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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.

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.

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.

Clustering phenomena are well known in nuclear physics for stable nuclei, both α-conjugate (N=Z, A=2N), like8Be,16O,20Ne, and non-α-conjugate, like6Li and7Li. In general, it is expected that light exotic nuclei may also exhibit cluster behavior. Moving out of the valley of stability configurations can be found where at least one of the clusters is unbound or weakly bound, thus not satisfying the strong internal correlation requirement of classical clusters. This is so-called exotic clustering. The study of such systems presents many difficulties, due, mainly, to the low intensities typical of radioactive ion beams. Therefore, few significant experimental studies have been performed so far. In this work we searched for α-cluster states in19Ne above its α-decay threshold measuring, for the first time, the15O(4He,4He) elastic scattering excitation function. Moreover, this study classified low-energy states in Ne in the astrophysically important region in this HCNO-break-out nucleus. European Unions Horizon 2020 659744

Emission M?ssbauer effect investigations were done simultaneously with resistivity measurements on two similar samples of La0.8Ca0.2Mn(57Co)O3, in one of which 18O was substituted for 16O. Only a few parts per million of 57Co were substituted for Mn with minimal perturbation of the system. For both compounds, the long range ferromagnetic spin order decreases anomalously below the transition temperature (Tc) and we observe three broad categories of electronic phases. Surprisingly, we find that 18O substitution brings about a stronger exchange interaction between Mn3+/Mn4+, and the internal field (Hint) is larger than that for the 16O compound at all normalized temperatures (T/Tc) observed. The stronger exchange interaction in the 18O compound is in apparent contradiction with the observation that the ferromagnetism in this compound starts crumbling at a lower T/Tc, forming small spin clusters exhibiting superparamagnetic-like behaviour. However, the 18O compound is more amenable to spin ordering under the influence of a magnetic field near Tc.

The scattering process on 1p-shell nuclei, having the cluster structure, can be seen in the anomaly increasing of cross sections for large angles. Most often, this increasing of cross sections is connected with mechanism of transfer of clusters or nucleons. The study of the α-cluster transfer mechanism in the elastic scattering of 20Ne ions on 16O nuclei is important for investigation burning process in evolution of the Universe immediately after the Big-Bang. Therefore new experiment on the heavy ion accelerator (Warsaw University) was carried out with a significant expansion of the range of angles up to 1700 in center mass system at E Lab =50.0 MeV. Data analysis of angular distribution was performed in framework of the optical model and coupled channel method. The optimal parameters of the optical potential were obtained and the spectroscopic factor was obtained 1 for 20Ne as α +16O.

The α-transfer reaction 16O(6Li, d)20Ne is investigated in order to extract the α- clustering probability of 20Ne. The relative wave function for the α-16O system is calculated by a microscopic cluster model. We show the angular distribution of the transfer cross section is a good probe to see the radial dependence of the α-clustering probability in the surface region.

We have presented a systematic study of two-particle rapidity correlations in terms of investigating the dynamical fluctuation observable in the forward–backward pseudo-rapidity windows by analyzing the experimental data of interactions at 4.5 AGeV/c, interactions at 4.1 AGeV/c, and interactions at 4.5 AGeV/c. The experimental results have been compared with the results obtained from the analysis of event sample simulated (MC-RAND) by generating random numbers and also with the analysis of events generated by the UrQMD and AMPT model. Our study confirms the presence of strong short-range correlations among the produced particles in the forward and the backward pseudo-rapidity region. The analysis of the simple Monte Carlo-simulated (MC-RAND) events signifies that the observed correlations are not due to mere statistics only; explanation of such correlations can be attributed to the presence of dynamical fluctuations during the production of charged pions. Comparisons of the experimental results with the results obtained from analyzing the UrQMD data sample indicate that the UrQMD model cannot reproduce the experimental findings. The AMPT model also cannot explain the experimental results satisfactorily. Comparisons of our experimental results with the results obtained from the analysis of higher energy emulsion data and with the results of the RHIC data have also been presented.

