  Observational gamma-ray astronomy was born some forty years ago, when small
detectors were flown in satellites, following a decade of theoretical
predictions of its potential to discover the origin of cosmic rays via the
pi-zero decay mechanism. The seventies were a golden era for gamma-ray and
cosmic-ray astrophysics, with the (re)discovery of the "diffuse shock
acceleration" theory for cosmic rays, and the first CO and GeV gamma-ray
surveys of the galactic plane, verifying the importance of pi-zero decay in the
large-scale gamma-ray emission of the Galaxy. But because of this strong
galactic background, GeV gamma-ray sources were hard to identify. The first
such sources definitely identified were three pulsars, with a suggestion that
supernova remnants interacting with molecular clouds in massive star-forming
regions ("SNOBs") were also gamma-ray sources. Because of their improved
sensitivity and spatial resolution, ground-based Cerenkov telescopes, detecting
gamma-rays at > TeV energies, are now able to resolve molecular cloud-sized
objects at a few kpc. SNOB-like objects like IC443 and W28 are detected at GeV
and TeV energies, and show spatial evidence for cosmic-ray interactions between
an SNR shock wave and nearby molecular clouds, and subsequent pi-zero decay.
However, the spectral evidence does not clearly support this mechanism. We
propose to use another tool for probing the interaction of the low-energy
component of the putative local cosmic rays, in the form of enhanced ionization
in TeV-bright molecular clouds, using millimeter observations.
