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Weber, J.; Britt, H. C.; Gavron, A.; Konecny, E.; Wilhelmy, J. B.

doi:10.1103/physrevc.13.2413

Cited by 38 publications

(37 citation statements)

References 15 publications

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“…Information about the saddle has been extensively studied by measuring angular distributions and excitation functions of fission products. The presence of two kinds of fission barriers (threshold energies) in the deformation process has been experimentally confirmed by several authors, such as [12][13][14][15][16][17][18][19][20]; the fission process that experiences the higher threshold energy leads to the fragment mass distribution centered around the half-mass of a fissioning nucleus, while the lower threshold process leads to the asymmetric mass-distribution. On the other hand, information on scission configurations has been obtained from fragment kinetic energies and mass-yield distributions influenced by shell structures of fragments near scission [21,22].…”

Section: Figmentioning

confidence: 92%

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Two-mode fission – experimental verification and characterization of two fission-modes

Nagame

Nakahara

2012

Radiochimica Acta

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Summary.Experimental verification and characterization of the two-mode fission are reviewed. The presence of two independent deformation-paths in low energy fission of actinides is demonstrated by studying correlation among saddle-point configurations, scission-point configurations, and mass-yield distributions; the elongated scission configuration is related with the fission process that goes over a higher threshold energy and results in a symmetric mass-division mode, while the compact scission configuration with the process that experiences a lower threshold ends up with an asymmetric mass-division mode. Based on an extensive systematic analysis of scission properties in a wide range of actinide fission, the bimodal fission observed in the spontaneous fission of the heavy actinides is interpreted as the result of the presence of two fission paths, namely, the ordinary asymmetric fission path and a strongly shell-influenced symmetric mode.

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Section: Figmentioning

confidence: 92%

“…3 for a wide range of actinides [20]. The data in the light mass region are taken from [14,34,35]. The difference (B [15].…”

Section: Excitation Function Of Fission Productsmentioning

confidence: 99%

Two-mode fission – experimental verification and characterization of two fission-modes

Nagame

Nakahara

2012

Radiochimica Acta

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“…The two-mode character was also supported by Britt, Wegner, and Gursky [2] who measured the kinetic-energy distribution of fission fragments as a function of mass ratio. Konecny, Specht, and Weber [3] and Weber et al [4] carefully measured fission probabilities and fragment anisotropies of Ac, ' Ra, and Ra by direct reactions and found different thresholds for symmetric and asymmetric fission and different angular anisotropies for the two components at the energy close to the fission barrier.…”

Section: Introductionmentioning

confidence: 99%

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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“…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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Fission ofRa228

Cited by 38 publications

References 15 publications

Two-mode fission – experimental verification and characterization of two fission-modes

Two-mode fission – experimental verification and characterization of two fission-modes

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

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

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