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Register a new userProduction of hot nuclei in Fermi energy domain: from peripheral to central collisions
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The production mechanism of highly excited nuclei in the Fermi energy domain is investigated. A phenomenological approach, based on the exciton model, is used for the description of pre-equilibrium emission. A model of deep inelastic transfer is employed for the peripheral collisions in the post-pre-equilibrium stage. An approach to describe more central collisions is proposed. A geometric overlap formula is employed in a way suitable for given energy domain. A simple geometric approach describing the interaction of participant and spectator zones is used to determine the incomplete fusion channel. Excitation energies of both fragments are determined. Results of the calculation are compared to available experimental data and an overall satisfactorily agreement is obtained. The models ability to describe the production of the hot nuclei can be employed in the study of multifragmentation and/or in the production of rare beams.
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A production mechanism of highly excited nuclei formed in violent collisions in the Fermi energy domain is investigated. The collision of two nuclei is decomposed into several stages which are treated separately. Simplified exciton concept is used for the description of pre-equilibrium emission. A modified spectator-participant scenario is used where motion along classical Coulomb trajectories is assumed. The participant and one of the spectator zones undergo incomplete fusion. Excitation energies of both cold and hot fragment are determined. Results of the calculation are compared to recent experimental data in the Fermi energy domain. Data on hot projectile-like, mid-velocity and fusion-like sources are described consistently. Geometric aspects of pre-equilibrium emission are revealed. Explanations to previously unexplained experimental phenomena are given. Energy deposited into non-thermal degrees of freedom is estimated.
Pauli blocking is carefully investigated for the processes of $NN rightarrow N Delta$ and $Delta rightarrow N pi$ in heavy-ion collisions, aiming at a more precise prediction of the $pi^-/ pi^+$ ratio which is an important observable to constrain the high-density symmetry energy. We use the AMD+JAM approach, which combines the antisymmetrized molecular dynamics for the time evolution of nucleons and the JAM model to treat processes for $Delta$ resonances and pions. As is known in general transport-code simulations, it is difficult to treat Pauli blocking very precisely due to unphysical fluctuations and additional smearing of the phase-space distribution function, when Pauli blocking is treated in the standard method of JAM. We propose an improved method in AMD+JAM to use the Wigner function precisely calculated in AMD as the blocking probability. Different Pauli blocking methods are compared in heavy-ion collisions of neutron-rich nuclei, ${}^{132}mathrm{Sn}+{}^{124}mathrm{Sn}$, at 270 MeV/nucleon. With the more accurate method, we find that Pauli blocking is stronger, in particular for the neutron in the final state in $NN rightarrow N Delta$ and $ Delta to Npi$, compared to the case with a proton in the final state. Consequently, the $pi^-/pi^+$ ratio becomes higher when the Pauli blocking is improved, the effect of which is found to be comparable to the sensitivity to the high-density symmetry energy.
Within a dynamical and statistical approach we study the main regularities in production of hypernuclei coming from projectile and target residues in relativistic ion collisions. We demonstrate that yields of hypernuclei increase considerably above the energy threshold for Lambda hyperons, and there is a saturation for yields of single hypernuclei with increasing the beam energy up to few TeV. Production of specific hypernuclei depend very much on the isotopic composition of the projectile, and this gives a chance to obtain exotic hypernuclei that may be difficult to reach in traditional hypernuclear experiments. Possibilities for the detection of such hypernuclei with planned and available relativistic ion facilities are discussed.
The short-range correlation (SRC) induced by the tensor force in the isosinglet neutron-proton interaction channel leads to a high-momentum tail (HMT) in the single-nucleon momentum distributions n(k) in nuclei. Owing to the remaining uncertainties about the tensor force, the shape of the nucleon HMT may be significantly different from the dilute interacting Fermi gas model prediction $n(k) sim1/k^4$ similar to the HMT in cold atoms near the unitary limit. Within an isospin- and momentum-dependent Boltzmann-Uehling-Uhlenbeck transport model incorporating approximately the nucleon HMT, we investigate hard photon emissions in $^{14}$N+$^{12}$C and $^{48}$Ca+$^{124}$Sn reactions at beam energies around the Fermi energy. Imprints of different shapes of the HMT on the energy spectrum, angular distribution and transverse momentum spectrum of hard photons are studied. While the angular distribution does not carry any information about the shape of the nucleon HMT, the energy spectra and especially the mid-rapidity transverse momentum spectra of hard photons are found to bare strong imprints of the shapes of nucleon HMTs in the two colliding nuclei.
Ensembles of single-source events, produced in peripheral and central collisions and correponding respectively to quasi-projectile and quasi-fusion sources, are analyzed. After selections on fragment kinematic properties, excitation energies of the sources are derived using the calorimetric method and the mean behaviour of fragments of the two ensembles are compared. Differences observed in their partitions, especially the charge asymmetry, can be related to collective energy deposited in the systems during the collisions.
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