The heaviest elements available in macroscopic amounts, e.g., from ORNL, are einsteinium (element 99) and fermium (element 100). Typical isotopes include Es-254 (half-life: 276 d), available in microgram quantity, and Fermium-257 (half-life: 100 d), available in picogram quantity. Further einsteinium isotopes are produced concurrently, including Es-253 (20.5 d) and Es-255 (40 d). These, however, decay largely during a six-month cooling period following irradiation, prior to the chemical separation. Nuclear decay properties in this region of the chart of nuclides provide for the possibility of producing a generator system based on 40-d Es-255, which has a 92% beta-minus decay branch, leading to 20-h Fm-255. In contrast to the situation in which Fm-255 is chemically isolated and vanishes with its short half-life, the availability of Es-255 precursor would allow for a constant milking of the Fm-255 daughter over a timeframe of many weeks, thus enabling more sophisticated studies of this element, even without the need of a dedicated Fm separation from the irradiated fuel. In a first optical experiment on Fm, for example, a sample of 2.7E10 atoms served for the first identification of atomic levels in Fm. The short 20-h half-life, though, precluded more extensive studies. With this contribution we like to highlight the opportunities that would arise from the availability of a sample enriched in Es-255. The resulting long-term availability of Fm-255 would allow, e.g., for highlight studies of its atomic structure, in the spirit of the pioneering studies performed in Mainz in 2002, or for ultra-precise state-of-the-art atomic mass measurements employing Phase-Imaging Ion-Cyclotron-Resonance Mass Spectrometry.

Einsteinium-255 generator for off-line studies of fermium-255?

254th National Meeting (2017)

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