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International audience; Secondary beams (6Li,7Be,8B) obtained by separation of fragmentation products of 15N beam (50 A MeV) impinging on a Be target using COMBAS spectrometer. The secondary products will be detected by a telescope consisting of five Si-detectors (dE) and CsI(Tl) detector (Er). By the dE-E method, the telescope allowed us to achieve unambiguous particle identification originating from incident secondary beams as well as theirs reaction products resulting from reactions with one of Si detectors chosen as the target. Accordingly, break-up reactions of 6Li, 7Be and 8B were studied in this experiment.

Preliminary results of measurements of the total reaction cross sections σR for weakly-bound 6,8He and 8,9Li nuclei at energy range (25–45)/A MeV on 27Al and 208Pb targets are presented. The secondary beams of 6,8He and 8,9Li were produced by bombardment of the 11B (33 A MeV) primary beam on Be (89 mg cm–2) target and separated by COMBAS fragment-separator. In dispersive focal plane a horizontal slit defined the momentum acceptance as 1% and a wedge degrader of 200 μm Al was installed. The B ρ of the second section of the fragment-separator was adjusted for measurements in energy range (25–45)/A MeV. The secondary products were detected by a telescope consisting of two Si ΔE detectors 300, 1000 μm and E-detector, which consisted of nine CsI/Tl granules.

Up to date analysis of velocity and isotope distributions of light fragments obtained in the projectile fragmentation reactions of 18O at 35 A MeV on 9Be and 181Ta targets measured at COMBAS fragment separator at the U400 M Research Facility in JINR are presented. The results of velocity spectra analytical parameterization and isotopic ratios are compared with the ones obtained in the experiments presented in the literature. The discussion of the different mechanisms involved in these types of the reactions is given.

The basic ion-optical characteristics of the luminosity and the high-resolution of kinematic separator COMBAS realized for the first time on the strong focusing principle are presented. The developed facility allows to separate the high-intensity secondary radioactive beams in a wide range of mass numbers A and atomic numbers Z which are produced in heavy ion reactions in the energy range of 20 ≤ E ≤ 100 MeV/A (Fermi energy domain). Two distinct detector systems such as realized Si strip detector telescope and the promising development of the three dimension time-projection chamber are discussed. Program of the investigations of nuclear reaction mechanisms at intermediate energies of 20–100 MeV/A, measurement of the radii of unstable nuclei, study of the cluster structure of light nuclei near the nuclear drip-line and search of 26,28O resonances in exchange reactions is proposed. The upgrading of experimental facility by the integration of COMBAS separator with the Ion Catcher is discussed.

The (ΔE1, ΔE2, E) multidetector telescope has been developed and tested. The telescope is a compact combination of two 32-strip silicon ΔE1-, ΔE2-detectors and a scintillation E-detector, which is a 3 × 3 array of CsI(Tl) crystals. A timing signal can be obtained from any of the Si detectors for time-of-flight (TOF) measurements. Single-channel and 32-channel charge-sensitive preamplifiers have been developed and manufactured for the multidetector module to serve the ΔE- and E-detectors with high efficiency and sensitivity. Reaction products obtained in the 40Ar (35 MeV/nucleon) + 9Be reaction have been unambiguously identified in the experiment by mass number A and atomic number Z.

Projectile fragmentation at Fermi energies is an important method to produce radioactive beams for the study of isospin asymmetric nuclear matter. Fragmentation is usually parametrized successfully by empirical phase space models. In this contribution we apply a microscopical method, semiclassical transport theory, to study in detail the reaction mechanism of the fragmentation process. We apply it to experimental data of 18O on 181Ta at E/A = 35 MeV measured in Dubna. We calculate consistently the excitation energy of the primary fragments and take into account their decay by a statistical model. It is found that the dissipative part of the fragment spectra is well described by transport theory. However, there are in addition important direct and collective contributions.

Peripheral collisions of heavy ions at Fermi energies are a powerful tool for producing new isotopes far from stability line. The mechanism of these reactions has features between direct and dissipative reactions, as is seen from the velocity distributions of the projectile-like fragments, which are peaked near the beam velocity and have a long tail to the smaller velocities. In this report we treat these heavy ion collisions in a Boltzmannlike transport approach, which describes the evolution of the phase space distribution function under the influence of a mean field and a two-body collision term. It is used to calculate the primary fragments after the collision phase, which are, however, still highly excited. The de-excitation of the fragments is calculated in a statistical model. We calculate isotope distributions and velocity spectra for the reaction of 40Ar as a projectile on targets of 9Be and 181Ta at E/A = 57 MeV and find reasonably good agreement with experimental data.

