Zum Vorkommen von Promethium in der Natur
Abstract
After a discussion of former publications on the problem of the existence of promethium in nature, studies o f our own on this problem are reported. In these researches, 200 kg of gadolinite were separated with regard to Pm by using one- and two-stage cation-exchange separations and nitrilotri-aceticacid for elution and Cu2+ as barrier-ion.
The experiments yielded a beta-activity in the mixture-fractions between Sm and Nd. Because of its chemical behaviour and its half-thickness of 4.4 mg/cm2 that corresponds with a β-maximum energy of 230 keV (147Pm: 223 keV), this beta activity could be identified as 147Pm. For the lanthanide oxides of gadolinite a 147Pm content of 7.3 · 10 - 17% could be deduced, which agrees well with the value of 4.5 · 10 - 17% found by Erämetsä in 20 t lanthanide oxides of 6000 t apatite. The possible origin o f the 147Pm-isotope we found in gadolinite is discussed (fallout, actinium anomaly, spontaneous fission of 238U, and others), and the reaction 11,Id 2,6a 14 6Nd (n, y) ? is supposed to be the cause of the relatively short-lived isotope. The difference between the neutron flux (36 n/cm2 · min) that was deduced from the saturation activity of 147Pm, and the values of the neutron flux at the earth's surface or crust (0.001-0.24 n/cm2 · min) that up to now have been looked upon as probable by other authors, is also mentioned. Moreover, the question of the possible existence of a long-lived isomer of one of the known Pm-isotopes is rised.- Publication:
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Zeitschrift Naturforschung Teil A
- Pub Date:
- December 1970
- DOI:
- 10.1515/zna-1970-1225
- Bibcode:
- 1970ZNatA..25.1945M