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We have measured the intensity and spectra of the cosmic ray secondaryisotopes 2H and 3He and the primary isotopes H and 4He between 20-85 MeV/nucduring a 5 year time period after Voyager 1 (V1) crossed the heliopause. Thedata reported here is from the B-end high energy telescope. The ratios of theintensities of the secondary to primary spectra of these nuclei at low energiesare sensitive indicators for determining the amount of matter traversed atthese energies by their galactic cosmic ray progenitor nuclei, afteracceleration, in this case mostly 4He nuclei. The measurements of secondary 3Heabundances indicate that cosmic ray 4He of energies between 30-100 MeV/nuc havetraversed between 7-9 g/cm2 of interstellar matter (90% H, 10% He) in a LeakyBox propagation model. This path length is also consistent with the productionof secondary 2H nuclei between 20-50 MeV/nuc, which is also produced mainly by4He in a LBM. The Boron abundance, studied in separate papers, is alsoconsistent with this path length at energies >30 MeV/nuc. These secondaryintensities imply that the interstellar cosmic ray path length may be describedin a LBM in a manner consistent with a mean path length,gamma= 20.6 beta P-0.45at rigidities above ~0.5 GV (30 MeV/nuc for A/Z=2 nuclei). Both 2H and Boronhave an excess intensity vs. the predictions for path lengths of 9 g/cm2 below30 MeV/nuc.

The Spectra of 2H and 3He Secondary Cosmic Ray Isotopes from ~20-85  MeV/nuc as Measured Using the B-end HET Telescope on Voyager beyond the  Heliopause and a Fit to These Interstellar Spectra Using a Leaky Box  Propagation Model