Measurement of the lunar neutron density profile

An in situ measurement of the lunar neutron density from 20 to 400 g/sq cm depth between the lunar surface was made by the Apollo 17 Lunar Neutron Probe Experiment using particle tracks produced by the B10(n, alpha)Li7 reaction. Both the absolute magnitude and depth profile of the neutron density are in good agreement with past theoretical calculations. The effect of cadmium absorption on the neutron density and in the relative Sm149 to Gd157 capture rates obtained experimentally implies that the true lunar Gd157 capture rate is about one half of that calculated theoretically

Association of molecules using a resonantly modulated magnetic field

We study the process of associating molecules from atomic gases using a magnetic field modulation that is resonant with the molecular binding energy. We show that maximal conversion is obtained by optimising the amplitude and frequency of the modulation for the particular temperature and density of the gas. For small modulation amplitudes, resonant coupling of an unbound atom pair to a molecule occurs at a modulation frequency corresponding to the sum of the molecular binding energy and the relative kinetic energy of the atom pair. An atom pair with an off-resonant energy has a probability of association which oscillates with a frequency and time-varying amplitude which are primarily dependent on its detuning. Increasing the amplitude of the modulation tends to result in less energetic atom pairs being resonantly coupled to the molecular state, and also alters the dynamics of the transfer from continuum states with off-resonant energies. This leads to maxima and minima in the total conversion from the gas as a function of the modulation amplitude. Increasing the temperature of the gas leads to an increase in the modulation frequency providing the best fit to the thermal distribution, and weakens the resonant frequency dependence of the conversion. Mean-field effects can alter the optimal modulation frequency and lead to the excitation of higher modes. Our simulations predict that resonant association can be effective for binding energies of order $h \times 1$ MHz.Comment: 8 pages latex, figures revised, references updated and typos correcte

Simultaneous dual-element analyses of refractory metals in naturally occurring matrices using resonance ionization of sputtered atoms

The combination of secondary neutral mass spectrometry (SNMS) and resonance ionization spectroscopy (RIS) has been shown to be a powerful tool for the detection of low levels of elemental impurities in solids. Drawbacks of the technique have been the laser-repetition-rate-limited, low duty cycle of the analysis and the fact that RIS schemes are limited to determinations of a single element. These problems have been addressed as part of an ongoing program to explore the usefulness of RIS/SNMS instruments for the analysis of naturally occurring samples. Efficient two-color, two-photon (1+1) resonance ionization schemes were identified for Mo and for four platinum-group elements (Ru, Os, Ir, and Re). Careful selection of the ionization schemes allowed Mo or Ru to be measured simultaneously with Re, Os, or Ir, using two tunable dye lasers and an XeCl excimer laser. Resonance frequencies could be switched easily under computer control, so that all five elements can be rapidly analyzed. In situ measurements of these elements in metal grains from five meteorites were conducted. From the analyses, estimates of the precision and the detection limit of the instrument were made. The trade-off between lower detection limits and rapid multielement RIS analyses is discussed

Partitioning of K, U, and Th between sulfide and silicate liquids: Implications for radioactive heating of planetary cores

The possibility of heating of planetary cores by K radioactivity has been extensively discussed, as well as the possibility that K partitioning into the terrestrial core is the reason for the difference between the terrestrial and chondritic K/U. We had previously suggested that U and Th partitioning into FeFeS liquids was more important than K. Laboratory FeFeS liquid, silicate liquid partition coefficient measurements (D) for K, U, and Th were made to test this suggestion. For a basaltic liquid at 1450°C and 1.5 GPa, D_U is 0.013 and D_K is 0.0026; thus U partitioning into FeFeS liquids is 5 times greater than K partitioning under these conditions. There are problems with 1-atm experiments in that they do not appear to equilibrate or reverse. However, measurable U and Th partitioning into sulfide was nearly always observed, but K partitioning was normally not observed (D_K ≲ 10^(−4)). A typical value for D_U from a granitic silicate liquid at one atmosphere, 1150°C, and low f0_2 is about 0.02; D_(Th) is similar. At low f0_2 and higher temperature, experiments with basaltic liquids produce strong Ca and U partitioning into the sulfide liquid with D_U > 1. D_(Th) is less strongly affected. Because of the consistently low D_K/D_U, pressure effects near the core-mantle boundary would need to increase D_U by factors of ∼10^3 with much smaller increases in DU in order to have the terrestrial K and U abundances at chondritic levels. In addition, if radioactive heating is important for planetary cores, U and Th will be more important than K unless the lower mantle has K/U greater than 10 times chondritic or large changes in partition coefficients with conditions reverse the relative importance of K versus U and Th from our measurements