A global analysis of the ro-vibrational spectra of 19 bands in the comet-tail (A2Πi−X2Σ+) system of the 12C16O+ cation is presented, and the precise molecular constants of the vibrational levels involved are obtained via a weighted nonlinear least-squares fitting procedure. Furthermore, the resultant precise equilibrium molecular constants enable us to achieve accurate Rydberg—Klein—Rees (RKR) potential curves for both the A and X states, yielding the accurate Franck—Condon factor and band origin of each band in this system.

A study of the 14C and 15C states was pursued at the Catania INFN-LNS laboratory by the 12C(18O,16O)14C and 13C(18O,16O)15C reactions at 84 MeV incident energy. The 16O ejectiles were detected at forward angles by the MAGNEX magnetic spectrometer. Exploiting the large momentum acceptance (20%) and solid angle (50 msr) of the spectrometer, energy spectra were obtained with a relevant yield up to 20 MeV excitation energy. The application of the powerful trajectory reconstruction technique did allow to get energy spectra and angular distributions with resolution of about 160 keV and 0.3°. In the energy spectra several known low lying states of 14C and 15C have been observed and some unknown resonant structures at about 10.5 and 13.6 MeV in 15C and 16 MeV in 14C appear.

The angular distribution for the elastic scattering of 16 O, 14 N and 12 C on 27 Al was measured at an energy of 1.75MeV per nucleon in the DC-60 INP NNC (Institute of Nuclear Physics, National Nuclear Centre) cyclotron located in Astana in order to study the elastic scattering mechanism in these nuclear systems. The experimental results were analyzed with the help of the optical potential code SPI-GENOA. Good agreement between the experimental data and the theoretical calculations was obtained by using suitable optical potential parameters. The elastic scattering of 16 O, 14 N and 12 C on 27 Al does not reveal any unusual features or threshold anomaly at this energy. PACS number: 24.10.Ht (Some figures in this article are in colour only in the electronic version.)

The 12C+12C fusion reactions are together with the reaction 12C(a,γ)16O the most important nuclear processes in the late stellar evolution. These fusion reactions play a key role in the understanding of various types of astrophysical objects. Thus, a measurement of the 12C+12C cross section at very low energies can serve as flagship experiment for a future underground accelerator laboratory. It is hoped that an appropriate facility for such a study will be created in the near future somewhere in the world. The prospects for the measurement of the carbon fusion reactions will be discussed in the present work.

The strongly oscillating angular distributions of the elastic scattering of 12C + 24Mg at energies around the Coulomb barrier (Ecm = 10.67 − 16.00 MeV) [1] were reproduced adding three Breit-Wigner resonance terms with J values of 6, 7 and 8 h respectively to the l = 6, 7 and 8 terms of the elastic S-matrix. The elastic scattering S-matrix was calculated using the double folding, deep, optical potential with non-local interaction, also called, Sao Paulo Potential [2]. All fifteen angular distributions could be well reproduced by the 3 resonances, located respectively at Ecm = 14.15, 15.8 and 16.9 MeV in the entrance channel, which correspond to excitation energies of 30.45, 32.1 and 33.2 MeV in the 36Ar compound nucleus. The J = 6, 7 and 8 h resonances fit well into a rotational molecular band, together with the J = 18, 20, 22 and 24 h resonances observed in the 16O + 20Ne elastic scattering [3]. The band head is at 29.5 MeV excitation energy in the 36Ar compound nucleus and has a large moment of inertia indicating a large deformation. Calculations of Rae and Merchant [4] propose the existence of a hyperdeformed band in 36Ar with 12C + 24Mg and 16O + 20Ne cluster structure.

The E1Σ+-X1Σ+ band system in the isotopic molecules 74Ge16O and 74Ge18O is analyzed. The spectral region from 1800 A to 2100 A is studied and the vibrational numbering is determined from the isotopic shifts. For 74Ge16O the following molecular constants of the E1Σ+ state are determined: Te = 46 041 cm-1, ωe = 533.9 cm-1, ωexe = 3.0 cm-1, Be = 0.3559 cm-1, De = 0.46 × 10-6 cm-1, and re = 1.8978 A.

