Purification of cerium, neodymium and gadolinium for low background experiments

¹ Institute for Nuclear Research, MSP 03680 Kyiv, Ukraine
² Institute of Theoretical and Experimental Physics, 117259 Moscow, Russia
³ INFN, Section of Rome “Tor Vergata”, I-00133 Rome, Italy
⁴ INFN, Section of Rome “La Sapienza”, I-00185 Rome, Italy
⁵ Department of Physics, University of Rome “Tor Vergata”, I-00133 Rome, Italy
⁶ Department of Physics, University of Rome “La Sapienza”, I-00185 Rome, Italy
⁷ INFN, Gran Sasso National Laboratories, I-67100 Assergi (Aq), Italy

^a e-mail: boiko@kinr.kiev.ua

Published online: 10 January 2014

Abstract

Cerium, neodymium and gadolinium contain double beta active isotopes. The most interesting are ¹⁵⁰Nd and ¹⁶⁰Gd (promising for 0ν2β search), ¹³⁶Ce (2β⁺ candidate with one of the highest Q_2β). The main problem of compounds containing lanthanide elements is their high radioactive contamination by uranium, radium, actinium and thorium. The new generation 2β 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-low-background 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 ²²⁸Th, from 0.04 Bq/kg to <0.006 Bq/kg in ²²⁶Ra, and from 0.9 Bq/kg to 0.04 Bq/kg in ⁴⁰K. The purification methods are much less efficient for chemically very similar radioactive elements like actinium, lanthanum and lutetium.