Separation of Trace Level Hafnium from Tungsten: A Step Toward Solving an Astronomical Puzzle

摘要

~(182)Hf (T_(1/2) velence 9 X 10~(6) y) is believed to be formed by pure r-process during a supernova explosion, and therefore, the search for minute traces of ~(182)Hf in the earth's crust is of great interest. Only accelerator mass spectrometry (AMS) is well suited for detecting such low levels of ~(182)Hf. But any attempt to measure ~(182)Hf by AMS must ensure that the sample is free from its naturally occurring stable isobar ~(182)W. A simple method for separation of tungsten and hafnium has been developed using radiometric simulation followed by checking the decontamination of tungsten from Hf in a synthetic sample by AMS. The separation studies were performed by a liquid-liquid extraction technique using tri-n-octylamine (TOA) as the organic reagent. It has been found that a very high separation factor (1.6 X 10~(6)) can be achieved when 0.3 M TOA diluted in cyclohexane is used as the organic phase and 6 M HCl (in the presence of small amount of H_(2)O_(2)) is used as the aqueous phase.