We have studied the production, destruction, and lifetimes of the ${\mathrm{He}}_{2}(a{^{3}\ensuremath{\Sigma}_{\mathrm{u}}}^{+})$ and
He(23S) metastable states of helium that are produced in electron-bombarded superfluid helium. The characteristic lifetime of a metastable molecule in the superfluid is shown to exceed 0.1 sec, while the lifetime of a metastable atom is only about 15 \ensuremath{\mu}sec. The production rates for the ${\mathrm{He}}_{2}(a{^{3}\ensuremath{\Sigma}_{\mathrm{u}}}^{+})$ and
He(23S) metastable states are about 500 and 450 per incident 160-keV electron, respectively.
A laser spectroscopic method was developed to directly observe the lifetimes of individual states in metastable antiprotonic helium atoms
(p4He+). Collisional effects with surrounding helium atoms were studied in cryogenic gas targets at pressures between 0.1 and 9.0 bars and at temperatures between 5.5 and 7.0 K. The metastable state
(n,l)=(39,35) showed a lifetime of 1.5 $\ensuremath{\mu}\mathrm{s}$, regardless of density, whereas the lifetime of the energetically lower-lying state
(37,34) was found to shorten from 1.3 to 0.1 $\ensuremath{\mu}$s with increasing density. The lifetimes of the states
(38,34) and
(36,33) were determined to be 10 ns and 5 ns, respectively, showing the effects of the internal Auger process. When extrapolated to zero density, the measured lifetimes agreed with the results of calculations for the radiative and Auger widths. Using the fact that the state
(37,34) becomes short lived at high density, the resonance $(38,35)\ensuremath{\rightarrow}(37,34)$ at 529.62 nm was detected.