1. 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 ~ 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

2. 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

3. 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 (2.5 GeV proton beam)