Low-background experiments to search for double ß decay, dark matter, investigate rare α and ß decays require very low, ideally zero level of radioactive contamination. The most dangerous contaminants are radioactive elements uranium, thorium, radium, potassium, actinium, rubidium, lanthanum, lutetium, samarium, while transition elements decrease quality of scintillation detectors. There are no commercially available compounds with the required and specified levels of radioactive contamination. Even commercial high purity grade materials have to be additionally purified. Purification of rare earth elements is particularly complicated task taking into account their similar chemical properties to other rare earth and to radioactive daughter elements of ²³²Th, ²³⁵U and ²³⁸U.
There are a lot of industrial techniques of rare elements separation, however, one need to develop specific approaches to remove radioactive impurities. On the seminar I will describe some physical and chemical methods of rare earth elements purification, particularly interesting from the point of view of double beta decay experiments: neodymium, gadolinium and cerium. The main advantage of these methods is that they can be realized in a chemical laboratory (e.g. as at the chemical laboratory of the Gran Sasso National Laboratory of INFN), without too much expensive equipment and reagents.

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Roman Boiko
National University of Life and Environmental Sciences of Ukraine, Kyiv, Ukraine
Institute for Nuclear Research, Kyiv, Ukraine