The symmetry energy and the isoscaling properties of the fragments produced in multifragmentation of 40Ar, 40Ca + 58Fe, 58Ni reactions at 25, 33, 45 and 53 MeV/nucleon were investigated within the framework of a statistical multifragmentation model. The isoscaling parameter, α from the hot primary and cold secondary fragment yield distributions, was studied as a function of the excitation energy, isospin (neutronto- proton asymmetry), and fragment symmetry energy. Through changing the symmetry energy in the statistical multifragmentation model to describe the experimental data, it is observed that the isoscaling parameter α decreases with increasing excitation energy and decreases with decreasing symmetry energy. The parameter α is also observed to increase with increasing difference in the isospin of the fragmenting system. The sequential decay of the primary fragments into secondary fragments show very little influence on the isoscaling parameter when studied as a function of excitation energy. However, the symmetry energy has a strong influence on the isospin properties of the hot fragments. The results indicate that the isospin properties of the fragments produced at high excitation energy and reduced density in multifragmentation reactions are sensitive to the symmetry energy, indicating that the properties of hot nuclei at excitation energies, densities, and isospin away from normal ground state nuclei are significantly different than those of normal (cold) nuclei at saturation density.

Many observables have been developed to study the effects of the two component nature of nuclei. This dissertation has experimentally probed caloric curves as well as scaling observables for their dependence on the asymmetric portion of the nuclear equation of state. Projectile fragmentation sources were identified from the reactions of 86,78Kr+64,58Ni at 35 MeV/A taken on the NIMROD-ISiS array. The angular coverage, excellent isotopic resolution, and Neutron Ball allow for quasi-complete event reconstruction in both charge and mass. A new thermometer for nuclear fragmentation studies has been derived and is presented here. In this thermometer, the temperature is obtained from fluctuations of the transverse momentum. The proton transverse momentum fluctuations are used in this thesis to study the N/Z dependence of the nuclear caloric curve. The caloric curve constructed from proton momentum fluctuations does not show a significant dependence on the source N/Z ratio. Two other thermometers have also been studied in this thesis: the double isotope ratio, and moving source slope thermometers. These thermometers show no statistically significant dependence on the source N/Z. The source density has been derived from the evolution of fragment Coulomb barriers with increasing E*/A. This density showed no source N/Z dependence. However, a strong evolution in source density over the E*/A=1.5-7.5 MeV region was observed. Fragment scaling was investigated through isoscaling and power law scaling. The power law scaling showed a strong dependence on the source N/Z. This source N/Z dependence was further investigated through isoscaling. The fragment yields of this data have been shown to exhibit consistent isoscaling for Z=1-17. In addition, isoscaling was observed in data cut on the E*/A of the source yielding decreasing slopes (a) as a function of E*/A. This decrease, normalized to the asymmetries of the sources (a/delta), has been linked to a decrease in the asymmetry coefficient Csym. This dissertation has shown that the experimentally observed decrease in Csym with E*/A is well correlated to the temperature and density changes experimentally observed in this data.

The symmetry energy is the energy difference between symmetric nuclear matter and pure neutron matter at a given density. Around normal nuclear density, i.e. p/p0 =1, and temperature, i.e. T = 0, the symmetry energy is approximately 23.5 MeV/nucleon for finite nuclear matter and 30 MeV/nucleon for infinite nuclear matter, but at other densities, the symmetry energies are very poorly understood. Since the symmetry energy is very important in understanding many aspects of heavy ion reactions, structure, and nuclear astrophysics, many different models have been developed and some predications of the density dependence of symmetry energy have been made. Intermediate energy heavy ion collisions provide a unique tool to probe the nuclear equation of state. The initial compression and the thermal shock in Fermi- Energy heavy ion collisions lead naturally to the production of nucleonic matter at varying temperatures and densities which are interesting in this context. Since the light particle emission during this stage witnesses each stage of the reaction, it carries essential information on the early dynamics and on the degree of equilibration at each stage of the reaction. The kinematic features and yields of emitted light particles and clusters in the invairant velocity frame have been exploited to probe the nature of the intermediate system and information on the Equation Of State (EOS) with emphasis on the properties of the low density participant matter produced in such collisions. In order to pursue this effort and broaden the density range over which the symmetry energies are experimentally determined we have now carried out a series of experiments in which the reactions of 112Sn and 124Sn with projectiles, ranging from 4He,10B, 20Ne, 40Ar to 64Zn, all at the same energy per nucleon, 47 Mev/u, were performed. In this series of experiments different collision systems should lead to different average densities. By careful comparisons of the yields, spectra and angular distributions observed for particle emission from these different systems we attempted to cleanly separate early emission resulting from nucleon-nucleon collisions from that resulting from evaporation from the thermalized system and obtain a much cleaner picture of the dynamic evolution of the hotter systems. The Albergo Model has been used to calculate the density and temperature, symmetry free energies with the isoscaling technique for systems with different N/Z ratios. Those are compared with Roepke Model results. Also other models like VEOS, Lattimer, and Shen-Toki have been added to calculate the alpha mass fraction in order to understand the properties of low density matter further.

