Simulation of quasi-monoenergetic Li(p,n) neutron source up to 50 MeV proton energy

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1 Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Nuclear Physics Institute Řež Simulation of quasi-monoenergetic Li(p,n) neutron source up to 50 MeV proton energy S.P. Simakov 1, P. Bém 2, V. Burjan 2, U. Fischer 1, M. Götz 2, M. Honusek 2, V. Kroha 2, J. Novák 2, E. Šimečková 2 1) Association Euratom-FZK, Institut für Reaktorsicherheit, Forschungszentrum Karlsruhe GmbH, Germany 2) Association Euratom-IPP/NPI.CR, Nuclear Physics Institute, Řež, Czech Republic Workshop on Activation Data EAF 2007, Prague, 2-4 October 2006

2 Computational Tools and Data for Li neutron Simulations up to 50 MeV Neutron production and transport calculation: - Charge particle transport code MCNPX (version 2.5) Cross sections files and models for (p,xn) reactions on light nuclei: Lithium-7 as a neutron source: E th = 1.88 MeV for 7 Li(p,n 0 ) 7 Be(g.s.) = 2.38 MeV for 7 Li(p,n 1 ) 7 Be(1st excited state = 0.43 MeV) = 3.70 MeV for 3-body breakup 7 Li(p,n 3 He) 4 He = 7.70 MeV for 7 Li(p,n 2 ) 7 Be(2nd excited state = 4.55 MeV) LA-150h proton cross sections library (S.G. Mashnik et al., Report LA-UR_ , Los Alamos 2000) Carbon as a proton beam stopper and parasitic neutron source: 12 C abundance 98.9% 13 C abundance 1.1% 12 C(p,n), E th = 19.6 MeV 13 C(p,n), E th = 3.2 MeV LA-150h library MCNPX in-build model 2-4 October 2006, Prague Workshop on Activation Data EAF

3 Double Differential Cross Sections (DDX) for 7 Li(p,xn) reaction at E p = MeV Known Measurements: 1. M. McNaughton, NIM 130(1975)555 E p = 15, 20,30 MeV, Θ = 0 deg (DDX not available in EXFOR) 2. J.W. Wachter, NIM 113(1973)185 Ep = 40.6, 63.8 MeV, Θ = 0 deg (data looks strange) 3. J. Jungerman, NIM 94(1971)421 E p = 39.3 MeV, Θ = 0 deg 4. M. Österlund, NIM B241(2005)419 E p = 21.8, 46.5 MeV, Θ = 0 deg (DDX not available in EXFOR yet) dσ/dedω (θ = 0 o ), mb/sr/mev Li(p,xn), E p = 39.3 MeV, Θ n = 0 o Wachter'73 MCNPX/LA-150h Jungerman' Neutron Energy, MeV The measured DDX for Li(p,xn) are scarce, only at 0 deg. ; LA-150 evaluation reasonable reproduces available (in EXFOR) experimental data; The high energy peak shares 40% of the whole neutron spectra at 0 deg! 2-4 October 2006, Prague Workshop on Activation Data EAF

4 Monoenergetic Neutron Sources employing Li(p,n) reaction Laboratory Neutron Energy, MeV Li thickness, mm Proton current, μa Reference With proton beam deflection magnet Louvain Univ., NIM A421 (1999) 284 Belgium TIARA, NIM A428 (1998) 454 Japan Uppsala Univ. Sweden NIM B241 (2005) 419 Without deflection magnet, 2 cm thick C proton beam stopper behind Li target CYRIC, ? NIM A389 (1997) 463 Japan NPI/Řež, Czech < P. Bĕm, this workshop For activation measurements the thin Li plate and thick C stopper looks more preferable than deflecting magnet, since the activation foil could be located closer to the neutron source, but the contribution of the C(p,xn) neutrons should be assessed. 2-4 October 2006, Prague Workshop on Activation Data EAF

5 Example of the Li Neutron Source with deflecting magnet at TSL, Uppsala /M. Österlund et al., NIM B241(2005)419/ Look as drawbacks for neutron activation experiments: - Activation foil being located close to the Li target will be irradiated by the protons (or use a ring shape with a hole for p-beam?), otherwise has to be positioned at 1 m from the Li target, where n-flux is much lower! - Deflecting magnet causes additional expenses 2-4 October 2006, Prague Workshop on Activation Data EAF

