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Lithospheric processes

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The main objective was to improve understanding of the origin and evolution of the Earth`s lithosphere by studying selected processes, such as deformation and magmatic intrusion during crustal extension, formation and extraction of mantle melts, fluid transport of heat and mass, and surface processes that respond to deep-seated events. Additional objectives were to promote and develop innovative techniques and to support relevant educational endeavors. Seismic studies suggest that underplating of crust by mantle melts is an important crustal-growth mechanism, that low-angle faults can be seismogenic, and that shear deformation creates mantle anisotropy near plate boundaries. Results of geochemical work determined that magmas from oceanic intraplate islands are derived from a uniform depth in the upper mantle, whereas melts erupted at mid-ocean ridges are mixed from a range of depths. The authors have determined the extent and style of fluid infiltration and trace-element distribution in natural magmatic systems, and, finally, investigated {sup 21}Ne as a tool for dating of surficial materials.
Date: November 1, 1997
Creator: Baldridge, W.S.; Wohletz, K. & Fehler, M.C.
Partner: UNT Libraries Government Documents Department

Exposure History of Separated Phases from the Kapoeta Meteorite

Description: The cosmogenic radionuclides, {sup 10}Be (1.5 Ma), {sup 26}Al (0.705 Ma), {sup 36}Cl (0.301 Ma), and {sup 53}Mn (3.7 Ma) were measured in selected clasts and matrix samples from the howardite Kapoeta. This work is an extension of that based on {sup 10}Be and {sup 26}Al [1]. Recent work based on measurements of cosmogenic {sup 21}Ne suggest the possibility of a complex recent exposure history for Kapoeta. The measurement of these radionuclides, in conjunction with production rates based on Monte Carlo calculations, can constrain exposure conditions and durations. Taken together, the radionuclide data are entirely consistent with a single stage 4{pi} exposure lasting {approximately} 3 Ma.
Date: January 14, 2000
Creator: Caffee, M W; Nishiizumi, K & Mazarik, J
Partner: UNT Libraries Government Documents Department

Measurement of the beta-neutrino correlation in laser trapped {sup 21}Na

Description: Trapped radioactive atoms are an appealing source for precise measurements of the beta-neutrino correlation coefficient, a, since the momentum of the neutrino can be inferred from the detection of the unperturbed low-energy recoil daughter nucleus. Sodium-21 is produced on-line at the 88'' cyclotron at Lawrence Berkeley National Laboratory, and 8e5 atoms have been maintained in a magneto-optical trap. A static electric field draws daughter Neon-21 ions to a microchannel plate detector and betas are detected in coincidence with a plastic scintillator beta detector. The Neon-21 time-of-flight distribution determines the beta neutrino correlation coefficient, a. The resulting charge-state distribution is compared to a simple model based on the sudden approximation which suggests a small but important contribution from nuclear recoil-induced ionization. A larger than expected fraction of the daughters are detected in positive charge-states, but no dependence on either the beta or recoil nucleus energy was observed. We find a = 0.5243 plus or minus 0.0092, which is in 3.6 sigma disagreement with the Standard Model prediction of a = 0.559 plus or minus 0.003. Aside from a deviation from the Standard Model, a possible explanation for the discrepancy is that the branching ratio to the first excited state is in error.
Date: June 1, 2003
Creator: Scielzo, Nicholas David
Partner: UNT Libraries Government Documents Department

Statistical methods for including two-body forces in large system calculations

Description: Large systems of interacting particles are often treated by assuming that the effect on any one particle of the remaining N-1 may be approximated by an average potential. This approach reduces the problem to that of finding the bound-state solutions for a particle in a potential; statistical mechanics is then used to obtain the properties of the many-body system. In some physical systems this approach may not be acceptable, because the two-body force component cannot be treated in this one-body limit. A technique for incorporating two-body forces in such calculations in a more realistic fashion is described. 1 figure.
Date: July 1, 1980
Creator: Grimes, S.M.
Partner: UNT Libraries Government Documents Department

