: see text]O beams, performed at HIT and GSI. This implies the measurements of 3D profiles of absorbed dose as well as several biological measurements. The latter includes the measurements of relative biological effectiveness along the range of linear energy transfer values from ≈20 up to ≈750 keV μ [Formula: see text], oxygen enhancement ratio values and the verification of the kill-painting approach, to overcome hypoxia, with a phantom imitating an unevenly oxygenated target. With the present implementation, our treatment planning system is able to perform a comparative analysis of different ions, according to any given condition of the target. For the particular cases of low target oxygenation, [Formula: see text]O ions demonstrate a higher peak-to-entrance dose ratio for the same cell killing in the target region compared to [Formula: see text]C ions. Based on this phenomenon, we performed a short computational analysis to reveal the potential range of treatment plans, where [Formula: see text]O can benefit over lighter modalities. It emerges that for more hypoxic target regions (partial oxygen pressure of ≈0.15% or lower) and relatively low doses (≈4 Gy or lower) the choice of [Formula: see text]O over [Formula: see text]C or [Formula: see text]He may be justified.

A reinterpretation of the complete energy spectrum of the Oxygen-16 nucleus up to 20 MeV, and partly beyond, is proposed. The underlying intrinsic shape of the nucleus is tetrahedral, as in the na\"ive alpha-particle model and other cluster models, and A, E and F vibrational phonons are included. The A- and F-phonons are treated in the harmonic approximation, but the E-vibrations are extended into a two-dimensional E-manifold of D2-symmetric, four-alpha-particle configurations, following earlier work. This allows for the underlying tetrahedral configuration to deform through a square configuration into the dual tetrahedron, so there is tunnelling between the tetrahedron and its dual, with the associated breaking of parity doubling. However, E-manifold states can still be interpreted in terms of E-phonons. Rotational excitations of the vibrational states are analysed as in the classic work of Dennison, Robson and others, with centrifugal corrections to the rotational energy spectrum included. States with F-phonons require Coriolis corrections too. The first-excited $0^+$ state at 6.05 MeV is modelled as a state with two E-phonons; this allows a good fit of the lowest $2^+$ and $2^-$ states as excitations with one E-phonon. The Coriolis parameter $\zeta$ is chosen positive to ensure the right splitting of the $3^+$ and $3^-$ states near 11 MeV. Altogether, about 80 states with isospin zero are predicted below 20 MeV, and these match rather well the more than 60 experimentally tabulated states. Several high-spin states are predicted, up to spin 9 and energy 30 MeV, and these match some of the high-spin, natural parity states in this energy range that have been observed. The model proposed here is mainly phenomenological but it receives some input from analysis of Skyrmions with baryon number 16., Comment: 27 pages, 7 figures. This version accepted for publication in Int. J. Mod. Phys. E

A detailed study of event-by-event pseudo-rapidity fluctuations in relativistic heavy-ion collisions in terms of the Φ measure and its multiplicity and target dependence has been carried out for heavy (AgBr) and light (CNO) groups of targets present in the nuclear emulsion using O 16 (at an incident momentum of 4.5 A GeV/c), Ne 22 (at an incident momentum of 4.1 A GeV/c), Si 28 (at an incident momentum of 4.5 A GeV/c) and S 32 (at an incident momentum of 4.5 A GeV/c) projectiles. For all the interactions, the total ensemble of events has been divided into three overlapping multiplicity classes depending on the number of shower particles. For all the interactions and for each multiplicity class, the Φ values are found to be greater than zero indicating the presence of strong correlation in the multiparticle production at Dubna energy. The measured Φ values are found to decrease with the increase of average multiplicity for all the interactions. The Φ values for the AgBr target are found to be greater than that for the CNO target for all the projectiles. This observation indicates the presence of stronger correlation for heavier projectiles. The experimental results have been compared with the modified FRITIOF model. It has been seen that the modified FRITIOF model cannot reproduce the experimental results.

