-delayed fission of neutron-deficient Fr and At isotopes Lars Ghys1,2 1Instituut voor Kern- en Stralingsfysica, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven 2 Belgian Nuclear Research Centre, SCK•CEN, Mol, Belgium

Outline -delayed fission Experimental set-up Calibration method Introduction Fission at low excitation energies : systematics Experimental set-up ISOLDE “Windmill” system Calibration method Experimental results df of 202Fr df of 200Fr df of 194,196At Summary ‘parasitic’ decay information Conclusions & outlook 03/06/2013 INPC conference 2013

β-delayed fission : introduction Q Bf   DF QEC βdf of 180Tl[1] : Expected : Symmetric 180Tl  180*Hg → 90Zr + 90Zr Observed: Asymmetric 180Tl  180*Hg → 100Ru + 80Kr Fission properties of other nuclei in Pb-region?? Near or sub barrier fission → sensitivity to microscopic shell effects Known ranges of spins & parities ‘classical’ U-region (N/Z ~ 1.5) and Pb-region (N/Z ~ 1.3) → study isospin dependence Study partial half lifes as a function of Q and Bf Deze slide nog veranderen!! [1]: A.N. Andreyev et al./ PRL 105 (2010) 252502 03/06/2013 INPC conference 2013

Fission at low excitation energies: systematics df of n-deficient At & Fr? [1]: A.N. Andreyev et al./ submitted to RMP 03/06/2013 INPC conference 2013

ISOLDE facility - CERN 2 µA of protons on UCx target 1.4 GeV protons HRS mass separator GPS mass GPS target Windmill position HRS target 2 µA of protons on UCx target isotopic (isomeric) pure beam beam energy of 30-60 keV S.Rothe et al./ Nature Comm 4 (2013) 1835 . 03/06/2013 INPC conference 2013

Experimental set-up: “Windmill system” Annular Si Si Isotopically pure beam from ISOLDE C-foils 20 mg/cm2 Si detectors Ge C-foils Si detecors 241Am ff /  ISOLDE beam Ge detector Ge annular Si Si 03/06/2013 INPC conference 2013

Calibration method – coincident fission events Measurement : pulse height detector 1 (X1) and detector 2 (X2) calibration E1 = (a1 + a’1M1)X1 + b1 + b’1M1 energy calibration det 1 (Lohengrin – ILL) E2 = (a2 + a’2M2)X2 + b2 + b’2M2 energy calibration det 2 (Lohengrin – ILL) M1E1 = M2E2 Conservation of linear momentum M1 + M2 = A Conservation of mass Extraction of M1, M2, E1 & E2 Additional corrections Energy loss in carbon foil (SRIM simulations) ΔEfront = 0.3 MeV ; ΔEback = 1.2 MeV [S. Sels] neutron emission Sifront Siback ~900 Ǻ 03/06/2013 INPC conference 2013

-delayed fission of 202Fr (IS466) - preliminary Total Kinetic Energy (TKE) ≈ 147 MeV 202Fr 2 isomers ! 202Fr A.N. Andreyev et al./ PRL 105 (2010) 252502 180Tl 180Tl Binning? TKE ≈ 135 MeV 03/06/2013 INPC conference 2013

-delayed fission of 200Fr (IS534) After ~20 hrs of measurement: 6 fission fragments 2 events in coincidence → sufficient to extract TKE and partial βdf half life 200Fr 200Fr PRELIMINARY Preliminary calibration Bdf = being patient (low statistics) But, even with low statistics : TKE and branching (partial half lifes) can be extracted 03/06/2013 INPC conference 2013

-delayed fission of 194,196At (IS534) - preliminary 2 isomers! TKE  152 MeV 196At 196At TKE  153 MeV Courtesy to Simon Sels 03/06/2013 INPC conference 2013

Mass distributions :Comparison 180Tl 194At Counts/ 4 amu 196At 202Fr Mass (amu) 03/06/2013 INPC conference 2013

Fission at low excitation energies: systematics 196Po 194Po 202Rn [1]: A.N. Andreyev et al./ submitted to RMP 03/06/2013 INPC conference 2013

‘Parasitic’ information on decay : 202Fr Electrons (~106)  Particles (~107) 202Fr : energy spectrum (Si) -  summing Fission fragments (116) 202Fr ~44 hrs of measuring Pure  spectra () -  coincidences  Construct decay schemes 198At 202Rn 198Po 03/06/2013 INPC conference 2013

Conclusions & outlook Conclusions df of 200,202Fr and 194,196At confirmed and studied at ISOLDE Transition region from asymmetric to symmetric fission Due to long measurement times  large statistics on decay spectroscopy Lifetime determinations Fine structure in  decay Identification of isomeric states …. Outlook Determine df branching and partial half lifes  compare with other nuclei Separation of isomers in 202Fr (CRIS) and 194At (RILIS) Discussion with theoretical groups (P. Möller, S. Panebianco, M. Warda, Dubna) 03/06/2013 INPC conference 2013

