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A density functional theory (DFT) computation on oxygen species adsorbed on platinum (Pt) catalyst surfaces has been carried out to elucidate oxygen isotope fractionation observed at the cathode of a polymer electrolyte membrane fuel cell (PEMFC). The Pt(111) catalyst surface was modelled by a Pt19 cluster, and O, OH, OHH, OO, OOH, OHOH and HOHOH were assumed to be the oxygen species adsorbed on the Pt(111) surface. The oxygen isotope reduced partition function ratios (RPFRs) of the adsorbed species were calculated using the vibrational frequencies obtained by normal mode analyses performed on the optimized structures. Various oxygen isotope exchange equilibria among the adsorbed oxygen species and oxygen and water molecules in the gas phase were examined using their RPFRs. Experimental observation that the lighter 16O is enriched in water molecules exhausted from the cathode is explainable in a satisfactory manner by assuming oxygen isotope exchange equilibria of O2 molecule with O, OH, OO and OOH adsorbed on the Pt(111) surface that appear in the first half of the conversion reaction from O2 to H2O and those of H2O molecule with the adsorbed oxygen species, OHH, OHOH and HOHOH, formed in the latter half of the conversion reaction.

The objective of this work is to propose a more effective way to prepare an in-house CO2 with known triple oxygen isotope compositions. The major experimental steps include: (1) the O2 is combusted to CO2 on a graphite rod at 750 °C with Pt-catalyst for 3-4 min; and (2) converted CO2 is subsequently purified by two cryogenic traps. The results show high reproducibility of δ13C and δ18O values of the converted CO2 within 0.010-0.020 ‰ and 0.006-0.010 ‰ (1σ, SD), and the identical δ18O value within error with that of the original O2. Additionally, we have measured the triple oxygen isotope compositions of converted CO2 using an O2-CO2 Pt-catalyzed oxygen-isotope equilibration method. The measured δ17O values of CO2 show high reproducibility within 0.006 ‰ (1σ, SD), and are identical within error with the original O2 as well. Notably, our experiments also found that the O2 with heavier oxygen isotope ratios (δ18O > 40 ‰, VSMOW) might have a lesser conversion efficiency, and this effect, combined with the lighter isotope preferential fractionations during the reaction processes of O2 to CO and CO to CO2, may explain the observed lower 17O/16O and 18O/16O ratios of the converted CO2 relative to the original O2.

The relative biological effectiveness (RBE) values were determined for single- and mixed-ion beams containing carbon and oxygen ions. The CHO-K1 cells were irradiated with beams with the linear energy transfer (LET) values of 236–300 and 461–470 keV/μm for 12C and 16O ions, respectively. The RBE was estimated as a function of dose, survival fraction (SF) and LET. The SF was not affected by varying contributions of the constituent ions to the total mixed dose. The RBE has the same value for single-ion exposures with ions with LET 300 (12C) and 470 keV/μm (16O).

Studies of rainfall isotopic composition in the Iberian Peninsula are scarce, and to date, none of them have provided analyses of the triple oxygen isotopes, preventing from the complete understanding of current atmospheric processes in this region. We investigate the rainwate rδ17O,δ18O, an dδD and derived parameters 17O-excess and d-excess ina mountain site in the Central South Pyrenees (Villanúa, Huesca, Spain) to identify themain factors (regional and local) controlling the isotopic composition of precipitation atevent scale. The samples were collected on a rainfall-event basis during 2 years (fromJuly 2017 to June 2019), and meteorological variables [temperature, relative humidity (RH), and rainfall amount] were monitored at the sampling site. The δ17O, δ18O, and δD values were higher during summer and lower during the rest of the year. In contrast, the17O-excess and d-excess were lower during summer and higher during the remaining months. We found that the isotopic parameters are weakly correlated with rainfall amount during each event, but they strongly depend on changes in air temperature and moderately on RH. We consider other factors affecting the isotopic composition of rainfall events that resulted to have an important role, such as the influence of the moisture source and trajectory throughout the variations in the synoptic pattern during rainfall events. This dataset can be useful for further comprehensive atmospheric andhydrological studies, with application to paleoclimatic investigations., This work was supported by the Spanish Governmenta nd the European Regional Development Funds [projects CGL2016-77479-R (SPYRIT) and PID2019-106050RB-I00 (PYCACHU)] and Villanúa Council economical support. MB was supported by a postdoctoral fellowship in the Juan de la Cierva Formation program provided by the Spanish Ministry of Science (ref.: FJCI-2017-31725). FG was financially supported by the “HIPATIA” research program of the University of Almería. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

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.

We report the interaction of isotopically labeled nitrous oxide ( 15 N 14 N 16 O) time-of-flight mass spectroscopy. The phase dependence of two-body fragmentation channels for linear and circular polarization reveals that the nitrogen–nitrogen bond fission channel is in accordance with the ‘selective ionization of oriented molecules’ mechanism, while the nitrogen–oxygen bond rupture involves an electron recollision mechanism. For the three-body-fragmentation channel resulting in 14 N 3+ ions it is demonstrated that it may proceed via a concerted and/or a sequential manner. The phase dependence of the sequential channel is indicative of the following dissociation route: 15 N 14 N 16 O → 15 N 14 N + 16 O → 15 N + 14 N + 16 O.

