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”

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 valuescomparison 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 LAHETLAHET - spallation reactions, transport of particles and high energy neutrons (E > 20 MeV) MCNPMCNP - transport of neutrons with E = MeV až 20 MeV MCNPXMCNPX - 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)

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

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

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

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

high energy proton reactions on Cu and Au (production of 48 V, 52 Mn, 58 Co, 44m Sc, 47 Sc, 191 Pt, 74 As) 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 Determination of beam geometry 3 cm beam target foils

Influence of beam geometry target beam foils

27 Al(n,α) 24 Na 27 Al(p,x) 24 Na (e.g. (p,3pn)) 197 Au(n,2n) 196 Au 197 Au(p,x) 196 Au (e.g. (p,np), (p,d)) 197 Au(n,4n) 194 Au 197 Au(p,x) 194 Au (e.g. (p,p3n), (p,d2n), (p,tn)) Influence of proton interactions in foils Foil distances:5 cm top9,3 cm top

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

Comparison between experimental results and simulations

LAHET+ MCNP versus MCNPX

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