A realistic microscopic approach to the heavy cluster spontaneous emission problem is presented. Nuclear wavefunctions are calculated in the framework of a Woods-Saxon+BCS approximation, using a large configuration space. The barrier penetration process has been treated within the WKB approximation. Applications are presented for the ^222-224Ra to ^208-210Pb+¹⁴C decays. The calculated total widths are within a factor of 5 to 10 of the currently accepted experimental values.