Performed experiments Nuclotron – set up ENERGY PLUS TRANSMUTATION The idea of this work consists in the experimental study of the spatial and the energetic distributions of the neutron field (we concentrated our attention mainly on high-energy neutrons) produced in the spallation reactions of high-energy protons on a thick lead target Spallation reactions can be used to produce high neutron fluxes by bombarding a thick, heavy target with a high-intensity relativistic proton beam The main aim is a so called benchmark test – comparison between experimental data and values obtained from the corresponding simulation codes Motivation and aim Synchrophasotron (lead target in moderator) November 1999 – 885 MeV June 2000 – 1.3 GeV & 2.5 GeV Nuclotron (blanket from natural uranium ~ 206.4 kg) December 2001 – 1.5 GeV June 2003 – 2 GeV November 2003 – 1 GeV June 2004 – 0.7 GeV design: 2.5 GeV experiment closed Performed experiments Nuclotron – set up ENERGY PLUS TRANSMUTATION Neutrons measured by activation analysis method activation detector - set of thin multi-layer foils Au, Al, Co, Bi foil size: 22 cm2 thickness: around 50 μm the foils were measured by the HPGe g-spectrometers ORTEC readout: 8192 channel histograms processed by code DEIMOS the acquired areas were corrected for coincidences and other standard decay effects the yield is the number of produced nuclei of certain isotope in activation detector during the whole period of irradiation divided by mass of the activation detector and total proton flux advantage: detectors can be simple and can have arbitrary format   it is possible to place them at any position of the set-up problems: neutron energy spectrum determination Fredholm equation Positions of the foils AT THE NUCLOTRON AT THE SYNCHROPHASOTRON 9,6 cm foils target polystyrene 17,6 cm 17,1 cm

0.9 GeV experiment at the Synchrophasotron 1.5 GeV experiment at the Nuclotron irradiation time ~ 2 h total proton flux (3.6 ± 0.3) × 1013 electrical current ~ 0.8 nA irradiation time ~ 12 h total proton flux (1.14 ± 0.05) × 1013 electrical current ~ 40 pA Determination of beam intensity determined by activation of beam monitors (composed of 1010 cm2 Cu foils with a thickness of 25 μm and Al foils with a thickness of 100 μm) placed 30 cm ahead of the target the measured yields of the reactions 27Al(p,3pn)24Na, 27Al(p,X)7Be and natCu(p,X)24Na the total proton flux determined by the activation was (3.6  0.3)1013 this value seems to be more reliable than the value 4.31013 determined by the current integrator, which suffered from a significant systematic error 10 cm proton beam 5 cm yields in units of [10-6 g-1 proton-1] for radioactive isotopes produced in Co-, Bi- and Au-sensor foils longitudinal distributions of yields are given on the left side and radial distributions on the right side Longitudinal and radial distributions of yields ratios of yields inside the Pb-target (at a radial distance of R = 3 cm) in the front and at the end of the U/Pb-assembly as a function of the reaction threshold energy ratios between production rates measured in the first gap at radial distances of 13.5 cm and 3.0 cm from the target axis as a function of the reaction threshold energy Determination of beam position with the use of high-energy proton reactions on Cu and Au (production of 48V, 52Mn, 58Co, 44mSc, 47Sc, 191Pt, 74As) a group of five Cu and Au foils placed closely in front of the target comparison of the yields in different foils  the beam was shifted (0.8  0.3) cm down and (0.8  0.3) cm right from the target axis & the beam radius was (3.5  0.3) cm 3 cm beam target foils Yields in foils along the target

How we Made Simulations AT THE SYNCHROPHASOTRON based on the mathematical Monte Carlo method use various physical models of spallation reactions and cross sections libraries of neutron induced reactions with nuclei LAHET {Los Alamos High Energy Transport Code} models spallation reactions, transport of particles and high energy neutrons (E > 20 MeV), generates cross sections for individual processes MCNP {Monte Carlo N-Particle Transport Code} models the transport of neutrons 10-11 MeV < E < 20 MeV, uses libraries of evaluation data as a source of the cross sections MCNPX links the advantages of both LAHET and of MCNP, exploits libraries of evaluated cross sections up to 150 MeV Simulation codes How we Made Simulations simulations were performed in 2 steps: calculation of neutron (proton) energy spectra  (E), calculation of the yields of produced nuclei by convolution of these spectra with the corresponding cross-sections  (E) we used LAHET 2.7. (Bertini INC model with preequilibrum phase) and MCNP4B Simulation of the neutron field at different places in the target AT THE SYNCHROPHASOTRON AT THE NUCLOTRON Comparison of experimental data with simulations AT THE SYNCHROPHASOTRON AT THE NUCLOTRON the simulations describe the shape of the spatial distribution quite good until the distance of 40 cm from the beginning of the target the maximum difference in absolute values is about 25 % beyond 40 cm, the simulation underestimates the experiment and the ratio of experimental values to the simulated ones reaches two the simulation underestimates the experiment also in the radial distance CONCLUSIONS the shape and intensity of neutron field produced in the reaction of relativistic protons in a thick lead target was measured by the activation analysis method energetic spectrum becomes harder at the end of the target the simulations are in good qualitative agreement with experimental data for high-energy neutron production the simulations underestimate production of isotopes in the blanket and at the end of the target it can indicate a difference between the development of the secondary-particle shower and the fission in uranium blanket in the real experiment and in the model used in the simulations a further detailed analysis of the sources of the differences between experiment and simulation are in progress, we plan also to carry out a comparison with experiments with different proton energies and set-ups next experiment in the JINR Dubna is scheduled for winter 2004 (2.5 GeV proton beam)