  The phenomenon of low-temperature superconductivity is intimately associated
with the condensation of weakly bound, very extended, strongly overlapping
Cooper pairs, and systematic experimental studies of the associated mean square
radius (coherence length) have been made. While the extension of BCS theory to
the atomic nucleus has been successful beyond expectation, to our knowledge, no
measurement of the nuclear coherence length (expected to be much larger than
nuclear dimensions) has been reported in the literature. Recent studies of
Cooper pair transfer across a Josephson-like junction, transiently established
in a heavy ion collision between superfluid nuclei, have likely changed the
situation, providing the experimental input for a quantitative estimate of the
nuclear coherence length, as well as the basis for a nuclear analogue of the
(ac) Josephson effect.
