V. L. Kravchuk

Optical and Scintillation Properties of Polydimethyl-Diphenylsiloxane Based Organic Scintillators

Polysiloxane based scintillators with high light yield have been synthesized. The polymer consists in cross-linked polydimethyl-co-diphenylsiloxane with different molar percentages of phenyl units. 2,5-diphenyl oxazole (PPO) and 2,5-bis(5-ter-butyl-2-benzoxazolyl)thiophene (BBOT) have been dispersed in the polymer as dopants. The energy transfer and scintillation capabilities have been investigated, for two different amounts of phenyl groups in the polymer network and for different concentrations of dye molecules, by means of fluorescence spectroscopy, ion beam induced luminescence (IBIL) and scintillation yield measurements with ¿ particles from an 241Am source. The luminescence features and the scintillation yields have been correlated to the composition of the scintillators.

GARFIELD + RCo digital upgrade: A modern set-up for mass and charge identification of heavy-ion reaction products

An upgraded GARFIELD + Ring Counter (RCo) apparatus is presented with improved performances as far as electronics and detectors are concerned. On the one hand fast sampling digital read out has been extended to all detectors, allowing for an important simplification of the signal processing chain together with an enriched extracted information. On the other hand a relevant improvement has been made in the forward part of the set-up (RCo): an increased granularity of the CsI(Tl) crystals and a higher homogeneity in the silicon detector resistivity. The renewed performances of the GARFIELD + RCo array make it suitable for nuclear reaction measurements both with stable and with Radioactive Ion Beams (RIB), like the ones planned for the SPES facility, where the physics of isospin can be studied.

Persistence of odd-even staggering in charged fragment yields from the

Odd-even staggering effects on charge distributions are investigated for fragments produced in semiperipheral and central collisions of 112Sn+58Ni at 35 MeV/nucleon. For fragments with Z<16 one observes a clear overproduction of even charges, which decreases for heavier fragments. In peripheral collisions staggering effects persist up to Z about 40. For light fragments, staggering appears to be substantially independent of the centrality of the collisions, suggesting that it is mainly related to the last few steps in the decay of hot nuclei.

^{112}Sn + ^{58}Ni

Dissipative 12C+12C reactions at 95 MeV are fully detected in charge with the GARFIELD and RCo apparatuses at LNL. A comparison to a dedicated Hauser-Feshbach calculation allows to select events which correspond, to a large extent, to the statistical evaporation of highly excited 24Mg, as well as to extract information on the isotopic distribution of the evaporation residues in coincidence with their complete evaporation chain. Residual deviations from a statistical behaviour are observed in \alpha yields and attributed to the persistence of cluster correlations well above the 24Mg threshold for 6 \alphas decay.

collision at 35 MeV/nucleon

Theoretical description of the experimentally obtained spectra for protons and α-particles and model calculations for the neutron spectra in the reactions with heavy ions has been presented. The hybrid model of non-equilibrium processes was used. Equilibrium evaporation process was analyzed in the framework of the statistical theory of nuclear reactions with Monte-Carlo simulation including certain dynamical and kinematical characteristics. This approach was included in PACE code, which permits to simulate Monte-Carlo de-excitation nuclear process. The Fermi-gas model and level-density phenomenological model for the variation of the nuclear level density parameters was used. In this approach data on 16O+116Sn reaction with Ebeam = 130, 250 MeV were analyzed. Double-differential light charged particle spectra for this reaction were measured using the GARFIELD apparatus in coincidence with evaporation residues. The experimental data were collected in four angular ranges from 29 to 41, 41 to 53, 53 to 67 and 67 to 82 degrees in the laboratory system. The results of the calculations are shown and discussed for these four angular ranges. The contributions from the evaporative and pre-equilibrium processes were analyzed in connection with different nucleus equilibration mechanisms.

\alpha-clustering effects in dissipative 12C+12C reactions at 95 MeV

Experimental data of the double-differential spectra of light particles emitted at pre-equilibrium stage of nuclear processes were obtained at Laboratori Nazionali di Legnaro for the heavy-ion reactions 130 and 250 MeV 16O + 116Sn. Light charged particles were measured in coincidence with evaporation residues in order to avoid unwanted competing mechanisms. The experimental data were collected in a wide angular range from 29 to 82 degrees in the laboratory system. Theoretical model was developed in order to describe simultaneously evaporative and pre-equilibrium emission of the light particles in heavy-ion reactions. Griffin exciton model was used for the description of the pre-equilibrium stage of the compound nucleus formation, while the equilibrium evaporation processes were analyzed in the framework of the statistical theory of heavy-ion reactions. Experimental data were compared with the results of the model calculations and new approach was suggested to take into account alpha cluster formation in t...

PRE-EQUILIBRIUM EFFECTS IN THE SECONDARY PARTICLE SPECTRA IN THE REACTIONS WITH HEAVY IONS

Abstract. Symmetry energy is a key quantity in the study of the equation of state of asymmetric nuclear matter. Heavy ion collisions at low and intermediate energies, performed at Laboratori Nazionali di Legnaro and Laboratori Nazionali del Sud, can be used to extract information on the symmetry energy coefficient Csym, which is currently poorly known but relevant both for astrophysics and for deeper knowledge of the structure of exotic nuclei.

PRE-EQUILIBRIUM ALPHA-PARTICLE EMISSION AS A PROBE TO EXPLORE ALPHA CLUSTERING IN NUCLEI

The γ -decay of the GDR in the 132 Ce compound nuclei produced by the reaction 64 Ni+ 68 Zn at Ebeam = 300 MeV, 400 MeV, 500 MeV (E ∗ of 100 MeV, 150 MeV and 200 MeV) has been measured. We have detected heavy recoil nuclei, light charged particles and γ -rays. The data obtained with the symmetric reaction 64 Ni+ 68 Zn indicate emission from a fully equilibrated compound nucleus as deduced from the analysis of charged particle spectra. The GDR parameters are found to be consistent with the predictions of the thermal fluctuation model. (Some figures in this article are in colour only in the electronic version)

Isotope analysis in central heavy ion collisions at intermediate energies

S. Valdréa,b, S. Piantellib, G. Casinib, S. Barlinia,b, M. Ciemałac M. Kmiecikc, A. Majc, K. Mazurekc, M. Cinauserod F. Gramegnad, V.L. Kravchuke, L. Morellif , T. Marchig S. Appannababuh, G. Baioccoi, P. Bednarczykc, G. Benzonij M. Binia,b, N. Blasij, A. Braccoj,k, S. Brambillaj, M. Brunof F. Cameraj,k, M. Cicerchiad,l, M. Colonnam, F.C.L. Crespij,k M. D’Agostinof , M. Degerliern, D. Fabriso, B. Fornalc O.V. Fotinap, A. Giazj,k, M. Krzysiekc, S. Leonij,k, J. Mabialad M. Matejska-Mindac, W. Męczyńskic, B. Millionj D. Montanarij,k, S. Myalskic, R. Nicolinij,k, A. Olmib G. Pasqualia,b, G. Preted, J. Styczeńc, B. Szpakc, E. Vardacir B. Wasilewskac, O. Wielandj, M. Zięblińskic

The γ-decay of the GDR in highly excited Ce nuclei

A study of fusion-evaporation and (partly) fusion-fission channels for the