G. Kaminski

Exposure of Nuclear Track Emulsion to 8 He Nuclei at the ACCULINNA Separator

Nuclear track emulsion is exposed to a beam of radioactive 8He nuclei with an energy of 60 MeV and enrichment of about 80% at the ACCULINNA separator. Measurements of 278 decays of the 8He nuclei stopped in the emulsion allow the potential of the α spectrometry to be estimated and the thermal drift of 8He atoms in matter to be observed for the first time.

VME-based data acquisition system for multiparameter measurements

The VME-based data acquisition system designed for physics experiments involving measurements of several hundreds of parameters is described. The equipment has been tested in the experiments with the 6He, 8He, 18Ne, and 27S beams at the ACCULINNA fragment separator (http://aculina.jinr.ru/) in the energy range of 20–35 MeV/nucleon. The system is composed of the RIO-3 processor module, which is used to read the VME bus, communicate with the CAMAC and FASTBUS crates, and transmit data to the personal computer; the TRIVA-5 master trigger module; standard analog-to-digital, charge-to-digital, and time-to-digital converters from CAEN (V785, V792, and V775 models); and related software. This data acquisition system is faster (by a factor of 10) than a CAMAC-based system and is capable of operating with new types of electronic modules, e.g., with digitizers.

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.

Asymmetry of velocity distributions in peripheral reactions with heavy ions at Fermi energies

The asymmetry of velocity distributions of projectile-like fragments produced in heavy ion collisions is considered. The calculations performed in the transport model approach (Vlasov kinetic equation with the collision term) are compared with the experimental data for the 22Ne (40MeV/nucleon) + 9Be and 18O (35 MeV/nucleon) + 9Be(181Ta) reactions. It is found that the velocity distributions contain two components: a direct component centered at the beam velocity and a dissipative component at lower energies, leading to asymmetry of velocity distributions. The direct component is interpreted empirically within the Goldhaber model, and the centroids and widths σ0 of the distributions for each fragment are extracted. It is found that value of σ0 derived from experimental data is smaller by a factor of 2 than the theoretical one. The dissipative (also called deep inelastic) component is described well by the transport calculations. It is shown that the ratio of yields of direct and dissipative components, which determines the asymmetry of velocity distributions, depends on shape of the deflection function.

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.

Dissipative processes in peripheral heavy ion collisions at Fermi energies

Peripheral heavy ion reactions are of interest for the production of new isotopes. In this contribution we present an investigation of reactions of light projectiles O and Ne on Be and Ta targets at Fermi energies in the framework of transport theory. Transport theory describes dissipative (deep-inelastic) processes, where considerable amounts of mass and energy are exchanged. The data, on the other hand, also seem to include a more direct component with small energy loss. We separate the two components on the basis of the velocity distribution and compare the dissipative component to the transport calculations. The primary fragments of the transport calculation still have considerable excitation energies. For the comparison with experiment we take into account the secondary evaporation in a statistical model. This improves the qualitative agreement with the data.

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.

Correlation investigations of the low-energy 10He spectrum

The spectrum of low-lying states in the 10He nucleus is investigated for the two-neutron transfer reaction 3H(8He, p)10He. The secondary beam of 8He nuclei with the energy 21.5 MeV/nucleon and a cryogenic tritium target are used in the experiment. The 10He ground state is observed in the missing mass spectrum at the energy of 2.1 MeV (Γ ∼ 2 MeV) above the decay threshold. Analysis of the angular correlations of the 10He decay products yields the spin and parity of two excited 10He states, Jπ = 1− in the energy range from 4 to 6 MeV and Jπ = 2+ at energies above 6 MeV.

Search for

Structure of nuclei located near and beyond the drip-lines plays important role in the explosive astrophysical processes. The problem of two-proton decay of the 17 Ne first excited state is a good example of such situation. The two-proton radiative capture is a possible bypass of the 15 O waiting point in the rp-process. The rate of this process drastically depends on the value of the weak 2

2p

S.I. SIDORCHUK, A.A. BEZBAKH, V. CHUDOBA, I.A. EGOROVA, A.S. FOMICHEV, M.S. GOLOVKOV, A.V. GORSHKOV, V.A. GORSHKOV, L.V. GRIGORENKO, G.KAMINSKI, S.A. KRUPKO, YU.L. PARFENOVA, P.G. SHAROV, R.S. SLEPNEV, S.V. STEPANTSOV, G.M. TER-AKOPIAN, R. WOLSKI Flerov Laboratory of Nuclear Reactions, JINR, Dubna, Russia; Institute of Physics, Silesian University in Opava, Czech Republic; Bogolyubov Laboratory of Theoretical Physics, JINR, Dubna, Russia; GSI Helmholtzzentrum fur Schwerionenforschung, Darmstadt, Germany; Institute of Nuclear Physics PAN, Krakow, Poland; Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, Russia