JINR Nuclotron Research Articles

Measurements of High Energy Neutron Spectrum (> 10 MeV) by Using Yttrium Foils in a U/Pb Assembly

Study of deep subcritical electronuclear systems and radioactive waste transmutation using relativistic beams were performed. This work is a preliminary step toward the study of the physical properties of Accelerator Driven Systems, in which a deeply subcritical active core is irradiated by a pulsed beam of relativistic ions. The long-range goal of the project is to study the capabilities of such systems with a hard neutron spectrum, for transmutation of radioactive nuclear wastes. Two experimental assemblies, “Energy plus Transmutation” (2006-2009) and “Quinta” (2011-), were irradiated by 1 to 6 GeV deuteron beams using the JINR NUCLOTRON accelerator. The main difference between the two experimental setups is the spallation target - lead or natural uranium. We attempt to obtain neutron energy spectra inside the volume of these assemblies using threshold reactions in natural yttrium (89Y) foils. Some results from three different experiments are presented.

Status of the polarized ions source for the JINR accelerator complex

The project assumes the design and construction of a universal high-intensity source of polarized deuterons (protons) using a charge-exchange plasma ionizer. The output D+↑ (H+↑) current of the source is expected to be at a level of 10 mA. The polarization will be up to 90% of the maximal vector (±1) for D+↑ (H+↑) and tensor (+1, −2) for D+↑ polarization. Realization of the project is carried out in close cooperation with INR of the RAS (Moscow). The equipment available from the CIPIOS ion source (IUCF, Bloomington, USA) is partially used for the Dubna setup. The new source at the JINR Nuclotron accelerator facility will make it possible to increase the polarized deuteron beam intensity up to the level of 1010 d/pulse. The first results of the source of polarized atoms testing are presented.

Nuclear diffraction dissociation of 16O, 22Ne, 28Si, 32S, 56Fe at 1–3.7 A GeV in nuclear emulsion

In this paper, we discuss various aspects of the nuclear diffraction dissociation interactions of 16O, 22Ne, 28Si, 32S, 56Fe nuclei accelerated at the Dubna–JINR Synchrophasotron and Nuclotron in the energy range 1–3.7 A GeV. We use criteria which separate electromagnetic dissociation events among the nuclear collisions. We describe their topology and study their characteristic parameters, relative rates of nuclear fragmentation, average multiplicities and the angular distributions of fragments as a function of the energy and of the nature of the primary nuclei. Nuclear emulsions were used for this purpose, which allowed the detection of all projectile and target fragments.

Measurement of the vector and tensor analyzing powers for dp-elastic scattering at 880 MeV

The vector Ay and tensor analyzing powers Ayy and Axx for dp-elastic scattering were measured at Tdlab=880 MeV over the c.m. angular range from 60° to 140° at the JINR Nuclotron. The data are compared with predictions of different theoretical models based on the use of nucleon–nucleon forces only. The observed discrepancies of the measured analyzing powers from the calculations require the consideration of additional mechanisms.

Measurement of Neutrons in Different Pb/U Setups Irradiated by Relativistic Protons and Deuterons by means of Activation Samples

The collaboration Energy and Transmutation of Radioactive Waste uses different setups consisting of lead, uranium and graphite irradiated by relativistic protons and deuterons to study transmutation of radioactive materials by produced neutrons. Our group measured spatial distribution of neutrons by means of activation samples during the assembly irradiation by the JINR Nuclotron beams. We also present results of simulations using MCNPX code and their comparison with obtained experimental data. We use Au, Al, Bi, In and Ta foils as activation detectors, but unfortunately almost no experimental cross-section data for observed threshold (n,xn) reactions are available for higher neutron energies. Therefore we carried out series experiments devoted to determination of neutron cross-sections of various threshold reactions using different quasi-monoenergetic neutron sources.

Experimental exposure of nuclear emulsion by xenon nuclei at the JINR nuclotron

Nuclear emulsion was exposed to xenon nuclei accelerated at the JINR Nuclotron. Visual and automated scanning of the extracted beam profile was performed using the exposed emulsion film.

