ABSTRACT. In order to better understand the densification of polar firn, firn cores from the three sites within ∼10 km of Dome Fuji, Antarctica, were investigated using surrogates of density: dielectric permittivities ε v and ε h at microwave frequencies with electrical fields in the vertical and horizontal planes respectively. Dielectric anisotropy Δε (=ε v − ε h ) was then examined as a surrogate of the anisotropic geometry of firn. We find that layered densification is explained as a result of complex effects of two phenomena that commonly occur at the three sites. Basically, layers with initially smaller density and smaller geometrical anisotropy deform preferentially throughout the densification process due to textural effects. Second, layers having a higher concentration of Cl − ions deform preferentially during a limited period from the near surface depths until smoothing out of layered Cl − ions by diffusion. We hypothesize that Cl − ions dissociated from sea salts soften firn due to modulation of dislocation movement. Moreover, firn differs markedly across the three sites in terms of strength of geometrical anisotropy, mean rate of densification and density fluctuation. We hypothesize that these differences are caused by textural effects resulting from differences in depositional conditions within various spatial scales.
An excess amount of Mo found in a 1.7X10 yr zircon sample from Cable Sands' Western Australia, yielded a half-life of (3.9+0.9}X 10' yr for the double beta decay of Zr to Mo.PACS number(s): 23.40.s, 27.60.+jThe precise determination of the decay constant of double beta decay has put a constraint on, and is expected to verify, the mass of the neutrino [1]. The half-life for this type of decay is estimated to be of the order of 10' -10 ' yr, as shown in the half-lives of 1 X 10 yr for s2Se and SX10 yr for ' Te [2]. Accordingly, it is difficult to directly detect the radioactivity accompanying double beta decays using counting methods. An alternative approach to counting methods is the detection of the decay product accumulated in very old natural minerals. In the present work, we have attempted to estimate the half-life of double beta decay of Zr from the amount of radiogenic Mo found in the Zr mineral. It is noted, however, that the concentration of molybdenum in natural zircon (ZrSi04) appears to be in the ppm range, which is too high a background to enable us to detect the Mo "anomaly. " Furthermore, the sensitivity of molybdenum in thermal ionization mass spectrometry (TIMS) is relatively low because of the high ionization potential of Mo. These difficulties hampered the success of a previous attempt [3]. Therefore, it was necessary to develop sophisticated empirical techniques in order to detect the positive anomaly of Mo in the Zr mineral.We analyzed 5.39 g of placer zircon found in a region south of Bunbury, Western Australia, which was provided from Cable Sands Pty. Ltd. The geological age was determined based on a measurement of the isotopic composition of lead and on the method by Kroth [4], and found to be 1.67X10 yr. The samples contained over 99% of zircon. This was confirmed by an analysis of zirconium with an ICP-MS after chemical dissolution of zircon (see below).Natural zircon (ZrSi04) usually contains a few ppm of molybdenum.Molybdenum, however, is believed to be present as a mineral inclusion (perhaps molybdenite, MoSz) and the proportion of Mo substituting for Zr ions in the crystal lattice is anticipated to be low. Thus it is expected that radiogenic Mo is not present in molybdenite inclusions but can be detectable in intrinsic portions of zircon. In order to reduce the Mo background and to find out the isotopic effect on Mo due to double beta decay of Zr, molybdenite inclusions must be re-moved from the zircon mineral. For this purpose, the crystals of zircon were crushed to a fine powder and treated with aqua regia to remove the molybdenite inclusions. Zircon is not eroded by this treatment, and the molybdenum produced by the decay of zirconium is considered to be maintained in the pure zircon crystal grains.Zircon, which had been treated with aqua regia, was then dissolved by hydrofiuoric acid (ten times the weight of the zircon sample) and a few drops of nitric acid in acid digestion bombs. (Prior to treatment with aqua regia, the sample had been heated overnight with HF + HC104 to remove s...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.