Excitation functions and angular distributions at backward angles have been measured for the reaction 28Si(12C,16O)24Mg as well as for elastic scattering of 16O from 24Mg. At peaks of the strongly structured excitation curves PJ2(cos theta )-type angular distributions are observed. Peak positions and J values show some similarities for the reaction data and the 16O+24Mg exit channel but disagree with recent data for the 12C+28Si entrance channel. No convincing evidence for resonant molecular states is found.

The isotopic-spin purity of some low-lying excited states in light nuclei is calculated in first order perturbation theory. Special attention is given to the odd parity states in even nuclei. The isotopic spin impurity caused by coulomb forces is shown to be sufficient to account for the electric dipole transition in 16O between the 7.12 MeV excited state and the ground state.

The (t, p) reactions induced in the target nuclei 10B, 12C, 16O and 27Al have been investigated at an incident triton energy of 5.5MeV. The angular distributions of the observed proton groups have been compared with a theory of double stripping and good agreement has been obtained with the theoretical predictions for transfers of 0, 1, 2 and (more tentatively) 3 units of orbital angular momentum. A new level in 12B at an excitation of 4.297 MeV is reported. Spin and parity assignments have been made for the levels of 14C at excitations of 6.582 MeV (1-), 6.725 MeV (probably 3-), a hitherto unreported level at 7.009 MeV (0+) and at 7.335 MeV (probably 2-). The existence of levels in 18O at 3.634 and 4.448 MeV has been confirmed and the spins and parities have been determined to be 0+ and 3- respectively. The spin and parity of the state in 18O at 3.915 MeV excitation have also been determined as 2+. The behaviour of the 16O(t, p)18O reaction leading to the ground and first four excited states of 18O has been found to be consistent with the 18O configurations predicted by the intermediate coupling theory. The atomic mass excess of 29Al has been found to be -9.647±0.015 MeV and the excitations of forty-two new levels of 29Al have been measured.

Cross sections for the following reactions with 36 MeV 16O ions have been measured: Neutron transfer 27Al(16O, 15O)28Al less-than-or-eq, slant7 μbn Proton transfer 27Al(16O, 17F)26Mg 210±50 μbn Neutron-proton exchange transfer 27Al(16O, 16F)27Mg 0.7±0.4 μbn The mechanism of the exchange transfer reactions is discussed in terms of the single transfer reactions. There is some evidence to suggest that an exchange reaction is not composed of two single transfer reactions.

A survey is given of recent developments in the theory of collective vibrations in nuclei based on the shell model. This covers work up to and including the International Conference on Nuclear Physics in Paris during 1964. The emphasis is on the application of the theory, which is illustrated by considering specific nuclei, for example 16O, 40Ca and 208Pb, for the simplest case of nuclei having both the neutron and proton shells closed. The nickel, tin and lead regions are studied to show the effect of pairing, when the shells are no longer closed but the nuclei are still assumed to be spherical. The additional complications with deformed nuclei are illustrated in the rare earth and transuranic regions, and also with magnesium.

The 16O(d, α)14N reaction has been investigated at bombarding energies of 6.8, 7.1, 7.2 and 8.9 mev. At these energies the intensity of the transition to the 2.31 mev, T=1 state of 14N has been measured. Angular distributions have been obtained for the alpha particles leading to the ground state and the 3.95 mev level of 14N for bombarding energies of 6.8 and 8.9 mev.

By an indirect method the energy-loss rate of protons channeled along close-packed directions in single crystals has been determined. The dechanneling effect observed in Rutherford scattering and nuclear reaction yields has been used. The method has been applied to different close-packed axes in single crystals of CaF2 and BaF2. Experimental values down to about 0.60 for the ratio of energy-loss rate in channel and random directions have been found.

