  Published data on the emission of charged particles following nuclear muon
capture are extremely limited. In addition to its interest as a probe of the
nuclear response, these data are important for the design of some current
searches for lepton flavor violation. This work presents momentum spectra of
protons and deuterons following $\mu^{-}$ capture in aluminum. It is the first
measurement of a muon capture process performed with a tracking spectrometer. A
precision of better than 10% over the momentum range of 100--190 MeV/c for
protons is obtained; for deuterons of 145--250 MeV/c the precision is better
than 20%. The observed partial yield of protons with emission momenta above 80
MeV/c (kinetic energy 3.4 MeV) is
$0.0322\pm0.0007(\text{stat})\pm0.0022(\text{syst})$ per capture, and for
deuterons above 130 MeV/c (4.5 MeV) it is
$0.0122\pm0.0009(\text{stat})\pm0.0006(\text{syst})$. Extrapolating to total
yields gives $0.045\pm0.001(\text{stat})\pm0.003(\text{syst}) \pm
0.001(\text{extrapolation})$ per capture for protons and
$0.018\pm0.001(\text{stat})\pm0.001(\text{syst})\pm
0.002(\text{extrapolation})$ for deuterons, which are the most precise
measurements of these quantities to date.
