Struktur Nuklir: Halo dan Pairing pada Neutron Rich Nuclei

Fenomena halo dan pairing merupakan perilaku unik dari neutron yang terdapat pada suatu inti atom. Halo neutron dalam nuklir digambarkan adanya kemunculan ’ekor’ dan adanya ’ruang kosong’ antara core dan ekor pada distribusi neutron akibat energi ikat yang lemah sedangkan pairing adalah fenomena kolektif yang terjadi akibat neutron yang berlebih dalam inti atom berpasangan. Fenomena pairing atau pasangan mengakibatkan perubahan energi ikat inti atom, fenomena ini dapat terlihat jelas pada nuklida dan isotop dengan jumlah neutron genap. Umumnya fenomena halo merupakan fenomena yang muncul akibat adanya faktor repulsif dalam inti atom sedangkan fenomena pairing diakibatkan faktor attraktif. Kedua fenomena ini bukanlah merupakan fenomena yang kontradiktif namun dapat muncul secara bersamaan dalam suatu nuklida terutama pada neutron rich nuclei atau inti atom yang kaya dengan neutron seperti isotop Sn.

EIKONAL MODEL ANALYSIS FOR 9Li+p AND 11Li+p ELASTIC SCATTERINGS AND HALO EFFECT

The elastic angular distributions for 9 Li+p and 11 Li+p at E lab /A = 60 and 62 MeV/nucleon, respectively, have been analyzed within the framework of the eikonal model. It is assumed that 11 Li has the halo structure of a 9 Li core plus two weakly bound neutrons and is treated such that the nuclear potential has a sum of the core and halo neutron contributions. We have found that the break-up effect of halo neutrons is essential to understand the elastic cross sections of 11 Li+p system at E lab /A = 62 MeV/nucleon. The near- and the far-side decompositions of elastic cross sections have also been performed by following the Fuller's formalism.

GAMMA-RAY BURSTS FROM HALO NEUTRON STARS CROSSING DARK CLUSTERS

Two classes of neutron stars may exist in the galactic halo: high velocity neutron stars originating from the disk and injected in the halo and neutron stars originating from globular clusters (via type II supernovae and/or accretion induced collapse of white dwarfs). Moreover, the halo dark matter is likely in the form of dark clusters made of Massive Astrophysical Compact Halo Objects (MACHOs) and cold molecular clouds, expected to be formed in the outer part of the galaxy. We suggest that halo neutron stars may emit gamma-ray bursts crossing dark clusters. This assumption allows us to explain all the observed properties of gamma-ray bursts (rate, isotropy, cumulative peak flux distribution), including the different spectral properties of the two classes of short and long bursts. Several methods to test this model, independently on observations of gamma-ray bursts, are discussed.