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A theoretical analysis of available experimental data on elastic and inelastic C scattering in the energy region extending up to 90 MeV is performed. The parameters of a semimicroscopic potential are found on the basis of the dispersive optical model. The potentials found in this way are used in analyzing, by the distorted-wave Born approximation, data that the authors recently measured for inelastic scattering at energies of 65 and 90 MeV. Experimental data for the states at 3.68 and 7.55 MeV are presented for the first time. These states are considered under the assumption that, within the standard rotational model, they are members of the ground-state rotational band. A satisfactory description of angular distributions is obtained, and deformation lengths are determined. A model phenomenological form factor is used for the remaining excitations in the energy range extending up to 11 MeV. The present analysis confirms the presence of a neutron halo in the 3.09-MeV state. A similarity of form of the inelastic form factors obtained for the 8.86-, 10.996-, and 11.08 MeV states and the proximity of their radii gives grounds to assume that the C nucleus in these three states has an enhanced size and similar structures. A comparison of the radial dependences of the form factors for the 9.90- and 8.86-MeV states shows that the wave function for the 9.90-MeV state has a substantially smaller spatial extension. These results agree with the values obtained for the radii of the states under discussion on the basis of the modified diffraction model. [ABSTRACT FROM AUTHOR]

The isobaric analog states with isospin T = 1 in triplet of the A = 14 nuclei: 14C, 14N, and 14O, are studied. The signs of a neutron halo in the 1− (6.09 MeV) state of 14C have been revealed earlier by two groups. We confirm this result and study isobaric analog 1− states of neighboring 14N and 14O nuclei. The differential cross sections for the 14C(α, α)14C* (6.09 MeV, 1−) inelastic scattering, the 13C(3He, d)14N* (8.06 MeV, 1−), and the 14N(3He, t)14O* (5.17 MeV, 1−) reactions are analyzed by two methods: the modified diffraction method and the method of asymptotic normalization coefficients. The rms radii for all three mirror nuclei in the studied 1− states are found almost the same: (2.7 ± 0.1) fm for 14C, (2.67 ± 0.07) fm for 14N, and (2.6 ± 0.2) fm for 14O. The signs of the proton halo in the 1− state of 14N are identified for the first time. [ABSTRACT FROM AUTHOR]

A method for determining the radii of excited states of nuclei by means of (He, t) charge-exchange reactions was proposed. Two versions of a comparison of differential cross sections for (He, t) reactions were considered. The first relies on a comparison with cross sections for inelastic-scattering processes leading to the formation of isobaric analog states, while the second involves (He, t) reactions leading to the production of the ground state. The two versions in question yield similar results and make it possible to determine the radius of the first excited state of the N nucleus. This state has the excitation energy of E* = 2.37 MeV, lying above the proton-emission threshold. The resulting radius proved to be enhanced in relation to the ground state and is close to the radius of the 3.09-MeV isobaric analog state of the С nucleus, which has a neutron halo. This permitted drawing the conclusion that the N nucleus in the 2.37-MeV state has a proton halo. The possibility of revealing a proton halo in other states of light nuclei is considered. [ABSTRACT FROM AUTHOR]

The root-mean-square radii of short-lived 0-states in O were obtained for the first time from an analysis of α+O diffraction scattering. Data on elastic and inelastic α+O 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 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 O nucleus in the 0 state has a rarefied structure and appears to be an analog of the known Hoyle state at 7.65 MeV (0) in C. [ABSTRACT FROM AUTHOR]

The differential cross sections for elastic and inelastic B + α scattering were measured at the alpha-particle energy of 65 MeV, the inelastic-scattering processes leading to the excitation of known states of B up to excitation energies of about 14 MeV. Data on elastic scattering were analyzed together with those that were published earlier for lower energies. The cross sections for inelastic scattering were analyzed on the basis of the distorted-wave method. A modified diffractionmodel was used to determine the root-mean-square radii of excited states. The radii of states whose excitation energies were below about 7MeV were found to agree with radius of the ground state to within 0.1 to 0.15 fm. This result complieswith the traditional idea that the low-lying states of B have a shell structure. The possibility that these states belong to the predicted rotational bands, which, if any, are truncated to three states, cannot be ruled out either. The majority of the observed highly excited states are distributed among four rotational bands. The moments of inertia of these bands are close; for the band based on the 3/2 state at E* = 8.56 MeV, they are even higher than those of the Hoyle state in the C nucleus. The measured radii of states associated with these bands of B are larger than the ground-state radius by 0.7 to 1.0 fm and are also close to the radius of the Hoyle state. The results of the present study agree with the existing predictions that the cluster structure of the B nucleus is diverse at high excitation energies. The hypothesis that the B nucleus features a 'giant' state of size commensurate with those in heavy nuclei was not confirmed. [ABSTRACT FROM AUTHOR]

