Accession Number:

AD0613750

Title:

SEARCH FOR ALUMINUM-26 IN DUST FROM THE GREENLAND ICE SHEET,

Descriptive Note:

Corporate Author:

SMITHSONIAN ASTROPHYSICAL OBSERVATORY CAMBRIDGE MASS

Report Date:

1964-07-29

Pagination or Media Count:

8.0

Abstract:

Large volumes of approximately 250-year-old Greenland glacier ice were filtered. Approximately 20,000 liters passed through 0.45 micron retention paper with a 2.5 ft surface area, and approximately 200,000 1. passed through 3 micron retention paper. Less than 4 x 10 dpm1. of aluminum-26 was found in the 3 micron collections, and less than 3 x 106 dpm1. in the 0.45 micron collection. These limits are significant for determinations of the exposure age, the chemical composition, and the accretion rate of extraterrestrial dust. For an accretion rate for the Earth of a million tons per year of silicates, the limit of 4 x 10 dpm1. corresponds to an exposure age of 4000 years. Although the filter collections do not contain aluminum-26, they do contain radioactivities. The principal one is thallium208, a thorium decay product attributed to terrestrial material in the collection. There is also a small positron activity, which disappeared with the purification of aluminum. Author

Subject Categories:

Distribution Statement:

APPROVED FOR PUBLIC RELEASE