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The n_TOF-Ph2 neutron fluence from the PTB fission chamber C. Guerrero (CERN)

The n_TOF-Ph2 neutron fluence from the PTB fission chamber C. Guerrero (CERN). The neutron fluence from the PTB fission chamber. A total of 201.4(5) mg 235 U divided in 5 deposits on Platinum backings.

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The n_TOF-Ph2 neutron fluence from the PTB fission chamber C. Guerrero (CERN)

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  1. The n_TOF-Ph2 neutron fluence from the PTB fission chamber C. Guerrero (CERN)

  2. The neutron fluence from the PTB fission chamber A total of 201.4(5) mg 235U divided in 5 deposits on Platinum backings. The PTB chamber is calibrated, meaning that the mass of 235U and the detection efficiency are well known from previous “international intercomparisons”. Aluminumchamber (ONLY IN 2009) 47 cm of air Stainless steal (0.55 mm)‏ MGAS (ONLY IN 2009) Aluminum window (1 mm)‏ Tantalum window (0.15 mm)‏ SiMon Platinum backings (0.125 mm, Ø 86 mm)‏ 235U deposits (1.138e-5 at/b, Ø 76 mm)‏ Tantalum electrodes (0.125 mm, Ø 86 mm)‏ • DAQ: 2 flash-ADC channels (signal with 90 ns rise-time) • Small dynamic range for good a/FF separation • Large dynamic range to minimize saturation of signals from Fission Fragments. • The results from both channels are in perfect agreement. PTB

  3. The neutron fluence from the PTB fission chamber Set-Up 2009 (water as moderator) Set-Up 2010 (10B-water as moderator) Experimental check of the alignment Electrical isolation from the grillage Aluminum container used when not WSTA

  4. Determination of the neutron fluence maximum 2009 Bias @ 0.45 of maximum 7-9% difference at thermal Aluminium dips Comparison of the expected yieldcalculated from the thin sample approximation and from detailed simulations of the assembly with MCNP (D. Villamarin@CIEMAT) Pulse Height distribution of the PTB fission chamber. The red blue lines correspond to the amplitude calculated from the pulse area. Calculation of the fluence from the Counting Rate (CR), efficiency (edet)and expected yield (natsn,f). Tantalum resonances

  5. The neutron fluence with normal and borated water (100 bpd) Artifacts related to the g-flash and the lack of electrical isolation in 2009 x18 x13 x1.6 Dstat=3% x1.2 Dstat=1% Figure 3. The n_TOF-Ph2 neutron flux (100 bins/decade) resulting from the analysis of the TB fission chamber.

  6. The neutron fluence: Borated vs. Water moderator Water 10B-water

  7. The neutron fluence: Borated vs. Water moderator Water 10B-water Dstat~3% ? ? ? AVG RATIOS 3-300 keV = 0.99 300-600 keV = 1.01 600-1000 keV=1.04

  8. PTB vs. Simulations: FULL ENERGY RANGE

  9. PTB vs. Simulations: LOW ENERGY RANGE ~18% difference at thermal! Difference in shape?

  10. PTB vs. Simulations: HIGH ENERGY RANGE

  11. PTB vs. Simulations: 3 – 100 keV 5% diff. in magnitude Normalization point Different depths?

  12. PTB vs. Simulations: 100 – 500 keV

  13. PTB vs. Simulations: 100 – 500 keV(MCNP scaled up 5%)

  14. PTB vs. Simulations: 500 – 1000 keV(MCNP scaled up 5%)

  15. Conclusions • The experimental data from the PTB have been fully analyzed, including all the statistics available. • The reduction in the neutron flux with 10B-water with respect to water is: • x18 at thermal • x1-1.6 in the eV • x1 above a few hundreds eV • The two fluxes agree within 1% in the region between ~3 keV and 600 keV • Above 600 keV, the flux with 10B-water is observed to be 4% smaller than that with water(why?) • Comparison with simulations (normalized to PTB @ 7-10 keV) • Thermal peak: simulation ~20% higher than data • Thermal tail (0.2-0.5 eV): slightly different shape • 3-20 keV: good agreement • 20-1000 keV: good agreement in shape, but simulation ~5% lower than data. • 600-1000 keV: data resolution very limited, but there seems to be some disagreement • (5-12%) between the dips in the experiment and simulations. • Questions (maybe answered from the analysis of MGAS and SiMon) • Are the PTB data in the high energy region? How does it compare to MGAS? • What could explain large (20%) difference at thermal • Could the thickness of Al explain the 5% factor above 20 keV? What about the aperture angle in MCNP?

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