Preparation for Liquid-Liquid Extraction Studies of Dubnium Using Homologue Models with the SISAK System

Abstract

Tracers of Nb, Ta, and the pseudo-homologue Pa were used to model the chemical behaviour of dubnium in the development of suitable liquid-liquid extraction systems for the SISAK centrifuge system. Extraction from sulphuric acid solutions into trioctyl amine in toluene and into Aliquat 336 in toluene were investigated as chemical separation systems. Distribution ratios for the homologues and the protactinium tracer, 233Pa, were measured in batch experiments, whereas short-lived cyclotron-produced tracers of Nb and Ta were measured in on-line separations using the SISAK system. SISAK is an automated centrifuge system purpose built to perform fast liquid-liquid extractions of short-lived nuclei. The results establish the optimal conditions for a SISAK dubnium experiment to explore its chemical properties in solutions relating to those of niobium and tantalum.

Addition of H2O2 to the Aliquat 336/H2SO4 system was investigated as part of this work. The addition suppresses the extraction of Nb. And also Ta, but to a lesser extent. This selective hydrogen peroxide complex formation might serve as the basis for an alternative way to investigate the complexing behaviour of Db.

Part of the work presented here is from participation in a SISAK experiment on 257Rf. In this experiment the distribution ratio for extraction into trioctyl amine in toluene from sulphuric acid was determined. The practical experience gained from the Rf experiment was important to ensure that the liquid-liquid extraction system developed here for dubnium is realistic, and furthermore was invaluable in understanding all the necessary requirements and conditions for performing such a complex experiment. The Rf experiments used for the first time a two-step extraction procedure with direct detection of alpha activity in both organic phases. Consequently, the distribution ratio can be determined without knowledge of the amount of activity entering the SISAK system, thereby reducing the uncertainty in the distribution measurement significantly. Due to the high amounts of liquid consumed by the SISAK system during transactinide experiments, which typically lasts several days, recycling of chemicals is necessary. This results in build-up of KCl in the aqueous phase (from the KCl-aerosol particles used as carriers in the gas jet). Thus, in a separate study the influence of KCl on the distribution ratios for zirconium and hafnium was determined to be negligible for the 5-time recycling currently used for the aqueous phase. It can, however, become a problem if the aqueous phase is more extensively recycled.