A doorway to Borromean halo nuclei: the Samba configuration

We exploit the possibility of new configurations in three-body halo nuclei, Samba type (the neutron-core form a bound system) as a doorway to Borromean systems. The nuclei Be-12, B-15, N-23 and F-27 are of such nature, in particular N-23 with a half-life of 37.7 s and a halo radius of 6.07 fm is an excellent example of Samba-halo configuration. The fusion below the barrier of the Samba halo nuclei with heavy targets could reveal the so far elusive enhancement and a dominance of one-neutron over two-neutron transfers, in contrast to what was found recently for the Borromean halo nucleus He-6 + U-238.

Tensor coupling and pseudospin symmetry in nuclei

In this work we study the contribution of the isoscalar tensor coupling to the realization of pseudospin symmetry in nuclei. Using realistic values for the tensor coupling strength, we show that this coupling reduces noticeably the pseudospin splittings, especially for single-particle levels near the Fermi surface. By using an energy. decomposition of the pseudospin energy splittings, we show that the changes in these splittings come mainly through the changes induced in the lower radial wave function for the low-lying pseudospin partners and through changes in the expectation value of the pseudospin-orbit coupling term for surface partners. This allows us to confirm the conclusion already reached in previous studies, namely that the pseudospin symmetry in nuclei is of a dynamical nature.

Spin and pseudospin symmetries in the antinucleon spectrum of nuclei

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Accessory Nuclei in the Oocytes of Pachycondyla (Neoponera) villosa (Hymenoptera: Ponerinae) as a Source of Annulate Lamellae

In insects' oocytes, structures called accessory nuclei can be observed. They are similar to the nucleus of the oocyte and have been detected in Hymenoptera as well as in other groups, with their source and functions still under discussion (Cassidy & King 1972). Through the use of histochemical techniques as well as ultrastructural ones, it was possible to observe several accessory nuclei surrounding the oocyte nucleus in the immature oocytes of Pachycondyla (Neoponera) villosa ants. Morphologically they were seen to be round and smaller than the germinal vesicle. When using these histochemical techniques, the only positive reaction was for proteins. Ultrastructurally they have the same morphology as the oocyte nucleus and a fine and electrondense granulation was observed inside them. The function of accessory nuclei in P (Neoponera) villosa is probably as a source of anullate lamellae and as an RNA reservoir in the oocytes. In mature oocytes (stage III), these structures are not observed, suggesting that they disappeared before this stage by releasing their contents into the oocytes' cytoplasm, according to Camargo-Mathias and Caetano (1993).

Cytochemical studies of the nuclei of the venom glands' cells of Apis mellifera (Hymenoptera, Apidae)

Cytochemistry studies of the nuclei of the venom glands' cells of worker bees of Apis mellifera indicated that there is a higher activity in the young workers while there is a predominance of degenerative characteristics in the older workers. In addition, we demonstrated that there is an occurrence of differential nuclear synthetic activities between the cells of the distal and the proximal regions of the secretory filament and of the venom reservoir. Signs of a higher nuclear activity were evidenced at the distal regions of this gland in 14-day old workers, while at the more proximal regions of the venom gland of 40-day old workers we identified the most obvious signs of degeneration. Therefore, it was evident that the process of glandular degeneration begins at the distal region of the venom gland instead of beginning at the proximal region as had been established previously. In addition, characteristics of nuclear synthetic activities were noted in the cells of the proximal region of the reservoir; these cells were thought to be non-secretory.

A simple procedure for rehybridization of nuclei analyzed previously by fish

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Radii in weakly-bound light halo nuclei

A systematic study of the root-mean-square distance between the constituents of weakly-bound nuclei consisting of two halo neutrons and a core is performed using a renormalized zero-range model. The radii are obtained from a universal scaling function that depends on the mass ratio of the neutron and the core, as well as on the nature of the subsystems, bound or virtual. Our calculations are qualitatively consistent with recent data for the neutron-neutron root-mean-square distance in the halo of Li-11 and Be-14 nuclei. (C) 2004 Published by Elsevier B.V.

The few scales of nuclei and nuclear matter

The well-known correlations of low-energy three and four-nucleon observables with a typical three-nucleon scale (e.g., the Tjon line) is extended to light nuclei and nuclear matter. Evidence for the scaling between light nuclei binding energies and the triton one are pointed out. We argue that the saturation energy and density of nuclear matter are correlated to the triton binding energy. The available systematic nuclear matter calculations indicate a possible band structure representing these correlations. (c) 2006 Elsevier B.V. All rights reserved.

Structure of large two-neutron halos in light exotic nuclei

The structure of three-body halo nuclei formed by two neutrons and a core (nnc) is studied using zero-range interactions. The halo wave function can be completely parameterized only by the s-wave scattering lengths and two-neutron separation energy. The sizes and the neutron-neutron correlation function of Li-11 and Be-14 are calculated and compared to experimental data. A general classification scheme for three-body halos with two identical particles is discussed as well as the critical conditions to allow excited Efimov states.

Neutron-neutron correlation in the halo dissociation of light exotic nuclei

We present model results for the two-halo-neutron correlation functions, C-nn, for the dissociation process of light exotic nuclei modelled as two neutrons and a core. A minimum is predicted for C-nn as a function of the relative momentum of the two neutrons, p(nn), due to the coherence of the neutrons in the halo and final state interaction. Studying the systems Be-14, Li-11, and He-6 within this model, we show that the numerical asymptotic limit, C-nn-> 1, occurs only for p(nn)greater than or similar to 400 MeV/c, while such limit is reached for much lower values of p(nn) in an independent particle model as the one used in the analysis of recent experimental data. Our model is consistent with data once the experimental correlation function is appropriately normalized.

Universal aspects of light halo nuclei

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

EXOTIC CARBON SYSTEMS IN TWO-NEUTRON HALO THREE-BODY MODELS

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Universality and Halo Nuclei

Universal aspects of few-body systems will be reviewed motivated by recent interest in atomic and nuclear physics. The critical conditions for the existence of excited states in three-body systems with two-identical particles will be explored. In particular, we consider halo nuclei that can be modeled as three-body nuclear systems, with two halo neutrons and a core. In this context, we also discuss the low-energy neutron-C-19 elastic scattering, near the conditions for the appearance of an Efimov state.

Classification of basis states for (p-f)-nuclei (41 <= A <= 80) with minimal configuration energy

We give a complete classification of basis with unitari (U(A-1), U(3)) and permutational (S)A)) symmetries. Thse are suitable as functions for (p-f)- nuclei (41<= A <= 80) with minimal configuration energy. We also give a brief survey of way in which are obtained.