114 Research and National Purpose 



bilized phase of 0.88 °K and that of the chromium stabilized 

 phase, 0.77°K. They then re-examined the studies of the super- 

 conductivity of alpha uranium, which was claimed to have a 

 transition temperature ranging from .7°K to somewhat above 

 1°K. Moreover, recently Dempsey, Gordon and Romer have 

 failed to find anomaly in specific heat measurements in the 

 appropriate temperature region and it now looks that the 

 alleged superconductivity of the alpha phase uranium is caused 

 by filaments of retained, stabilized alpha prime, beta and 

 gamma phases or perhaps even of filaments of other compounds. 

 The sensitivity of such a structure to mechanical Avorking was 

 demonstrated by Matthias and co-workers and they suggested 

 there may also be a very fine-meshed network of beta stabilized 

 filaments in alpha uranium phases. Now this indication has 

 broad significance for many of the solid state properties of this 

 interesting element, and yet a deeply specialized investigation 

 of particular properties of uranium was necessary in order to 

 reveal something about the phase composition which has been 

 sought by other means for decades. 



Yet another example is the extraordinary insights which are 

 arising about electrical plasmas in solids. Ruthemann and 

 Lang first observed plasma oscillations in metals, about 20 

 years ago, apparently resulting from high frequency density 

 waves in the "gaseous" conduction electrons after excitement 

 by an energetic electron beam. But it is now found that in the 

 presence of a simple dc magnetic field, low frequency electro- 

 magnetic waves propagate in solid state plasmas. In ordinary 

 metals with high electron densities, plasma frequencies are 

 high, such as about 10*^ radians per second. The quantum of 

 plasma oscillation or plasmon has an energy Hwp of about 10 

 electron volts. This, of course, is so much greater than kT at 

 room temperature that we do not see much of plasmons in 

 metals until outside energy is put in, such as by a controlled 

 electron beam. In semiconductors, electron densities lie in a 

 range of lO^^ to lO^^ per cc as contrasted to about 10^2 per cc 

 in metals. Hence their plasma frequencies are in the microwave 



