Transport of angular momentum in damped nuclear reactions

Abstract

EXECUTIVE SUMMARYThe operation of an OTEC plant will result in the m~x~ng of large volumes of seawater from different depths within the ocean. Associated with this seawater will be suspended particulate material.This solid material is capable of both adsorbing and releasing transition metals. Because suspended particulate material is intimately involved in marine food webs and transition metals such as copper can have toxic effects, it is important to develop a sound methodology for characterizing and quantifying transition metals which will be associated with solid material passing through an OTEC plant.The characterization of soild-phase associated transition metals in the marine environment has largely been directed at marine sediments. Studies of sediment-associated transition metals have generally indicated that it is not possible to uniquely identify the solid phases or chemical speciation of a given metal. There are many reasons for this difficulty, but the probable major analytical problems arise from the fact that many of the transition metals of interest are present only in trace concentrations as adsorbed species on amorphous oxides or as coprecipitates. These difficulties have led to an approach in which transition metals are classified according to how easily they are solubilized when exposed to different types of chemical attack, as defined in chemical extraction schemes.There are at present a large number of different transition metal extraction schemes in use. Only rarely have these different techniques been carefully compared on a variety of solids from the marine environment. Consequently, it is often not possible to make a sound assessment of the results obtained by investigators who have used different extraction methods to characterize solid-phase associated transition metals or to select the most appropriate methodology for making measurements on a given type of solid material.In this study, several of the most widely accepted techniques were compared for many of the most commonly measured transition metals. The use of a variety of marine sediments, rather than trapped suspended particulate matter, was necessitated by both the relatively large amount of material needed for an examination of all the methods and the lack of any OTEC program collected particulate material.In order to determine the true extraction efficiency of the methods studied, all solid concentrations have been normalized to total metal concentration values as obtained by neutron activation analysis and/or x-ray fluorescence measurements.On weak, four intermediate strength and two strong metal extraction methods were studied individually.The weak method had the lowest extraction efficiency, but dissolved all solid carbonate phases. A potential problem with the weak method is that it does not retain extracted metals quantitatively in solution, but allows them to be adsorbed on remaining solids. The simplest of the four methods (0.5 N HCl) caused the release of lower amounts of most metals studied when compared to the other ...

Transport properties of isospin asymmetric nuclear matter using the time-dependent Hartree-Fock method

“…However, difficulties exist in modeling these reactions due to their timedependent non-equilibrium nature. The portioning of excitation energy between the final fragments [3,[24][25][26], the amount of irreversible energy dissipation as opposed to excitation of collective modes, conversion of angular momentum to intrinsic spins of the final fragments [27], influence of transfer [23,28,29] have all been subject to experimental [15,[30][31][32] scrutiny with often less than satisfactory comparisons [3,33]. Part of the complication arises from the model dependence of the experimental analysis.…”

Effect of nuclear periphery on nucleon transfer in peripheral collisions

“…An isoscaling study was carried out on the reactions 86 Kr+ 112 Sn and 86 Kr+ 124 Sn at 25 AMeV [3] and a correlation of the isoscaling parameter with isospin equilibration was observed [7]. Peripheral nucleus-nucleus collisions can be described theoretically using the model of deep-inelastic transfer [8] in combination with an appropriate model of de-excitation. Very good description of experimental observables was obtained [2,5,6,9] using the DIT model of Tassan-Got [10] and the de-excitation codes SMM [11] and GEMINI [12].…”

Beyond mean-field approach to heavy-ion reactions around the Coulomb barrier

“…According to the Langevin equation, neglecting contributions from the drift term, the variance is related to the diffusion coefficient according to [31,32] …”