  Local interstellar spectra (LIS) of secondary cosmic ray (CR) nuclei,
lithium, beryllium, boron, and partially secondary nitrogen, are derived in the
rigidity range from 10 MV to ~200 TV using the most recent experimental results
combined with the state-of-the-art models for CR propagation in the Galaxy and
in the heliosphere. The lithium spectrum appears somewhat flatter at high
energies compared to other secondary species that may imply a primary lithium
component. Two propagation packages, GALPROP and HelMod, are combined to
provide a single framework that is run to reproduce direct measurements of CR
species at different modulation levels, and at both polarities of the solar
magnetic field. An iterative maximum-likelihood method is developed that uses
GALPROP-predicted LIS as input to HelMod, which provides the modulated spectra
for specific time periods of the selected experiments for the model-data
comparison. The proposed LIS accommodate the low-energy interstellar spectra
measured by Voyager 1, HEAO-3, and ACE/CRIS as well as the high-energy
observations by PAMELA, AMS-02, and earlier experiments that are made deep in
the heliosphere. The interstellar and heliospheric propagation parameters
derived in this study are consistent with our earlier results for propagation
of CR protons, helium, carbon, oxygen, antiprotons, and electrons.