Within the quantum diffusion approach, the capture of a projectile nucleus by a target nucleus is studied at bombarding energies above and below the Coulomb barrier. The effects of deformation of interacting nuclei and neutron transfer between them on the total and partial capture cross sections and the mean angular momentum of the captured system are studied. The results obtained for the 16O + 112Cd, 152Sm, and 184W; 19F +175Lu; 28Si +94,100Mo and 154Sm; 40Ca +96Zr; 48Ca+ 90Zr; and 64Ni +58,64Ni, 92,96Zr, and 100Mo reactions are in good agreement with available experimental data.

In searches along a track in the chamber irradiated at the Laboratory of High Energies at the Joint Institute for Nuclear Research (JINR, Dubna) with oxygen ions accelerated to a momentum of 4.5 GeV/c per nucleon, 215 events containing two or more doubly charged fragments of the primary nucleus were found. Emission angles in the track-emulsion plane were measured in these events. Their distribution is consistent with that which alpha particles are expected to have in an oxygen nucleus prior to its interaction with a track-emulsion nucleus. Events of the 16O → 28Be → 4α type were discovered for the first time. They are treated as events of the coherent electromagnetic dissociation of an oxygen nucleus. Among all events, about 14% of the 8Be → 2α decays proceed through the ground state of spin-parity 0+; an approximately the same fraction of such decays proceed through the first excited state of spin-parity 2+.

The alpha inelastic scattering from 24Mg was measured to obtain the isoscalar natural-parity excitation strengths and to search for the α-condensed states. The multipole decomposition analysis for the measured cross sections was performed. The strength distributions for the \({{\Delta}L=0{-}3}\) were successfully obtained and the possible candidates for the α-condensed states around the 16O core were found.

The cluster radioactivity exhibited by 128–134Gd isotopes with the exotic emission of certain clusters like 4He, 8Be, 12C, 16O, 20Ne, 24Mg, and 28Si have been studied. The half-life values for different cluster emissions were calculated by considering the interacting potential barrier as a sum of Coulomb potential and proximity potential. The emission of 28Si cluster from 128Gd isotope leads to the formation of 100Sn daughter nucleus which is a doubly-magic nucleus. Hence, the 28Si cluster emission is expected to have the lowest half-life and therefore highly favorable for measurements. Our calculations also corroborate this point and thus emphasize the role of 100Sn in the exotic decay process. The Geiger-Nuttall plots for different cluster emissions were found to be linear, but with different slopes and intercepts. We have studied the variation of these slopes and intercepts as a function of the proton number of clusters. Based on this, we have arrived at a handy and convenient expression for half-life values for emissions of various clusters from 128–134Gd isotopes.

β − -decay rates are of crucial importance in stellar evolution and nucleosynthesis, as they are a key component in stellar processes. Tabulated values of the decay rates as functions of both temperature T and density ρ are necessary input to stellar evolution codes such as MESA, or largescale nucleosynthesis simulations such as those performed by the NuGrid collaboration. Therefore, it is interesting to know the uncertainties in these rates and the effects of these uncertainties on stellar structure and isotopic yields. We have calculated β-strength functions and reaction rates for nuclei ranging from 16O to 339136, extending from the proton drip line to the neutron drip line based on a quasi-particle random-phase approximation (QRPA) in a deformed folded-Yukawa single-particle model. Q values are determined from the finite-range droplet mass model (FRDM). We have investigated the effect of model uncertainty on astrophysical β − -decay rates calculated by the FRDM. The sources of uncertainty considered are Q values and deformation. The rates and their uncertainties are generated for a variety of temperature and density ranges, corresponding to key stellar processes. We demonstrate the effects of these rate uncertainties on isotopic abundances using the NuGrid network calculations.

The 18O(p, ?)15N reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as 19F, 18O, and 15N. Fluorine is synthesized in the intershell region of asymptotic giant branch (AGB) stars, together with s-elements, by ? radiative capture on 15N, which in turn is produced in the 18O proton-induced destruction. Peculiar 18O abundances are observed in R-Coronae Borealis stars, having 16O/18O 1, hundreds of times smaller than the galactic value. Finally, there is no definite explanation of the 14N/15N ratio in pre-solar grains formed in the outer layers of AGB stars. Again, such an isotopic ratio is influenced by the 18O(p, ?)15N reaction. In this work, a high accuracy 18O(p, ?)15N reaction rate is proposed, based on the simultaneous fit of direct measurements and of the results of a new Trojan Horse experiment. Indeed, current determinations are uncertain because of the poor knowledge of the resonance parameters of key levels of 19F. In particular, we have focused on the study of the broad 660?keV 1/2+ resonance corresponding to the 8.65?MeV level of 19F. Since ? ~ 100-300?keV, it determines the low-energy tail of the resonant contribution to the cross section and dominates the cross section at higher energies. Here, we provide a reaction rate that is a factor of two larger above T ~ 0.5 109?K based on our new improved determination of its resonance parameters, which could strongly influence present-day astrophysical model predictions.