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"

The effects of laser wavelength (355 nm and 532 nm) and laser pulse energy on the quantitative analysis of LiFePO4 by atom probe tomography are considered. A systematic investigation of ultraviolet (UV, 355 nm) and green (532 nm) laser assisted field evaporation has revealed distinctly different behaviors. With the use of a UV laser, the major issue was identified as the preferential loss of oxygen (up to 10 at%) while other elements (Li, Fe and P) were observed to be close to nominal ratios. Lowering the laser energy per pulse to 1 pJ/pulse from 50 pJ/pulse increased the observed oxygen concentration to nearer its correct stoichiometry, which was also well correlated with systematically higher concentrations of 16O2+ ions. Green laser assisted field evaporation led to the selective loss of Li (~33% deficiency) and a relatively minor O deficiency. The loss of Li is likely a result of selective dc evaporation of Li between or after laser pulses. Comparison of the UV and green laser data suggests that the green wavelength energy was absorbed less efficiently than the UV wavelength because of differences in absorption at 355 and 532 nm for LiFePO4. Plotting of multihit events on Saxey plots also revealed a strong neutral O2 loss from molecular dissociation, but quantification of this loss was insufficient to account for the observed oxygen deficiency.

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.

The effect of 16O → 18O oxygen isotope substitution has been studied for (Pr1−yEuy)0.7Ca0.3CoO3 cobaltites (0.12 < y < 0.26). A pronounced isotope shift has been found for the spinstate transition temperature, which increases with the oxygen isotope mass. In contrast, the ferromagnetic transition temperature has slightly lower values for the samples with heavier oxygen. The observed phenomena and constructed phase diagram confirm the results reported previously for (Pr1 − ySmy)0.7Ca0.3CoO3 in [G. Y. Wang, X. H. Chen, T. Wu, et al., Phys. Rev. B 74, 165113 (2006)]. The measurements of the specific heat have been performed for (Pr1 − yEuy)0.7Ca0.3CoO3 with the main emphasis on the analysis of the isotope effect. The contributions to the isotope effect coming from the lattice and magnetic components of the specific heat have been separated. The mechanisms underlying the large isotope effect are discussed.

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.

The effect of oxygen isotope substitution on the properties of Pr{sub 0.5}Ca{sub 0.5}Mn{sub 1-x}Cr{sub x}O{sub 3} manganites (x = 0, 0.02, 0.05) have been studied. The introduction of chromium favors (i) the decomposition of a charge-ordered state and (ii) the appearance of a ferromagnetic metallic phase in Pr{sub 0.5}Ca{sub 0.5}Mn{sub 1-x}Cr{sub x}{sup 16-18}O{sub 3}. The isotope substitution {sup 16}O {sup {yields}} {sup 18}O leads to a decrease in the content of the ferromagnetic phase, an increase in the charge-ordering transition temperature (T{sub CO}), and a decrease in the ferromagnetic transition temperature (T{sub FM}). The isotope mass exponent is evaluated.

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.

Doppler-free saturated-absorption Lamb dips were measured on weak rovibrational lines of (12)C(16)O2 between 6189 and 6215 cm(-1) at sub-Pa pressures using optical feedback frequency stabilized cavity ring-down spectroscopy. By referencing the laser source to an optical frequency comb, transition frequencies for ten lines of the 30013←00001 band P-branch and two lines of the 31113←01101 hot band R-branch were determined with an accuracy of a few parts in 10(11). Involving rotational quantum numbers up to 42, the data were used for improving the upper level spectroscopic constants. These results provide a highly accurate reference frequency grid over the spectral interval from 1599 to 1616 nm.

The O + O2 isotope exchange reactions play an important role in determining the oxygen isotopic composition of a number of trace gases in the atmosphere, and their temperature dependence and kinetic isotope effects (KIEs) provide important constraints on our understanding of the origin and mechanism of these and other unusual oxygen KIEs important in the atmosphere. This work reports a quantum dynamics study of the title reactions on the newly constructed Dawes-Lolur-Li-Jiang-Guo (DLLJG) potential energy surface (PES). The thermal reaction rate coefficients of both the (18)O + (32)O2 and (16)O + (36)O2 reactions obtained using the DLLJG PES exhibit a clear negative temperature dependence, in sharp contrast with the positive temperature dependence obtained using the earlier modified Siebert-Schinke-Bittererova (mSSB) PES. In addition, the calculated KIE shows an improved agreement with the experiment. These results strongly support the absence of the "reef" structure in the entrance/exit channels of the DLLJG PES, which is present in the mSSB PES. The quantum dynamics results on both PESs attribute the marked KIE to strong near-threshold reactive resonances, presumably stemming from the mass differences and/or zero point energy difference between the diatomic reactant and product. The accurate characterization of the reactivity for these near-thermoneutral reactions immediately above the reaction threshold is important for correct characterization of the thermal reaction rate coefficients.