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Photo-fission at the S-DALINAC

SFB 634. Photo-fission at the S-DALINAC. A. Göök, SFS-KF, Örebro, 18.11.2009. Photo-fission at the S-DALINAC Experiments on 238 U( γ , f) and 234 U( γ , f) Motivation Experimental setup Data analysis Results Summary and Outlook. Photo-fission at the S-DALINAC.

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Photo-fission at the S-DALINAC

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  1. | Institut für Kernphysik | Alf Göök | 1 SFB 634 Photo-fission at the S-DALINAC A. Göök, SFS-KF, Örebro, 18.11.2009 • Photo-fission at the S-DALINAC • Experiments on 238U(γ, f) and 234U(γ, f) • Motivation • Experimental setup • Data analysis • Results • Summary and Outlook

  2. 18.11.2009 | Institut für Kernphysik | Alf Göök | 2 Photo-fission at the S-DALINAC Search for parity non-conservation (PNC) in photo-fission Role of weak interaction? Weak- vs. strong interaction (Ratio of coupling constants)  PNC ~ 10-7 Neutron induced fission experiments  PNC ~ 10-4 Perturbation theory: high level density  dynamical enhancement Other enhancement effects? Alternate probe  photons Brems -Target Fission - Target Longitudinal polarized e- Circular polarized photons Forward-backward asymmetry

  3. Brems -Target Fission - Target Longitudinal polarized e- Circular polarized photons Forward-backward asymmetry How to measure PNC • PNC forward-backward asymmetry • Fission fragments properties • Angular distribution • Small effect  High integrated luminosity • Double ionization chamber • Fragment properties (TKE, mass) from 2E-measurement • Emission angle from electron drift time • Radiation hard 18.11.2009 | Institut für Kernphysik | Alf Göök | 3

  4. Cu- Radiator Collimator e- Experimental Setup: Bremsstrahlung • Continuous spectra: Nγ(E) • Endpoint Energy: E0 = Ee- • Average excitation energy:

  5. 3 cm ~20 cm Experimental Setup: Twin Frisch-grid ionization chamber S-DALINAC Injector E0<10 MeV I~50 μA 18.11.2009 | Institut für Kernphysik | Alf Göök | 5

  6. Emission Angle Determination:Drift Time Method • Electron drift time  Emission angle:  Corrections for: • Grid inefficiency • Energy loss in target corrections 18.11.2009 | Institut für Kernphysik | Alf Göök | 6

  7. Resolution in cosθ • Collinear fragments: • Target thickness • Angular straggling • Range uncertainty • Compared to traditional method • Drift time method competitive 18.11.2009 | Institut für Kernphysik | Alf Göök | 7

  8. Determining fragment energy & mass • 2E-technique • Prompt neutron evaporation • Pulse height defect 18.11.2009 | Institut für Kernphysik | Alf Göök | 8

  9. Results: 238U(γ, f) • Agreement with literature: • S. Pommé et al. Nucl. Phys. A572 (1994) 237 • Experimental method and analysis under control 18.11.2009 | Institut für Kernphysik | Alf Göök | 9

  10. Results: 234U(γ, f) • Comparison with 233U(d, pf) • Y. Patin et al. Nucl. Phys. A382 (1982) 31 • σm discrepancy • Mass resolution effect? 18.11.2009 | Institut für Kernphysik | Alf Göök | 10

  11. 238U(γ,f): <E*>= 7.1 MeV Identification of Fission Modes • Fission modes  Parameterization of Y(m,TKE) • Agreement with literature • New results for 234U(γ,f) at low <E*> 238U(γ,f) 234U(γ,f) 18.11.2009 | Institut für Kernphysik | Alf Göök | 11

  12. Summary and Outlook • Functionality of the double ionization chamber • Drift time method for emission angle determination • Determination of Fragment properties • Solid target • Target thickness ↔ resolution • Active target • UF6: gas at 57°C • Target = Counting gas • Energy loss problem eliminated • Next steps • Properties of counting gas: test chamber • Pixelated anode for PNC-experiment 18.11.2009 | Institut für Kernphysik | Alf Göök | 12

  13. Collaboration A. Göök, R. Barday, M. Chernykh, C. Eckardt, R. Eichhorn, J.Enders, P. von Neumann-Cosel, Y. Poltoratska, A. Richter, M. Wagner Institut für Kernphysik, Technische Universität Darmstadt, Germany F.-J. Hambsch, S. Oberstedt EC-JRC, Institute for Reference Materials and Measurements (IRMM), 2440 Geel, Belgium A. Oberstedt Akademin för naturvetenskap och teknik, Örebro universitet, Sweden 18.11.2009 | Institut für Kernphysik | Alf Göök | 13

  14. Mass resolution • 2E-technique • Intrinsic: target thickness  simulation • 238U: ∆m = 6 amu (FWHM) • 234U: ∆m = 8 amu(FWHM) • Inherent: prompt neutron evaporation • Mass dependent: ~3 amu(FWHM) • Total: • 238U: ∆m ~ 7 amu(FWHM) • 234U: ∆m ~ 9 amu(FWHM) 18.11.2009 | Institut für Kernphysik | Alf Göök | 14

  15. Targets 238 (234)UF4: 130 (190) μg/cm² Au: 50 μg/cm² Polyimide: 35 μg/cm² 18.11.2009 | Institut für Kernphysik | Alf Göök | 15

  16. MM-RNR

  17. PNC-enhancement • Forward-backward asymmetry • “Dynamical” enhancement • Perturbation theory • High resonance density • “Structural” enhancement • Structural effects  • Large in low energy (sub-barrier) fission

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