6 Li/C Neutron Source at CYRIC, Tohoku University /Y. Uwamino et al., NIM A389(1997)463/ Target set-up: - 2 mm thick 7Li - 12 mm thick carbon stopper Neutron Spectra measurement: - TOF technique - NE 213 scintillator at 12 m - Proton Energies = MeV 2-4 October 2006, Prague Workshop on Activation Data EAF

7 Neutron Flux (θ = 0 o ), n/mev/sr/μc Validation of MCNPX calculations against CYRIC data Energy Differential Neutron Yield 7 Li/C + protons (E p = 40 MeV), Θ n = 0 o Li/C+p(40MeV) nat C+p(39.2 MeV) 12 C(p,xn) 7 Li+p(40MeV) thick C + p(39.2mev) 13 C(p,xn) Neutron Energy, MeV MCNPX/LA-150h reasonable reproduces CYRIC neutron source spectrum and thick carbon neutron yield 2-4 October 2006, Prague Workshop on Activation Data EAF

8 Li/C neutron source set-up at NPI/Řež /P. Bem et al., this Workshop/ 7 cm 18 cm CH 2 Radiator 45 o 42 cm Foil to be activated DΔE2 Following details of the set-up were simulated in MCNPX: Li-plate, C-stopper, Cooling media, Al-flange, Activation foil, CH2 radiator, E-E proton detector DΔE1 2-4 October 2006, Prague Workshop on Activation Data EAF

9 Neutron Flux, n/mev/sr/μc Energy Neutron Fluxes in Activation Foil and CH 2 Radiator as predicted by MCNPX/LA-150h Energy differential Fluxes 7 Li/C Target, E p = 30 MeV 10 7 Foil dia. 1.4 cm at 7 cm 7 Li+C(p,xn) C(p,xn) CH 2 radiator dia 1.6 cm at 18 cm Neutron Energy, MeV - the high energy peak of Li/C source at NPI/Rez facility amounts 40%, ΔE = 1.7 MeV - neutrons from Carbon stopper contributes only 3% and mainly below 5 MeV NPI/Řež: Flux for 10 μa proton current Position Flux, n/cm 2 /s Activation Foil at 7 cm, Li+C Only C stopper CH 2 Radiator at 18 cm Total (3%) >25MeV (36%) (41%) Comparison with 14 MeV sources: 1. TU/Dresden: n/cm 2 /s /K. Seidel et al. this Workshop/ 2. SNEG-13/Sergiev Posad: n/cm 2 /s /V.D. Kovalchuk et al. IAE-5589/8 (1992)/ 2-4 October 2006, Prague Workshop on Activation Data EAF

10 Proton Flux, p/mev/sr/μc Proton Recoil Spectrum from CH 2 Radiator 7 Li/C + p (30 MeV) H(n,p)n, Θ p = 45 o Calculations without with energy resolution protons or noise? Experiment Proton Energy, MeV Details of calculations: 1. no counts in the MCNPX proton tally (?) 2. for transformation neutron => proton spectra we used: E p = E n * cos 2 (Θ p ) dσ(e p )/dω = σ np (E n )*cos(θ p ) - good prediction of the main proton group ; - the reason of the underestimation below 10 MeV could be the Si detector noises or Li target neutrons (?) 2-4 October 2006, Prague Workshop on Activation Data EAF

11 Conclusions The MCNPX code and Los Alamos evaluation for the 7 Li(p,n) and 12 C(p,n) reactions cross sections was shown reasonably reproduce available spectral data for neutron source consisting of the thin lithium foil and thick carbon beam stopper and driven by the proton beam Such a source at, e.g., 30 MeV incident proton energy and 10 μa current will produce neutrons/cm 2 /s in the small foil located at the distance of a few cm: - 40% of the neutrons being a monoenergetic group with energy 28 MeV and width 1.7 MeV - the neutrons born in the Carbon beam stopper contribute around 3% of Li(p,n) ones and have the energy distribution with a maximum below 5MeV The main energy group in the proton spectra of the recoil telescope has been successfully reproduced by employing n-p scattering classical formula, whereas the low energy part needs further analyses 2-4 October 2006, Prague Workshop on Activation Data EAF

Simulation of the 7Li(p,n) quasi-monoenergetic neutron source at NPI/ Řež

Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Nuclear Physics Institute Řež, near Prague Simulation of the 7Li(p,n) quasi-monoenergetic neutron source at NPI/ Řež S.P. Simakov, U. Fischer Institute