156 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



and small meteors.^ Between magnitudes +6 and +9 the average 

 velocity of meteors detected on the radar system has changed by 5 

 km sec "^ This is attributed to the smaller orbits shown by the fainter 

 meteors. The faint meteors show total fragmentation as they enter 

 the upper atmosphere of the earth. In general, each meteor disinte- 

 grates into several hundred fragments, which together act as a cloud 

 of independent particles. 



The objective of the Photographic Meteorite Recovery Program,* 

 under the direction of Dr. McCroslr^, is to photograph the trails of 

 extremely bright meteors so that the corresponding meteorite impacts 

 may be determined and a search instigated for the meteorites. In the 

 past year the project has completed the design of the station buildings, 

 the cameras, and the photoelectric and control systems; selected and 

 leased land at 16 sites in the Midwest ; selected local station attendants 

 and their alternates at each site ; completed 16 buildings to the point 

 where they are ready to receive cameras and begin operation; as- 

 sembled, in Lincoln, Nebr., a team of four field personnel to operate 

 the network and to recover freshly fallen meteorites ; operated a proto- 

 type station at Havana, 111., for 3 months; and initiated production on 

 all major components of the stations. 



The program for measuring radioactivities in material from outer 

 space has continued on an expanded scale. In addition to tritium and 

 argon radioactivities, Dr. Edward L. Fireman and his associates are 

 now measuring carbon-14 and gamma-ray radioactivities from such 

 isotopes as aluminum-26, manganese-54, sodium-22, and cobalt. 



During the past year Dr. Fireman and James C. DeFelice have 

 measured tritium, argon-3T, and argon-39 in several meteorites, includ- 

 ing the recently fallen Peace River. The resultant data provide 

 comparative information on the production, intensity, and constancy 

 of cosmic rays in space during a period of minimal solar activity. 

 The absence of argon-39 in the Potter and Estacado meteorites indi- 

 cates that they fell more than 1,500 years ago. The Estacado meteorite 

 has been erroneously associated with an 1882 fireball. The argon-39 

 and tritium contents of Farmington are similar to those of other 

 chondrites, but the aluminum-26 content of Fannington is a factor 

 of more than 50 lower than in other chondrites. The content of these 

 radioactivities permits the determination of the exposure age from 

 radioactive isotopes alone. The cosmic-ray exposure age of the Farm- 

 ington meteorite is between 7,000 and 25,000 years. 



Studies of tritium concentrations in the metal phases of stony 

 meteorites and in iron meteorites have continued during the past year. 

 Dr. Fireman, Dr. David Tilles, and Mr. DeFelice plan further meas- 

 urements to test the tentative hypothesis that tritium is lost from 



See footnotes on p. 164. 



