On-Line Isothermal Gas Chromatography Experiments With NbBr₅ and NbOBr₃

The retention behaviour of volatile bromide and oxybromide of short-lived isotope of niobium in quartz column was studied using on-line isothermal gas chromatography apparatus. The ⁹⁹Nb nuclide with a half-life of 15 s was produced by spontaneous fission of californium-252. The fission products were continuously and rapidly transported through the capillary to the isothermal chromatography apparatus using the N₂/KBr gas-jet techniques. Volatile molecules are formed at the reaction zone kept at 900℃ by adding HBr as reactive gas. Depending on trace amounts of oxygen and water vapour in the system, two species NbBr₅ and NbOBr₃ are formed. While without oxygen and water vapour, only NbBr₅ is formed. After separation, the products were collected by activated charcoal filters and measured synchronously. On the basis of the experimental data and stimulated by the Monte JP2Carlo method, an adsorption enthalpy of （-92±5）kJ/mol for NbBr₅ and （-153±5）kJ/mol for NbOBr₃ are deduced.