M.I. Prudêncio

Final Analysis and Results of the Phase II SIMPLE Dark Matter Search

We report the final results of the Phase II SIMPLE measurements, comprising two run stages of 15 superheated droplet detectors each, with the second stage including an improved neutron shielding. The analyses include a refined signal analysis, and revised nucleation efficiency based on a reanalysis of previously reported monochromatic neutron irradiations. The combined results yield a contour minimum of σp=5.7×10(-3)  pb at 35  GeV/c2 in the spin-dependent sector of weakly interacting massive particle (WIMP) proton interactions, the most restrictive to date for MW}≤60  GeV/c2 from a direct search experiment and overlapping, for the first time, with results previously obtained only indirectly. In the spin-independent sector, a minimum of 4.7×10(-6)  pb at 35  GeV/c2 is achieved, with the exclusion contour challenging a significant part of the light mass WIMP region of current interest.

Behavior of REE and other trace and major elements during weathering of granitic rocks, Évora, Portugal☆

The distribution of elements within a weathering profile depends on several factors, including the relative stability of the mineral phases of the parent rock, redox and leaching conditions. Three main processes are involved in weathering: ( 1 ) the breakdown of the parent minerals; (2) the removal in solution of some of the released constituents; and (3) the formation of secondary phases with components from the atmosphere (water, oxygen and carbon dioxide), from the parent rock and from shallower levels, and transported by the percolating solutions (Fritz and Ragland, 1980; Nesbitt, 1980; Chesworth et al., 1981 ). The purpose of this work is to investigate how major and trace elements behave during the weathering of granitic rocks from l~vora, Portugal. The prevailing climatic characteristics of this region are: 700 mm annual rainfall; dry summers; and a mean annual temperature of 16°C.

Clay mineral assemblages in weathered basalt profiles from central and southern Portugal: climatic significance

Abstract Mineralogical and chemical changes during weathering of basalts from central and southern Portugal were studied. Both regions have a temperate Mediterranean type climate, the Algarve being more arid. The areas concerned are the Lisbon (72 Ma) and the Runa Volcanic Complexes (100–70 Ma), and Rio Maior (160–130 Ma) in central Portugal, and Budens (170–180 Ma) in the south. The basalts are generally rich in olivine phenocrysts. Clay minerals are in general well crystallised and comprise smectites, associated with 1:1 minerals (principally halloysite), illite and palygorskite. Kaolin minerals prevail in topographic highs, whilst smectites predominate in lower areas. Smectites were analysed from the

New Data on Sixteen Reference Materials Obtained by INAA

We report instrumental neutron activation analysis results for 15 elements (K, Fe, Sc, Cr, Co, Zn, As, Rb, Sb, Cs, Ba, Hf, Ta, Th, and U) in 16 geochemical reference samples, namely SDC-1, SCo-1, SGR-1, STM-1, RGM-1, BIR-1, MAG-1 and BHVO-1 from USGS (United States Geological Survey, Reston), Soil-5, Soil-7 and SL-1 from IAEA (International Atomic Energy Agency, Vienna), and GSS-1, GSS-4, GSS-7, GSR-2 and GSR-3 from IGGE Institute of Geophysical and Geochemical Prospecting, Peoples Republic of China), The results are compared with literature values. In general our results agree well with recommended or proposed values.

REE distribution of present-day and ancient surface environments of basaltic rocks (central Portugal)

Abstract Rare earth elements are mobilized, fractionated and precipitated during weathering processes of basaltic rocks of the Lisbon Volcanic Complex. In general there is an increase in the REE contents in the whole samples with increasing weathering and fractionation between LREE and HREE. Cerium is partially oxidized and Ce4+ is retained resulting in negative Ce anomalies in the whole samples of the base and middle profile zones. In the clay fraction there is an increase in the REE contents from the top to the bottom of the profiles, except for Ce, giving rise to positive Ce anomalies in the top and negative anomalies of this element in the middle and bottom of the profiles. Significant positive Ce anomalies occur in the finer fractions of palaeoweathered (Upper Cretaceous/ Lower Eocene) basalts associated with low REE contents relative to the whole samples indicating more intense leaching conditions in the Upper Cretaceous/Lower Eocene than at the present day. However, in both cases no positive Ce anomalies were found in the whole samples. There appears to be a negative correlation between the (La/Yb)ch ratio variation and the clay mineralogy/drainage conditions.

New data on the GSJ reference rocks JB-1a and JG-1a by instrumental neutron activation analysis

Two reference rocks of the Geological Survey of Japan have been analyzed for Na, K, Sc, Cr, Fe, Co, Zn, Rb, Cs, Ba, La, Ce, Nd, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Th and U, using instrumental neutron activation analysis. The results are reported and compared with consensus values proposed in the literature. In general, the agreement is good except for Cs.

Interference from uranium fission products in the determination of rare earths, zirconium and ruthenium by instrumental neutron activation analysis in rocks and minerals

A numerical procedure is given to correct for the interference of U in the determination of the light rare earths, Zr, and Ru. The corresponding interference factors were calculated and their values compared with experimental results. The agreement is favourable in most cases.

Factor for correcting the ruthenium interference in instrumental neutron activation analysis of barium in uraniferous samples

The fission spectral interference of ruthenium on the instrumental neutron activation analysis of barium in samples containing uranium is extensively discussed. In particular the dependence of the correction factor on the phi epi/phi th ratio is studied. An excellent agreement between experimental and calculated values is achieved. A procedure is suggested for the resolution of multiple interferences in the general case where uranium, barium and/or ruthenium are present in samples to be analysed.

Geochemistry of rare earth elements in a passive treatment system built for acid mine drainage remediation

Rare earth elements (REE) were used to assess attenuation processes in a passive system for acid mine drainage treatment (Jales, Portugal). Hydrochemical parameters and REE contents in water, soils and sediments were obtained along the treatment system, after summer and winter. A decrease of REE contents in the water resulting from the interaction with limestone after summer occurs; in the wetlands REE are significantly released by the soil particles to the water. After winter, a higher water dynamics favors the AMD treatment effectiveness and performance since REE contents decrease along the system; La and Ce are preferentially sequestered by ochre sludge but released to the water in the wetlands, influencing the REE pattern of the creek water. Thus, REE fractionation occurs in the passive treatment systems and can be used as tracer to follow up and understand the geochemical processes that promote the remediation of AMD.

Rare earths and other trace elements in cretaceous clays from central Portugal

Eight rare-earth elements (REE), namely La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu, as well as other elements (Na, K, Sc, Cr, Fe, Co, Rb, Cs, Ba, Hf, Ta, and Th), have been determined in fifteen cretaceous clay samples of continental facies by instrumental neutron activation analysis. It was found that the REE contents are variable in absolute and relative values, but the means of these values are similar to those of European, shales. Analyses have also been made of the fractions <38 μm and <2 μm (clay-sized). The mineral contents of the clay-sized fraction were determined semi-quantitatively by X-ray diffraction. The results suggest the preferential presence of REE, Hf, and Th in fractions 2–38 μm, which can be explained by the presence of apatite, monazite, and zircon. A correlation study of chemical and mineralogical data of the clay-sized fraction showed that kaolinite is correlated with REE, specially the lighter ones; illite with K, Rb, and Cs; and smectite with Na.