  We investigate radioactivity from the decay sequence of 44Ti in young
supernova remnants (SNRs), Cassiopeia A (Cas A) and SN 1987A. It is shown by a
linear analysis that ionization of 44Ti, a pure electron capture decay isotope,
affects the radioactivity contradistinctively in these two SNRs: Ionization of
44Ti to H-like and He-like states enhances its present radioactivity in Cas A,
while such high-ionization decreases its radioactivity in SN 1987A. We briefly
discuss the enhancement factor of the present radioactivity of Cas A
considering microscopic (atomic/nuclear) physics combined with a hydrodynamical
SNR evolution model. For SN 1987A, we have obtained the initial 44Ti mass of
(0.82-2.3) X 10^{-4} M_solar from our Monte-Carlo simulations. The resulting
fluxes of gamma and hard X-rays emerged from the 44Ti decay are given for the
current and future experiments.
