Voyager 1 Observations of Galactic Cosmic-Ray Isotopes in the Very Local Interstellar Medium: Evidence for Primary ²H and B

We present the first measurements of the energy spectra of the isotopes of Galactic cosmic rays (GCRs) with nuclear charge Z = 1–14 in the very local interstellar medium (VLISM). We also update our previously published energy spectra of GCR elements in the VLISM from Z = 1–28 for a new longer time period of observations, 2013 January 1 through 2021 December 31. The observations are from the Cosmic Ray Subsystem on the Voyager 1 (V1) spacecraft and cover the Z-dependent energy range from ∼3 to 661 MeV nuc⁻¹. The data are fit to eight models using the GCR propagation code GalProp, which differ by having four options for fragmentation and two options for production cross sections. The models are all plain diffusion models with injection spectra as power laws in rigidity, where the propagation parameters and the injection power-law index are the same for all species, and derived self-consistently and independently for each model. The VLISM energy spectra generated by the models agree reasonably well with the observed VLISM energy spectra for the elements with Z = 1–28 and with the isotopes with Z = 1–14. However, to achieve reasonable fits to the ²H and B energy spectra, it was necessary to add a primary source of ²H and B.