The systematics of the fission barrier shapes of a total of 47 doubly even actinide and transactinide nuclei have been studied using the double-humped fission barrier model. The fission barrier has been parametrized in terms of four smoothly joined parabolic segments. The penetrabilities through such double-humped fission barriers have been calculated in the Wentzel-Kramers-Brillouin approximation, and the various fission half-lives have been determined using the formalism given earlier by Nix and Walker. The various parameters of such fission barriers have been deduced by requiring their simultaneous consistency with the various relevant fission observables, namely, the near-barrier fission cross sections, isomeric energies and isomeric half-lives, where available, and the ground-state spontaneous fission half-lives in the region 90≤Z≤98, and such model calculations with some further justifiable asssumptions have been extended to the region of the still heavier nuclei with Z≥100. The results of our systematic study of the heights of the inner and the outer barriers of the double-humped fission barriers corresponding to such doubly even nuclei suggest that while the height of the inner barrier remains approximately constant in the entire region of such nuclei, the deduced heights of the outer barrier decrease rather sharply and continuously with the increase in the value of the fissility parameter until one reaches the element Rf (Z=104).

For the still heavier doubly even transactinides with Z=106 and 108, the deduced values of the height of the outer barrier remain approximately constant. Our deduced heights of the outer barrier for the various isotopes of a given element heavier than Pu also exhibit a maxima around the neutron number N=152, reflecting the experimentally observed extra stability in a similar variation of the ground-state spontaneous fission half-lives occurring presumably due to an apparent closure of a deformed subshell at N=152. This subshell effect is also found to disappear at Rf and for the heavier transactinide nuclei. While the various fission observables are reasonably reproduced in terms of a single set of fission barrier parameters for a given nucleus for most of the 47 doubly even actinide and transactinide nuclei considered in the present work, major difficulties remain for the odd-mass and for the doubly odd nuclei where the calculated ground-state spontaneous fission half-lives are found to be several orders of magnitude larger than those measured. Possible reasons for such discrepancies are briefly mentioned.

• Received 24 October 1991

DOI:https://doi.org/10.1103/PhysRevC.45.2803