States that exhibit the properties of an α-cluster or an α-binucleon condensate are studied in 1p-shell nuclei. The generalized Hamiltonian of the Elliott SU(3) model is used to classify these states and to calculate their spectra. The results of the calculations are found to be in good agreement with experimental data. States not observed so far in the cluster spectra of the 12C, 16O, 10Be, and 12Be nuclei are predicted.

We have measured the cross sections of the 16O(n,t) reactions above 18.1 up to 33.1 MeV in an neutron activation method. H2O (water) as an 16O target was irradiated with semi-monoenergetic neutrons generated from the 9Be(p,n)9B reaction with 25–35 MeV protons. The neutron flux was obtained with the aid of previous study by Uwamino et al. (Nucl Instr Methods A 271:546, 1988). The tritium activities were measured by using the liquid scintillation counting (LSC) method. The present value for the cross section of 16O(n,t) reaction agrees with previous values measured by using the same LSC method at similar neutron energy ranging from 18.1 up to 33.1 MeV.

The elastic scattering of 16O + 12C at various collision energies is discussed in the framework of the optical model with repulsive core nucleus-nucleus potential. The cross sections on backward angles are strongly raised due to repulsive core. It is shown by using the near-side/far-side decomposition method that the near-side component of the scattering amplitude mainly contributes to the elastic scattering cross sections on forward and backward angles. The repulsive core of 16O + 12C potential takes place at distances R ≲ 3 fm.

A systematic investigation of the elastic scattering of the 9Be nucleus, which is among themost loosely bound stable nuclei was performed.Differential cross sections for elastic 9Be + 16O scattering were measured at a c.m. energy of 47.5 MeV (beam of 132-MeV 16O nuclei). Available data at different energy values and data for neighboring nuclei were included in our analysis. As a result, the very fact of rainbow scattering was reliably established for the first time in systems involving 9Be. In addition, the analysis in question made it possible to identify Airy minima and to determine unambiguously the nucleus-nucleus potential with a high probability.

Realistic coupled-channel calculation results for the 18 [O] + 58,60,64 Ni systems in the bombarding energy range 34.5 ⩽ E Lab ⩽ 65 MeV are presented. The overall agreement with existing experimental data is quite good. Our calculations predict an unexpected fusion suppression for above-barrier energies, with an important contribution of the two neutron ( 18 O, 16 O) transfer channel couplings. The sub-barrier fusion enhancement and the above barrier suppression, predicted by the calculations, are consistent with the nuclear structure of the Ni region. Comparisons with recently reported similar effects in reactions induced by the 6 He projectile are discussed.

An exclusive study of the characteristics of interactions accompanied by backward emission (θlab ≥ 90°) of shower and grey particles in collisions of a 4.5 AGeV/c 16O beam with emulsion nuclei is carried out. The experimental multiplicity distributions of different particles emitted in the forward (θlab < 90°) and backward hemispheres due to the interactions with the two emulsion components (CNO, AgBr) are presented and analyzed. The correlations between the different emitted particles are also investigated. The results indicate that there are signatures for a collective mechanism, which plays a role in the production of particles in the backward hemisphere. Hence, the backward multiplicity distribution of the emitted shower and grey particles at 4.5 AGeV/c incident momentum can be represented by a decay exponential law formula independent of the projectile size. The exponent of the power was found to increase with decreasing target size. The experimental data favor the idea that the backward particles were emitted due to the decay of the system in the latter stages of the reactions.

A combined description of elastic scattering of the systems 16O + 16O and 16O + 12C by means of the optical model and the distorted wave approximation is proposed. The account of exchange processes has allowed good description of experimental data in the range of backward angles.

