Several other promethium isotopes (144Pm, 146Pm, 147Pm etc.) also have a positive energy release for alpha decay; their alpha decays are predicted to occur but have not been observed.
其他幾個Pm同位素（144Pm，146Pm，钷-147等）的也有正面α衰變的能量釋放;預測他們的α衰變會發生的但都沒有被觀察到。