Purification of cerium, neodymium and gadolinium for low background experiments

Cerium, neodymium and gadolinium contain double beta active isotopes. The most interesting are Nd and Gd (promising for 02 search), Ce (2 candidate with one of the highest Q2). The main problem of compounds containing lanthanide elements is their high radioactive contamination by uranium, radium, actinium and thorium. The new generation 2 experiments require development of methods for a deep purification of lanthanides from the radioactive elements. A combination of physical and chemical methods was applied to purify cerium, neodymium and gadolinium. Liquid-liquid extraction technique was used to remove traces of Th and U from neodymium, gadolinium and for purification of cerium from Th, U, Ra and K. Co-precipitation and recrystallization methods were utilized for further reduction of the impurities. The radioactive contamination of the samples before and after the purification was tested by using ultra-lowbackground HPGe gamma spectrometry. As a result of the purification procedure the radioactive contamination of gadolinium oxide (a similar purification efficiency was reached also with cerium and neodymium oxides) was decreased from 0.12 Bq/kg to 0.007 Bq/kg in Th, from 0.04 Bq/kg to <0.006 Bq/kg in Ra, and from 0.9 Bq/kg to 0.04 Bq/kg in K. The purification methods are much less efficient for chemically very similar radioactive elements like actinium, lanthanum and lutetium.