On the volatility of protactinium in chlorinating and brominating gas media

A multi-target recoil chamber technique was applied to study online chemical properties of protactinium in chlorinating and brominating gas media using Pa-226 (T (1/2) = 1.8 min) decaying by alpha emission (74%) and beta(+)/EC decay (26%). A 58 MeV proton beam passing 15 x 50 mu g/cm(2) thick Th-232 targets enabled production of Pa-226 formed in the reaction Th-232(p,7n). Isothermal gas chromatography in quartz columns allowed for the determination of adsorption enthalpies of oxohalides and pure halides of Pa5+ compounds. On the basis of empirical correlations, these adsorption enthalpies (Delta H-0 (ads)) could be converted to sublimation enthalpies (Delta H-0 (subl)). Resulting values for the assumed compounds PaCl5, PaOCl3, PaBr5, and PaOBr3 were 113 +/- 15, 329 +/- 16, 165 +/- 5 and 235 +/- 17 kJ/mol, respectively. These values are rather similar to known Delta H-0 (subl) data for group-5 elements Nb, Ta and Db in support of the assumption that Pa is a pseudo-group 5 element.