The development of an experimental facility based on the high-luminosity COMBAS fragment separator and a fast ion catcher is discussed. The main characteristics of the COMBAS fragment separator and the ion catcher determining the advantages of the proposed combination are presented. The developed facility is expected to allow production of secondary radioactive beams with a quality higher than the quality of beams obtained using the in-flight separation technique. It is planned that the facility will be used in a tandem with a post-accelerator for producing single-isotope and monochromatic high-intensity secondary radioactive beams in a wide range of mass numbers A and atomic numbers Z. A list of perspective scientific problems requiring high-intensity and high-quality secondary beams of exotic nuclei is proposed.

The basic ion-optical characteristics of the COMBAS fragment separator are analyzed. The momentum distributions of radioactive 6He, 8He, and 9Li nuclei obtained in the reaction 11B (33 A MeV, where A is the mass number of a particle) + 9Be (332.6 mg/cm2) have been investigated in forward-angle measurements on the COMBAS fragment separator. The momentum and angular (horizontal) acceptances of the COMBAS separator have been measured using the 6He, 8He, and 9Li beams. It has been ascertained that the images of the 6He, 8He, and 9Li nuclear beams in final achromatic focus of the separator Fa approximately twofold exceed the size of the beam on a producing target (input focus F0), at which the primary beam has a diameter of 6 mm. The intensities of 6He, 8He, and 9Li beams obtained at a 5-μA intensity of the primary 11B beam are 6.9 × 105, 2 × 104, and 4.7 × 105 particles/s, respectively. These values are sufficient for use in spectroscopic measurements. It is proposed that time-of-flight analysis of nuclear reaction products at the exit from the COMBAS separator will be used not only to measure the energy of transported particles over the whole operating range of the momentum acceptance, but also to identify them by mass A and charge Z without loss of these particles. The problem of reducing the count rates of detectors and further improvement of their energy resolution for detected particles can be solved by placing a high-resolution magnetic spectrometer past the second target accepting the secondary radioactive nuclear beams.

International audience; The total nuclear reaction cross sections (σR) measurements have long been of interest since they tell us about the radii and transparency of these nuclei and give clues to understanding of their structure. For studies of unstable nuclei, in particular the physical properties of halo nuclei and the neutron skin thickness, it is valuable to know not only the root-mean-square radii (rms) but it is important to know the details of nucleusnucleus potentials. Our goal was to study total reaction cross sections (σR) by a direct measurement technique (the so-called beam attenuation or transmission method) which allows to extract model independent information. The interaction radii for 6He, 8,9Li were extracted, which are in agreement with the previous measurement at the similar energies (about a few tens of AMeV) Our results show a tendency of increasing radii as function of mass of the secondary targets.

The problem of magnetic field reconstruction inside a sub-region in R3 from magnetic measurements on the closed boundary of this sub-region is considered. Efficiency of the proposed method, the algorithm and associated software for precision magnet systems are discussed. The results of the software verification and numerical experiments are presented. A comparison between the reconstructed field and the measured field in the M1 magnet of the separator COMBAS is given. Requirements to the position accuracy of sensors consistent with the required accuracy of magnetic field reconstruction are defined. Recommendations on magnetic scheme design for field mapping are given. These investigations have been performed at the Flerov Laboratory of Nuclear Reactions, JINR.

The high-resolution wide aperture separator COMBAS was installed and commissioned in the Flerov Laboratory of Nuclear Reactions, JINR (Dubna) [Nucl. Instr. and Meth. A 306 (1991) 123; 426 (1999) 605; 479 (2002) 467]. It is designed for in-flight radioactive beam production of short-lived isotopes and experiments with them. The separator operates in the (20–50)A MeV ion energy region. It consists of the two stages, dispersive and achromatising. The second half of the separator is a mirror symmetrical counterpart of the first one, the intermediate focal plane being the plane of the symmetry. Multipole magnets with special profiled poles are used to correct higher order aberrations at the intermediate and final foci. The 3D magnetic measurements of the analysing magnets of the separator were done. The KOMPOT program for the 3D magnetic field calculations [Doinikov et al., 1986, Preprint/CNNI atominform: B-0741, 13p; Belyaev et al., Int. Conf. “Optimisation of Finite Element Approximations”, St.Pt., Russia, 25–29 June 1995, p.101; IEEE Transact. On Magnetics, 28 (1) (1992) 908; Frenkel, Selected works, USSR Academy of Sciences publ., Moscow–Leningrad, v.1 (Electrodynamics), 1956; Proc. IEEE, 114 (7) (1967) 995; Livingston, Blewett, Particle accelerators, No. 7, McGraw-Hill, 1962, p. 253] was used for the analysis of these magnetic measurements data, as well as for the reconstruction of the magnet fields inside the total volume closed by the 3D surface, where the magnetic measurements had been performed. As a result of the magnetic field reconstruction we obtained field maps, which would be used in simulations of particle trajectories.

