Accession Number : AD0690487

Title :   SIZE EFFECTS IN LIQUID HELIUM II AS MEASURED BY FOURTH SOUND AND THE ATTENUATION OF FOURTH SOUND.

Descriptive Note : Technical rept.,

Corporate Author : CALIFORNIA UNIV LOS ANGELES DEPT OF PHYSICS

Personal Author(s) : Kriss,Michael Allen

Report Date : JUN 1969

Pagination or Media Count : 121

Abstract : When Liquid He II is confined to a system with a large surface to volume ratio, the superfluid density and the superfluid onset temperature are reduced below their values found in bulk He II. The tightly packed fine powders (90A to 5 micrometers in diameter) used in fourth sound resonators create a system with a large surface to volume ratio. As the pore size in the packed powders decreases (increasing surface to volume ratios) the superfluid density at any temperature decreases, and the superfluid onset temperature also decreases. Experiments show that the superfluid density versus temperature curves form a family of curves whose characteristic parameter is the superfluid onset temperature. Onset temperatures as low as 1.79K have been observed. The onset temperatures and values of the superfluid density are consistent with existing theories on size effects in He II when the statistical distributions of the pores in the packed powders are taken into consideration. Measurements of the quality factor of fourth sound resonances indicate that the attenuation of fourth sound is due to motion of the normal field. (Author)

Descriptors :   (*HELIUM, *SOUND TRANSMISSION), SUPERFLUIDITY, LIQUEFIED GASES, POWDERS, ATTENUATION, RESONATORS, TEMPERATURE, PRESSURE, DENSITY, THESES

Subject Categories : Thermodynamics

Distribution Statement : APPROVED FOR PUBLIC RELEASE