Representative-vector method for calculating operator-moments

Description: The utility of operator-moments or traces in the various applications of spectral-distribution theory is well documented. To take full advantage of the powerful entree that spectral distribution theory offers in nuclear physics, it may be generally necessary to have many moments beyond th first two hamiltonian moments <H> and <H/sup 2/>. In order to calculate, for one example, level densities reliably in the excitation-energy regions of physical interest, it may be necessary to have the moments <J/sub z//sup 2/H/sup n/> and of course <H/sup n/> with n ranging as high as 8 or so. The subject of this paper is a new method for obtaining these higher moments which is based on the use of random multiparticle vectors, called random representative vectors (RRV), in conjunction with an appropriate shell-model space and hamiltonian. With this method it is possible to calculate average properties of very large spaces with well-defined symmetries by averaging the results over a relatively few RRV. The demonstration of the statistical formulas of the RRV method is given in the next section. In the following section numerical results are given for the test case of 5 nucleons in the single-particle orbits 1d/sub 5/2/, 2s/sub 1/2/; and 1d/sub 3/2/ (A = 21), as well as some results for 12 nucleons in the same orbits plus the 1f/sub 7/2/ orbit (A = 28). With the representative-vector method one can evaluate average moments of any operator O that commutes with H so long as the application of O to the RRV does not produce a new vector which exceeds the memory capacity of the computer. 3 figures, 5 tables. (RWR)
Date: September 1, 1979
Creator: Bloom, S.D. & Hausman, R.F. Jr.
Partner: UNT Libraries Government Documents Department

Half life of /sup 26/Al

Description: The half-life of /sup 26/Al has been redetermined because of suggestions of an error in the accepted value based on its use in calculating /sup 21/Ne production rates from cosmic rays in meteorites. Two solutions of /sup 26/Al were analyzed for the specific radioactivity and mass spectrometric determination of the /sup 26/Al concentration. The half-life obtained for /sup 26/Al was 7.05 x 10/sup 5/ years +- 3.7% at the two sigma level. This is identical to the accepted value of 7.16 x 10/sup 5/ years and indicates that problems with the /sup 21/Ne production rate is not due to an erroneous half-life.
Date: January 1, 1983
Creator: Norris, T.L.; Gancarz, A.J.; Rokop, D.J. & Thomas, K.W.
Partner: UNT Libraries Government Documents Department

Calculation of spin cutoff parameters using moment techniques

Description: Spectral distribution methods are often applied to the calculation of nuclear level densities. If their distribution in spin is required in addition to the total number of levels at each energy, the spin-cutoff parameter and its energy dependence must be known. Recent calculations of the spin-cutoff parameters have shown qualitative agreement with data. Reasons for the remaining discrepancies are discussed, and proecdures for improving agreement between theory and experiment are suggested. 8 figures.
Date: September 1, 1979
Creator: Grimes, S.M.
Partner: UNT Libraries Government Documents Department

Transfer and breakup reactions at intermediate energies

Description: The origin of the quasi-elastic peak in peripheral heavy-ion reactions is discussed in terms of inelastic scattering and transfer reactions to unbound states of the primary projectile-like fragment. The situation is analogous to the use of reverse kinematics in fusion reactions, a technique in which the object of study is moving with nearly the beam velocity. It appears that several important features of the quasi-elastic peak may be explained by this approach. Projectile-breakup reactions have attractive features for the study of nuclear structure. They may also be used to determine the partition of excitation energy in peripheral reactions. At intermediate energies, neutron-pickup reactions leading to four-body final states become important. Examples of experiments are presented that illustrate these points. 15 refs., 14 figs.
Date: April 1, 1986
Creator: Stokstad, R.G.
Partner: UNT Libraries Government Documents Department

Mound Facility activities in chemical and physical research: July-December 1979

Description: Research is reported in the following fields: isotope separation (Ar, C, He, Kr, Ne, O, Xe), low-temperature research (H intermolecular potential functions, gas analysis in trennschaukel), separation chemistry (/sup 229/Th, /sup 231/Pa, /sup 230/Th, /sup 234/U), separation research (liquid thermal diffusion, Ca isotope separation, molecular beam scattering, mutual diffusion of noble gas mixtures, lithium chemical exchange with cryptands), and calculations in plutonium chemistry (algorithms, valence in natural water). (DLC)
Date: June 18, 1980
Partner: UNT Libraries Government Documents Department