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Title	$β$ -delayed fission of isomers in $^{188}$Bi
Related title	β -delayed fission of isomers in Bi188
Author(s)	Andel, B (Leuven U. ; Comenius U.) ; Andreyev, A N (York U., England ; JAEA, Ibaraki) ; Antalic, S (Comenius U.) ; Al Monthery, M (York U., England) ; Barzakh, A (St. Petersburg, INP) ; Bissell, M L (Manchester U.) ; Chrysalidis, K (CERN) ; Cocolios, T E (Leuven U.) ; Cubiss, J G (York U., England) ; Day Goodacre, T (Manchester U. ; CERN) ; Dubray, N (CEA DAM) ; Farooq-Smith, G J (Leuven U.) ; Fedorov, D V (St. Petersburg, INP) ; Fedosseev, V N (CERN) ; Gaffney, L P (West Scotland U.) ; Garcia Ruiz, R F (Manchester U.) ; Goriely, S (Brussels U., IAA) ; Granados, C (Leuven U.) ; Harding, R D (York U., England ; CERN) ; Heinke, R (Mainz U.) ; Hilaire, S (CEA DAM) ; Huyse, M (Leuven U.) ; Lemaître, J F (Brussels U., IAA) ; Lynch, K M (CERN) ; Marsh, B A (CERN) ; Molkanov, P (st. petersburg, in) ; Mosat, P (Comenius U.) ; Péru, S (CEA DAM) ; Raison, C (York U., England) ; Rothe, S (CERN) ; Seiffert, C (CERN) ; Seliverstov, M D (St. Petersburg, INP) ; Sels, S (Leuven U.) ; Studer, D (Mainz U.) ; Sundberg, J (cern ; U. Gothenburg (main)) ; Van Duppen, P (Leuven U.)
Publication	2020
Number of pages	12
In:	Phys. Rev. C 102 (2020) 014319
DOI	10.1103/PhysRevC.102.014319
Subject category	Nuclear Physics - Experiment
Accelerator/Facility, Experiment	CERN ISOLDE
Abstract	$β$-delayed fission ($β$DF) decay of a low-spin (ls) and a high-spin (hs) isomer in $^{188}$Bi was studied at the ISOLDE facility at CERN. Isomer-selective laser ionization and time gating were employed to investigate each isomer separately and their $β$DF partial half-lives were determined: $T_{1/2\mathrm{p},β\mathrm{DF}} (^{188}\mathrm{Bi^{ls}})=5.6(8)×10^3$ s and $T_{1/2\mathrm{p},β\mathrm{DF}} (^{188}\mathrm{Bi^{hs}})=1.7(6)×10^3$ s. This work is the first βDF study of two states in one isotope and allows the spin dependence of low-energy fission to be explored. The fission fragment mass distribution of a daughter nuclide $^{188}$Pb, following the $β$ decay of the high-spin isomer, was deduced and indicates a mixture of symmetric and asymmetric fission modes. Experimental results were compared with self-consistent mean-field calculations based on the finite-range Gogny D1M interaction. To reproduce the measured $T_{1/2\mathrm{p},β\mathrm{DF}} (^{188}\mathrm{Bi^{hs}})$, the calculated fission barrier of $^{188}$Pb had to be reduced by ≈30%. After this reduction, the measured $T_{1/2\mathrm{p},β\mathrm{DF}} (^{188}\mathrm{Bi^{ls}})$ was in agreement with calculations for a few possible configurations for $^{188}\mathrm{Bi^{ls}}$. Theoretical $β$DF probabilities for these configurations were found to be lower by a factor of 4–9 than the $β$DF probability of $^{188}\mathrm{Bi^{hs}}$. The fission fragment mass distribution of $^{188}$Pb was compared to the scission-point model SPY and the calculations based on the finite-range liquid-drop model. The first observation of $β$DF for $^{190}$Bi is also reported.
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