Haloes, giant

Fig. 9. Radioactive halos around large central monazite inclusions in biotite from Madagascar. Top giant halo, bottom from left to right thorium and uranium halos around, and a well-resolved uranium halo with a small central grain. All photographs are on the same scale the outer diameter of the halo at top is 250 pm. From R.V. Gentry [53],...

Sparks, C.J., Raman, S., Yakel, H.L., Gentry, R.V., Krause, M.O. Search with synchrotron radiation for superheavy elements in giant-halo inclusions. Phys. Rev. Lett. 38, 205-208... 

Abstract. I present preliminary results for a sample of 700 red giants in u> Cen, observed during the Ital-FLAMES Consortium GTO time in May 2003, for the Bologna Project on u Cen. Preliminary Fe and Ca abundances confirm previous results while the metal-poor and intermediate populations show a normal halo o-enhancement of [a/Fe] +0.3, the most metal-rich stars show a significantly lower [a/Fe] +0.1. If the metal-rich stars have evolved within the cluster in a process of self-enrichment, the only way to lower their a-enhancement would be SNe type la intervention. 

Stars with masses similar to the Sun are chosen in different populations of different ages, such as the thin or thick part of the disk, the halo or a globular cluster. Care is taken to ensure that their surfaces are not contaminated by internal nuclear processes, so that their compositions accurately reflect their date and place of birth. Red giants are therefore avoided. These stars... 

The s process is slow to start moving, for it is related to stars in the asymptotic giant branch. These have a maximum mass of 8 M , implying a lifetime of at least 20 million years. It is not surprising then to observe that abundances in old halo stars carry a clear r-process signature (Fig. 8.6). 

Fig. JO. Proton-induced x-ray spectrum of a monazite inclusion in the center of a giant radioactive halo (at top). The region in the gap around channel 400 is shown enlarged at the bottom (solid line) together with the spectrum of a U-Th halo (dashed line) and a smoothed background. From R.V. Gentry et al. [51].

Perhaps the earliest reference to the use of Rn in prospecting is found in Le Radium (1904) where the use of a giant ionisation chamber for the measurement of soil emanations is described and collection of Rn from a stream using an inverted cone-and-bottle assembly is illustrated. In those days the quest was for radioactive springs for health spas rather than for U, which had few known uses. Some years later, Behounek (1927) concluded from atmospheric and soil-air Rn measurements in St. Joachimstal that the radioactive halo around U mineralisation was measurable within a 300 m radius. Most recently Rn has been used for earthquake monitoring and prediction (Hauksson, 1981 Sato etal., 1980). 

Hill, V., Plez, B., Cayrel, R., Beers, T.C., Nordstrom, B., Andersen, J., Sbite, M., Sbite, F., Barbuy, B., Bonifacio, P., Debagne, E., Francois, P., Primas, F. 2002 First stars. I. The extreme r-element rich, iron-poor halo giant CS 31082-001. Implications for the r-process site(s) and radioactive cosmochronology. A A 387, 560. 

Ba/Eu] is low in halo stars, indicating that the s-process (which is the main source of Ba) has not had sufficient time to contribute to the abundances in halo stars, while the r-process (the main source of Eu) dominates in metal-poor stars. Indeed, very metal-poor halo giants show evidence for a purely r-process contribution to the abundances of heavy neutron capture elements (Sneden et al. 2000). 

In NASA photographs, Neptune looks like a luminous turquoise marble, almost without features. Astronomers classify Neptune as a gas giant because, like Uranus, it s essentially a ball of gasses swirling around a metal core. It sports a dim halo of barely visible rings and has at least eight moons, including Triton — the coldest place in the solar system. 

Gentry, R.V. Giant radioactive halos indicators of unknown radioactivity Science 169, 670-673 (1970)... 

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