The thesis studies the bulk deformation properties of the Skyrme nuclear energy densityfunctionals. Following simple arguments based on the leptodermous expansion andliquid drop model, the current research applies the nuclear density functional theory toassess the role of the surface symmetry energy in nuclei. To this end, one can validatethe commonly used functional parametrizations against the data on excitation energies ofsuperdeformed band-heads in Hg and Pb isotopes, and fission isomers in actinide nuclei.After subtracting shell effects, the results of our self-consistent calculations are consistentwith macroscopic arguments and indicate that experimental data on strongly deformedcongurations in neutron-rich nuclei are essential for optimizing future nuclear energy densityfunctionals. The resulting survey provides a useful benchmark for further theoreticalimprovements. Unlike in nuclei close to the stability valley, whose macroscopic deformabilityhangs on the balance of surface and Coulomb terms, the deformability of neutron-richnuclei strongly depends on the surface-symmetry energy; hence, its proper determinationis crucial for the stability of deformed phases of the neutron-rich matter and descriptionof fission rates for r-process nucleosynthesis. The results and consequent discussions fromthe thesis were published in Ref. [134].

Thesis advisor: Kevin S. Bedell / We investigate the structure of the equation of state of finite nuclear matter by examining the nature of isospin dependence in the (a)symmetry energy term. In particular, we include in the description of the binding energy fourth-order dependence with respect to the asymmetry factor, (N-Z)/A, and the regime of the l=0 Landau parameter, F0´ , is required to be less than –1. This modified equation predicts a minimum binding energy where N≠Z, in addition to the standard symmetric minimum when N=Z. Results with the new asymmetry energy term are compared with experimental binding and symmetry energies from standard semi-empirical mass formulas. Importantly, this method reveals one possible mechanism for producing the phenomenon of neutron excess which is seen in physical nuclei. / Thesis (BS) — Boston College, 2004. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Physics. / Discipline: College Honors Program.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23700号 / 理博第4790号 / 新制||理||1686(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 永江 知文, 准教授 銭廣 十三, 教授 中家 剛 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The Equation of State (EoS) of asymmetric nuclear matter has been explored through the study of mid-rapidity fragment dynamics from the 35 MeV/u $^{70}$Zn $^{70}$Zn, $^{64}$Zn $^{64}$Zn, and $^{64}$Ni $^{64}$Ni systems. The experimental data was collected at the Texas A and M Cyclotron Institute using the 4 NIMROD-ISiS array, which provided both event characterization and excellent isotopic resolution of charged particles. The transverse collective flow was extracted for proton, deuteron, triton, 3He, alpha, and 6He particles. Isotopic and isobaric effects were observed in the transverse flow of the fragments. In both cases, the transverse flow was shown to decrease with an increasing neutron content in the fragments. The (N/Z)sys dependence of the transverse flow and the difference betwen the triton and 3He flow were shown to be sensitive to the density dependence of the symmetry energy using the stochastic mean-field model. A stiff parameterization of Esym(p) was found to provide better agreement with the experimental data. The transverse flow for intermediate mass fragments (IMFs) was investigated, providing a new probe to study the nuclear EoS. A transition from the IMF flow strongly depending on the mass of the system, in the most violent collisions, to a dependence on the charge of the system, for the peripheral reactions, was observed. Theoretical simulations were used to show that the relative differences in the IMF flow are sensitive to the density dependence of the symmetry energy. The best agreement between the experiment and theory was achieved with a stiff Esym(p). A new method was developed in which correlations between the projectile-like and mid-rapidity fragments were examined using a scaled flow. Theoretical simulations were used to show that the scaled flow of the particles was connected to their average order of emission. The experimental results suggest that the mid-rapidity region is preferentially populated with neutron-rich light charged particles and the Z=3-4 IMFs at a relatively early stage in the collision. This work presents additional constraints on the nuclear EoS and insight into the mid-rapidity dynamics observed in Fermi energy heavy-ion collisions.

