Methods and systems are provided for cyclical enrichment, especially of rare earth elements and isotopes. A tube, or ampule, with two coaxially opposite crucibles in fluid communication, is used to hold a source material in vacuum and irradiate the source material to enrich it with product material. Following the irradiation of the source substance (e.g., Yb, enriched with 176Yb) to yield the product substance (e.g., 177Lu), the mixture may be sublimated to remove most of the source substance and concentrate the target material, e.g., by heating the lower part of the lower crucible while cooling the upper part of the ampule, to condense the sublimating source structure on the receiving crucible. Consecutively, the concentrated product substance may be purified, while the solidified source structure may be reused.