arXiv subjects

Aldo Bonasera

Publications and source records attributed to Aldo Bonasera.

At least 37 records · Page 2Linked to original sources

arXiv2013

Using Light Charged Particles to Probe the Asymmetry Dependence of the Nuclear Caloric Curve

Recently, we observed a clear dependence of the nuclear caloric curve on neutron-proton asymmetry $\frac{N-Z}{A}$ through examination of fully reconstructed equilibrated quasi-projectile sources produced in heavy ion collisions at E/A = 35 MeV. In the present work, we extend our analysis using multiple light charged particle probes of the temperature. Temperatures are extracted with five distinct probes using a kinetic thermometer approach. Additionally, temperatures are extracted using two probes within a chemical thermometer approach (Albergo method). All seven measurements show a significant linear dependence of the source temperature on the source asymmetry. For the kinetic thermometer, the strength of the asymmetry dependence varies with the probe particle species in a way which is consistent with an average emission-time ordering.

nucl-ex↗

arXiv2012

Asymmetry Dependence of the Nuclear Caloric Curve

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. The caloric curve extracted with the momentum quadrupole fluctuation thermometer shows that the temperature varies linearly with quasi-projectile asymmetry (N-Z)/A. 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.

nucl-ex↗

arXiv2012

On The Expansion and Fate Of The Universe

The evolution of the universe from an initial dramatic event, the Big-Bang, is firmly established. Hubble's law [1] (HL) connects the velocity of galactic objects and their relative distance: v(r)=Hr, where H is the Hubble constant. In this work we suggest that HL is not valid at large distances because of total energy conservation. We propose that the velocity can be expanded in terms of their relative distance and produce a better fit to the available experimental data. Using a simple 'dust' universe model, we can easily calculate under which conditions an (unstable) equilibrium state can be reached and we can estimate the values of the matter present in the universe as well as the 'dark energy'. We do not need to invoke any 'dark energy', its role being played by the kinetic correction. The resulting picture is that the universe might reach an unstable equilibrium state whose fate will be decided by fluctuations: either collapse or expand forever.

physics.gen-ph↗

arXiv2012

Hydrodynamic Scaling Analysis of Nuclear Fusion driven by ultra-intense laser-plasma interactions

We discuss scaling laws of fusion yields generated by laser-plasma interactions. The yields are found to scale as a function of the laser power. The origin of the scaling law in the laser driven fusion yield is derived in terms of hydrodynamic scaling. We point out that the scaling properties can be attributed to the laser power dependence of three terms: the reaction rate, the density of the plasma and the projected range of the plasma particle in the target medium. The resulting scaling relations have a predictive power that enables estimating the fusion yield for a nuclear reaction which has not been investigated by means of the laser accelerated ion beams.

physics.plasm-ph↗

arXiv2011

Higher Order Corrections to Density and Temperature of Fermions from Quantum Fluctuations

A novel method to determine the density and temperature of a system based on quantum Fermionic fluctuations is generalized to the limit where the reached temperature T is large compared to the Fermi energy εf . Quadrupole and particle multiplicity fluctuations relations are derived in terms of T . The relevant Fermi integrals are numerically solved for any values of T and compared to the analytical approximations. The classical limit is obtained, as expected, in the limit of large temperatures and small densities. We propose simple analytical formulas which reproduce the numerical results, valid for all values of T . The entropy can also be easily derived from quantum fluctuations and give important insight for the behavior of the system near a phase transition. A comparison of the quantum entropy to the entropy derived from the ratio of the number of deuterons to neutrons gives a very good agreement especially when the density of the system is very low.

nucl-th↗

arXiv2011

Non-Abelian behavior of $α$ Bosons in cold symmetric nuclear matter

The ground state energy of infinite symmetric nuclear matter is usually described by strongly interacting nucleons obeying the Pauli exclusion principle. We can imagine a unitary transformation which groups four non identical nucleons (i.e. with different spin and isospin) close in coordinate space. Those nucleons, being non identical, do not obey the Pauli principle, thus their relative momenta are negligibly small (just to fulfill the Heisenberg principle). Such a cluster can be identified with an $α$ boson. But in dense nuclear matter, those $α$ particles still obey the Pauli principle since are constituted of Fermions. The ground state energy of nuclear matter $α$ clusters is the same as for nucleons, thus it is degenerate. We could think of $α$ particles as vortices which can now braid, for instance making $^8Be$ which leave the ground state energy unchanged. Further braiding to heavier clusters ($^{12}C$, $^{16}O$..) could give a different representation of the ground state at no energy cost. In contrast d-like clusters (i.e. N=Z odd-odd nuclei, where N and Z are the neutron and proton number respectively) cannot describe the ground state of nuclear matter and can be formed at high excitation energies (or temperatures) only. We show that even-even, N=Z, clusters could be classified as non-Abelian states of matter. As a consequence an $α$ condensate in nuclear matter might be hindered by the Fermi motion, while it could be possible a condensate of $^8Be$ or heavier clusters.