One-nucleon halo nuclei are exotic nuclei which can be seen as a core around which orbits a loosely-bound valence nucleon. They are usually studied through reactions such as elastic scattering and breakup. The ratio method has been developed as a tool to study one-neutron halo nuclei at high energies. It consists of the ratio of angular cross sections, breakup and elastic scattering, which removes most of the sensitivity to the reaction mechanism and to the reaction model. In the simple recoil excitation and breakup (REB) model, the ratio simplifies to a form factor dependent solely on the wave function of the projectile. By measuring this observable and comparing it to the REB form factor, i.e. in the ratio method, more detailed information on the structure of the halo could be obtained. For neutron-halo nuclei at high energy, the ratio observable obtained from accurate CDCC and DEA theoretical calculations follows its REB prediction. I study the extension of this method to lower energies of the reaction which could make the measurement appropriate to facilities such as SPIRAL2 (GANIL, Caen, France) and ReA12 at FRIB (Michigan State University) and to proton halos. This is done by comparing the REB form factor to dynamical calculations of the ratio. The reactions investigated are the reaction of 11Be, the archetypical one-neutron halo nucleus, on 12C, 40Ca and 208Pb targets at 20 MeV/nucleon and of 8B, the archetypical one-proton halo nucleus, on 12C, 58Ni and 208Pb targets at44 MeV/nucleon.For these reactions, the adiabatic assumption is no longer valid due to the effect of the Coulomb interaction. This effect is mainly visible at forward angle for 11Be and is aggravated for 8B by the fact that the halo is charged. The ratio works less well than for neutron-halos at intermediate and high energies. Nevertheless, the ratio is shown to be very sensitive to the orbital angular momentum l0 in which the halo is bound and its binding energy E0, i.e. the single-particle structure of the projectile. Variations of l0 and E0 induce visible changes in shape and in magnitude (up to several orders) of the ratio. Also, the agreement of the ratio with its REB prediction is best when the projectile is loosely-bound and for low l0, i.e. for s and p waves. The validity of the method is not affected by the use of energy ranges—or bins— in the projectile continuum. These tend to increase the cross section without changing the agreement of the ratio with its REB prediction. The applicability of the method is finally explored at high energy for proton-rich nuclei 17F, 25Al and 27P. I show that the ratio method works the latter since this nucleus is bound by a mere 0.870 MeV in the s-wave. For the other nuclei, although the agreement of the ratio with its REB prediction is less good than for neutron-halo nuclei at high energy, it still provides estimates of nuclear-structure features, such as l0 and E0 and could be applied in what can be called an approximate application of the ratio method. Heavy nuclei exhibit a neutron skin, i.e. a thin layer around the nucleus where only neutrons are found. The thickness of the skin is highly correlated with the slope of the symmetry energy. The process of coherent neutral-pion photoproduction is used to extract the nuclear density and hence the neutron-skin thickness of heavy nuclei. In order to analyse recent data on the photoproduction on 12C, 40,48Ca, 116, 120, 124Sn and 208Pb, I build a reaction code. My model uses the formalism of Kerman, McManus and Thaler (KMT) which allows to build the photoproduction matrix on a nucleus from the ones describing the elementary process on a single nucleon. Within the impulse approximation, the photoproduction is seen as the coherent sum of the photoproduction on each of the nucleons. In the plane wave impulse approximation (PWIA), no rescattering of the pion is considered after its production and the cross section is directly proportional to the Fourier transform of the density. Such process is taken into account at the distorted wave impulse approximation (DWIA) by considering a potential simulating the pion-nucleus interaction and built from the KMT formalism.The agreement of my model with the data is good, especially for 208Pb. The distortion has a significant impact on the photoproduction process. The sensitivity of the process to the density of the target is analysed by performing the calculations with several different densities calculated in different structure models. The distortion has the effect of deteriorating this sensitivity. In the particular case of a 208Pb target, the impact of variations of the neutron-skin thickness of around 0.1 fm on the photoproduction cross section is ten times smaller than the size of the error bars on the experimental data. These results, although less dramatic, hold for the tin targets, for which preliminary data exists. In the light of these results, the coherent neutral-pion photoproduction process does not seem to be suited in the study of the neutron-skin thickness. This conclusion goes in contrast to the results of recent measurements on 208Pb, for which the method was shown to be sensitive to fine details of the density. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished