The other isotopes detectable from individual supernovae are ⁴⁴Ti, ⁵⁷Co, and ⁶⁰Co. Models for Type II supernovae predict a ⁴⁴Ti mass from 0 to 2x10^-4 M_o. Since this isotope comes from the deepest layers ejected in the supernova, its ejection is sensitive to the uncertain explosion mechanism and to the details of the fall back (e.g., whether the supernova makes a black hole). Recently, COMPTEL has reported the detection of the 1.157 MeV line from the ⁴⁴Ti-⁴⁴Sc decay from the youngest known galactic supernova remnant, Cas A. The implied yield, 1- 2x10^-4 M_o, is consistent with models, but it remains a mystery why Cas A was not a brighter supernova given that ⁴⁴Ti ejection implies ⁵⁶Co ejection. Assuming a comparable⁴⁴Ti yield in other Type II supernovae, the planned INTEGRAL mission should discover several other young remnants in our galaxy. However, it should be noted that ⁴⁴Ti decay also produces comparable fluxes in lines at 67.85 keV and 78.38 keV. It may be that hard X-ray instruments can be built with greater sensitivity. SN 1987A is also expected to have made ~0.5x10-4 M_o of ⁴⁴Ti (highly uncertain) implying a flux for the next few decades of about 2x10^-6 cm^-2 s^-1.
Gamma-ray lines of ⁵⁷Co (T1/2 = 271.8 d) were detected from SN 1987A by OSSE implying a ratio ⁵⁶Fe/⁵⁷Fe of about 1.5 times the solar value, an interesting constraint on both the star's evolution (i.e., the neutron excess in the silicon shell) and galactic chemical evolution. However, the signal of this isotope and ⁶⁰Co (T1/2 = 5.27 y) are such that they are only likely to be detected from fortuitous supernovae in the local group. The most prominent radioactivity expected to produce gamma-lines from classical novae is ²²Na. The synthesis of this species is highly uncertain and is sensitive to the nature of convection during the explosion and whether the nova event occurs on a carbon-oxygen white dwarf or a neon-oxygen white dwarf (the signal is much stronger from the latter).

2.1.2 GALACTIC NUCLEOSYNTHESIS The 1.809 MeV line from the decay of the very long-lived (mean life 1.07x10⁶ years) ²⁶Al was the first nucleosynthetic gamma-ray line to be detected. It shows that nucleosynthesis is an ongoing process in the galaxy. Most recently, images in the 1.809 MeV line have revealed a broad, patchy longitude distribution that is very different from that of the 0.511 MeV line which is strongly peaked at the galactic center. This result demonstrates that the two line emissions have different origins. The observed line fluxes suggest that there is roughly 1 to 2 M_o of ²⁶Al in the galaxy, which is consistent with that expected from recent estimates of Type II supernova yields and occurrence rates. Although Wolf-Rayet stars have also been suggested as a source, they do not appear to be significant because recent observations of the Vela supernova remnant show an enhancement in the 1.809 MeV line intensity, clearly supporting a supernova origin of the ²⁶Al, while no significant emission was seen from the nearby Wolf-Rayet star g Vel. The total amount of ²⁶Al observed is consistent with current models of supernovae and galactic chemical evolution.