Experimental data on inelastic scattering of alpha particles by the B, C, and C nuclei are analyzed using the modified diffraction model and the radii of these nuclei in some 'abnormal' excited states are found. It is shown that the 0 (7.65 MeV) Hoyle state in the C nucleus is the base state for a new 0-2-4 rotational band (in addition to the ground-state band), in which the third member is the discovered 4 (13.75 MeV) state. The radii of the C nucleus in the above-mentioned three states are 25-30% larger than its ground state radius. It is found that the radii of the 1/2 (8.86 MeV) state in the C nucleus and the 3/2 (8.56 MeV) state in the B nucleus are close to the radius of the Hoyle state in C and that a similar rotational band is based on the 8.56 MeV state. The above C and B states can be regarded as analogues of the Hoyle state. The prediction of the alpha-condensation model that a similar analogue in B is the 12.56 MeV state with a radius that is comparable with the nuclear radius of uranium was not confirmed. [ABSTRACT FROM AUTHOR]

Differential cross sections for C(α, α') inelastic scattering at E(α) = 65 and 90 MeV with the excitation of the 9.90-MeV state in the C nucleus have been studied. The analysis within the modified diffraction model has shown that the rms radius of the nucleus in this state can be approximately 20% smaller than its radius in the ground state. [ABSTRACT FROM AUTHOR]

The angular distributions of α + C elastic and inelastic (to the 4.44 MeV, 2; 7.65MeV, 0; and 9.64MeV, 3 states) scattering at 110 MeV are characterized by pronounced enhancement and strong oscillations at large angles. We performed calculations of the differential cross sections of these reactions assuming a potential scattering in the forward hemisphere and the direct transfer of Be cluster θ > 90°. We showed that the α + Be cluster configuration with relative angular momentum L = 0 dominates in the Hoyle state being 4.4 times larger than that in the ground state. This result also contributes to the verification of αBEC hypothesis and is consistent with the conjecture of a dilute 3 α structure of the Hoyle state. In the 9.64 MeV, 3 state, a positive interference of all allowed α + Be configurations with a dominance of the p-orbital (49%) α-Be relative motion is found. This finding manifests the exotic 3 α, but hardly condensed structure of the 9.64-MeV 3 state in C. [ABSTRACT FROM AUTHOR]

Differential cross sections for inelastic scattering leading to the excitation of some nuclear states situated near neutron-emission thresholds were analyzed. With the aid of a modified diffraction model, abnormally large radii were found for the 1/2 state of the C nucleus at 3.09 MeV, for the first levels of positive-parity rotational bands in the Be (1/2 level at 1.68 MeV and 5/2 level at 3.05 MeV) and Be (5/2 level at 1.78 MeV and 3/2 level at 3.41 MeV) nuclei, and for the 2 state of the Be nucleus at 1.54 MeV and 1 state of the Be nucleus at 2.7 MeV. All of these states possess signatures typical of neutron halos. [ABSTRACT FROM AUTHOR]

The coupled reaction channels model calculations of the direct 8Be transfer in the α+12C elastic and inelastic (to the 7.65 MeV $0_2^ + $ and the 9.65 MeV $3_1^ - $ states) scattering have been performed. It is shown that the cluster configuration with zero relative angular momentum dominates in $0_2^ + $ state being 4.4 times larger than that in the ground state. In the $3_1^ - $ state, a dominance of the p-orbital motion is found. The condensed properties are confirmed in the Hoyle state. The 3α exotic, but hardly a condensed structure of the $3_1^ - $ state is found. [ABSTRACT FROM AUTHOR]

Differential cross-sections of inelastic scattering leading to the excitation of some levels near the thresholds of neutron emission were analyzed. The abnormally large radii were identified for $1/2_1^ + $ (3.09 Mev) state of 13C, first members of the rotational bands based on the 1/2+ levels of 9Be (1.68 MeV) and 11Be (gr. st.), $2_1^ +$ (1.54 MeV) and $1_1^ -$ (2.7 MeV) states of 14Be and 12Be correspondingly. All these states can be considered as having neutron halos. [ABSTRACT FROM AUTHOR]

Recently, it was supposed the nα light nuclei may have structures resembling the diluted gas of α particles which could be considered as Bose-Einstein condensate ( αBEC) in nuclear systems. At the present time, the only more or less definite candidate for an αBEC state predicted by theory is the second 0+ state of 12C ( E = 7.65 MeV) located near the threshold 12C → 3 α. We discuss several possible experimental approaches to study the properties of interest of the 7.65-MeV level of 12C. Among them are shift of the positions of the rainbow minima in the inelastic scattering to this level, extraction of the empirical inelastic form factor from the α and 3He scattering and its comparison with theoretical predictions, and getting information on the 8Be transfer reaction form factor. The conclusion was drawn that new measurements of 12C( α, α′) 12C(7.65) inelastic scattering at ∼120 MeV in the full angular range would be most adequate to solving the problem. The possibility of observation of αBEC effects in heavier n α nuclei is also discussed. In particular, 112Ba is of great interest owing to possible existence of an α-particle “halo” outside the Z = N = 50 core. [ABSTRACT FROM AUTHOR]