A systematic study of the forward-angle production of nuclei with 2⩽Z⩽11 induced in nucleus–nucleus collisions of 18O with 9Be and 181Ta in the Fermi energy domain (35 A MeV) has been performed. The reaction products were measured by using the double achromatic fragment-separator COMBAS in the spectrometry mode. The inclusive velocity, the isotopic and element distributions were measured. The dominant role of low-energy reaction mechanisms is observed.

The high-resolving wide aperture separator COMBAS has been designed and commissioned at the FLNR, JINR. Three-component magnetic measurements of all the magnets were performed. The measured data allow reconstruction of the 3D-distributions of the fields in all the magnets. 3D-maps are needed for particle trajectory simulations throughout the entire separator. The magnetic fields of analysing magnets, M 1 , M 2 , M 7 , and M 8 , contain quadrupole components of alternating sign that provide necessary beam focusing. All the magnets M 1 –M 8 , contain sextupole and octupole field components, which minimizes the second and third order aberrations. All this allowed one to increase their apertures, to form effectively a beam of the required sizes and to decrease the channel length.

A systematic investigation of the forward-angle inclusive yields of 2≤Z≤11 isotopes produced in collisions of 18O projectile nuclei with a 9Be target in the Fermi energy region (35A MeV) is performed. The measurements were based on the use of the COMBAS double achromatic kinematical separator in the spectrometry mode at the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research, FLNR (JINR, Dubna). The velocity, isotopic, and element distributions are presented. There is no unique mechanism that would explain the total set of results obtained in this experiment. A dominant role of low-energy reaction mechanisms is observed. The intensity of secondary beams of halolike nuclei 11Li, 12Be, and 14Be is determined.

Preliminary results of measurements of the total reaction cross sections σR and neutron removal cross section σ-xn for weakly bound 6He, 8Li, 9Be and 10Be nuclei at energy range (20-35) A MeV with 28Si target is presented. The secondary beams of light nuclei were produced by bombardment of the 22Ne (35 A MeV) primary beam on Be target and separated by COMBAS fragment-separator. In dispersive focal plane a horizontal slit defined the momentum acceptance as 1% and a wedge degrader of 200 μm Al was installed. The Bρ of the second section of the fragment-separator was adjusted for measurements in energy range (20-35) A MeV. Two-neutron removal cross sections for 6He and 10Be and one –neutron removal cross sections 8Li and 9Be were measured.

The COMBAS large solid angle and high momentum acceptance and high-resolving kinematic separator has been created at the Flerov Laboratory of Nuclear Reactions, JINR, to efficiently collect extremely short-lived nuclei near the zero angle which are produced in intermediate energy fragmentation reactions with wide momentum and wide angular distributions. For the first time the M 1 M 2 M 3 M 4 F d M 5 M 6 M 7 M 8 F a magneto-optical configuration of the COMBAS separator has been realized on the strong focussing principle. The separation and trajectory analysis of particles by the separator are carried out by three parameters: the magnetic rigidity (B· ρ ), the energy loss difference in the degrader (Δ E /Δ x ) and the time-of-flight (Δ T ) of the analyzed particles. The COMBAS separator can be used efficiently both in the mode of a high- resolving spectrometer to study reaction mechanisms and in the mode of an in-flight separator in experiments on the synthesis and study of properties of short-lived exotic nuclei near the drip-lines.

