Alpha backgrounds in NaI(Tl) crystals of COSINE-100

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 ?????? decay and a decay. Analysis of the a channel complements the background model as observed in the ??????/?????? channel. We present the measurement of the quenching factors and Monte Carlo simulation results and activity quantification of the a decay components of the COSINE -100 NaI(Tl) crystals. The data strongly indicate that the a 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 most current measurements.