SECRETARY'S REPORT 169 



39, and carbon-14 contents are similar to those obtained for other stony 

 meteoroids. 



Earlier measurements of tritium in satellite fragments have been 

 extended by Dr. David Tilles and Mr. DeFelice, who have obtained 

 upper limits for the tritium content of Discoverer llf, and for the 

 amount of tritium in a trapped state in August 1960. These measure- 

 ments, com.bined with measurements previously reported in other 

 satellites, have given evidence for an increase of at least an order of 

 magnitude in trapped tritium flux in less than 4 months and a decrease 

 of at least an order of magnitude in less than 7 months. Such time 

 variations are believed to have been caused by direct injection of solar- 

 flare tritons into the Van Allen belts in November 1960. 



Dr. Merrihue's analysis of data on xenon and krypton from minerals 

 and chondrules from the Bruderheim meteorite indicates that chon- 

 drules, enriched in Xe^^^ yet depleted in xenon, are the most primitive 

 material yet studied and reflect an early high-temperature origin. 

 Based on a Xe^^®-xenon correlation, the minerals appear to be an equi- 

 librum aggregation. The difference between meteoritic and terrestrial 

 xenon can be attributed to a fast proton irradiation of meteoritic mate- 

 rial and the accumulation in meteorites of fission xenon, possibly from 

 Pu^** spontaneous fission. 



Dr. Merrihue has devised a method of trace-element determinations 

 by mass spectrometiy of neutron-irradiated samples. Preliminary 

 results, based on data collected at Berkeley, were obtained for U^^°, Se, 

 Te, I, Br, and CI, and also for the Br^Br^^ ratio, which appears to be 

 anomalous in meteorites. Also, a new method of potassium-argon 

 dating, applicable to minute samples, has been established, based on 

 A*°/A^ ratios in neutron-irradiated samples in which A^^ is produced 

 bytheK^(n,p) reaction. Thus both potassium and radiogenic argon 

 are determined in the same sample, and a correction for air contamina- 

 tion can be applied using the measured A^®. This represents a con- 

 siderable improvement over conventional methods. 



The rare-gas mass spectrometer has been completed by Dr. Tilles 

 and his associates.^ As a first application of the instrument, the 

 group plans searches of deep-sea sediment for evidence of material 

 of extraterrestrial origin. Similar searches are planned in particulate 

 matter from Greenland ice, collected by Dr. Fireman and Mr. Lang- 

 way, The major research emphasis with this spectrometer will be on 

 studies of meteoritic samples — isotopic composition and amounts of all 

 noble gases in separated phases of meteorites. 



From the theoretical aspect. Dr. Henri E. Mitler is studying the 

 effects of cosmic-ray bombardment on meteorites. Quantitative analy- 

 sis of radionuclides produced can lead to estimates of the preatmos- 



See footnotes, p. 177. 



