[en] The isotopic and isobaric scaling behavior of the yield ratios of heavy projectile residues from the collisions of 25 MeV/nucleon ⁸⁶Kr projectiles on ¹²⁴Sn and ¹¹²Sn targets is investigated and shown to provide information on the process of N/Z equilibration occurring between the projectile and the target. The logarithmic slopes α and β' of the residue yield ratios with respect to residue neutron number N and neutron excess N-Z are obtained as a function of the atomic number Z and mass number A, respectively, whereas excitation energies are deduced from velocities. The relation of the isoscaling parameters α and β' with the N/Z of the primary (excited) projectile fragments is employed to gain access to the degree of N/Z equilibration prior to fragmentation as a function of excitation energy. A monotonic relation between the N/Z difference of fragmenting quasiprojectiles and their excitation energy is obtained indicating that N/Z equilibrium is approached at the highest observed excitation energies. Simulations with a deep-inelastic transfer model are in overall agreement with the isoscaling conclusions. The present residue isoscaling approach to N/Z equilibration offers an attractive tool of isospin and reaction dynamics studies in collisions involving beams of stable or rare isotopes

[en] The production of neutron-rich rare isotopes around the Fermi energy is investigated in the present work. A large enhancement in the production of neutron-rich projectile residues has been observed in the reactions of a 25 MeV/nucleon ⁸⁶Kr beam with the neutron rich ⁶⁴Ni and ¹²⁴Sn targets relative to the predictions of the EPAX parametrization of high-energy fragmentation, as well as relative to the reaction with the less neutron-rich ¹¹²Sn target. The present data demonstrate the significant influence of the target neutron-to-proton ratio (N/Z) in peripheral collisions at Fermi energies. A hybrid model based on a deep-inelastic transfer code (DIT) followed by a statistical de-excitation code was found to account for part of the observed large cross sections. The DIT simulation indicates that the neutron skins of the neutron-rich ⁶⁴Ni and ¹²⁴Sn target nuclei play an important role in the production mechanism. From a practical viewpoint, such reactions between massive neutron-rich nuclei offer a novel synthetic avenue to access extremely neutron-rich rare isotopes towards the neutron-drip line

[en] The production of n-rich rare isotopes around and below the Fermi energy is investigated using beams from the K500 Superconducting Cyclotron and the MARS recoil separator at the Cyclotron Institute of Texas A and M University. The experimental results from the reactions of 25 MeV/nucleon ⁸⁶Kr + ⁶⁴Ni and 21 MeV/nucleon ¹²⁴Sn + ¹²⁴Sn are presented and compared with simulations. The calculations involve a deep inelastic transfer (DIT) code for the primary interaction stage followed by the code GEMINI for the de-excitation stage. The results are also compared with the EPAX parametrization. The data on the 25 MeV/nucleon ⁸⁶Kr + ⁶⁴Ni reaction show that both proton-removal and several-neutron pick-up isotopes are produced. An enhancement is observed in the production of n-rich isotopes close to the projectile relative to the predictions of DIT/GEMINI and the expectations of EPAX. The data of 21 MeV/nucleon ¹²⁴Sn + ¹²⁴Sn for fragments away from the projectile (Z=30-20) show also production of very n-rich nuclides, despite the less peripheral character of these collisions. In general, the large cross sections of n-rich nuclides from these reactions around the Fermi energy indicate that they may be exploited to produce beams of very n-rich rare isotopes. The application of such reactions in current plans of rare beam production at Texas A and M using a superconducting solenoid line will be described

No abstract available

[en] The production of secondary beams of radioactive ions has begun to play an important role in the investigations of heavy-ion reaction mechanisms. The values of isospin available from these exotic beams allows another degree of freedom to be investigated in the equilibration and fragmentation of hot nuclei. The first experiments of isospin equilibration are discussed. Fragment yields and energy spectra are presented as a function of the N/Z of the colliding system. The equilibration of the N/Z degree of freedom on the timescale of emission of IMFs is examined as a function of the collisional energy of the system. The implications on fragmentation models are explored. And, future directions for reaction mechanism studies with beams of radioactive ions are discussed

[en] The combination of the K500 superconducting cyclotron and the recoil spectrometer MARS have been used to generate secondary radioactive ion beams ranging from ⁷Be at 12 MeV/u to ⁶²Ga at 37 MeV/u. Secondary beams are produced via transfer reactions in inverse kinematics using stable beams from the cyclotron on gas targets. The radioactive beams have been used for reaction measurements and β-decay studies

[en] The cross sections and velocity distributions of heavy residues from the reaction of 20 A MeV ¹²⁴Sn+²⁷Al have been measured at forward angles using the MARS recoil separator at Texas A and M in a wide mass range. A consistent overall description of the measured cross sections and velocity distributions was achieved using a model calculation employing the concept of deep-inelastic transfer for the primary stage of peripheral collisions, pre-equilibrium emission and incomplete fusion for the primary stage of more violent central collisions and the statistical model of multifragmentation (SMM code) for the deexcitation stage. An alternative calculation employing the sequential binary decay (GEMINI code) could not reproduce the observed yields of the residues from violent collisions (A<90) due to different kinematic properties. The success of SMM demonstrates that the heavy residues originate from events where a competition of thermally equilibrated fragment partitions takes place rather than a sequence of binary decays

[en] Isotopic composition of the fragments emitted during the multifragmentation of ⁵⁸Ni+⁵⁸Ni, ⁵⁸Fe+⁵⁸Ni, ⁵⁸Ni+⁵⁸Fe, and ⁵⁸Fe+⁵⁸Fe was studied at beam energies of 30, 40, and 47 MeV/nucleon. Within the context of a grand-canonical approach, relative free neutron and proton densities, extracted from the measured isotope and isotone yield ratios, suggest that the neutron content of the vapor phase increases with the isospin (N/Z) of the initial colliding nuclei and decreases with the beam energy

[en] Properties of a logarithmic, large-solid-angle detector telescope for measuring the spectra of light charged particles and/or complex fragments produced in intermediate-energy nuclear reactions are described. Light-ion identification with a phoswich detector which consists of transmission photodiode ΔE and CsI(T ell) E elements is also discussed, as is the response of silicon microstrip detectors to fission fragments. 6 figs., 4 figs

[en] For many years it has been speculated that excited nuclei would undergo a liquid to vapor phase transition. For even longer, it has been known that clusterization in a vapor carries direct information on the liquid-vapor equilibrium according to Fisher's droplet model. Now the thermal component of the 8 GeV/c pion + 197 Au multifragmentation data of the ISiS Collaboration is shown to follow the scaling predicted by Fisher's model, thus providing the strongest evidence yet of the liquid to vapor phase transition