Yu. G. Teterev

WIDE APERTURE KINEMATIC SEPARATOR COMBAS REALIZED ON THE STRONG FOCUSING PRINCIPLE

Abstract 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.

Upgrading the genome facility for radiobiological experiments with heavy-ion beams

The Genome-M facility for the automatic fast irradiation of thin biological samples with accelerated heavy ions at the U-400M cyclotron of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, is described. It allows a great deal of various samples to be irradiated within a few hours using radiation with preset and controlled characteristics. Methods for monitoring beam quality and calibrating the ionization chamber in absorbed dose units and the facility control software are also described.

3D magnetic measurements of the combined function magnets in separator COMBAS

Abstract 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.

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.

Forward-angle yields of 2≤Z≤11 isotopes in the reaction of 18O(35A MeV) with 9Be

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.

Neutron yields from structural metals during bombardment by heavy ions with 2.5 MeV/nucleon energy

Neutron yields during irradiation of structural metals and polymer film by argon, krypton, and xenon ions with 2.4 and 2.5 MeV/nucleon energies are measured on the CYTRACK and DC-110 cyclotrons. The angular distributions of neutrons from the target are measured. The LISE++ is used for extrapolating the data obtained to other ions, their energy, and to other targets. The program was tested on experimental data found in the literature. As a result of comparison, it is established that the calculation results coincide with the experimental data within a coefficient of two.

Investigation of 6He yield in 7Li(γ, p) reaction with 22 MeV electron beam

The possibility of producing exotic 6He nuclei in the 7Li(γ, p) reaction with 22 MeV electron beam at the MT-25 microtron in the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research (FLNR JINR), is studied. The 6He yield from the Li2CO3 target made up 6 × 105 s−1 per 1 μA of the electron beam current. The obtained result is quite promising, taking into account the further improvement of the target unit, the possibility of using another lithium compound, and the increase in the target material temperature and the electron beam current up to 20 μA. The application of this approach for the further production of a monochromatic beam of accelerated 6He nuclei with an intensity on the order of 107 s−1 would make a large number of experiments on investigating the structure of this nucleus and the mechanisms of nuclear reactions with its participation feasible. This method for obtaining 6He nuclei may turn out to be one of the most optimal (and inexpensive) currently available.

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.

Ionization Profilometer of the Beam Position on the Target of the COMBAS Fragment-Separator

The operation principle of a newly designed ionization profilometer is described, and results of its tests with a 30-MeV/nucleon 40Ar ion beam are presented. The measured beam density distribution over its cross section is given. The space resolution of this profilometer is ∼1 × 1 mm. The image of this beam on a fluorescent screen is shown for comparison. It is determined that the minimum value of the beam current at which it is still possible to measure its profile is 3 nA. The measurements were performed at residual gas pressures of 2 × 10–3 and 7 × 10–3 Pa.

Secondary fusion reactions in the bombardment of light-element targets with low-energy heavy ions

Neutron emission was observed experimentally at the DC-60 cyclotron at the Institute of Nuclear Physics (Astana, Kazakhstan). The neutron yields were measured in the bombardment of light-element (Be, C, Al, Al2O3, and LiF) targets with heavy ions (Ar, Kr, and Xe) with energies below the Coulomb barrier. The angular distributions of neutrons from the targets were also measured. It was found that the observed neutrons were produced in secondary nuclear reactions between the resting target nuclei and recoil nuclei that acquire energy in the process of elastic scattering. The experimental results were compared with calculations based on the abovementioned secondary-reaction mechanism. The calculations allow one to estimate the yields of secondary reactions to within a coefficient of 2.