I. A procedure for the analysis of polonium-210 and lead-212 in rocks. II. A characterization of the meteorite flux at the earth's orbit.

• Main Author: Millard, Hugh Thompson, Jr.
• Format: Others
• Published: 1962
• Online Access: https://thesis.library.caltech.edu/6612/1/Millard_ht_1962.pdf; Millard, Hugh Thompson, Jr. (1962) I. A procedure for the analysis of polonium-210 and lead-212 in rocks. II. A characterization of the meteorite flux at the earth's orbit. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/WEPX-9Q33. https://resolver.caltech.edu/CaltechTHESIS:08232011-094813077 <https://resolver.caltech.edu/CaltechTHESIS:08232011-094813077>

Part I. A method for the analysis of polonium-210 (138.4 day half-life) and lead-212 (10.6 hour half-life) in rocks has been studied. The procedure involves dissolution of the sample and addition of 10 mg. lead carrier. The polonium is separated by spontaneous electrodeposition on a silverfoil disk at room temperature from a 0.5F HCl medium containing 0.05F hydrazine and the alpha-activity from the polonium-210 measured, with a scintillation counter. Sodium tartrate is added to the solution remaining from the polonium deposition, the pH raised to 4.7, and the lead-212 deposited with the lead carrier on a second silver-foil disk. The yield of lead is determined gravimetrically and the decaying alpha-activity supported by the lead-212 observed with the scintillation counter. The procedure has been calibrated by using minerals which had been analyzed for lead-210 and thorium-232 by other methods. The effects of temperature, volume, and inhibiting ions on the yield and rate of deposition of polonium were also studied. The procedure was tried on a synthetic uraninite-thorite mixture and on the zircon from the Pacoima Canyon pegmatite. The results indicate that extreme care must be taken to get all material into solution and to avoid high temperatures during fusion of the sample. The weight equivalent uranium found from the polonium-210 analysis on the zircon agreed with the mass spectrometric value for the uranium content to 3.3%. Part II. A study has been conducted in order to better characterize the meteorite flux at the earth's orbit with respect to type, mass, direction, and magnitude. A survey of the meteorite data was made by placing the information on punch cards and sorting these cards according to various categories. On the basis of the year of fall, it was noted that the achondrites were more abundant than the irons from 1850 to 1870 and that the reverse was true from 1890 and 1910. No enstatite chondrites fell prior to the 1860's and a large number of this type fell during 1930. A chi-squared test applied to the monthly patterns of fall indicates that the distributions for the veined-hypersthene chondrites, the veined-white hypersthene chondrites, the achondrites, and the howarditic achondrites were those least likely to be random, suggesting that these types may travel in definite orbits. As for the direction of the flux, the hourly patterns are heavily biased toward the daylight hours with no 6:00 maximum as in the case of sporadic meteors. The achondrites display an interesting bimodal distribution during the daylight hours. The magnitude of the flux shows significant variations with year among which the decrease since 1940 appears to be most important. The functional relationship between the rate of meteorite recovery and the rural population density has been investigated and an average value of 1.0 meteorite/10^6 sq. km.-year found for the total flux, R_o, arriving at the bottom of the atmosphere for the period 1810 to 1950.