The irradiation history of the Ghubara (L5) regolith breccia

Abstract— We measured cosmic‐ray products—noble gases, radionuclides, thermoluminescence, and nuclear tracks—and trace element contents and mineralogy of samples of three orthogonal and mutually intersecting cores (41–46 cm long) of a 101.6 kg Ghubara individual (1958,805) at The Natural History Museum, London. The xenoliths, like the host, have high concentrations of trapped solar gases and are heavily shocked. While contents of noble gases and degree of shock‐loading in this individual and three others differ somewhat, the data indicate that Ghubara is a two‐generation regolith breccia. Contents of cosmogenic ²⁶Al and ¹⁰Be and low track densities indicate that the Ghubara individuals were located more than 15 cm below the surface of an 85 cm meteoroid. Because of its large size, Ghubara's cosmic‐ray exposure age is poorly defined to be 15–20 Ma from cosmogenic nuclides. Ghubara's terrestrial age, based on ¹⁴C data, is 2–3 ka. Not only is Ghubara the first known case of a two‐generation regolith breccia on the macroscale, it also has a complicated thermal and irradiation history.     

Exposure History of H5 Chondrite Gujargaon

Abstract— Cosmic ray produced tracks, He and Ne isotopes and radionuclides have been studied in the recently fallen H5 chondrite Gujargaon. The results indicate an exposure age of about 7 Ma. The high track production rates of 0.25 to 0.69 × 10⁶ cm^?2 Ma^?1 suggest that the Gujargaon meteoroid had a small size (Re = 9–10 cm) in space and suffered 1–3 cm ablation in the atmosphere. The conclusion about the meteoroid size is supported by the low activity of neutron capture isotope ⁶⁰Co and high spallogenic ²²Ne/²¹Ne ratio of about 1.25. The data on long lived isotopes ¹⁰Be, ⁵³Mn and ²⁶Al are used to derive production rates of these isotopes in a rock having a radius of 9 cm and the activity levels of the short lived isotopes ²²Na and ⁵⁴Mn are used to estimate the effect of modulation of galactic cosmic rays at the time of solar maximum of 1982.     

The Torino,H6, meteorite shower

Abstract— A meteorite shower fell at Torino, Italy on 18 May 1988. Petrographic studies indicate that the stone is an H6 chondrite having features of moderate to severe shock. Chemical analyses of the meteorite are reported. Cosmic ray produced ³He, ²¹Ne and ¹²⁶Xe yield an exposure age of about 48 Ma. The cosmic ray track densities in three fragments range between 1.8 to 5 × 10⁵/cm² suggesting about 99% mass ablation in the atmosphere. Twelve radioisotopes with half lives ranging between 5.6 days to 7.3 × 10⁵ years have been measured with high precision (2 to 10%). Marginal signals were observed for several short-lived nuclides and upper limits were obtained for the activity levels of eight radionuclides (²⁴Na, ⁴⁸Cr, ⁵⁷Ni, ⁴⁷Sc, ⁴⁷Ca, ⁵⁹Fe, ⁴²Ar and ⁴⁴Ti) some of which have not been hitherto detected in fresh falls. The data are generally consistent with the nuclide production by galactic cosmic rays when modulation due to the solar cycle is taken into consideration. The preatmospheric radius of the chondrite is estimated to be 20 cm, consistent with track densities and activity levels of ⁶⁰Co, ²⁶Al and other radionuclides.     

THE LAHRAULI UREILITE

A meteorite which fell at Lahrauli, district Basti, U.P. (India) in 1955 has been examined for mineralogical, chemical and cosmogenic characteristics. It contains pigeonite Wo_7.7Fs₁₈ (with Cr₂O₃ = 1.2% and Al₂O₃ = 0.4%), olivine Fo₇₉ (with CaO = 0.3% and Cr₂O₃ = 0.7%) and diamond. The basic similarities of this meteorite to Goalpara, Dyalpur, Havero and Novo Urei indicate that it is a ureilite. Cosmic ray tracks have been measured in the olivine and pyroxene grains. Track density of 2.3 × 10⁶ per cm² in olivines and VVH/VH ratio of 10^?3 is similar to that observed in other meteorites.     

Cosmogenic21Ne and22Ne depth profiles in chondrites

The production rate profiles of²¹Ne and²²Ne as a function of depth in meteoroids due to spallation by solar flare cosmic rays (SCR) and galactic cosmic rays (GCR) are calculated and their dependence on size and composition of meteoroids has been evaluated. The GCR production rate at a given depth increases with size for radii<25cm and then decreases whereas the²²Ne²¹Ne ratio (NeR) generally decreases with size and depth. The calculated GCR production rates and NeR are consistent with the measurements in several Chondrites. A plot of track production rate vs. NeR shows that some chondrites have NeR values smaller than those expected for their sizes. Thes obeervation suggestsat least a two-stage irradiation for such meteorites; the meteoroid exposure as a small body in the interplanetary space must have been preceded by exposure under deep shielding, possibly in its parent body.     

Convective Cloud Detection and Tracking from Series of Infrared Images

The most significant part of prediction of precipitation is the detection and identification of convective (cumulonimbus) clouds, also the tracking of cloud movement is important for identification of location of precipitation. A very simple methodology for detecting convective clouds and then tracking its movement from a series of infrared (IR) images is proposed in this paper. IR image is segmented using k-means clustering algorithm, which has been implemented using Euclidean, Manhattan and Mahalanobis distances and the results have been compared. Cloud clusters have been identified from segmented image and subsequently the large clusters were extracted. Center of Mass (CoM) was calculated for each selected cloud cluster and its position after every 30 min was predicted and compared with the actual values. If the predicted position deviates, the proposed models automatically adjusts itself, and the next prediction becomes closer to original values of position.