74 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



Meteoritical studies. — Dr. E. L. Fireman, Dr. David Tilles, and 

 J. De Felice continue their measurements of radioactive isotopes in 

 recently fallen meteorite and satellite material. Dr. Fireman has 

 established that the Ehole meteorite fell August 31, 1961. The quanti- 

 ties of helium-3, argon-37, and argon-39 present are similar to those 

 found in the previously measured Bruderheim and Hamlet meteorites, 

 an indication of a similar history of cosmic-ray bombardment. Al- 

 most completed are measurements of those isotopes in the separated 

 stone and iron phases of the Harleton meteorite, to determine the 

 sources of excess argon-37. Dr. Fireman and Mr. De Felice have 

 measured helium-3 and argon-39 in the metallic phase of a stony 

 (Bruderheim) meteorite. Results of their analysis of uranium, po- 

 tassium, argon-40, and krypton-xenon in iron meteorites by neutron 

 activation will be important in determining the age and early history 

 of the meteorites. 



The most important results from the study of radioactive isotopes in 

 recovered satellites were the discoveries that solar flares contain 1 

 percent tritium and that Van Allen particles also contain 1 percent 

 tritium. The program will continue to provide information on the 

 intensity, energy spectra, and isotopic composition of the trapped 

 hydrogen nuclei in the Van Allen belts, as well as on the flux of pri- 

 mary high-energy cosmic rays in the vicinity of the earth. 



Dr. Ursula B. Marvin, while investigating accessory minerals in 

 meteorites, discovered in an iron sample the presence of cristobalite, 

 which appears to contradict metallurgical evidence requiring far 

 higher pressures of atmospheres than this mineral can theoretically 

 tolerate. In association with Professor C. Frondel she has also studied 

 the meteoritic phosphate mineral merrilite, apparently having the 

 structure of whitlockite. Analysis of both these minerals should 

 provide useful information on the geochemical environment of the 

 meteorites at the time of formation. 



With Dr. Fireman and Dr. Tilles, she is attempting to separate 

 100 mg. mineral samples from stony meteorites to determine the areas 

 of noble gas isotopes and trace elements. The study seeks light on 

 the early history of the meteorites and the solar system. For such 

 analysis and other isotopic measurements, Dr. Tilles continues work 

 on the construction of a high sensitivity mass spectrometer, which, 

 when completed, should augment present scanty knowledge of pri- 

 mordial and radiogenic noble gases in iron meteorites and help eluci- 

 date the age, cooling history, and formation of the irons. Dr. Tilles 

 has initiated an additional investigation of hydrogen and tritium 

 retention in the metal of meteorites as a means of studying their 

 temperatures in space and to help explain the widely varying tritium 

 content of the metal phase of stony and iron-nickel meteorites. 