The time-of-flight and slow-neutron threshold techniques in conjunction with 3He particles of energies of up to 11MeV, have been used to measure the Q value of the 16O(3He, n) reaction and to locate levels in 14O and 18Ne. The Q value, -3.199 ± 0.006 MeV, requires a mass defect of 10.649 ± 0.008 MeV for 18Ne. Levels were found in 14O at 5.905 ± 0.012, 6.30 ± 0.03, and 6.586 ± 0.012 MeV; and in 18Ne at 1.880 ± 0.010, 3.362 ± 0.011 and 3.608 ± 0.012 MeV. Excitation functions were measured between 2.0 and 5.7 MeV for both reactions. Angular distributions of the 12C(3He, n) reaction measured at 4.65, 4.98 and 5.26 MeV, have been compared with theory for a double stripping process. The data suggest that a direct process is competing strongly with compound nucleus formation in this energy region.

The reactions 16O(3He, α)15O, 24Mg(3He, α)23Mg and 28Si(3He, α)27Si have been investigated at an incident energy of 5.8 MeV by magnetic analysis. The following levels were observed: 15O, 5.174, 5.233 MeV; 23Mg, 0.451, 2.048, 2.356, 2.712, 2.768, 2.904, 3.792, 3.856, 3.968, 4.353 MeV; 27Si, 0.782, 0.958, 2.165, 2.651, 2.866, 2.908, 3.540, 3.800, (4.13) MeV.

The angular distribution of five proton groups from the reaction 16O(3He, p)18F have been measured at incident energies of 5.9 and 9.16 MeV. An attempt has been made to explain the observations by a double stripping process and some tentative spin and parity assignments have been made.

A search was made for gamma rays following the positron decay of Ne/ sup 18/ in order to locate the 0/sup +/, T = 1 level in F/sup 18/. Ne/sup 18/ was produced in the reaction O/sup 16/(He/sup 3/,N)Ne/sup 18/. Th e He/sup 3/ beam could be interrupted by a tantalum shutter. Pulseheight spectra obtained during "beam-off" periods showed a gamma ray with an energy of about 1 Mev. The possibility of the peak arising from random coincidences between 0.511Mev annihilation quanta was ruled out. The observed gamma ray was identified with a transition from the 1.04-Mev level in F/sup 18/. It is probable that the level excited is the analog of the ground state of Ne/sup 18/ and has the assignmert 0/ sup +/, T = 1. (M.C.G.)

Measurements are presented of the cross sections for the separate production of the 6.06, 6.14, 6.92 MeV states of 16O in the 16O (p, p') reaction induced by 150 MeV protons. Energy resolution adequate to observe the production of these states separately was obtained by observing coincidences between their de-excitation gamma radiation and the outgoing protons. Angular correlations between the gamma rays and the protons were also measured. The results are discussed to show the information they provide about the 16O nucleus. Some measurements of the 16O (p, p α) reaction made at the same time are also presented.

The distortion produced by a spin-dependent optical potential in the scattering and polarization of fast nucleons by light nuclei is discussed for the case of excitation of the target nucleus to a low-lying state. The distorted Born approximation is used, with the distortion calculated according to the WKB approximation. The results are applied to the scattering of protons at around 185 Mev from C/sup 12/,O/sup 16/, and Ca/sup 40/. The approximate equality of polarization and asymmetry is discussed in relation to the surface nature of the spin-orbit potential. (auth)

It is shown that it is possible to write down α-particle wave functions for the ground states of 8Be, 12C and 16O, which become, when antisymmetrized, identical with shell-model wave functions. The α-particle functions are used to obtain potentials which can then be used to derive wave functions and energies of excited states. Most of the low-lying states of 16O are obtained in this way, qualitative agreement with experiment being found. The shell structure of the 0+ level at 6.06 MeV is analysed, and is found to consist largely of single-particle excitations. The lifetime for pair-production is calculated, and found to be comparable with the experimental value. The validity of the method is discussed, and comparison made with shell-model calculations.

The experimental arrangement and method of investigation by the photographic plate technique of (d, n) reaction at a deuteron bombarding energy of 8 MeV are described. The positions are reported of some of the energy levels of the residual nuclei 13N, 17F and 33Cl. It has also been possible to determine spins and parities of the corresponding levels from measurements of the angular distributions of some of the neutron groups. A comparison of the mirror nuclei 13C13N, 17O17F and 33S33Cl is made.

