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Effects of Hydrogen on Resistivity Recovery of Tantalum Cold-Worked at 4.2 K

High purity tantalum specimens with 15∼50 at.ppm of hydrogen were cold worked at 4.2 K to investigate the recovery of point defects by a resistivity measurement. The resistivity instability, which has been revealed by the resitometric studies of Va metals, was confirmed to be caused by the small amount of hydrogen. A method to controll the state of hydrogen, Precipitated or dispersed, was devised to enable one to perform a stable resistivity measurement at 4.2 K after heat treatments at higher temperatures. The method proved to be useful both for a reproducible resistivity measurement at 4.2 K in hydrogen contaminated Ta and for determining the amount of H in cold worked Ta. Also, the possibility of hydrogen trapping by point defects is suggested.