nucl-th↗

arXiv2011

Density and Temperature of Bosons from Quantum Fluctuations

A method to determine the density and temperature of a system is proposed based on quantum fluctuations typical of Bosons in the limit where the reached temperature T is close to the critical temperature $T_c$ for a Bose condensate at a given density $ρ$. Quadrupole and particle multiplicity fluctuations relations are derived in terms of $\frac{T}{T_c}$. This method is valid for weakly interacting infinite and finite Boson systems. As an example, we apply it to heavy ion collisions using the Constrained Molecular Dynamics (CoMD) approach which includes the Fermi statistics. The model shows some clusterization into deuteron and $α$ clusters which could suggest a Bose condensate. However, our approach demonstrates that in the model there is no Bose condensate but it gives useful informations to be tested experimentally. We stress the differences with methods based on classical approximations. The derived 'quantum' temperatures are systematically higher than the corresponding 'classical' ones. The role of the Coulomb charge of fragments is discussed.

nucl-th↗

arXiv2011

Deuteron-induced reactions generated by intense Lasers for PET isotope production

We investigate the feasibility of using laser accelerated protons/deuterons for positron emission tomography (PET) isotope production by means of the nuclear reactions $^{11}$B($p,n$)$^{11}$C and $^{10}$B($d,n$)$^{11}$C. The second reaction has a positive Q-value and no energy threshold. One can, therefore, make use of the lower energy part of the laser-generated deuterons, which includes the majority of the accelerated deuterons. The $^{11}$C produced from the reaction $^{10}$B($d,n$)$^{11}$C is estimated to be 7.4 $\times$ 10$^{9}$ per laser-shot at the Titan laser at Lawrence Livermore National Laboratory. Meanwhile a high-repetition table top laser irradiation is estimated to generate 3.5 $\times$ 10$^7$ $^{11}$C per shot from the same reaction. In terms of the $^{11}$C activity, it is about 2 $\times$ 10$^4$ Bq per shot. If this laser delivers kHz, the activity is integrated to 1 GBq after 3 minutes. The number is sufficient for the practical application in medical imaging for PET.

physics.plasm-ph↗

arXiv2010

Density and Temperature of Fermions from Quantum Fluctuations

A novel method to determine the density and temperature of a system is proposed based on quantum fluctuations typical of Fermions in the limit where the reached temperature T is small compared to the Fermi energy $ε_f$ at a given density $ρ$. Quadrupole and particle multiplicity fluctuations relations are derived in terms of $\frac{T}{ε_f}$. This method is valid for infinite and finite fermionic systems, in particular we apply it to heavy ion collisions using the Constrained Molecular Dynamics (CoMD) approach which includes the Fermi statistics. A preliminary comparison to available experimental data is discussed as well. We stress the differences with methods based on classical approximations. The derived 'quantum' temperatures are systematically lower than the corresponding 'classical' ones. With the proposed method we may get important informations on the Equation of State (EOS) of quantum Fermi systems to order O($\frac{T}{ε_f})^3$, in particular near the Liquid-Gas (LG) phase transition and at very low densities where quantum effects are dominant.

nucl-th↗

arXiv2010

Virial Expansion of the Nuclear Equation of State

We study the equation of state (EOS) of nuclear matter as function of density. We expand the energy per particle (E/A) of symmetric infinite nuclear matter in powers of the density to take into account 2,3,. . .,N-body forces. New EOS are proposed by fitting ground state properties of nuclear matter (binding energy, compressibility and pressure) and assuming that at high densities a second order phase transition to the Quark Gluon Plasma (QGP) occurs. The latter phase transition is due to symmetry breaking at high density from nuclear matter (locally color white) to the QGP (globally color white). In the simplest implementation of a second order phase transition we calculate the critical exponent ? by using Landau's theory of phase transition. We find ? = 3. Refining the properties of the EOS near the critical point gives ? = 5 in agreement with experimental results. We also discuss some scenarios for the EOS at finite temperatures.

nucl-th↗

arXiv2009

Circumstantial evidence for a non-Maxwellian plasma from femtosecond laser-matter interaction

We study ion acceleration mechanisms in laser-plasma interactions using neutron spectroscopy. We consider different types of ion-collision mechanisms in the plasma, which cause the angular anisotropy of the observed neutron spectra. These include the collisions between an ion in the plasma and an ion in the target, and the collisions between two ions in the hot plasma. By analyzing the proton spectra, we suggest that the laser-generated plasma consists of at least two components, one of which collectively accelerated and can also produce anisotropy in the angular distribution of fusion neutrons.

