We investigate the helium flash (He-flash) on neutron stars where accreted matter is assumed to be pure helium. Then, we present the results of numerical calculations and compare them with the observation of 4U 1820-30 which is considered the site of the He-flash. Furthermore, we examine the carbon flash (C-flash) with X(12C) = 0.1, which has been proposed to cause superbursts.
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