Complexity of the Potential-Energy Surface for Fission of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">U</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>238</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>

Gavron, A.; Britt, H. C.; Goldstone, P. D.; Wilhelmy, J. B.; Larsson, S E

doi:10.1103/physrevlett.38.1457

Cited by 37 publications

(6 citation statements)

References 6 publications

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“…22. These results are in agreement with those reported by Tang and Wilhelmy [25], and Gavron et al [24].…”

Section: Discussionsupporting

confidence: 94%

“…Therefore, the level density parameters for symmetric fission had to be taken larger than those for the asymmetric a&, ) aI, by 3 -13%, and, then, the barrier heights were changed for the best fit to the observed peak-to-valley ratios and the excitation functions. This choice of level density parameters is qualitatively in agreement with the earlier observation by Gavron et al [24] who pointed out the necessity of including y deformation for the reAection-symmetric second saddle. The barrier curvature parameters (A'co) were fixed at the commonly used value of 1.0 MeV because they were insensitive to the fitting in the present excitation energy region.…”

Section: B General Considerationsupporting

confidence: 90%

“…-228 -16 9 -18 9-16[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] 10-32 10-1812,18 10-189 -16 10-16 Theoretically, Pashkevich[16] and Brosa and co-workers[17,18] claim that there are two kinds of saddles in the potential energy surface, one symmetric and the other asymmetric with respect to the reAection plane perpendicular to the nuclear symmetry axis. The second postulate is that there is only one-saddle at the deformation of the second barrier which is reAection asymmetric in shape[6] according to the microscopic-macroscopic calculation using the Strutinsky prescription[7,8] and this saddle determines the fission rate.…”

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confidence: 99%

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Systematic variation of fission barrier heights for symmetric and asymmetric mass divisions

1993

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The excitation functions and the mass yield curves for proton-induced fissions of U, U, U, Np, Pu, Pu, Pu, 'Am, and Am targets were studied. The excitation functions for nearsymmetrically divided fragments were found quite different in shapes and threshold energies from those of asymmetrically divided ones in all the fissioning systems studied. In order to obtain the fission barrier heights for symmetric and asymmetric mass division, the conventional Bohr-Wheeler type calculations for the competition between fission and neutron emission were performed. In the calculation, two independent fission channels, symmetric and asymmetric, were assumed, and fission barrier heights and level density parameters that could best reproduce the shapes of the excitation functions (incident energy dependence) of typical symmetric and asymmetric products were deduced. Barrier heights for symmetric and asymmetric mass divisions both decrease as the mass of fissioning nuclide Af increases, and they also exhibit slight dependence on the atomic number. Difference between the two barrier heights is 2.0 -2. 5 MeV in the region of Af =236-245. From similar analysis of excitation function data reported in literature, it is found that the difference changes from a large positive value for N -150, neutron number of the fissioning nuclide, to a large negative value for 1V-126, and the two barrier heights become comparable at N= 135 -138.PACS number(s): 25.85.Ge, 27.90.+b

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“…22. These results are in agreement with those reported by Tang and Wilhelmy [25], and Gavron et al [24].…”

Section: Discussionsupporting

confidence: 94%

Section: B General Considerationsupporting

confidence: 90%

mentioning

confidence: 99%

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Systematic variation of fission barrier heights for symmetric and asymmetric mass divisions

1993

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“…At saddle and ground-state deformations K rot (U ) is defined by the symmetry class, adopted from shell-model calculations [2,14,15]. At inner saddle we assume axial symmetry for neutron numbers N 144 and triaxial shape for N > 144.…”

Section: Statistical Modelmentioning

confidence: 99%

Actinide symmetric/asymmetric nucleon-induced fission up to 200 MeV

Maslov

2004

Physics Letters B

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The fission cross sections of the symmetric SL-mode and the asymmetric lumped (S1 + S2)-mode of the 235 U(n, F), 237 Np(n, F) and 238 U(p, F) reactions are calculated up to E n = 200 MeV within a statistical model. For each fissioning nuclide, emerging in (n, xnf) reactions, a separate triaxial outer fission barrier is assumed for the SL-mode. To reproduce the measured branching ratio of symmetric and asymmetric fission events, strong contribution of fission from neutron-deficient nuclei is assumed. Damping of the contribution of triaxial collective modes to the level density at the SL-mode outer saddle seems to be essential for the description of the branching ratio. The sensitivity of the calculated branching ratio to the fissility of the target nuclide and the incident particle is investigated.

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“…That means the contribution of the fission reactions of neutron-deficient 233−x Th nuclides with low intrinsic excitation energies would be relatively high. That might lead to the lowering of r S L for the 232 Th(n,f) reaction, but this effect could be more than compensated, since for Th nuclei the relative heights of the symmetric and asymmetric outer fission barriers (E S L f B − E AS f B ), as was already mentioned, might change in favor of symmetric fission contribution [10][11][12][25][26][27]. The experimental estimates of the branching ratios r S L for Th nuclides with A ≤ 226 by Itkis et al [11], Pokrovsky et al [12] and Schmidt et al [10] correspond to different excitation energies of composite nuclei.…”

Section: Branching Ratio Of Symmetric-to-observed Fission Eventsmentioning

confidence: 99%

^225-232Th symmetric/asymmetric neutron-induced fission up to 200 MeV

Maslov

2007

Nd2007

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Abstract. The transition from asymmetric to symmetric fission as a function of the excitation energy and the nucleon composition of fissioning Th nuclei is investigated for the 232 Th(n,f) reaction. Observed neutron-induced fission cross section is described in a fission/evaporation approximation. A separate relatively high outer fission barrier E S L f B with significant curvature was assumed for the symmetric (SL) mode, while the inner one (E S L(AS ) f A ) was assumed to be the same for symmetric and asymmetric (AS) modes. Axial asymmetry and mass symmetry is assumed for the outer saddle of the SL-mode, as distinct from the AS-mode. A drop of (E S L f A − E AS f A ) = 3.5 MeV to 1-1.5 MeV for Th nuclei with A ≤ 226 is responsible for the increase of the symmetric fission contribution to 225,229,230,231,232 Th(n,f) fission cross sections with neutron energy up to E n = 200 MeV. It is shown above 80 MeV the 229,230,231,232 Th(n,f) fission cross sections are no longer dependent on the Th target nuclide fissility.

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Complexity of the Potential-Energy Surface for Fission ofU238

Cited by 37 publications

References 6 publications

Systematic variation of fission barrier heights for symmetric and asymmetric mass divisions

Systematic variation of fission barrier heights for symmetric and asymmetric mass divisions

Actinide symmetric/asymmetric nucleon-induced fission up to 200 MeV

^225-232Th symmetric/asymmetric neutron-induced fission up to 200 MeV

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