(Once again) The n_TOF-Ph2 neutron fluence (2010)

1. (Once again) The n_TOF-Ph2 neutron fluence (2010) C. Guerrero (CERN), M. Barbagallo (INFN/Bari), A. Tsinganis (CERN), N. Colona (INFN/Bari), E Mendoza (CIEMAT) et al.

2. Situation in the last meeting (April 2011) and plan • SiMon and MGAS-B10 seem to be in good agreements up to at least 10 keV. • High energy limit for SiMon and MGAS-B10 not clear. • Analysis conditions (amp. cuts) to be studied in detail. • (PTB+MGAS-U5) in 6-9% disagreement wrt (SiMon+MGAS-B10) in ~7-100 keV • FLUKA+MCNP simulation in overall agreement with data, except in the Al dips and above ~600 keV (~5% difference) • […] Review the full analysis -Transmission through material along the beam. - Analysis conditions for the analysis of each detector - Detection efficiency dependence with En of each detector - Identify high energy limit of each detector - Corrections from transmission through the material along the beam - Correction of t0 for TOF/En conversion Complete FLUKA+MCNP simulations

3. Expected reaction yield (transmission ≠ 1) Detailed MCNP simulations by Emilio Mendoza (CIEMAT) [n_TOF-INT-2011-001] 182.2 m 183.25 m 182.9 m 60 mm Ta windows (0.15mm) Ta electrodes (0.125mm) Air (7 cm) Air (20 cm) MGAS (30 cm) [ONLY IN 2009] Ar (1 atm) 45 cm Ar (1 atm) n B U Li Pt electrodes (0.125mm) 235U samples (444 mg/cm2 (total 201.4 mg in 76 mm diameter deposits) Al window (500mm) Kapton windows (50 mm each ) Li = Mylar (1.5mm, 1.4 g/cm3) + C (0.045 mm, 2.15 g/cm3) + 6Li (6 mm, 0.5 g/cm3) + C (0.045 mm, 2.15 g/cm3) B = Kapton (25mm,1.42 g/cm3) + Cu(2mm,8.94 g/cm3) + 10B4C (2mm,2.52g/cm3) + Cu (5mm,8.94 g/cm3) + Kapton (25mm,1.42 g/cm3) + Cu (5mm,8.94 g/cm3) U = Al(20mm,2.7 g/cm3) + 235UF4(0.47mm,6.7 g/cm3) + Cu (5mm,8.94g/cm3 )+ Kapton (50mm , 1.42g/cm3) + Cu(5mm,8.94 g/cm3)

4. Expected reaction yield (transmission ≠ 1)

5. MGAS-10B: Selection cuts and Hi-En limit 1-100 eV 0.1-1 keV 1-10 keV 10-30 keV 30-100 keV 100-300 keV Selection cut: MGASamp > 62.5 + 5.277e-5*En + 3.83e11*En2 300-500 keV

6. MGAS-10B: detection efficiency MGAS sees only those a’s emitted FORWARD Angular distribution has an effect!! F. J. Hambsch, I. Ruskov, Nucl. Sc. and Eng. 163 1 (2009) 1-16 “The 10B(n,0)7Li and 10B(n,1)7Li Alpha-Particle Angular Distributions for En < 1 MeV” Efficiency calculated as ratio of forward to background emission prob. 9%

7. SiMon: Selection cuts and Hi-En limit Amplitude cut depends on the neutron energy 10-100 eV 100-1000 eV 1-10 keV 10-100 keV 100-300 keV 300-500 keV Because of Ang. Distr., efficiency depends also on neutron energy (very large correction above 10-20 keV)

8. Comparison MGAS(10B) & SiMon (6Li) ±3%

9. Summary and strategy ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Thermal All measurements normalized to PTB (235U) ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Below 25 keV 6Li and 10B cross sections: standard (and smooth) cross sections! 235U cross section: non standard + non-smooth URR SiMon & MGAS(10B) in good agreement ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 25 -150 keV 235U cross section: Point-wise without resonant/interference effects SiMon has larger uncertainty due to Ang. Distr. (but it is in better agreement with PTB than MGAS) FLUKA+MCNP simulation available for helping resolve the Al dips (normalized at 10 keV) ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 150-250 keV 235U, 6Li and 10B cross sections: standard. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Above 250 keV Both SiMon and MGAS start having problems (statistics, g-flash, recoils,…) --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

10. The evaluated neutron fluence (2010) [update wrt that of /afs/]

11. The evaluated neutron fluence (2010): thermal to 25 keV

12. The evaluated neutron fluence (2010): 25 to 250 keV

13. The evaluated neutron fluence (2010): 250 keV to 1 MeV

14. The evaluated neutron fluence (2010): 10 keV to 1 MeV

15. Actually, it is not so nice..... Main open questions are: PTB disagrees ~8-25 keV (10%) Simulation disagrees ~1-10 keV (5%) MGAS dips too “small”! (10-20%) TOF/E relation pending!

16. The evaluated n_TOF-Ph2 2010 neutron fluence: version (final-1)