Some studies of the electronic spectrum given by magnesium in a vacuum are in oxygen 18, and in a mixture of 16O and 18O have been made. The measurements of isotope shift are given for the green and for the ultra-violet system. The isotope effect in the green system confirms the vibrational analysis of Mahanti and Lagerqvist. The bands in the ultra-violet region are again attributed to a polyatomic molecule containing magnesium and oxygen atoms. The assignment is partly supported by the isotope shift, but the molecule only contains a single oxygen atom.

Gamma rays produced by 15 MeV neutron interactions in N, O, Mg and Al have been measured with a 7 mm Ge(Li) spectrometer. Differential ?-ray production cross sections at 80? have been determined relative to the cross section for the 4.44 MeV ?-ray line produced in 12C(n,n')12C.

The energy levels of F/sup 18/ were investigated using the reactions O/ sup 16/(He/sup 3/,p)F/sup 19/(He/sup 3/, alpha )F/sup 18/. In both cases magnetic analysis was employed and the incident He/sup 3/ energy was 5.9 Mev. The excitation energies of 40 levels were determined below 7.493 Mev. (auth)

Angular distributions have been measured of some of the proton, deuteron and α-particle groups emitted from targets of beryllium, carbon, nitrogen and oxygen when bombarded by 9 MeV deuterons. The proton angular distributions have been compared with those calculated from the stripping theories enabling assignments of spins and parities to be made to levels of the residual nuclei. Calculations have also been made of the relative capture probabilities and reduced widths and in the cases of carbon and nitrogen it was possible to express them in absolute units.

The reaction 13C(α, n)16O has been examined from 1.0 to 2.5 MeV bombarding energy. The positions and widths of seven resonances have been measured. Angular distributions have been obtained in five cases, and some tentative spin and parity assignments made. Measurements of the absolute cross section are given and values of reduced neutron and alpha-particle widths have been calculated for three levels in 17O.

The mean lives of the first 2+ states of 12C, 16O, 20Ne, and 28Si have been measured using recoil methods with following results: 12C τ = 2.6 ± 0.9 × 10-14sec. 16O τ less, similar 2.5 × 10-14sec. 20Ne τ = 7.6 ± 3.3 × 10-13sec. 28Si 9 × 10-13 less, similar τ (or τ less, similar 3 × 10-14).

The disintegration by π--meson capture of the elements helium and carbon is discussed. Two types of meson theory, scalar and pseudo-scalar, are considered. The relative probabilities of the various modes of disintegration of helium are calculated and the energy spectra of the most likely one, viz. proton emission, are shown. The disintegration of carbon into two α-particles and one singly charged particle is considered, using a simple α-particle model. The energy spectra and angular correlations of the α-particles obtained by a direct transition and by a transition via an excited state of 8Be are compared.

Calculations show that configuration mixing in the 16O ground state can account for alpha -particle strengths to the 5p-1h states in 20Ne, but not for the 3He cluster strengths to 4p-1h states in 19Ne. These are, however, consistent with published wavefunctions which include configuration mixing in the 19Ne negative-parity states.

This paper reports some results obtained in an attempt to determine a nucleon-nuclear potential of the Morse function type that contains velocity-dependent, spin-orbit splitting, energy-dependent, centrifugal interaction, etc., terms. The single-particle energy formula for all nuclei in the Morse-type potential well has been shown as convenient as in the harmonic type and as reliable as perhaps Hartree-Fock calculations. In particular the neutron separation energies for 16O and 40Ca have been calculated and compared with the recently published results obtained from similar calculations and compared with the recently published results obtained from similar calculations and also with the other theoretical and experimental works. The results are found to be in very good agreement with the data and are consistent with the other calculations except with those published recently.

The energy levels of Mg/sup 24/ below 12 Mev are investigated, using the reaction C/sup 12/(O/sup 16/, alpha )Mg/sup 24/. Evidence is found f or energy levels at 6.44, 11.08, and 11.73 Mev, in addition to the established levels. (T.F.H.)