Collaboration Comenius University, Bratislava A.N. Andreyev D. Jenkins V. Truesdale H. de Witte J. Elseviers L. Ghys M. Huyse D. Radulov M. Rajabali C. Van Beveren P. Van den Bergh P. Van Duppen B. Andel S. Antalic Z. Kalaninova X. Derkx J. Lane V. Liberati T. E. Cocolios E. Rapisarda ISOLDE & RILIS K. Nishio, Y. Nagame, JAEA, Tokai, Japan F.P. Hessberger, SHIP (GSI), Darmstadt, Germany U. Koster, ILL, Grenoble, France R. Page, OLL, University of Liverpool P. Möller, Los Alamos National Laboratory, US L. Ghys L. Popescu D. Pauwels 03/06/2013 INPC conference 2013

Thank you! 03/06/2013 INPC conference 2013

Back-up 03/06/2013 INPC conference 2013

Total kinetic energy (TKE) and prompt neutron emission TKE when no prompt neutrons are emitted = 147(1) MeV Fragment excitation energy ≈ [Q(fission)-TKE+QEC]/2 N/Z (202Rn) = 1.35 1.30 < N/Z < 1.40 Rode punten een beetje groter maken. (gedaan -> cluster) Up to 2 prompt neutrons can be emitted in a fission event. TKE when 2 prompt neutrons are emitted : 148(1) MeV 03/06/2013 INPC conference 2013

Pulse height defect (PHD) Why use Si detectors? intrinsic efficiency ≈100 % good energy resolution : FWHM ~ 1.5 MeV compact size Disadvantage : Pulse height defect Energy loss in detector dead layer Electron – hole recombination Nuclear collisions Schmitt calibration [1] : E = aX + b → E = (a+a’M)X+ b + b’M [1] : H. W. Schmitt et al. / Phys. Rev. 137 (1965) B837 – B847 http://www.quantumdiaries.org Lowering of recorded pulse height 03/06/2013 INPC conference 2013

Calibration measurements – Lohengrin, ILL Fission framents from 235U(n,f) Energy/q and mass/q selection Energy accuracy of ~100 keV 5 detectors tested : 2x PIPS; 3x surface barrier (1x annular) Mass range : 48 – 149 amu Energy range : 12 – 100 MeV 03/06/2013 INPC conference 2013

Calibration Measurements – Lohengrin ILL SB PIPS Pulse height defect = Eion – aXion - b Schmitt calibration valid for typical fission masses (80 – 136 amu) and energies (30 – 100 MeV) 180Hg – fission products: EL  61 MeV ; MH  100 amu EH  74 MeV ; ML  80 amu Perpendiculair vs. Grazing (45°) incidence  effect of dead layer 03/06/2013 INPC conference 2013

Calibration method E1 = (a1 + a’1M1)X1 + b1 + b’1M1 Schmitt calibration det 1 E2 = (a2 + a’2M2)X2 + b2 + b’2M2 Schmitt calibration det 2 M1E1 = M2E2 Conservation of linear momentum M1 + M2 = A Conservation of mass Extraction of M1, M2, E1 & E2 Additional corrections Energy loss in carbon foil (SRIM simulations) ΔEfront = 0.3 MeV ; ΔEback = 1.2 MeV [Simon] neutron emission Close geometry  wide angular range of detected particles ILL calibration measurements 03/06/2013 INPC conference 2013

Total kinetic energy 202Rn: TKE ≈ 147 MeV 180Hg σ = 8(1) MeV Preliminary: up to 2 prompt neutrons / fission event possible 180Hg TKE = 134.6(7) MeV (no neutrons) σ = 5.6(8) MeV 0 or 1 prompt neutron emitted 03/06/2013 INPC conference 2013

βdf in the neutron-deficient Pb region nucleus facility reference 180Tl ISOLDE, CERN A.N. Andreyev et al./ PRL 105 (2010) 252502 192,194At SHIP, GSI A.N. Andreyev et al./ PRC 87 (2013) 14317 178Tl V. Liberati et al., submitted 186,188Bi J. Lane et al./ PRC 87 (2013) 14318 200,202Fr L. Ghys et al. - preliminary 194,196At V. Truesdale, S. Sels et al - preliminary 200,202Fr 192,194,196At 186,188Bi 178,180,182Tl 03/06/2013 INPC conference 2013

‘Parasitic’ information on decay : 202Fr - plot : 202Fr Single ’s 202Fr 198At Kleurencode gebruiken! 03/06/2013 INPC conference 2013 M. Huyse et al./ PRC 46 (1992) 1209