The semiclassical theory of laser cooling is applied for the analysis of cooling of unbound atoms with the values of the
ground and exited state angular moments 1/2 in a one-dimensional nondissipative optical lattice. We show that in the
low-saturation limit with respect to the pumping field a qualitative interpretation of the cooling mechanisms can be made
by the consideration of effective two-level system of the ground-state sublevels. It is clarified that in the limit of weak
Raman transitions the cooling mechanism is similar to the Doppler mechanism, which is known in the theory of two-level
atom. In the limit of strong Raman transitions the cooling mechanism is similar to the known Sisyphus mechanism.
In the slow atom approximation the analytical expressions for the coefficients of friction, spontaneous and induced
diffusion are given, and the kinetic temperature is estimated.