Quasielastic deuteron and triton knockout from 12C and 16O nuclei has been studied infull kinematics using a 0.72-GeV/c pion beam. The momentum distributions of the intranuclear quasideuteron motion, excitation-energy spectra of the residual nuclei, and the effective numbers N d eff of quasideuterons are determined. The parameters of the quasideuteron intranuclear motion are in reasonable agreement with the results obtained in other beams. The N d eff in the nuclei from 6Li to 16O measured in full kinematics are virtually independent of the atomic number in contrast to the analogous values in the inclusive deuteron-knockout reaction induced by protons. The phenomenon of triton knockout from these nuclei is observed, which makes possible estimation of the cross section of backward pion-triton elastic scattering in yet unexplored regions of energy and momentum transfer.

An investigation of refractive effects in heavy-ion scattering is continued. For the elastic scattering of 16O nuclei on a 13C target at E(16O) = 132 MeV, the differential cross sections are measured for the first time in addition to previous measurements for targets from the carbon isotopes 12C and 14C. Airy structures that are similar for all isotopes and which have close cross sections are observed and are found to be consistent with the energy systematics of Airy minima that were obtained previously. The volume integrals of the real and imaginary parts of the optical potentials found in the present study are nearly identical for all of the isotopes considered here and are also in good agreement with the systematics obtained previously.

The elastic and inelastic scattering of 17,18O with light targets has been undertaken at 12 MeV/nucleon in order to determine the optical potentials needed for the transfer reaction 13C(17O,18O)12C. Optical potentials in both incoming and outgoing channels have been determined in a single experiment. This transfer reaction was used to infer the direct capture rate to the 17F(p,γ)18Ne which is essential to estimate the production of 18F at stellar energies in ONe novae. We demonstrate the stability of the ANC method and OMP results using good quality elastic and inelastic scattering data with stable beams. The peripherality of our reaction is inferred from a semiclassical decomposition of the total scattering amplitude into barrier and internal barrier components. Comparison between elastic scattering of 17O, 18O and 16O projectiles is made.

We propose to measure the γ-ray emission probability from excited states above 5 MeV including giant resonance of 16O and 12C as a function of excitation energy in 1-MeV step. Here, we measure both the excitation energy (Ex=5-30MeV) at the forward scattering angles (0°-3°) of the 16O, 12C (p, p’) reaction using Grand-Raiden Spectrometer and the energy of γ-rays (Eγ) using an array of NaI(Tl) counters. The purpose of the experiment is to provide the basic and important information not only for the γ-ray production from primary neutral-current neutrino-oxygen (-carbon) interactions but also for that from the secondary hadronic (neutron-oxygen and -carbon) interactions.

Slow neutron captures are responsible for the production of about $50\%$ of elements heavier than iron, mainly, occurring during the asymptotic giant branch phase of low-mass stars ($1$ $\lesssim M$/M$_{\odot}$ $\lesssim$ $3$), where the main neutron source is the $^{13}$C($\alpha$,n)$^{16}$O reaction. This last is activated from locally-produced $^{13}$C, formed by partial mixing of hydrogen into the He-rich layers. We present here the first attempt at describing a physical mechanism for the formation of the $^{13}$C reservoir, studying the mass circulation induced by magnetic buoyancy and without adding new free parameters to those already involved in stellar modelling. Our approach represents the application, to the stellar layers relevant for $s$-processing, of recent exact, analytical 2D and 3D models for magneto-hydrodynamic processes at the base of convective envelopes in evolved stars in order to promote downflows of envelope material for mass conservation, during the occurrence of a dredge-up phenomenon. We find that the proton penetration is characterized by small concentrations, but extended over a large fractional mass of the He-layers, thus producing $^{13}$C reservoirs of several $10^{-3}$ M$_{\odot}$. The ensuing $^{13}$C-enriched zone has an almost flat profile, while only a limited production of $^{14}$N occurs. In order to verify the effects of our new findings we show how the abundances of the main $s$-component nuclei can be accounted for in solar proportions and how our large $^{13}$C-reservoir allows us to solve a few so far unexplained features in the abundance distribution of post-AGB objects.