The new source of polarized ions for the JINR Accelerator Complex

The project assumes the design and construction of a universal high-intensity source of polarized deuterons (protons) using a charge-exchange plasma ionizer. The output ↑D+ (↑H+) current of the source is expected to be at a level of 10 mA. The polarization will be up to 90% of the maximal vector (±1) for ↑D+ (↑H+) and tensor (+1,−2) for ↑D+ polarization. Realization of the project is carried out in close cooperation with INR of RAS (Moscow). The equipment available from the CIPIOS ion source (IUCF, Bloomington, USA) is partially used for the Dubna device. The new source at the JINR NUCLOTRON accelerator facility will make it possible to increase the polarized deuteron beam intensity up to the level of 1010 d/pulse. Previous test runs on acceleration of polarized deuterons at the NUCLOTRON up to about 1 GeV/u and slow extraction of the beam to the beam transfer lines, have shown the absence of depolarization resonances. The first dangerous resonance is predicted at the beam energy of 5.6 GeV/u. The source could be transformed into a source of polarized negative ions if necessary.

Investigation of fast neutron spectra in the uranium assembly of the experimental setup “energy plus transmutation” in the JINR Nuclotron proton beam at an energy of 1.5 GeV

The “energy plus transmutation (EPT)” electro-nuclear experimental assembly (lead target surrounded with natural uranium blanket) was irradiated with protons of energy 1.5 GeV from the Nuclotron accelerator of the JINR. The energy spectrum of the neutrons in the EPT was determined by examination of 5000 proton recoil tracks in the nuclear emulsion spectrometer that was developed for these measurements. The measured energy spectrum was corrected for the laboratory background events in the emulsion. The neutron spectrum extends from 0.5 to 200 MeV. The weighted mean energy of the neutrons is in the range of 4–6 MeV depending on the energy cutoff boundaries of the spectrum. The obtained experimental results were compared with Monte Carlo calculations using the MCNPX 2.6C code and the origins of the observed discrepancies are discussed.

Research program of the NIS-GIBS project at JINR Nuclotron

The research program planned for extracted proton and relativistic nuclei beams of the JINR Nuclotron is briefly outlined in this talk. The program is to be realized with the NIS-GIBS spectrometer and consists of two parts. The first one is aimed to search for effects of nucleon polarized strangeness in production of φ and ω mesons in pp and np scattering. The latter one is devoted to the investigation of hydrogen hypernuclei isotopes.

Search for a mixed quark-hadron phase of QCD matter at the JINR nuclotron

Physics aspects of a JINR project to reach the planned 5 A GeV energy for the Au and U beams and to increase the bombarding energy up to 10 AGeV are discussed. The project aims to search for a possible formation of a strongly interacting mixed quark-hadron phase. The relevant problems are exemplified. The need for scanning heavy-ion interactions in bombarding energy, collision centrality, and isospin asymmetry is emphasized.

Full Size Model Magnets for the FAIR SIS100 Synchrotron

The planned FAIR synchrotron SIS100 has to deliver high intensity beams. Following the JINR Nuclotron, GSI has chosen to build this machine using fast-cycling 4 T/s, 2 T superferric magnets. Cycle repetition rates of about 1 Hz cause high AC power losses in the magnet components. Eddy currents deteriorate the field quality. After millions of operation cycles and high radiation flux the coil support structure can loose mechanical stability. Therefore these effects were analyzed to warrant the magnet's performance over its lifetime. Following intensive experimental and computational investigations on short test models three full size dipoles and a 1.2 m long quadrupole with a maximum field gradient of 27 T/m in the aperture of 135 mm 65 mm will be manufactured until the end of 2007. Two of the dipoles are straight 2.7 m long 2.1 T magnets with a beam aperture of 130 mm 60 mm (width x height), while the third one is a curved 1.9 T dipole 3.0 m long with a reduced horizontal aperture of 115 mm. All the models use a superconducting hollow NbTi/Cu composite cable cooled with two-phase helium flow. The main design features and estimated operation parameters are given. In parallel preliminary tests of a 2.8 m SIS100 equivalent dipole system was performed. The cooling stability of the system at different SIS100 operation cycles was checked experimentally for the first time. These results are discussed as well as possible design options to fulfil additional operation requirements.

