G. A. Kononenko

The COMBAS fragment separator

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.

Investigation of the fragmentation of 20Ne and 40Ar ions at the COMBAS setup

Properties of the COMBAS fragment separator are compared with respective properties of similar setups. Results of experiments aimed at obtaining products of one-proton-stripping reactions induced by a beam of 40Ar ions with an energy of 35 MeV/A and two-neutron-stripping reactions induced by a beam of 20Ne ions with an energy of 52 MeV/A are presented. A high resolution of the fragment separator in obtaining secondary neutron-rich 39Cl and neutron-deficient 18Ne ion beams is demonstrated.

Reconstructing the parameters of cluster breakup of light nuclei

Kinematics of two-body Coulomb breakup of a prototype 11B nucleus into 4He and 7Li fragments is considered. The factors affecting the accuracy in measuring the breakup parameters are analyzed, and the corrections having an influence on the accuracy in reconstructing the primary parameters of the cluster breakup are estimated. A method for estimating the effect of an unknown contamination in the target and the use of this method for separating true and background events are discussed. The influence of background factors occurring in heavy ion fragmentation reactions is analyzed, and random coincidences due to high background fluxes of parasitic products are estimated. It is proposed to use magnetic analysis of correlated breakup products to reduce the background particle flux and substantially (by several orders of magnitude) improve the accuracy in measuring the cluster energies.

Total reaction cross sections measurement for 6,8He and 8,9Li nuclei with energies of (25–45)/A MeV on natAl and natPb

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 Bρ 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.

Detection system of the COMBAS fragment separator

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.

A proportional counter for low intensity heavy ion flow measurements

A proportional counter designed for heavy ion flux measurements is described. The working gas of the counter is air. The counter is composed of three parallel glass-fiber frames with wire electrodes coiled on them. Based on the counter, there has been developed a diagnostic product measuring the density distribution of accelerated ion flux for radioelectronic device testing. To prevent the dependence of measurement results on weather conditions (atmospheric pressure, temperature, humidity) as well as on the type and energy of ions, there has been applied an automatic correction methodology. In the process of the set-up operation it has been established, that the counter is characterized by a high radiation resource, resistance to extreme downloads, adequate performance of up to 106 ions/s, it is not sensitive either to neutrons or to γ-quanta, and it is convenient to use.

Total reaction cross sections and neutron-removal cross sections of neutron-rich light nuclei measured by the COMBAS fragment-separator

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.

Radioactive nuclear beams of COMBAS facility

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.

A secondary beam separator: A combination of the COMBAS fragment separator with the ion catcher

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.

STUDY OF ISOTOPE AND VELOCITY DISTRIBUTIONS OF LIGHT FRAGMENTS IN THE 11B (32.9 AMeV) + 9Be (27Al, 197Au) REACTIONS

The longitudinal velocity and isotopic distributions of forward emitted fragments have been measured in the 11B (32.9 AMeV) + 9Be (27Al,197Au) reactions. The range of isotopes from Helium to Nitrogen has been observed. The particular interest of this experiment has been to investigate the influence of direct and dissipative processes on the fragment production for different targets. The fast velocity component characterized by a Gaussian shape is rather well described in the frame of simple statistical fragmentation model, but with smaller value of the width of the distribution. Isotopic and velocity distributions have been compared to Universal Parameterization model implemented in the LISE + + code. Increased yields of 4He and 7Li isotopes are observed as a possible influence of the cluster structure of the 11B nuclei on the total reaction mechanisms.