First observation of the competing fission modes in the neutron-deficient sub-lead region

Article
Report number	arXiv:1804.01832
Title	First observation of the competing fission modes in the neutron-deficient sub-lead region
Related title	First observation of the competing fission modes in the sub-lead region
Author(s)	Tsekhanovich, I. (CENBG, Gradignan) ; Andreyev, A.N. (York U., England ; JAEA, Ibaraki ; CERN) ; Nishio, K. (JAEA, Ibaraki) ; Denis-Petit, D. (CENBG, Gradignan) ; Hirose, K. (JAEA, Ibaraki) ; Makii, H. (JAEA, Ibaraki) ; Matheson, Z. (Michigan State U., East Lansing (main)) ; Morimoto, K. (Nishina Ctr., RIKEN) ; Morita, K. (Nishina Ctr., RIKEN ; Kyushu U., Fukuoka (main)) ; Nazarewicz, W. (Michigan State U., East Lansing (main)) ; Orlandi, R. (JAEA, Ibaraki) ; Sadhukhan, J. (Calcutta, VECC ; HBNI, Mumbai) ; Tanaka, T. (Nishina Ctr., RIKEN ; Kyushu U., Fukuoka (main)) ; Vermeulen, M. (JAEA, Ibaraki) ; Warda, M. (Lublin, Curie U.)
Publication	2019-03-10
Imprint	2018-04-05
Number of pages	6
Note	6 pages, 4 figures
In:	Phys. Lett. B 790 (2019) 583-588
DOI	10.1016/j.physletb.2019.02.006 (publication)
Subject category	nucl-ex ; Nuclear Physics - Experiment
Abstract	Fragment mass distributions from fission of excited compound nucleus $^{178}$Pt have been deduced from the measured fragment velocities. The $^{178}$Pt nucleus was created at the JAEA tandem facility in a complete fusion reaction $^{36}$Ar + $^{142}$Nd, at beam energies of 155, 170 and 180 MeV. The data are indicative of a mixture of the mass-asymmetric and mass-symmetric fission modes associated with higher and lower total kinetic energies of the fragments, respectively. The measured fragment yields are dominated by asymmetric mass splits, with the symmetric mode contributing at the level of $\approx1/3$. This constitutes the first observation of a multimodal fission in the sub-lead region. Most probable experimental fragment-mass split of the asymmetric mode, $A_{L}/A_{H}\approx 79/99$, is well reproduced by nuclear density functional theory using the UNEDF1-HFB and D1S potentials. The symmetric mode is associated by theory with very elongated fission fragments, which is consistent with the observed total kinetic energy/fragment mass correlation.
Copyright/License	publication: (License: CC-BY-4.0) preprint: (License: arXiv nonexclusive-distrib 1.0) © 2019 Published by Elsevier B.V.

$PES of $^{178}$Pt in the ($Q_{20}$, $Q_{30}$) plane (a) and in the ($Q_{30}$, $Q_{40}$) plane at $Q_{20}=190$\,b (b) obtained in D1S. The solid thick line in (a) indicates the static fission path obtained by the local minimization of PES. Dashed lines in (b) indicate the symmetric PESs corresponding to compact (smaller $Q_{40}$) and elongated (larger $Q_{40}$) fragments. The minimum corresponding to the static fission path in (a) is marked by the red dot.$ $(a) Two-dimensional TOF1-TOF2 raw-data spectrum for coincident events at $E_{\rm beam}=170$ MeV. Events in the black contour are from fission; remaining events are from the projectile-target scattering. (b) Summed energy signals from the MWPC detectors for $E_{\rm beam}=170$ MeV plotted against the difference in their timing signals (coincidence with MCPs not demanded). Contoured are fission events producing more ionization in detectors, due to their significantly larger ionic charge states and, hence, higher effective charges that scattered beam/target nuclei. (c) FF velocities after calibration with the scattered $^{36}$Ar beam, corrected for attenuation in the target and TOF detectors. The inset shows a typical (free) fit of the data at $E_{\rm beam}=170$ MeV. (d) Events from (a) represented in terms of their total kinetic energy and mass both calculated from experimentally obtained velocities, assuming fission process as the only events' origin. Group of events in the plot's center is coincident with data in contours in (a) and (b).$ $PES of $^{178}$Pt in the ($Q_{20}$, $Q_{30}$) plane calculated in UNEDF-HFB. The solid thick line indicates the static fission path obtained by the local minimization of PES. To illustrate the shapes on the way to fission, and the emergent pre-fragments, the neutron localization functions~\cite{Zhang2016,Sadhukhan2017} corresponding to various intrinsic configurations along the asymmetric (ABCD) and symmetric (ABcd) paths are plotted.$ Show more plots

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