Properties of strongly interacting matter and the search for a mixed phase at the JINR nuclotron

A physical program is formulated for new facilities opening in Dubna for the acceleration of heavy ions with an energy up to 5A GeV.

SEARCH FOR RESONANT STRUCTURE IN THE PION PRODUCTION REACTION ON THE NUCLOTRON INTERNAL BEAM

We have searched for an enhancement in the excitation function of the yield of pions in the pion production reaction by protons and deutrons at bombarding energies near 350 MeV/nucleon. The measurements was carried out on the JINR Nuclotron internal beam and target in March and June 2004 Nuclotron Runs for Ag , Cu , Al and C targets.

Fragmentation channels of relativistic 7Be nuclei in peripheral interactions

At the JINR Nuclotron, 7Li nuclei are accelerated. The charge-exchange reaction involving these nuclei at an external target provides a secondary 1.23-A-GeV 7Be beam. This beam is used to irradiate emulsion chambers. The mean free path λinel(7Be) = 14.0 ± 0.8 cm for inelastic 7Be interactions in an emulsion coincides within the errors with those for 6Li and 7Li nuclei. More than 10% of the 7Be events are associated with the peripheral interactions in which the total charge of the relativistic fragments is equal to the charge of the 7Be nucleus and in which charged mesons are not produced. An unusual ratio of the helium isotopes is revealed in the composition of the doubly charged fragments of the 7Be nuclei: the number of the 3He fragments is twice as large as that of the 4He fragments. Each of 50% of peripheral interaction events includes two doubly charged fragments. The channels of the 7Be fragmentation into charged fragments are presented. In 50% of events, the 7Be fragmentation occurs only into charged fragments without the emission of neutrons. The 4He + 3He channel dominates, whereas each of the 4He + d + p and 6Li + p channels constitutes 10%. Two events without neutron emission are observed in the 3He + t + p and 3He + d + d three-body channels. The mean free path for the coherent dissociation of relativistic 7Be nuclei into 4He + 3He is equal to 7 ± 1 m. The main features of the fragmentation of relativistic 7Be nuclei in such peripheral interactions are explained by the 3He + 4He two-cluster structure of the 7Be nucleus.

Transmutation studies with GAMMA-2 setup using relativistic proton beams of the JINR Nuclotron

A spallation neutron source consisting of an extended lead target surrounded with a paraffin moderator irradiated by 1, 1.5, and 2.0 GeV protons is used to study neutron capture and transmutation reaction rates in 139La, 129I and 237Np samples in secondary neutron fluences. Reaction rates are obtained by activation analysis using HPGe detectors. The results are compared with calculations using a cascade-evaporation model.

U-Pb accelerator-driven sub-critical systems research at the proton beam of the JINR NUCLOTRON

AbstractNeutron spectra, yields and energies of particles generated by a uranium electro-nuclear set-up which is now used in Dubna for transmutation research of various isotopes with a proton beam of an energy of 1–2 GeV, were analyzed by means of mathematical modelling based on the Monte Carlo code CASCADE. The influence of space dispersion on the proton beam and its possible deviation from the center of a lead target is investigated. It is shown that the polyethylene radiation shielding that is being used now, does not protect the measuring room from neutrons and γ-rays.

Beryllium (boron) clustering quest in relativistic multifragmentation (BECQUEREL Project)

A physical program of irradiation of emulsions in beams of relativistic nuclei named the BECQUEREL Project is reviewed. It is destined to study in detail the processes of relativistic fragmentation of light radioactive and stable nuclei. The expected results would make it possible to answer some topical questions concerning the cluster structure of light nuclei. Owing to the best spatial resolution, the nuclear emulsions would enable one to obtain unique and evident results. The most important irradiations will be performed in the secondary beams of He, Be, B, C, and N radioactive nuclei formed on the basis of JINR Nuclotron beams of stable nuclei. We present results on the charged state topology of relativistic fragmentation of the 10B nucleus at low energy-momentum transfers as the first step of the research.