Impactor material records the ancient lunar magnetic field in antipodal anomalies

The Moon presently has no dynamo, but magnetic fields have been detected over numerous portions of its crust. Most of these regions are located antipodal to large basins, leading to the hypothesis that lunar rock ejected during basin-forming impacts accumulated at the basin antipode and recorded the ambient magnetic field. However, a major problem with this hypothesis is that lunar materials have low iron content and cannot become strongly magnetized. Here we simulate oblique impacts of 100-km-diameter impactors at high resolution and show that an ~700 m thick deposit of potentially iron-rich impactor material accumulates at the basin antipode. The material is shock-heated above the Curie temperature and therefore may efficiently record the ambient magnetic field after deposition. These results explain a substantial fraction of the Moon’s crustal magnetism, and are consistent with a dynamo field strength of at least several tens of microtesla during the basin-forming epoch.

Rapidly Solidified Thick Deposit of Fe-B-Cr Alloy by Plasma Spraying

Fe-B-Cr alloy powder in diameter of 32-53 μm made by argon atomization is low-pressure plasma sprayed to produce a rapidly solidified iron base composite deposit with finely dispersed boride particles. The constituents of the as-sprayed deposit formed on a water-cooled substrate are α phase and amorphous phase that are supersaturated with chromium and boron due to high cooling rate during solidification of the melt. Heat treatment of deposit at 873K leads to decomposition of the amorphous phase, resulting in the formation of Fe3B. The deposit heat treated above 1073K is composed of α phase and (Fe,Cr)2B. The as-sprayed deposit produced on a non-cooled substrate consists of α phase and (Fe,Cr)2B. The fine precipitates of about 0.1 μm in the as-sprayed deposit coated on a non-cooled substrate are boride. As deposit temperature increases, the coarsening of the precipitate particles results in lowered hardness of deposits.

Large Area Cu(In,Ga)Se2 Films and Devices on Flexible Substrates Made by Sputtering

A reactive sputtering process was developed for the production of Cu(In,Ga)Se2 films on a moving stainless steel substrate, in simulation of the operation of a roll coater. Cu, In and Ga fluxes were provided through magnetron sputtering and were reacted in a flux of Se on the heated substrate. CdS films were deposited either by chemical bath deposition (CBD) or by sputtering. Devices of the type steel/Cr/Mo/CIGS/CdS/ZnO/Ag were completed by sputtering ZnO layers and by screen printing grid lines. We made devices with efficiency values above 9%. A uniformity study was performed on a CIGS film and on small area devices made from it. The target length was 12”. Targets of this size are expected to produce a uniformly thick deposit over a range of 6-8”. The film thickness was 2.54 μm over a range of 6” with a standard deviation ó of 0.04 μm. The film composition was uniform over a range of 16”. The values of Cu/III and Ga/III were 0.84 and 0.31, with ó values of 0.02 and 0.01, respectively. The efficiency of allsputtered devices was uniform over a range of 12”, well beyond the 6” wide range of constant CIGS film thickness. Their efficiency was 6.6% on average with ó=0.6%.

Behavior of Suction Caissons Measured in Laboratory Pullout Tests

Laboratory experiments are being conducted to study the behavior of suction casissons used for deep offshore moorings. Tests with a 100-mm diameter by 910-mm long caisson prototype, which is installed using dead weight or suction, are performed in a 1.1-m thick deposit of normally consolidated kaolinite. Instrumentation is used to record displacements, axial forces, and pore water pressures (at five locations along the interior and exterior surfaces of the caisson) during extraction of the caisson. Axial pullout tests have been conducted on caissons inserted using dead weight only or dead weight plus suction pressure, on caissons pulled with a vented or sealed top cap, and with rapid (undrained) versus slow (drained) pullout. Measured pullout capacities are interpreted in terms of the weight of extracted soil, side resistance on the caisson walls, and the reverse end bearing capacity at the tip.

Time Scales for Dissolution of Calcite Fracture Fillings and Implications for Saturated Zone Radionuclide Transport at Yucca Mountain, Nevada

An analysis was performed to estimate time scales for dissolution of calcite fracture fillings in the fractured tuff aquifer that underlies Yucca Mountain (YM), Nevada, where groundwater is chemically undersaturated with respect to calcite. The impetus for this analysis originates from speculation that undissolved calcite in the saturated zone is evidence for limited diffusive exchange between fracture and matrix waters. Assuming that matrix diffusion is the rate-limiting process, the time scale for dissolution of calcite fracture fillings depends on the amount of calcite initially deposited, the distance between flowing fractures, the degree of chemical disequilibrium, and the rate of diffusion. Assuming geochemistry of J-13 well water in free-flowing fractures, estimated time scales for complete dissolution of matrix-entrapped calcite range from about 104yr for a 2 mm-thick deposit located I m from a flowing fracture, to over 107 yr for a 2 cm-thick deposit located 100 m from a flowing fracture. We conclude that, given the geochemical and hydrologic characteristics observed at YM, the persistence of calcite minerals over geologic time scales in aquifers where flowing water is under-saturated with calcite does not necessarily preclude matrix diffusion as a dilution mechanism. However, our model suggests that the effective spacing between flowing fractures may be large enough to diminish the overall benefit of matrix diffusion to proposed high-level waste repository performance.