  Dark matter particles scattering off some target nuclei are expected to
deposit very small energies in form of nuclear recoils (below 100 keV). Because
of the low scintillation efficiency for nuclear recoils vs. electron recoils,
in most of the scintillating targets considered in the search for dark matter,
the region below 10 keVee concentrates most of the expected dark matter signal.
For this reason, very low energy threshold (at or below 2 keVee) and very low
background are required. This is the case of the ANAIS (Annual modulation with
NaI Scintillators) experiment. A good knowledge of the detector response
function for real scintillation events, a good characterization of other
anomalous or noise event populations contributing in that energy range, and the
development of convenient filtering procedures for the latter are mandatory to
achieve the required low background at such a low energy. In this work we will
present the specific protocols developed to select bulk scintillation events in
NaI(Tl), and its application to data obtained with the ANAIS-0 prototype.
Slight differences in time constants are expected in scintillation pulses
produced by nuclear or electron recoils in NaI(Tl), so in order to analyze the
effect of these filtering procedures in the case of a recoil population
attributable to dark matter, data from a neutron calibration have been used.
