delayed fission studies of At and Fr at

β-delayed fission studies of At and Fr at ISOLDE & outlook to ISOL@MYRRHA Lars Ghys lars. ghys@sckcen. be <generated automatically> 1 Copyright © 2016 SCK • CEN

Outline l Introduction l β-delayed fission (βDF) l Low-energy fission in the nuclear chart l βDF of neutron-deficient At and Fr at ISOLDE l Experimental set-up l Results l Comparison with theory l βDF studies at ISOL@MYRRHA l Extending known range of βDF isotopes l Measuring (detailed) mass distributions l Conclusions & Outlook <generated automatically> 2 Copyright © 2016 SCK • CEN

β-delayed fission (βDF) DF 1. Q β decay l l Bf 2. Fission l l l Excitation energy < Qβ Spin/ parity sensitivity U and Pb region Mass/energy distributions βDF-branching ratio Elongation <generated automatically> 3 Copyright © 2016 SCK • CEN

Low-energy fission throughout the nuclear chart asymmetry transition ? ? ? A. N. Andreyev , M. Huyse and P. Van Duppen/ Rev. Mod. Phys. 85 (2013), 1541 <generated automatically> 4 Copyright © 2016 SCK • CEN

ISOLDE facility (Geneva, Switzerland) target mass separator e. V 1. 4 G ns o prot target mass separator l 2 µA of protons on UCx target l isotopic (isomeric) pure beam l beam energy of 30 -60 ke. V Windmill S. Sels, master thesis, KU Leuven <generated automatically> S. Rothe et al. / Nature Comm 4 (2013) 1835. 5 Copyright © 2016 SCK • CEN

Detection system – ‘Windmill’ Si front Si back Si detectors C foil ISOLDE beam FF 241 Am C-foils e-/e+ particles Si spectrum - summing Fission fragments <generated automatically> 6 Copyright © 2016 SCK • CEN

Experimental results: mass distributions A. N. Andreyev , M. Huyse and P. Van Duppen/ Rev. Mod. Phys. 85 (2013), 1541 <generated automatically> 7 Copyright © 2016 SCK • CEN

Comparison with Finite-Range Liquid Drop Model (FRLDM) Experimental triple-humped ↔ calculated double-humped transition <generated automatically> Calculations by P. Möller and J. Randrup 8 Copyright © 2016 SCK • CEN

Systematics in βDF partial half-lives l Concerns on accuracy <generated automatically> L. Ghys et al. / Phys. Rev. C 91 (2015), 044314 9 Copyright © 2016 SCK • CEN

βDF studies at ISOL@MYRRHA ISOLDE ISOL@MYRRHA Beam energy (Ge. V) 1. 4 0. 6 Beam intensity (µA) 2 200 Beam time Days weeks → Increase of βDF statistics with two orders of magnitude <generated automatically> 10 Copyright © 2016 SCK • CEN

Extend known region for βDF neutron-deficient lead region l Neutron-deficient Au and At (detection limit bdf rate ~ 0. 1 h -1) l Isotope T 1/2 (s) TβDF (calc) α/s exp (ISOLDE) βDF rate (h-1) (ISOL@MYRRHA) 176 Au 1 106~108 ~1 10 -5~10 -3~10 -1 178 Au 2. 6 107~1011 ~100 10 -5~10 -1 10 -3~10 195 At 0. 36 105~107 ~10 10 -4~10 -2~1 198 At 2. 4 1013~107 ~1000 10 -6~10 -1 10 -4~10 182 Tl l Expected (systematics) : TβDF = 105~106 l Observed (ISOLDE): TβDF > 1. 4(1) x 108 l 204 Fr , … Neutron-rich 228, 230, 232 Fr l Upper limits for βDF branching available l Need for dedicated β-decay setup <generated automatically> 11 Copyright © 2016 SCK • CEN

Establishing mass distributions βDF at ISOLDE (May 2012) 178 Tl βDF at ISOLDE [1] Counts 200 Fr Energy (Me. V) l 6 fission fragments in 20 hours (!) l βDF observed l TβDF = 70 [+60, -30] s l ISOL@MYRRHA → establish mass distribution <generated automatically> l 8 fission fragments l βDF observed l TβDF = 4(2) x 102 s l ISOL@MYRRHA → confirm asymmetric fission 12 [1]: V. Liberati et al. / Phys. Rev. C 88 (2013), 044322 SCK • CEN Copyright © 2016

Details of mass distributions Dependence of total kinetic energy (TKE) vs masses → evidence for multimodal fission 196 At Similar features in βDF of 194 At, 202 Fr → need for higher statistics <generated automatically> 13 Copyright © 2016 SCK • CEN

Conclusion & Outlook l βDF of 200, 202 Fr and 194, 196 At observed in ISOLDE l Triple-humped mass distributions l Features not described by current fission models →Need for dynamical description of fission process l Exponential dependence of TβDF to (Qβ-Bf) l Valid for TβDF spanning 7 orders of magnitude, mainly on neutron-deficient side l Estimate βDF rates in next-generation facilities l Future βDF studies at ISOL@MYRRHA l Higher RIB yields and longer run times →increase statistics by at least 2 orders of magnitude l Extension of known βDF region around Z=82 l Measure (detailed) mass distributions <generated automatically> 14 Copyright © 2016 SCK • CEN

Copyright © 2016 - SCK CEN PLEASE NOTE! This presentation contains data, information and formats for dedicated use ONLY and may not be copied, distributed or cited without the explicit permission of the SCK • CEN. If this has been obtained, please reference it as a “personal communication. By courtesy of SCK • CEN”. SCK • CEN Studiecentrum voor Kernenergie Centre d'Etude de l'Energie Nucléaire Belgian Nuclear Research Centre Stichting van Openbaar Nut Fondation d'Utilité Publique Foundation of Public Utility Registered Office: Avenue Herrmann-Debrouxlaan 40 – BE-1160 BRUSSELS Operational Office: Boeretang 200 – BE-2400 MOL <generated automatically> 15 Copyright © 2016 SCK • CEN

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Fission-fragment mass and energy distributions Reference ~27 FF/h ~43 FF/h ~8 FF/h ~2 FF/h L. Ghys et al. / Phys. Rev. C 90 (2014), 041301 <generated automatically> 17 Copyright © 2016 SCK • CEN