Chinese Physics C > 1985, Vol. 9 > Issue(4): 454-460

THE SHELL EFFECT IN SEQUENTIAL FISSION INDUCED BY²³⁸U WITH ENERGY JUST ABOVE COULOMB BARRIER

DAI Guang-Xi^,,
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Abstract：
The experimental results of sequential fission are presented for collision of ²³⁸U (5.4MeV/u) on ⁴⁸Ca, ⁴⁵S and ²³⁸U(6.0MeV/u) on ¹⁶O, ⁴⁸Ca, ⁴⁵Sc, ⁴⁸Ti, ⁵⁸Fe, ⁶⁴Ni and ⁸⁹Y targets. The measurements of ternary events in exit channel have been performed by triple coincidence among 4 PPAC with area of 20 cm×30 cm. The reconstrction of ternary events are performed by direct kinematics and the fission partner among three fragments is identified by relative velocities between them. The detection geomentry efficiency is determind by a Monte-Carlo simulation.
Before the sequential fission, U-like fragments are scattered near grazing angle. The most probable value of TKEL in the scattering process associated with S.F.changes from 25 MeV to 55 MeV for different reaction systems. The angular distributions of debris of S.F. in second C.M. are isotropic.
In conclusion, because of lower fission threshold at Uranium region, the sequential fission mainly follows quasielastic scattering, in S.F. cross-section σ _S.Fthere is strong shell effect. A simple relationship between σ _S.Fover σ _R, the total reaction cross-section and Sommerfeld parameters S for nuclei with magic number are obtained.

References

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W. Brüchle et al., GSI Scientific Report, 1980, P. 4.[2] H. Backe et. al., GSI Scientific Report, 1930 , P. 3.[3] D. V. Havach et. al., Pyhs. Rev. Lett.. 42(1979) 1728.[4] A. Gobbi et. aI., private communication.[5] G. Dai et. al., GSI Scientific Report, 1982, P. 225.[6] V. E. Viola, Jr., Nucl. Data, A1(196d), 39.

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DAI Guang-Xi, THE SHELL EFFECT IN SEQUENTIAL FISSION INDUCED BY ²³⁸U WITH ENERGY JUST ABOVE COULOMB BARRIER[J]. Chinese Physics C, 1985, 9(4): 454-460.

DAI Guang-Xi, THE SHELL EFFECT IN SEQUENTIAL FISSION INDUCED BY ²³⁸U WITH ENERGY JUST ABOVE COULOMB BARRIER[J]. Chinese Physics C, 1985, 9(4): 454-460. shu

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Received: 1900-01-01
Revised: 1900-01-01

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沈阳化工大学材料科学与工程学院沈阳 110142

THE SHELL EFFECT IN SEQUENTIAL FISSION INDUCED BY²³⁸U WITH ENERGY JUST ABOVE COULOMB BARRIER

DAI Guang-Xi^,

Corresponding author:DAI Guang-Xi,

Received Date:1900-01-01
Accepted Date:1900-01-01
Available Online:1985-08-05

Abstract:The experimental results of sequential fission are presented for collision of²³⁸U (5.4MeV/u) on⁴⁸Ca,⁴⁵S and²³⁸U(6.0MeV/u) on¹⁶O,⁴⁸Ca,⁴⁵Sc,⁴⁸Ti,⁵⁸Fe,⁶⁴Ni and⁸⁹Y targets. The measurements of ternary events in exit channel have been performed by triple coincidence among 4 PPAC with area of 20 cm×30 cm. The reconstrction of ternary events are performed by direct kinematics and the fission partner among three fragments is identified by relative velocities between them. The detection geomentry efficiency is determind by a Monte-Carlo simulation.
Before the sequential fission, U-like fragments are scattered near grazing angle. The most probable value of TKEL in the scattering process associated with S.F.changes from 25 MeV to 55 MeV for different reaction systems. The angular distributions of debris of S.F. in second C.M. are isotropic.
In conclusion, because of lower fission threshold at Uranium region, the sequential fission mainly follows quasielastic scattering, in S.F. cross-section σ_S.Fthere is strong shell effect. A simple relationship between σ_S.Fover σ_R, the total reaction cross-section and Sommerfeld parameters S for nuclei with magic number are obtained.