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238 U Neutron Capture with the TAC

238 U Neutron Capture with the TAC. Toby Wright University Of Manchester. n_TOF Analysis Meeting CERN October, 2011. Introduction. High accuracy (n, γ ) 238 U cross-section measurement Joint future analysis with the same measurement using C6D6 detectors at nTOF and GEEL

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238 U Neutron Capture with the TAC

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  1. 238U Neutron Capture with the TAC Toby Wright University Of Manchester n_TOF Analysis Meeting CERN October, 2011

  2. Introduction • High accuracy (n,γ) 238U cross-section measurement • Joint future analysis with the same measurement using C6D6 detectors at nTOF and GEEL • Aim of reducing the uncertainty in the cross-section from ~5% to ~2% • Currently being measured at nTOF

  3. The Sample • 6.125 ± 0.002 Grams • Isotopic analysis done in 1984 • <1 ppm 233U • <1ppm 234U • ~11ppm 235U • <1ppm 236U • Wide sample, with perfect alignment it covers ~97% of the beam (53.90 x 30.30 mm) • ‘Bonbon’ casing with ~60 microns of Al, ~75 microns Kapton

  4. TAC Calibrations - Time • 40 detectors going into 5 different streams • Each stream contains 2 digitizers, each with its own clock • Clocks have an accuracy to 2ppm therefore each detector must be calibrated to one reference • Done using the two gamma rays of Y88 Delta t (ns) TOF (ns)

  5. TAC Calibrations - Time

  6. TAC Calibrations - Energy • Three calibration sources used: • 137Cs (661.7 keV) • 88Y ( 0.898 and 1.836 MeV) • AmBe (4.44 MeV) • Gaussians are fitted after the background has been subtracted • Routines for the 137Cs and 88Y have been rewritten, but are not completely finished

  7. TAC Calibrations - Energy Counts Channel Number

  8. TAC Calibrations - Energy Counts Channel Number

  9. TAC Calibrations - Energy

  10. Detector Resolution • Resolution = 2.35*FWHM/Energy • In this case, we have used channel number instead of Energy • Individual detectors resolution determined at the peak of 137Cs (661.7 keV) 2004

  11. Counting Rate

  12. Counting Rate (20-300 eV)

  13. Proton Beam Intensity

  14. 238U Initial Results • 26 days more running time (20 days completed) • Everything seems to be going well!! • As of this morning, we have : • 268e15protons for 238U (normal nominal and parasitic) (~2e5 events) • 21299 ‘events’for beam off • 52.8e15protons for sample out (~4e4 events) • 14.8e15protons at low intensity (~1.4e4 events) • 12.45e16protons at high intensity (~7e3 events)

  15. TAC Deposited Energy

  16. TAC Deposited Energy

  17. TAC Deposited Energy

  18. TAC Deposited Energy

  19. TAC Neutron Energy

  20. TAC Neutron Energy

  21. First Resonances Second Resonance Third Resonance First Resonance

  22. Statistics • Aim to have at least 1000 counts per resonance with reasonable binning • We already have this for the larger resonances • We are well on track for reaching this goal Plot for runs 12983-13008 (4000 bins between 1 and 2 keV) Approximately 7% of total statistics

  23. Effect of the gamma flash on the TAC

  24. Effect of the gamma flash on the TAC

  25. Conclusions • Measurement is going smoothly • Preliminary analysis shows promising results • The TAC should be able to be used to measure at higher energies (100keV?) than in the past

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