  The {\gamma}-emission probability of the 66.73 keV line in the decay of 171Tm
has been experimentally determined using {\gamma}-spectrometry and inductively
coupled mass spectrometry. Using a set of two reference sources, namely 60Co as
primary standard and 44Ti/44Sc in secular equilibrium as secondary standards,
we were able to deduce the detection efficiency at 67.87 keV of the used
{\gamma}-spectrometry setup with high precision. The emission probability of
the 66.73 keV {\gamma}-transition in the decay of 171Tm has been determined
with a set of three radioisotopically pure 171Tm samples to be 0.159(6) %.
