Interaction of secondary neutrons with natU nuclei has been experimentally investigated. Secondary neutron field has been generated as a result of irradiation of the massive lead target with the JINR Phasotron proton beam with energy 660 MeV. A set of two natU samples placed at the surface of the target has been studied. The results on reaction rates of a large number of residual nuclei have been obtained. Keywords: proton, secondary neutrons, reaction rate, nucleus, uranium, lead, gamma spectrum.

The experimental test of possible expansion for the Higgs sector is proposed. The lepton family violation will be studied. To reach this goal we are going to carry out the search for the scalar Goldstone boson in the neutrinoless muon decay mu+ to e+ and alpha. The asymmetry of the muon decay near the high energy edge of Michel spectrum is to be measured. To examine previous TRIUMF data the experiment FAMILON is prepared at the surface muon beam of JINR (Dubna) accelerator. The setup consist of the precision magnetic spectrometer and the device for muSR - analysis.

An intensive beam of 660 MeV protons from the Dubna Phasotron was directed towards a thick, lead target (not surrounded by shielding or neutron reflector) for 10 minutes. Detectors and iodine samples were placed around the target. The neutron field and the transmutation of 129I were studied by the Activation Analysis Method.

The spallation target model of an accelerator driven system (ADS), consisting of six 5 cm thick and 16 cm in diameter Pb segments, was constructed. Three sets of 17 Bi samples (1/2 inch in diameter and 1 mm thick) were placed in 3 Pb disc-shaped holders inside the target at 5, 10 and 15 cm from its front. After irradiation with 660 MeV proton beam gamma-spectra of radioisotopes produced in Bi were collected several times for each sample with the use of HPGe detectors in order to identify the radioisotopes and to determine their absolute activities. Their spatial distributions were then compared with respective values obtained in the calculations made with the use of FLUKA and/or MCNPX code. A fair agreement with the experiment has been observed.

Two NaI (85% 129-I and 15% 127-I) targets were exposed to a beam of 660-MeV protons. Cross sections for formation of 76 residual nuclei were obtained by the induced activity method. The results are compared with other experimental data on 127-I and theoretical calculations by eleven models contained in the codes LAHET3 (using the Bertini+Dresner, ISABEL+Dresner, INCL+Dresner, and INCL+ABLA options), CASCADE, CEM95, CEM2K, LAQGSM+GEM2, CEM2k+GEM2, LAQGSM+GEMINI, and CEM2k+GEMINI. Most of the models describe spallation products with masses close to the target reasonably well while the reliability of the codes differs greatly in the deep spallation and fission/fragmentation regions. The difficulties in describing products with A=40-80 by all of the codes tested here except for CEM2k+GEMINI and LAQGSM+GEMINI is related to the neglect of fission (and fragmentation) processes for targets as light as 129-I.

Experiments on simplified ADS (Accelerator Driven System) setups are done at the Joint Institute for Nuclear Research Dubna. Relativistic protons are directed at heavy targets, and transmutation is studied in the neutron field produced. Experimental values are used to test program codes. In this study, Phasotron Experiment and the MCNPX 2.4.0 simulations of the experimental setup are presented, the influence of the various parts of the setup on calculations is discussed, and the efficiency of parallel computing for simulations of similar experiments is studied. The experiment is quantitatively well described by MCNPX simulations, even when using a simplified description of the experimental setup. A cluster of computers in our laboratory showed that the speed of our calculations almost linearly increases with the sum of processor power. Many of our other experiments are well described by simulations, promising that MCNPX could well describe larger, and more complex ADS systems.

A sodium tank method for measuring the neutron flux produced by the interactions of 660-MeV protons with an extended lead target is described. The problems of optimizing the tank size and minimizing the activity induced in the irradiated solution are considered. In comparison to other methods for measuring neutron fluxes, the sodium tank method is easy to use, and its relative error is within ∼10%.

241Am, 237Np and 129I radioactive targets were irradiated by proton beams with energy 0.66 GeV. The cross- sections of formation of 80, 53 and 86 residual nuclei from 241Am, 237Np and 129I are determined. The experimental results are compared with the theoretical cross-sections calculated by the cascade-evaporation model (CEM).

The burning of radioactive waste is investigated. Targets from 241 Am and 237 Np were irradiated with 0.66-GeV proton beams. The cross sections for the formation of 60 and 80 residual nuclei from 237 Np and 241 Am are determined. The experimental results are compared with the theoretical cross sections calculated by the cascade-evaporation model.

Report presents project for the construction of a low power integral system on the basis of the proton accelerator of energy 660 MeV and sub-critical MOX blanket with uranium-plutonium fuel. Installation includes sub-critical core with a nominal thermal power of 15-20 kW. Multiplication coefficient keff = 0.95 and the accelerator beam power of 0.75-1 kW. The experimental programme for SAD will be focused on solving different aspects of reactor physics, reaction rates measurements and benchmarking. The first conceptual design of the SAD experiment is completed in the form of the ISTC Project Proposal #2267. Realisation of the SAD facility may be expected in about 3-4 years.

The mu SR spectrometer installed on the surface muon beam of the JINR phasotron is described. The possibility of using the surface muon beam with high contamination of positrons in investigations of a solid state by the mu SR method is shown. Discrimination of muons From positrons is performed by amplitude analysis and time-of-flight technique. The investigation has been performed at the Laboratory of Nuclear Problems, JINR (Dubna). (C) 2000 Elsevier Science B.V. All rights reserved.

The complete statistical base acquired in the SPINP-JINR joint experimental search for muonium-antimuonium conversion has been analyzed. A total of 3.44 X 10(11) muons passed through the target over the two series of physical measurements of the conversion process. One event which qualifies as a muonium-antimuonium conversion was detected. An experimental estimate W(MMBAR) < 5.1 X 10(-7) (90% C.L.) is found for the upper limit on the probability for the conversion process. Results of a study of the probabilities for background processes in the existing formulation of the experiment are reported.

The first results of the formation and transportation of therapeutic proton beams at the JINR phasotron are presented. To ensure flat-top depth-dose distributions with a steep back slope, a method of forming a beam with a necessary energy spectrum from a non-monoenergic beam is employed. Extension of the flat hop of depth-dose distribution is 4.7 g/cm2 for a proton beam with the mean energy of 200 MeV.

A brief consideration of the hardware and software of the automated control system for proton beam therapy in the clinicophysical complex at the JINR Laboratory of Nuclear Problems is presented.