Mapping Low-Energy Fission with RIBs (in the lead region) Andrei Andreyev University of York, UK Japan Atomic Energy Agency (JAEA), Tokai, Japan Low-energy fission in the new regions of the Nuclear Chart Beta Delayed Fission (bdf) at ISOLDE at 60 kev Fusion-fission reactions at ~5 AMeV Coulex-induced fission with SOFIA@GSI at 1 AGeV Chamrousse, 21 March 2017
Chamrousse-2008
Outlook Many nuclear properties change far from stability line (e.g. disappearance of traditional magic numbers; appearance of new shell gaps; halos, skins ) What happens to fission far from stability, e.g. on the extremely proton-rich or neutron-rich side? Problem 1: Very difficult to get to them need RIBs Problem 2: to fission these nuclei at low excitation energy (E*~B f )
Experimental information on low-energy fission Nuclei with measured charge/mass split (RIPL-2 + GSI) Heavy Actinides, N/Z~1.56: predominantly asymmetric; spontaneous fission, fission isomers Z=82 187 Ir 196 Au - particle induced x - e.m. induced E*~11 MeV K.-H. Schmidt et al.
Experimental information on low-energy fission Nuclei with measured charge/mass split (RIPL-2 + GSI) Heavy Actinides, N/Z~1.56: predominantly asymmetric; spontaneous fission, fission isomers Region of our interest I: betadelayed fission of A~180-200 N/Z~1.22-1.3: Tl,Bi, At, Fr ISOLDE(CERN) Z=82 180 Hg N/Z=1.25 187 Ir 196 Au - particle induced x - e.m. induced E*~11 MeV Pre-actinides, light Ir-Th N/Z~1.4-1.5: predominantly symmetric, e.g. FRS(GSI)
Beta-Delayed Fission 180Tl 180Hg Two step process: b decay followed by fission Low-energy fission (E*~3-12 MeV, limited by Q EC ) e.g. 180 Tl: Q EC =10.4 MeV, B f,calc =9.8 MeV Relatively low angular momentum of the state e.g. 180 Tl: I=4 or 5 (some cases: up to 10) A.N. Andreyev, M. Huyse, P. Van Duppen, Reviews of Modern Physics, 85, 1541 (2013)
Beginning: bdf of 180 Tl at ISOLDE (CERN) Hot cells HRS Target 50 g/cm 2 GPS Target 50 g/cm 2 Proton beam 1.4 ma, 1.4 GeV from PSB GPS Magnet RILIS HRS Magnets 180 Tl + Control Room Experiments
Detection system for bdf studies at ISOLDE Annular Si Si MINIBALL Ge cluster pure 180 Tl 30-60 kev from RILIS+ISOLDE C-foils 20 mg/cm 2 Annular Si beam from ISOLDE ff Si a f f Si detectors C-foil A.N. Andreyev et al. PRL 105 (2010)
Mass distribution of fission fragments in bdf of 180 Tl (the fission of 180 Hg) ASYMMETRIC energy split! Thus asymmetric mass split: M H =100(4) and M L = 80(4) E ff1 -E ff2 coincidences ~330 events Singles 1111 ff ~20 ff/h A problem: low-energy FF s - 1 AMeV only, Z identification difficult 9 The most probable fission fragments are 100 Ru (N=56,Z=44) and 80 Kr (N=44,Z=36)
New Type of Asymmetric Fission in Proton-Rich Nuclei via bdf of 180 Tl E Q EC ( 180 Tl)=E * max=10.44 MeV Q EC ( 180 Tl)-B f ( 180 Hg)=0.63 MeV P bdf ( 180 Tl)=3.6(7) 10-5 80 Kr 100 Ru 90 Zr+ 90 Zr Calculations according to 5D fission model (P. MÖller et al., Nature 409, 785 (2001))
Two types of asymmetry: what s the difference? 180 Hg 238 U
