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Experimental Study of Neutron Production Distribution in Proton-Irradiated Thick Lead Target

This experimental study investigates the spatial and energetic distributions of the neutron field, especially high-energy neutrons, in spallation reactions of high-energy protons on a thick lead target. The study compares experimental and simulated values, considering factors such as setup simplifications, beam uncertainties, and neutron and proton field mixing. The results show good agreement between experiment and simulation, with slight differences at the end of the target. Further analysis is needed to determine the sources of these differences and account for systematic errors.

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Experimental Study of Neutron Production Distribution in Proton-Irradiated Thick Lead Target

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  1. Experimental studies of spatial distribution of neutron production around thick lead target irradiated by 0.9 GeV protons Antonín Krása & Vladimír Wagner for collaboration „Energy plus transmutation”

  2. The sense and the aim • experimental study of the spatial and energetic distributions of the neutron field (mainly high energy neutrons) in the spallation reactions of high energy protons on thick lead target • comparison between experimental and simulated values it’s necessary at first to determine the influence of : • simplifications in set-up, which enter to simulations • uncertainties in beam trajectory, form and intensity determination • neutron and proton field mixing • LAHET - spallation reactions, transport of particles and high energy neutrons (E > 20 MeV) • MCNP - transport of neutrons with E = 10-11 MeV až 20 MeV • MCNPX - links advantages of LAHET and MCNP • we made systematic measurements of neutron field in different set-ups and beam energies (in collaboration NPI Řež and JINR Dubna)

  3. Proton beam 885 MeV Experimental set-up and conditions Moderator Granulated polyethylene with boron Size: 100100 100 cm Thermal isolation Expanded polystyrene Size: 17.6  17.1  52.6 cm Pb target Size: d = 9.8 cm, l = 50 cm

  4. Neutrons measured byactivation analysis • Activation detector - set of thin multi-layer foils • (Foil size: 22 cm Thickness: around 50 μm) • Au • 197Au (n,2n) 196Au Ethres = 8,5 MeV • 197Au (n,4n) 194Au Ethres = 24,5 MeV • 197Au (n,g) 198Au • Al • 27Al (n,α) 24Na Ethres = 5,5 MeV • Cu • high energy proton and neutron reactions • 63Cu (n, γ) 64Cu • Advantage: simple and small detector is possible to locate to any place of set-up • Problems: neutron energy spectrum determination

  5. foils 17,6 cm target polystyrene 9,6 cm 17,1 cm Location of activation detectors

  6. Production of 198Au, 196Au, 194Au, 24Na in foils along the target

  7. target 3 cm foils beam Determination of beam geometry • high energy proton reactions on Cu and Au (production of 48V, 52Mn, 58Co, 44mSc, 47Sc, 191Pt, 74As) • simple assumptions: • central foil is fully covered • homogenous proton distribution • beam has circular cross section • comparison different foils activity  determination of beam centre and beam size: beam shifted 0.8 cm down and 0.8 cm right from the target centre, beam radius 3.5 cm

  8. foils target beam Influence of beam geometry

  9. Influence of proton interactions in foils 27Al(n,α)24Na 27Al(p,x)24Na (e.g. (p,3pn)) 197Au(n,2n)196Au 197Au(p,x)196Au (e.g. (p,np), (p,d)) 197Au(n,4n)194Au 197Au(p,x)194Au (e.g. (p,p3n), (p,d2n), (p,tn)) Foil distances: 5 cm top 9,3 cm top

  10. Influence of polystyrene and polyethylene on threshold reactions • full simulation: take account all components • simple simulation: take account only target

  11. Comparison between experimental results and simulations

  12. LAHET+ MCNP versus MCNPX

  13. Conclusions • study of neutron production in relativistic proton reactions on thick lead target • course and intensity of neutron field measured by activation analysis • important influence of beam geometry • important influence of protons on yields (~ 10 %) • inconsiderable influence of polyethylene and polystyrene on high energy neutron production - we can include only target! • good agreement between experiment and simulation in high energy production (greater difference only at the end of the target) • the difference between values from LAHET+MCNP and MCNPX is not significant in our case • it will be necessary to find out influence of all systematic errors, detailed analysis of sources of differences between experiment and simulations

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