The electron-capture ( EC ) decay rate of ^ { 7 } Be in metallic Cu host and the \beta ^ { - } -decay rate of ^ { 198 } Au in the host alloy Al-Au have been measured \it simultaneously at several temperatures , ranging from 0.350 K to 293 K. No difference of the half-life of ^ { 198 } Au between 12.5 K and 293 K is observed to a precision of 0.1 \% .
By utilizing the special characteristics of our double-source assembly , possible geometrical effects that influence the individual rates could be eliminated .
The ratio of ^ { 7 } Be to ^ { 198 } Au activity thus obtained also remains constant for this temperatures range to the experimental precision of 0.15 \pm 0.16 % .
The resulting null temperature dependence is discussed in terms of the inadequacy of the often-used Debye-H \ddot { u } ckel model for such measurements .