  The study of transfer-induced gamma-decay probabilities is very useful for
understanding the surrogate-reaction method and, more generally, for
constraining statistical-model calculations. One of the main difficulties in
the measurement of gamma-decay probabilities is the determination of the
gamma-cascade detection efficiency. In [Nucl. Instrum. Meth. A 700, 59 (2013)]
we developed the Extrapolated Efficiency Method (EXEM), a new method to measure
this quantity. In this work, we have applied, for the first time, the EXEM to
infer the gamma-cascade detection efficiency in the actinide region. In
particular, we have considered the 238U(d,p)239U and 238U(3He,d)239Np
reactions. We have performed Hauser-Feshbach calculations to interpret our
results and to verify the hypothesis on which the EXEM is based. The
determination of fission and gamma-decay probabilities of 239Np below the
neutron separation energy allowed us to validate the EXEM.
