The elements undergo fractionation during particle formation, due to their different volatility. Refractory elements (Sr, Y, Zr, Nb, Ba, La, Ce, Pr, Nd, Pm) form oxides with high boiling points; these precipitate the fastest and at the time of particle solidification, at temperature of 1400 °C, are considered to be fully condensed. Volatile elements (Kr, Xe, I, Br) are not condensed at that temperature. Intermediate elements have their (or their oxides) boiling points close to the solidification temperature of the particles (Rb, Cs, Mo, Ru, Rh, Tc, Sb, Te). The elements in the fireball are present as oxides, unless the temperature is above the decomposition temperature of a given oxide. Less refractory products condense on surfaces of solidified particles. Isotopes with gaseous precursors solidify on the surface of the particles as they are produced by decay.