The in-flight heavy-ion fragmentation technique has been used to produce a secondary beam of tritons (3H) at intermediate energies ( E t > 100 MeV / nucleon ) from primary 16,18O beams of 150 and 120 MeV/nucleon, respectively. The best results are obtained with a 16O beam of 150 MeV/nucleon, producing a 115 MeV/nucleon triton beam. The triton beam will be used in (t,3He) charge-exchange experiments at the S800 spectrometer at the NSCL. At the target of the S800, a triton rate of 5 × 10 6 particles per second is achieved, for a primary 16O beam of 100 pnA. The (t,3He) reaction using this beam was tested with a 24Mg target. An excitation-energy resolution of 190 ± 15 keV is achieved.

In order to study complete and incomplete fusion in heavy ion reactions, the excitation functions for several residues produced in the system 16O + 159Tb have been measured in the energy range ≈ 70 – 95 MeV , employing activation technique. The measured excitation functions have been compared with those calculated using computer codes CASCADE, PACE2 and ALICE-91. Comparison of measured and theoretically calculated excitation functions has indicated significant contributions from incomplete fusion in some α-emission channels. In the present experiment, the recoil range distributions of several residues at ≈ 90 MeV incident beam energy have also been measured using recoil catcher technique and off-line gamma ray spectrometry. Analysis of the recoil range distributions has further confirmed the presence of contributions from incomplete fusion reactions. An attempt has been made to separate out the relative contributions of complete and incomplete fusion channels.

Evaporation residue cross sections in the {sup 16}O+{sup 238}U reaction were measured for the energy range from above-to extreme subbarrier. We used a He-gas-jet system to transport the fusion products, and the {alpha} decay of the evaporation residues was measured by using a rotating wheel system. The measured cross sections for {sup 248,249,250}Fm are reproduced by a statistical model calculation, for which partial cross sections are calculated by a coupled-channel model taking into account the prolate deformation of {sup 238}U. We conclude that complete fusion is the main process in the subbarrier energy region, and quasifission is not an important channel.

A microscopic complex folding-model potential that reproduces the scattering amplitude of Glauber-Sitenko theory in its optical limit is obtained. The real and imaginary parts of this potential are dependent on energy and are determined by known data on the nuclear-density distributions and on the nucleon-nucleon scattering amplitude. For the real part, use is also made of a folding potential involing effective nucleon-nucleon forces and allowing for the nucleon-exchange term. Three forms of semimicroscopic optical potentials where the contributions of the template potentials—that is, the real and the imaginary folding-model potential—are controlled by adjusting two parameters are constructed on this basis. The efficiency of these microscopic and semimicroscopic potentials is tested by means of a comparison with the experimental differential cross sections for the elastic scattering of heavy ions 16O on nuclei at an energy of E ∼ 100 MeV per nucleon.

The excitation function of elastic α-particle scattering on 14C has been measured in the laboratory energy range 16.3–19.2 MeV using a backscattering technique with a thick target. These data were analyzed together with the old low-energy data of G.L. Morgan et al. in the framework of the R-matrix formalism. Spin-parity assignments were made for 32 states in 18O in the excitation range 9–20 MeV. The estimates of the widths of the states are also presented. The 0+ and 0−α-cluster bands appeared to be well separated by 5.6 MeV (as in 16O and 20Ne). We have not found a confirmation of existence of the negative-parity molecular states proposed by M. Gai et al. We observed an effect of a doubling of α-cluster levels in 18O similar to that found in 22Ne.

The inclusive cross section for pion double charge exchange on 16O at T0 = 0.5 and 0.75 GeV was measured with the superconducting kaon spectrometer (SKS) at KEK in a joint ITEP/KEK experiment. The result shows a relatively weak energy dependence of the measured cross section, which is in contradiction with its rapid drop predicted within the conventional model of two sequential single charge exchanges. The data of this experiment agree with the results that were obtained previously from similar measurements at ITEP and which are indicative of a significant contribution from the mechanism of inelastic Glauber rescatterings for T0 ≳ 0.6 GeV.

