  COSINE-100 is a dark matter direct detection experiment with 106 kg NaI(Tl)
as the target material. 210Pb and daughter isotopes are a dominant background
in the WIMP region of interest and are detected via beta decay and alpha decay.
Analysis of the alpha channel complements the background model as observed in
the beta/gamma channel. We present the measurement of the quenching factors and
Monte Carlo simulation results and activity quantification of the alpha decay
components of the COSINE-100 NaI(Tl) crystals. The data strongly indicate that
the alpha decays probabilistically undergo two possible quenching factors but
require further investigation. The fitted results are consistent with
independent measurements and improve the overall understanding of the
COSINE-100 backgrounds. Furthermore, the half-life of 216Po has been measured
to be 143.4 +/- 1.2 ms, which is consistent with and more precise than recent
measurements.
