Hyper-deformed minimum in the Am isotopes

The nuclear fission is one of the most complex nuclear phenomena in nature and many aspects remain only partially understood even in the 75th year of its discovery. The third minimum has been discussed in the literature for many nuclides like thorium isotopes. The mic-mac approach with Cassini Ovaloid Shape parameterization for the nuclear potential has been utilized to calculate the potential energy surfaces in the actinides. This formalism is due to Garcia et al. The aim of the work is to search for the triple-humped fission barrier which may support the existence of hyper-deformed isomers. The paper look into such a hyper-deformed isomer near the magic numbers predicted around the 3:1 shapes. For the anisotropic-oscillator, the deformed magic numbers for the axes ratio 2:1 are 2, 4, 10, 16, 28, 40, 60, 80, 110, 140 and 182, which are also upwardly modified due to the spin-orbit term as recently shown for the super-deformed nuclei similar to the harmonic oscillator potential for spherical magic numbers. As we go to the higher deformation at 0.86 with axes ratio 3:1, the numbers become 2, 4, 6, 12, 18, 24, 36, 48, 60, 80, 100, 120, 150, 180, and 210. The spin-orbit interaction will modify these numbers upwards too. Therefore, the search for the third well near those magic numbers which lie in the actinide region is focussed. The potential energy surfaces are calculated for the nuclei having Z = 93 to 96 and N ∼ 150 for the search of triple-hump barrier. The calculations show that the third well corresponding to the 3:1 shell structure begins to appear in the deformation range 0.7-0.8 near neutron number 150 and above. The outer barrier decreases as we go from Z=93 to 95 due to increasing Coulomb energy contribution to the barrier. It starts to be more flat and leads to the existence of the deeper third well in the neutron-rich side of the particular isotopic chain. These calculations show that the Am nuclides may be the best candidates for third minimum. The deepest third minimum is observed in 250Am with a depth of 1.29 MeV. The next possible candidate is 251Am. However, the experimentally accessible isotopes may be 244,245Am. These nuclides have sufficiently deep minimum to observe hyper-deformed isomer. However, further calculations are in progress to establish this