Using symmetric 112Sn+112Sn, 124Sn+124Sn collisions as references, we probe isospin diffusion in peripheral asymmetric 112Sn+124Sn, 124Sn+112Sn systems at an incident energy of E/A=50 MeV. Isoscaling analyses imply that the quasiprojectile and quasitarget in these collisions do not achieve isospin equilibrium, permitting an assessment of isospin transport rates. We find that comparisons between isospin sensitive experimental and theoretical observables, using suitably chosen scaled ratios, permit investigation of the density dependence of the asymmetry term of the nuclear equation of state.
We report a study of ν(μ) charged-current quasielastic events in the segmented scintillator inner tracker of the MINERvA experiment running in the NuMI neutrino beam at Fermilab. The events were selected by requiring a μ- and low calorimetric recoil energy separated from the interaction vertex. We measure the flux-averaged differential cross section, dσ/dQ², and study the low energy particle content of the final state. Deviations are found between the measured dσ/dQ² and the expectations of a model of independent nucleons in a relativistic Fermi gas. We also observe an excess of energy near the vertex consistent with multiple protons in the final state.
Isotope, isotone and isobar yield ratios are utilized to obtain an estimate of the isotopic composition of the gas phase, i.e., the relative abundance of free neutrons and protons at breakup. Within the context of equilibrium calculations, these analyses indicate that the gas phase is enriched in neutrons relative to the liquid phase represented by bound nuclei.
We have isolatedνµ charged-current quasi-elastic interactions occurring in the segmented scintillator tracking region of the MINERvA detector running in the NuMI neutrino beam at Fermilab. We measure the flux-averaged differential cross-section, dσ/dQ 2 , and compare to several theoretical models of quasi-elastic scattering. Good agreement is obtained with a model where the nucleon axial mass, MA, is set to 0.99 GeV/c 2 but the nucleon vector form factors are modified to account for the observed enhancement, relative to the free nucleon case, of the cross-section for the exchange of transversely polarized photons in electron-nucleus scattering. Our data at higher Q 2 favor this interpretation over an alternative in which the axial mass is increased.
We develop an improved Statistical Multifragmentation Model that provides the capability to calculate calorimetric and isotopic observables with precision. With this new model we examine the influence of nuclear isospin on the fragment elemental and isotopic distributions. We show that the proposed improvements on the model are essential for studying isospin effects in nuclear multifragmentation. In particular, these calculations show that accurate comparisons to experimental data require that the nuclear masses, free energies and secondary decay must be handled with higher precision than many current models accord.
The fusion cross section for 12 C+ 13 C has been measured down to Ec.m.=2.6 MeV at which the cross section is of the order of 20 nb. By comparing the cross sections for the three carbon isotope systems, 12 C+ 12 C, 12 C+ 13 C and 13 C+ 13 C, it is found that the cross sections for 12 C+ 13 C and 13 C+ 13 C provide an upper limit for the fusion cross section of 12 C+ 12 C over a wide energy range. After calibrating the effective nuclear potential for 12 C+ 12 C using the 12 C+ 13 C and 13 C+ 13 C fusion cross sections, it is found that a coupled-channels calculation with the Incoming Wave Boundary Condition (IWBC) is capable of predicting the major peak cross sections in 12 C+ 12 C. A qualitative explanation for this upper limit is provided by the Nogami-Imanishi model and level density differences among the compound nuclei. It is found that the strong resonance found at 2.14 MeV in 12 C+ 12 C exceeds this upper limit by a factor of more than 20. The preliminary result from the most recent measurement shows a much smaller cross section at this energy which agrees with our predicted upper limit.
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