Several new infrared absorption bands for 32S16O3 have been measured and analyzed. The principal bands observed were ν1+ν2 (at 1561 cm−1), ν1+ν4 (at 1594 cm−1), ν3+ν4 (at 1918 cm−1), and 3ν3 (at 4136 cm−1). Except for 3ν3, these bands are very complicated because of (a) the Coriolis coupling between ν2 and ν4, (b) the Fermi resonance between ν1 and 2ν4, (c) the Fermi resonance between ν1 and 2ν2, (d) ordinary l-type resonance that couples levels that differ by 2 in both the k and l quantum numbers, and (e) the vibrational l-type resonance between the A1′ and A2′ levels of ν3+ν4. The unraveling of the complex pattern of these bands was facilitated by a systematic approach to the understanding of the various interactions. Fortunately, previous work on the fundamentals permitted good estimates of many constants necessary to begin the assignments and the fit of the measurements. In addition, the use of hot band transitions accompanying the ν3 band was an essential aid in fitting the ν3+ν4 transitions since these could be directly observed for only one of four interacting states. From the hot band analysis we find that the A1′ vibrational level is 3.50 cm−1 above the A2′ level, i.e., r34=1.75236(7) cm−1. In the case of the 3ν3 band, the spectral analysis is straightforward and a weak Δk=±2, Δl3=±2 interaction between the l3=1 and l3=3 substates locates the latter A1′ and A2′ “ghost” states 22.55(4) cm−1 higher than the infrared accessible l3=1 E′ state.

The effect of the nuclear shell structure on the heavy-ion fusion reaction was investigated for the reaction systems 8 2 Se + 1 3 8 Ba, 8 2 Se + 1 3 4 Ba, 1 6 O + 2 0 4 Pb, 8 6 Kr + 1 3 4 Ba, 8 6 Kr + 1 3 8 Ba and 8 2 Se + n a t . Ce. Evaporation residues for these fusion reactions were measured using a recoil mass separator (JAERI-RMS) near Coulomb barrier region. The measured evaporation residue cross sections for the reactions 8 2 Se + 1 3 8 Ba and 8 6 Kr + 1 3 8 Ba were two orders of magnitude and one order of magnitude larger than those for the reactions 8 2 Se + 1 3 4 Ba and 8 6 Kr + 1 3 4 Ba, respectively, at the excitation energy region of 10 ∼ 30 MeV. The evaporation residue cross sections were compared with those of the other reaction systems that make the same or similar compound nuclei as the present reaction systems. It was found that the evaporation residue cross sections correlate strongly with the sum of the shell energies for both projectile and target nuclei, i.e. the evaporation residue cross sections increase as the sum of the shell energy decreases.

Existence of the parity-doublet cluster bands with the 16 O+ 12 C cluster structure in 28 Si is shown by using a global deep potential determined from 16 O+ 12 C rainbow scattering. The 16 O+ 12 C cluster bands structure and Airy structure in 16 O+ 12 C scattering are understood consistently. The existence of the superdeformation with the 16 O+ 12 C cluster structure is discussed.

For improved cross-section measurements of the reaction 12C(α,γ)16O in inverted kinematics, a recoil separator ERNA is developed at the 4MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with high efficiency. Due to the emission of the capture γ-rays, the kinematically forward directed 16O recoils are described by an angle and energy spread. Thus, the acceptances in angle and energy of ERNA must cover these spreads in order to extract reliable cross-section values. We report on such acceptance measurements over the energy range Ecm=0.7-5.0 MeV, using an 16O pilot beam. © 2003 Elsevier B.V. All rights reserved.

A folding potential describing the $\alpha$ -scattering on 16O over a broad energy range 25.8-146.0 MeV is constructed on the basis of $\alpha$ -like cluster and unclustered-nucleon configurations of 16O. The resulting potential does not need any renormalization to fit the angular distribution of elastic cross-sections. The effects of the repulsive part of $\alpha$ - $\alpha$ and $\alpha$ -nucleon interactions are investigated. The analysis suggests that both the $\alpha$ - $\alpha$ repulsive potential and the unclustered nucleonic configuration in the target are important to describe the scattering data over a broad range of incident energies. The root-mean-square radius for the 16O nucleus is deduced.

Transfer reactions are verified to be an important tool for the study of light unbound nuclei. We have studied the proton-rich unbound nuclei 15 F and 11 N, 10 N respectively through the 16 O( 14 N, 15 C) 15 F and 12 C( 14 N, 15 C) 11 N, 10 B( 14 N, 13 B) 11 N, 10 B( 14 N, 14 B) 10 N reactions. Resonance energies and width were obtained.

We used the technique of the separation of Coulomb and diffraction dissociation of incident heavy ion to select the events due to induced neutron from 16 O leaving sub-oxygen nucleus to break-up. The characteristics of these events of neutron emulsion collisions are displayed and compared with that obtained from incident proton at the same energy. The studied interactions are classified according to the type of target nucleus (H, CNO and AgBr) by using the method of separation. Cascade-evaporation model (CEM) calculations are taken into account and compared with that obtained from the interactions of induced neutron from 16 O (4.5 A GeV/ c ) with emulsion nuclei and with the results of incident proton at the same target and energy. CEM can describe the distributions of proton and neutron interactions. It is conjuctured that it may be possible to develop a similar theoretical model based on the modern methods of nonlinear dynamics, neural network and complexity [Randomness and Undecidability in Physics, World Scientific, Singapore, 1993].

We present an exhaustive analysis on the direct search of multi-nucleon clusters in 28Si-AgBr, 32S-AgBr and 16O-AgBr interactions at 14.5 AGeV, 200 AGeV and 60 AGeV, respectively. A comparison with Monte Carlo simulation reveals that clusters of three and four particles are present in the multi-nucleon production at 200 AGeV.

Absolute elastic cross sections have been measured at 12.45°, 16.45°, 20.45° and 28.0° for targets of 9Be, 12C, 16O, 28Si and 197Au being bombarded by beams of 13 MeV 6,7Li and 24 MeV 16O. The reliability of a method previously proposed for low mass multielemental analysis [1,2] depends to some extent on the precision and accuracy of the cross sections reported here. The 16O-beam reactions, except the 16O + 9Be reaction, are found to be consistent with the Rutherford predictions. This allows us to obtain target thickness independent cross sections with uncertainties of approximately 7% for the reactions initiated with 6,7Li beams. Most of these cross sections are found to be non-Rutherford. Comparisons made with previous investigations give strong support to the cross section values obtained in this work.

Folding model potentials of 12C and 16O are obtained for neutrons, using a nucleon-density distribution and the effective nucleon-nucleon interaction DDM3 Y. These folded potentials, instead of a phenomenological optical potential, are applied to the calculation for the direct capture of low-energy neutrons on 12C and 16O. As a result, it is concluded that an observation of the neutron direct capture would be very useful to acquire the information on the nucleon-density distribution near the nuclear surface.

We introduce a novel coupling potential for the scattering of deformed light heavy-ion reactions. This new approach is based on replacing the usual first-derivative coupling potential by a new, second derivative coupling potential in the coupled-channels formalism. The new approach has been successfully applied to the study of the $^{12}$C+$^{12}$C, $^{12}$C+$^{24}$Mg, $^{16}$O+$^{28}$Si and $^{16}$O+$^{24}$Mg systems and made major improvements over all the previous coupled-channels calculations for these systems. This paper also shows the limitations of the standard coupled-channels theory and presents a global solution to the problems faced in the previous theoretical accounts of these reactions., 7 pages with 4 figures

We investigate refractive phenomena of the 16 O+ 16 O system at Elab = 124, 145, 250 and 350 MeV using the microscopic coupled-channels method. The coupling potentials are constructed by the double folding model using the three effective nucleon-nucleon interactions, M3Y, DDM3Y-ZR and DDM3Y-FR (DDM3Y1). With respect to the transition density matrix elements of the 16 O nucleus, we employ the orthogonal condition model based on the microscopic α+ 12 C cluster picture. We perform coupled-channels calculations that include both the 3 − (Eex = 6.13 MeV) and the 1 − (Eex = 7.12 MeV) excitations of the 16 On ucleus. We show that the characteristic features of the nuclear rainbow phenomena can be reproduced successfully by our coupled-channels calculations with the DDM3Y-FR folding potential. The absolute values of the experimental cross sections for inelastic scattering at Elab = 350 MeV can also be reproduced by our calculation. The coupling effects from inelastic channels are mainly absorptive and weakly repulsive in the refractive phenomena at these energies in the 16 O+ 16 O system.