Brownian Metropolis Shape Motion based on J. Randrup and P. Moller, PRL 106, 132503 (2011) Phys. Rev. C 85, 024306 (2012)
Improved Scission-Point Model asymmetric Inter-fragment distance is not fixed and calculated. values of ~0.5-1 fm result (Wilkins fixed at 1.4 fm) Symmetric! Mass symmetry/asymmetry doesn t change as a function of E* (up to E*~60 MeV) good for future experiments
Self-consistent Scission-Point Model
Mean-field HFB+Gogny D1S
From Asymmetry to Symmetry Lightest Hg isotopes with N/Z~1.25: asymmetric 180 Hg Heavy Actinides, N/Z~1.56: predominantly asymmetric; spontaneous fission, fission isomers Z=82 178,180 Hg ISOLDE 187 Ir 198 Hg - particle induced x - e.m. induced E*~11 MeV Pre-actinides, light Ir-Th N/Z~1.4-1.5: predominantly symmetric, e.g. FRS(GSI)
Energy in Si2 (MeV) Energy in Si2 (MeV) Energy in Si2 (MeV) Mass Distributions of 194,196 Po via bdf of 194,196 At at ISOLDE 196 At 10 ff/h Energy in Si1 (MeV) 180 Hg 20 ff/h 194 At 40 ff/h Clear difference in energy (thus, mass) distribution Energy in Si1 between (MeV) 2-peaked fission of 180 Hg and a broad distribution in 194,196 Po Energy in Si1 (MeV)
Bimodal Mass Distributions in bdf of 194,196 At and 200,202 Fr L.Ghys et al., Phys. Rev. C 90, 044305 (2014) 20 ff/h 40 ff/h 10 ff/h 0.2 ff/h
Bimodal Mass Distributions in bdf of 194,196 At and 200,202 Fr L.Ghys et al., Phys. Rev. C 90, 044305 (2014) 20 ff/h 40 ff/h 10 ff/h J. D. McDonnell et al., PRC90, 021302(2014) 0.2 ff/h
180 Hg: More surprises? How does 180 Hg fission at higher excitation energies? 36 Ar+ 144 Sm 180 Hg* E*=34-66 MeV 2010-2014: JAEA,Tokai Beam 36 Ar FF2 MWPC1 FF1 144 Sm MWPC2 Even at E*=66 MeV: asymmetric mass split with A 1 ~100, A 2 ~80 K. Nishio et al, PLB (2015) Supported by Reimei Foundation (JAEA)
180 Hg: One or two fission modes?
Fusion-Fission of 182,195 Hg at ANU
Excitation-energy dependence of shell effects and of the fission barrier in the lead region (SKM*) SkM and a density-dependent pairing interaction.
Excitation-energy dependence of shell effects and of the fission barrier in the lead region (SKM*)
SOFIA@GSI Studies Of FIssion with Aladin Courtesy Julie-Fiona Martin and Julien Taieb (CEA) See also: J-F.Martin, 16 th ASRC JAEA Workshop: http://asrc.jaea.go.jp/soshiki/gr/chiba_gr/workshop3/&martin.pdf
SOFIA Fission studies at GSI ~2 days a few hours
SOFIA Fission studies at GSI
Summary A.N. Andreyev, K. Nishio, K.-H. Schmidt, Review on Experimental Progress in Fission, submitted to Reports on Progress in Physics
Beta Delayed Fission (bdf) at ISOLDE at 60 kev Transfer-induced fission at HIE-ISOLDE at 5 AMeV Coulex-induced fission with SOFIA@GSI at 1 AGeV Transfer-induced fission with SAMURAI@RIKEN at 350 AMeV Transfer-induced fission at VAMOS@GANIL at 6 AMeV Further plans (ELISe@FAIR, SCRIT@RIKEN) Conclusions: Bright future for fission studies with RIBs Access to both proton- and neutron- rich nuclei Un-precedented precision in Z,A determination