We investigate projectile fragmentation using transport theory coupled with statistical decay codes for the excited primary fragments. We concentrate on isotope distributions and on an isoscaling analysis of isotope ratios to obtain information about the symmetry energy. The analysis is performed depending on the impact parameter since the thermodynamic properties of the primary fragments depend on it strongly. We compare reaction systems with different neutron and proton excess, Ar-38, Ca-40+Be-9 and Ca-48, Ca-40+Be-9 both at 140 AMeV, to investigate the range of validity of the isoscaling assumption. We find it is well-justified for isotopes which are mainly produced by the secondary decay. However, for isotopes with N or Z near the incident projectile for grazing impact parameters, the process is more direct and the distributions are not well-represented by statistical ensembles. In the range of validity, the extracted symmetry energies are generally reasonable.

Using fragment‐separator COMBAS [1] in forward‐angle measurements the velocity, isotopic and element distributions of products with Z

Performance and characteristics of a large volume electronic track detector, time projection chamber (TPC), are described. The spatial resolution in the Z (vertical) direction is 0.2 mm, in the Y (horizontal) direction is 1 mm and the double track resolution in the Y- and Z-direction is 4.5 mm and 10 mm, respectively. A possible utilization of the TPC for experiments with heavy ions is discussed.

A magnetic channel, COMBAS, is being constructed at the Laboratory of Nuclear Reactions, JINR for providing radioactive nuclear beams. The COMBAS is a compact achromatic beam line with a high resolution and large acceptance, which consists of D 1 D 2 D 3 D 4 D 5 D 6 D 7 D 8 Q 1 Q 1 configuration, where D 1,2,7,8 , D 3,4,5,6 and Q represent dipole, correcting dipole and quadrupole magnets, respectively. The method of isotopic separation is based on a combination of the magnetic rigidity analysis and the energy loss. The details of the optical designs are presented.

Five new very neutron-rich isotopes, 42Si,45,46p, 48 S and 51CI, are identiled from the interaction of a 44 MeV/b 48Ca beam with a 64Ni target.

Neutron-rich isotopes of nitrogen and oxygen have been produced as projectile-like fragments in the reaction of a 44 MeV/u 48 Ca beam with a 173mg/cm 2 181 Ta target. The fragments have been analyzed by the doubly achromatic spectrometer LISE and implanted in a semiconductor identification telescope, surrounded by a 4π neutron detector in order to observe their radioactive decay. The β-delayed neutron emission has been measured for the isotopes 21,22 N and 23,24 O for the first time and the β-half-lives T 1 2 and delayed neutron-emission probabilities P n are determined. These values are discussed within the framework of a QRPA calculation. The influence of the decay energy Q β used in the calculation is examined, indicating the reliability of predicted matrix elements. Furthermore, P n values are calculated and compared to the experimental data.

Very neutron-rich isotopes have been produced by the fragmentation of 55 MeV/u 48 Ca projectiles from GANIL onto a 181 Ta target. The nuclei were separated by means of the doubly achromatic spectrometer LISE and implanted into a semiconductor telescope for identification in Z and A . Their β-delayed neutron radioactivity is observed by means of a 4π β -n coincidence detector. The results include first measurements of the half-life T 1 2 and the neutron emission probability P n for the isotopes 20 C, 40,41,42 p and 43,44 S. They are compared to current theoretical predictions.

On the basis of data in the literature and calculations carried out by the present authors of the KLn X-ray transitions in Si, S and Cl atoms of heavy ion-excited molecules, the main factors determining the formation of such spectra for the third period elements have been clarified. It has been demonstrated that in analysing the experimental values of KLn line energies it is necessary to take into account the effects of atomic and extra-atomic relaxation, multiplet effects and the possible ionisation of the outer electron shells of target atoms. A simple technique of treating X-ray satellites of multiple ionisation has been developed and tested. This technique allows one to determine from experimental spectra the contribution of extra-atomic relaxation effects to the chemical shifts of KLn lines. These data can be used for analysing the tendencies of changes in the electron polarisability of the substance.

In the reactionnatAg+40Ar (285 MeV) there have been measured the energy spectra of the isotopes of elements from H to Cl at an emission angle of 40°, the energy spectra and angular distributions of1H,2H,3H, and4He, and the angular distributions of Li, Be, B, and C. The contribution from multinucleon transfer reactions to the formation of light charged particles is discussed.

After magnetic separation, identification through time of flight and δE×E measurements has allowed the observation of the new nuclei,29F,35,36Mg,38,39Al,40,41Si,43,44P,45,46,47S;46,47,48,49Cl;49,50,51Ar from the interaction of a48Ca beam of 55 MeV/u with tantalum targets.