Half-lives of unstable nuclei produced in supernovae

The half-life of an unstable nucleus measured in laboratory cannot always be applied directly to astrophysical situation, in particular to situation under a supernova. This comes from the difference of ionization states of the nuclei: The half-life values measured in laboratories are for neutral atoms, while nuclei can be highly ionized in supernovae or in young supernova remnants. 44Ti is such an example: The decay of highly ionized 44Ti atoms is retarded, since 44Ti decays by electron capture only. Here I summarize this ionization effect on the yield of 44Ti produced in a supernova explosion. Details are found in Mochizuki et al., Astronomy and Astrophysics, 346, 831 (1999). I also mention the internal conversion for 44Ti decays and point out other examples of unstable nuclei which decays are needed to be investigated from the viewpoint of ionization or excitation in the universe. (author)