Clustering in alpha conjugate nuclei Schmidt, K.; Kim, E. J.; Wuenschel, S. ...
EPJ Web of Conferences,
01/2015, Letnik:
88
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Characteristics of the decay of alpha like nuclei produced in various reactions with alpha conjugate nuclei are discussed. We observe a significant number of events in which a large fraction of the ...system breaks up into alpha-conjugate nuclei. Lighter fragments in the various decay channels appear to originate from a neck-like region between 4 and 7 cm/ns whereas the heavier fragments appear to originate from velocities near the beam velocity. This behavior is consistent with a hierarchy effect that cannot be explained by statistical processes.
Yields of equatorially emitted light isotopes, 1 ≤ Z ≤ 14, observed in ternary fission in the reaction 241Pu(nth,f) are employed to determine apparent chemical equilibrium constants for ...lowtemperature and low-density nuclear matter. The degree of equilibration and role of medium modifications are probed through a comparison of experimentally derived reaction quotients with equilibrium constants calculated using a relativistic mean-field model employing a universal medium modification correction for the attractive σ meson coupling. The results of these comparisons indicate that equilibrium is achieved for the lighter ternary fission isotopes. For the heavier isotopes experimental reaction quotients are well below calculated equilibrium constants. This is attributed to a dynamical limitation reflecting insufficient time for full equilibrium to develop. The role of medium effects leading to yield reductions is discussed as is the apparent enhancement of yields for 8He and other very neutron rich exotic nuclei.
Nuclear fragment yield data has been analyzed using the Landau free energy description to investigate the critical phenomena in the fragmentation of quasiprojectile in the reactions 78,86Kr+58,64Ni ...at beam energy of 35 MeV/nucleon. The data on mirror nuclei yield ratio for A=3 and 7 showed an exponential dependence on the isospin asymmetry of the quasiprojectile as predicted by the Landau free energy approach. The slope parameter, obtained from linear fit to the plots of the logarithm of mirror nuclei yield ratios as a function of isospin asymmetry of the fragmenting source provided a reasonable estimate of the nuclear symmetry energy, and showed a systematic decrease with increasing excitation energy of the quasiprojectile.
In order to reconstruct the yields of the primary hot fragments at the time of their formation, the neutron multiplicity associated with intermediate mass fragments (IMFs) was determined ...experimentally using the kinematical focusing of light particles emitted along the direction of each IMF. The reaction system 64Zn + 112Sn has been studied at 40 A MeV. IMFs were isotopically identified with Z up to 18. Neutrons were measured at 16 angles around the direction of the IMFs. The exctrated neutron multiplicities are in good agreement with those calculated AMD+Gemini simulations.
A basic feature of the nuclear equation of state is not yet understood: the dependence of the nuclear caloric curve on the neutron-proton asymmetry. Predictions of theoretical models differ on the ...magnitude and even the sign of this dependence. In this work, the nuclear caloric curve is examined for fully reconstructed quasi-projectiles around mass A = 50. Two independent thermometers, the momentum quadrupole fluctuation thermometer and the Albergo yield ratio thermometer, are used to extract the caloric curve. For both methods, the caloric curve extracted shows that the temperature varies linearly with quasi-projectile asymmetry For the momentum quadrupole fluctuation thermometer, an increase in asymmetry of 0.15 units corresponds to a decrease in temperature on the order of 1 MeV. These results also highlight the importance of a full quasi-projectile reconstruction in the study of thermodynamic properties of hot nuclei.
The experimental liquid-gas phase transition signals are examined for the quasiprojectile (QP) reconstructed from the reactions of 40Ar + 27Al, 48Ti, 58Ni at 47 MeV/nucleon, using measures of caloric ...curve, multiplicity derivative, moment parameters, and fluctuation of maximum fragment charge number (NVZ). The QP source is reconstructed, using moving source parametrizations on an event-by-event basis. For the determination of the temperature, a quadrupole fluctuation thermometer is used. Deuterons are chosen for the thermometer to minimize the Coulomb and secondary sequential decay effects. Here, a new event-by-event method is proposed for the thermometer to determine the temperature. All measures show a characteristic signature around the temperature T = 9.0 ± 0.4 MeV, which may suggest that the QP system goes into the liquid-gas phase transition at Tc = 8.3 ± 0.4 MeV after the Coulomb correction.
We will show that the Thick Target Inverse Kinematics (TTIK) technique can be used to investigate the breakup of excited selfconjugate nuclei into many alpha particles. Two test runs were performed ...at Cyclotron Institute of Texas A&M University to study the reaction 20Ne+α at maximum beam energies of 10 and 12 AMeV. Due to the limited statistics, only events with alpha multiplicity up to three were analyzed. The analysis of the three α-particle emission data allowed the identification of the Hoyle state and other 12C excited states decaying into three alpha particles. The results will be shown and compared with other data available in the literature.
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