physics.plasm-ph↗

arXiv2008

Application of the X-ray laser to muon-catalyzed d-t fusion

We discuss the alpha-muon sticking coefficient in the muon-catalysed d-t fusion in the framework of the Constrained Molecular Dynamics model. Especially the influence of muonic chaotic dynamics on the sticking coefficient is brought into focus. The chaotic motion of the muon affects not only the fusion cross section but also the muon-alpha sticking coefficient. Chaotic systems lead to lar ger enhancements with respect to regular systems because of the reduction of the tunneling region. Moreover they give smaller sticking probabilities than those of regular events. By utilizing a characteristic of the chaotic dynamics one can avoid losing the muon in the muCF cycle. W e propose that the application of the so-called microwave ionization of a Rydberg atom to the present case could lead to the enhancement of the reactivation process by using X-rays.

physics.atom-ph↗

arXiv2007

Isospin Effects on Astrophysical S-Factors

We estimate the ratios of bare astrophysical S-factors at zero incident energy for proton and deuteron induced reactions in a model which assumes a compound nucleus formation probability plus a statistical decay. The obtained ratios agree well with available experimental values, as far as the reactions which have dominant s-wave entrance channel components are investigated. Due to its simplicity the model could be used as a guidance for predictions on reactions which have not been investigated yet.

nucl-th↗

arXiv2007

Bound Electron Screening Corrections to Reactions in Hydrogen Burning Processes

How important would be a precise assessment of the electron screening effect, on determining the bare astrophysical $S$-factor ($S_b(E)$) from experimental data? We compare the $S_b(E)$ obtained using different screening potentials, (1) in the adiabatic limit, (2) without screening corrections, and (3) larger than the adiabatic screening potential in the PP-chain reactions. We employ two kinds of fitting procedures: the first is by the conventional polynomial expression and the second includes explicitly the contribution of the nuclear interaction and based on a statistical model. Comparing bare $S$-factors that are obtained by using different screening potentials, all $S_b(E)$ are found to be in accord within the standard errors for most of reactions investigated, as long as the same fitting procedure is employed. $S_b(E)$ is, practically, insensitive to the magnitude of the screening potential.

nucl-th↗

arXiv2006

Alpha-muon sticking and chaos in muon-catalysed "in flight" d-t fusion

We discuss the alpha-muon sticking coefficient in the muon-catalysed ``in flight" d-t fusion in the framework of the Constrained Molecular Dynamics model. Especially the influence of muonic chaotic dynamics on the sticking coefficient is brought into focus. The chaotic motion of the muon affects not only the fusion cross section but also the $μ-α$ sticking coefficient. Chaotic systems lead to larger enhancements with respect to regular systems because of the reduction of the tunneling region. Moreover they give smaller sticking probabilities than those of regular events. By utilizing a characteristic of the chaotic dynamics one can avoid losing the muon in the $μ$CF cycle. We propose the application of the so-called ``microwave ionization of a Rydberg atom" to the present case which could lead to the enhancement of the reactivation process by using X-rays.

physics.atom-ph↗

arXiv2005

Influence of the Electronic Chaotic Motion on the Fusion Dynamics at Astrophysical Energies

We perform semi-classical molecular dynamics simulations of screening by bound electrons in low energy nuclear reactions. In our simulations quantum effects corresponding to the Pauli and Heisenberg principle are enforced by constraints. In addition to the well known adiabatic and sudden limits, we propose a new "dissipative limit" which is expected to be important not only at high energies but in the extremely low energy region. The dissipative limit is associated with the chaotic behavior of the electronic motion. It affects also the magnitude of the enhancement factor. We discuss also numerical experiments using polarized targets. The derived enhancement factors in our simulation are in agreement with those extracted within the $R$-matrix approach.

nucl-th↗

arXiv2005

Constrained Molecular Dynamics Simulations of Atomic Ground-States

Constrained molecular dynamics(CoMD) model, previously introduced for nuclear dynamics, has been extended to the atomic structure and collision calculations. Quantum effects corresponding to the Pauli and Heisenberg principle are enforced by constraints, in a parameter-free way. Our calculations for small atomic system, H, He, Li, Be, F reproduce the ground-state binding energies within 3%, compared with the results of quantum mechanical Hartree-Fock calculations.

physics.atom-ph↗

arXiv2004

Chaos driven fusion enhancement factor at astrophysical energies

We perform molecular dynamics simulations to assess the screening effects by bound target electrons in low energy nuclear reactions in laboratories. Quantum effects corresponding to the Pauli and Heisenberg principle are enforced by constraints. We show that the enhancement of the average cross section and of its variance is due to the perturbations induced by the electrons.This gives a correlation between the maximum amplitudes of the inter-nuclear oscillational motion and the enhancement factor. It suggests that the chaotic behavior of the electronic motion affects the magnitude of the enhancement factor.

nucl-th↗