SO_2-rock interaction on Io: Reaction under highly oxidizing conditions

Laboratory simulations have been carried out to test the possibility that interactions of SO_2 and silicates can produce Na-S compounds which can account for the observed surface enrichment of Na relative to Si on Io. A wide variety of silicate compositions were heated under oxidizing conditions with a SO_2/O_2 = 1 gas phase at a mid-level crustal temperature for Io (1123K). All experiments produced sulfate deposits on the silicate surfaces. The nature of the sulfate changed systematically with the silicate Ca/Na ratio, with mixtures of CaSO_4 and Na-rich sulfate formed by basaltic compositions having higher Ca/Na but only alkali-rich sulfates formed for more granitic (low Ca/Na) compositions. For crystalline albite and an albite-orthoclase eutectic glass composition, K and Al-rich sulfates were formed. Assuming that burial of SO_2 to the temperatures of our experiments is plausible on Io and that somewhat less oxidizing conditions do not qualitatively change the results, SO_2-rock interactions producing Na-rich sulfates could account for the Io surface enrichment in Na. Observations on minor elements, such as K or Ca, in the atomic cloud or in magnetospheric ion spectra could be used to identify sulfates as Io surface phases and, conceivably, even define Ionian crustal magma types. Many analyses show significant S excesses which are best interpreted as due to the presence of bisulfate (HSO_4.) components, and NaHSO_4 deserves consideration as an Io surface mineral. The possibility of elemental S on Io can be regarded as a totally separate issue from the problem of the surface Na enrichment

Extreme Pu-U and Possible Pu-REE Fractionation in Unequilibrated Chondrites

The purpose of this study is to understand actinide chemistry in chondrites and to evaluate unequilibrated chondrites for either Pu/U or Pu/Nd chronology. Using fission track radiography for Nadiabondi (H5/(Murrell and Burnett, 1982), Dhajala (H3,4), Bremervorde (H3), Sharps (H3), and Tieschitz (H3), we find that U is primarily located in chondrule glass (50-500 ppb, average of ~ 100 ppb). Apatite from the unequilibrated chondrites contains 150-200 ppb U while whitlockite contains < 17 ppb [low compared to type-6 chondrites which have 1-6 ppm U in apatite and ~ 200 ppb in whitlockite (Pellas and Storzer, 1975)]. Nadiabondi phosphates are intermediate (Murrell and Burnett, 1982). These observations suggest that the phosphate U content increases with petrologic type (Pellas and Storzer, 1975), with U obtained from chondrule glass during metamorphism

EBSD mapping of herringbone domain structures in tetragonal piezoelectrics

Herringbone domain structures have been mapped using electron backscatter diffraction (EBSD) in two tetragonal piezoelectrics, lead zirconate titanate, [Pb(Zr,Ti)O&lt;sub&gt;3&lt;/sub&gt;] and bismuth ferrite – lead titanate, [(PbTi)&lt;sub&gt;0.5&lt;/sub&gt;(BiFe)&lt;sub&gt;0.5&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;]. Analysis of the domain misorientations across the band junctions shows that the structures correspond very well to crystallographic models. High resolution mapping with a 20 nm step size allowed the crystal rotation across one of these band junctions in lead zirconate titanate to be studied in detail and allowed an improved estimation of the peak strain at the junction, of 0.56 GPa. The significance of this for crack nucleation and propagation in such materials is discussed

