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The Nuclear Fission Process with STEFF and nTOF

A.G. Smith, J. Dare, R.Frost, A. Pollitt, E. Murray The University of Manchester W. Urban, T. Soldner ILL Grenoble I. Tsekhanovich, J. Marrantz CENBG Bordeaux. The Nuclear Fission Process with STEFF and nTOF. nTOF Workshop Manchester 2013. STEFF Design Objectives.

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The Nuclear Fission Process with STEFF and nTOF

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  1. A.G. Smith, J. Dare, R.Frost, A. Pollitt, E. Murray The University of Manchester W. Urban, T. Soldner ILL Grenoble I. Tsekhanovich, J. Marrantz CENBG Bordeaux The Nuclear Fission Process with STEFF and nTOF nTOF Workshop Manchester 2013

  2. STEFF Design Objectives Spectrometer for fission fragments. Direct measurement of Energy, Mass, Atomic number and direction. Cope with high fission rates, segmentation. Coupled to gamma and neutron detector arrays.

  3. Design Solid angle 60 mstr 2-Energy, 2-velocity Spectrometer.

  4. Fragment mass measurement Time-of-flight -> velocity Bragg Ionisation chamber->energy Design Objective mass resolution 2.2% 1% 1%

  5. STEFF @ ILL • Installed at PF1b, Institut Laue-Langevin, Grenoble for 2x 25 days • 235U target 100µgcm-2 on a Nickel backing • Thermal neutron flux 1.8x1010 neutrons cm-2s-1 • Measured mass resolution 4 amu

  6. Characteristics of bragg pulse

  7. Digital Bragg Pulse Processing • Digital Pulse Processing: • High-pass filter • Ballistic Def. Correction • Integration • Low-pass filter: noise reduction • Currently Noise ~0.2 percent

  8. Nuclear charge distribution for light mass group IC measurements, when velocity if fixed: Where before any corrections: Sensitivity to Z (FWHM) of about 2 units. b = 2/3

  9. Gamma-ray Energy and Multiplicity Response to NEA High Priority Request of more accurate knowledge of heating caused by gamma emission in the next generation of nuclear reactors Coincidence with emission of prompt gamma rays as a function of the fragment mass and energy 12 NaI detectors around the uranium target provide a 6.8% photo peak detection efficiency

  10. Gamma decay of fission fragment As fragment cools, statistical and yrast emissions remove angular momentum and lower excitation energy. Overall multiplicity yrast & statistical contributions

  11. Monte Carlo simulation (decay) Probability of spin state is generated based statistical model: • Number of yrast gamma rays linked to mean spin ~ B. • Geometric distributions give statistical gamma rays for each fragment. • Interaction with array: e, scattering

  12. 235U Gamma-ray multiplicities Measured fold distribution Use χ2 minimisation to deduce multiplicity distribution Mean multiplicity≈ 7 ± 1 Jrms = 7.1 Statistical = 1.5

  13. Gamma Energy Spectra Deconvolved NaI spectra using GEANT4 NaI response functions Can we combine with multiplicities to obtain Total Gamma Energy?

  14. Future Plans • Combine with Ge detectors, e.g. loan pool. • Further thermal neutron-induced fission (ILL) Pu-239 • Fast neutron induced fission: nTOF or NFS • Fission mechanism: energy and spin and angular distributions

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