  Measurement of the chemical and isotopic composition of cosmic rays is
essential for the precise understanding of their propagation in the galaxy.
While the model parameters are mainly determined using the B/C ratio, the study
of extended sets of ratios can provide stronger constraints on the propagation
models. In this paper the relative abundances of the light nuclei lithium,
beryllium, boron and carbon are presented. The secondary to primary ratios
Li/C, Be/C and B/C have been measured in the kinetic energy range 0.35-45
GeV/nucleon. The isotopic ratio 7Li/6Li is also determined in the magnetic
rigidity interval 2.5-6.3 GV. The secondary to secondary ratios Li/Be, Li/B and
Be/B are also reported. These measurements are based on the data collected by
the Alpha Magnetic Spectrometer AMS-01 during the STS-91 space shuttle flight
in 1998 June. Our experimental results are in substantial agreement with other
measurements, where they exist. We describe our light-nuclei data with a
diffusive-reacceleration model. A 10-15% overproduction of Be is found in the
model predictions and can be attributed to uncertainties in the production
cross-section data.