The national health system in Portugal: from expansion to crisis between 1970

Purpose: The purpose of this article is to discuss the idea that governments should not take policy measures for the development and growth of National Health System (NHS) without taking into account their financial sustainability. Design/methodology/approach: This article is based on a review of existing theories, documents and statistics. findings: This article analyses the major developments in public health policy in Portugal between 1970 and 2012. It presents the measures that established the National Health Service (NHS) in 1976, signalling the start of an expansionary health policy that led to quality health care provision, but at the cost of very high spending. From 1990, governments have focussed on reducing public expenditure on health, due to growth-rates in this area outstripping increases in GDP. Paradoxically, despite this position, in practice, all the governments have increased the amount of infrastructure supporting the NHS, which in turn has been funded through public debt. This debt was extended in all areas of public administration and became unsustainable, obliging the Portuguese government to ask the European Commission for financial assistance in 2011. Due to the austerity measures imposed by lenders, for the first time since the creation of the NHS, there was a real reduction of public expenditure on health in 2011 and 2012.info:eu-repo/semantics/publishedVersio

Relict grains in CAls, revisited

Although the Type B CAI are clearly igneous rocks, they were probably not completely molten (1, 2), thus the possibility exists that preexisting materials can be recognized and characterized. Relict phases were proposed to explain high U and Th concentrations in both melilite and fassaite which would require unreasonably high partition coefficients (D} if due to crystal-liquid partitioning (3). More detailed study showed very rare perovskite grains and enigmatic Ti hot spots in melilite (4). Kuehner et al. (5) subsequently reported very high lithophile trace element contents, including actinides, for fassaite inclusions in melilite which they proposed as relict phases, but Simon et al. (6) show that the fassaite inclusions can be better explained as being the last drops of liquid crystallization. In any case, the original observations and interpretations of (3) still point to an actinide-rich relict host phase. To be able to say what levels of Ti, U, and Th in melilite can be explained by igneous partitioning, we have measured D(mel) for these elements in a synthetic CAI composition under controlled fD_2 conditions, extended down to nebular conditions by carrying out experiments in graphite crucibles in pure CO. Actinide partition coefficients are quite low: D(Th} = 0.008 and D(U) = 0.0007 (possibly a record low in measured D values). The D for trivalent U should be around 0.1-0.3 depending on Ak content as the ionic radius of U^(+3) is similar to La. Thus, for solar nebula fD_2's and CAI compositions less than 1 % of the U is trivalent. The measured D prove that igneous partitioning fails to explain the average U contents of type B CAI melilites, the difference being a factor of 600. D(Ti) is 0.018 at Ak23 and increases with Ak content. D(Ti) is relatively similar in air and at solar nebula fD_2s, surprising given the documented importance of trivalent Ti. In any case, the measured D(Ti) show that melilite Ti levels around 200-300 ppm in early crystallizing melilite can be explained by igneous partitioning, but higher levels would be indicative of resorbed Ti-rich relict phases (e.g., perovskite). To make a closer comparison ofU and Ti in CAI melilites, the fission track images of (3) have been quantitatively mapped at 20 microns resolution for two mm-sized rim and one mantle melilite. High resolution quantitative U distribution data on adjacent fassaites were also obtained. One rim grain shows several U-rich fassaites like those of(5), but the other melilites do not. There are broad U-rich regions in all grains which will be characterized in more detail. The mantle grain is especially rich in detail, but some of this may be correlated with secondary alteration. There is rough correlation ofU content and Ti in the rim grains, but the scale of the Ti analyses, based on electron probe points, is much smaller than that for U. If relict phases, e.g., perovskite, dominate the actinide distributions, they might also affect other lithophile trace elements, e.g., REE. References: (1) Wark D. (1983) thesis. (2) Stolper E. and Paque J. (1986) Geochim., Cosmochim. SO, 2159. (3) Murrell M. and Burnett D. (1987) Geochim. Cosmochim. SI, 985. (4) Johnson M., Burnett D. and Woolum D. (1988) Meteoritics 23, 276. (5) Kuehner S., Davis A. and Grossman L. (1989) Geophys. Res. Lett. 16, 775. (6) Simon S., Davis A. and Grossman L. (1990) LPSC 21, 1161