Evolution of multimodal fission with energy in <math><mmultiscripts><mi>Np</mi><mprescripts/><none/><mn>238</mn></mmultiscripts></math> populated by <math><mrow><mmultiscripts><mi>Li</mi><mprescripts/><none/><mn>6</mn></mmultiscripts><mo>+</mo><mmultiscripts><mi>Th</mi><mprescripts/><none/><mn>232</mn></mmultiscripts></mrow></math> - INSPIRE

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Evolution of multimodal fission with energy in ${}^{238}{Np}$ populated by ${}^{6}{Li} + {}^{232}{Th}$

Dec 4, 2023

11 pages

Published in:

Phys.Rev.C 108 (2023) 6, 064601

Published: Dec 4, 2023

DOI:

10.1103/PhysRevC.108.064601 (publication)

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Abstract: (APS)

Background: Nuclear fission is influenced by shell effects. Fission modes are a strong signature of the compound nucleus formation in heavy ion induced reactions. The evolution of the relative strengths of the fission modes with excitation energy is a matter of intense interest. Purpose: We investigate the signatures of fission modes in

{}^{238}{Np}

populated by the

{}^{6}{Li} + {}^{232}{Th}

reaction through the mass–total kinetic energy distribution. Method: The mass–total kinetic energy distributions of fission fragments of the reaction

{}^{6}{Li} + {}^{232}{Th}

are measured at four laboratory energies,

E_{lab} = 28.5

, 40, 45, and 62.5 MeV. Mass–total kinetic energy distributions of

{}^{6}{Li} + {}^{232}{Th}

are described by the multimodal random neck rupture model. Results: Channel probabilities of different fission modes are obtained obtained through a two-dimensional fitting procedure. The contribution of the standard 1 (S1) mode is found to become

\approx 2 %

at

E_{lab} = 40

MeV. The heavy fragments of S1 and standard 2 (S2) modes are found to be associated with

Z \approx 52

and

Z \approx 55

shells, respectively. The slope of the asymmetric to symmetric fission yields ratio with the excitation energy of

{}^{6}{Li} + {}^{232}{Th}

is found to be similar to that of

{}^{18}O + {}^{208}{Pb}

(previously reported). Conclusions: The analysis of mass–total kinetic energy distribution data reveals the presence of fission modes in

{}^{6}{Li} + {}^{232}{Th}

. The average kinetic energy release in fission obtained from Viola systematic matches well with the one of the of S2 mode. The liquid-drop-like broad symmetric (SL) mode is found to peak at a lower energy than predicted by Viola systematic. This is associated with the decrease of the total kinetic energy in the asymmetric fission mode due to the fading out of shell effects with increasing excitation energy.

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