  In this Thesis, we describe the development of a three-dimensional radiative
transfer code using Monte Carlo technique and its application to various
astrophysical problems. This code is capable of simulating the radiation
spectra coming out of the electron cloud of an accretion disk around compact
objects, such as black hole X-ray binaries (XRBs). Physical processes included
in this code are the relativistic Maxwell-Juttner momentum distribution of the
electrons, Compton scattering with these electrons, and gravitational red shift
of the photons. Due to general nature of the code, processes like synchrotron
radiation, bremsstrahlung radiation, Coulomb coupling and the pair production
are also possible to incorporate. Various types of photon energy distribution
(e.g., mono-energetic, power-law, black-body and multi-colour black body) and
geometry of the photon source (e.g., point or disk) can be used. In this
Thesis, we have mainly used multi-color black body photons coming out of a
Keplerian disk as the source of soft radiation. This soft radiation is
intercepted by the electron cloud. Depending on the optical depth of the cloud,
and energy of the electrons, the soft photons may get Comptonized and
inverse-Comptonized via multiple scattering or may suffer no scattering at all,
and they emerge out of the cloud as a relatively harder radiation. Our
simulations provide information regarding the accretion disk and the central
compact object.
