The half-life of the α decaying nucleus 221Fr was determined in
different environments, i.e. embedded in Si at 4 K, and embedded in Au at 4 K
and about 20 mK. No differences in half-life for these different conditions
were observed within 0.1%. Furthermore, we quote a new value for the absolute
half-life of 221Fr of t1/2​ = 286.1(10) s, which is of comparable
precision to the most precise value available in literature