  Ambient radiation background contributed by the penetrating cosmic ray
particles and the radionuclides present in the rock materials have been
measured at an underground laboratory located inside a mine at 555 m depth. The
laboratory is being set up to explore rare event search processes, such as
direct dark matter search, neutrinoless double beta decay, axion search,
supernova neutrino detection, etc., that require specific knowledge of the
nature and extent of the radiation environment in order to assess the
sensitivity reach and also to plan for its reduction for the targeted
experiment. The gamma ray background, which is mostly contributed by the
primordial radionuclides and their decay chain products, have been measured
inside the laboratory and found to be dominated by rock radioactivity for
$E_\gamma \lesssim 3 \,{\rm MeV}$. Shielding of these residual gamma rays for
the experiment was also evaluated. The cosmic muon flux, measured inside the
laboratory using large area plastic scintillator telescope, was found to be:
$(2.051 \pm 0.142 \pm 0.009) \times 10^{-7}\, {\rm cm}^{-2}.{\rm sec}^{-1}$,
which agrees reasonably well with simulation results. The neutron background
flux has been measured for the radiogenic neutrons and found to be: $(1.61 \pm
0.03) \times 10^{-4} \, {\rm cm}^{-2}.{\rm sec}^{-1}$ for no threshold cut.
Detailed GEANT4 simulation for the radiogenic neutrons and the cosmogenic
neutrons have been carried out. Effects of multiple scattering of both the
types of neutrons within the surrounding rock and the cavern walls were studied
and the results for the radiogenic neutrons are found to be in reasonable
agreement with experimental results. Neutron fluxes contributed by those
neutrons of cosmogenic origin have been reported as function of the energy
threshold.
