The observation of neutrino avor oscillations by Super-Kamiokande col-
laboration and Sudbury Neutrino Observatory has established that neutrino
is a non-zero rest mass particle. Those experiments provided the only scale
of mass and upper limits on the half-life of the decay where the mass of the
heaviest neutrino mass eigenstate can't be less than 0.05 eV. Up to now, no
one knows what is the mass of the neutrino and it is unclear that neutrinos are
Dirac particle or Majorana particle. Neutrinoless double-beta (0v) decay is
a decay mode of an atomic nucleus where the two neutrons convert into two
protons and two electrons. If this decay occurs, the neutrino is it's own an-
tiparticle, meaning Majorana particle. The observation of 0v decay would
determine whether the neutrino is a Majorana or Dirac particle and provide
information on the absolute mass of the neutrino. The Advanced Mo-based
Rare process Experiment (AMoRE) is an experiment using cryogenic tech-
nique that aims to search the neutrino mass through 0v decay of 100Mo in
48deplCa100MoO4 crystals discoveries. AMoRE experiment requires extremely
low radioactive background contributions from crystals and detector materials.
To reach those goals, it is extremely important to use ultra-clean materials to
intensify the detector performance following by sophisticated background re-
jection technique and an excellent understanding of background contributions.
However, crystals naturally can be contaminated with radioactive isotopes such
as 238U, 232Th, 235U, and their daughter decay that might be produced from the
chemical powder that is used in crystal growing or during the cleaning process.
Additionally, the other concern about background contribution is also coming
from surface contamination, impurities attached to the exposed surface of the
crystal or other detector components. Some of the long-lived decay such as
238U or 232Th might be implanted inside the surface of the material. 0v is -
like events, however, surface contamination can produce degraded 's making
continuum energy distribution that extends to double- energies, obscuring
a possible signal of 0v. Due to the short-range of particles and recoil
nuclei, contamination can be originated from the crystal and the detector
components that directly facing the crystal. To suppress the radioactive back-
ground, understanding of background sources and complete simulation that
accurately models the background-energy spectra measured by the detector
are important. Simulation plays a primary role in background identication
and reduction through background modeling. Properly study about the mea-
sured background relies on Monte Carlo (MC) simulation to clarify the possible
background sources and its contamination. In this study, eects of radioactive
isotopes such as 238U, 232Th, and 235U including their daughter isotopes inside
the crystal and 210Pb inside the re
ector are simulated. Additionally, to reduce
the presence of possible contaminants on the surface, understanding of surface
contamination is also carried out. The eect of surface contamination is inves-
tigated by simulating some events randomly within the depths to produce the
background spectra at various surface depths. To clarify the contributions of
background sources and surface contamination quantitatively, a Monte Carlo
simulation is conducted by using the GEANT4 toolkit. All the background
sources in the simulation are compared and tted to the measured data using
log-Likelihood Fitting by constraining known activities (mBq/kg) as conser-
vative upper limits and t parameters. Meanwhile, the unknown fractions
of the background spectra are set as
oating parameters to quantify the un-
known fractions of the background compositions. The MC background spectra
are well described the measured data. Through study that was conducted, a
successfully understanding of the backgrounds is obtained.