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Four series of experiments had been carried out for correct ytterbium isotope ratios measurements (IRM).(1) For erbium IRM, 167 Er/ 166 Er ~0.682 60, derived from recently published thermal ionization mass spectrometry (TIMS) measurements, was applied as an internal normalization factor. (2) Ytterbium has no calibrated isotope ratio values. In an erbium-ytterbium-hafnium mixture solution we determined ( 171 Yb/ 172 Yb) Er-corr ~0.653 436(4) using the above 167 Er/ 166 Er ratio as external normalization factor. In the same mixture we also determined ( 171 Yb/ 172 Yb) Hf-corr ~0.653 297(25) using the well-known IUPAC value for the ratio 179 Hf/ 177 Hf ~0.732 50 as external normalization factor. In these measurements no atomic isobaric interference exists at the corresponding mass numbers. (3) These two 171 Yb/ 172 Yb ratios, derived with data at mass intervals 166-167 and y178, were interpolated to mass interval 171-172, applying linear and slightly curved (exponential) line interpolations. 171 Yb/ 172 Yb ~0.653 367 and 0.653 344 are the linear and curved line interpolated values, respectively. Then, all ytterbium isotope ratios were measured in pure ytterbium solutions and internally corrected with each of the two 171 Yb/ 172 Yb ratios. ( 4) Using the literature value for 178 Hf/ 177 Hf ~1.467 290, we obtained 179 Hf/ 177 Hf ~0.732 49(2), which is in very good agreement with the above mentioned IUPAC value. The exponential correction equation was applied in this work. The mean Er ratio values are in good agreement with literature, except for the 162 Er/ 166 Er ratio, which is 2.19% lower than the reported absolute TIMS value. The mean Yb ratio values obtained in this work are in fair agreement with data reported in the last 25 years. We believe that they are the closest to the true values. The precision (2s) is at least 3-8 times better comparing to the measured TIMS precision.

Evidence for the existence of long-lived neutron-deficient isotopes has been found in a study of naturally-occurring Th using inductively coupled plasma-sector field mass spectrometry. They are interpreted as belonging to the recently discovered class of long-lived high spin super-and hyperdeformed isomers.In recent years, long-lived high spin super-and hyperdeformed isomeric states with unusual radioactive decay properties have been discovered in heavy and very heavy nuclei [1][2][3][4] . This discovery motivated us to perform a search for naturally-occurring long-lived isomeric states. (Up to now there is only one such isomeric state known, namely the 75.3 keV excited state in 180 Ta with a half-life of >1.2x10 15 y (ref. 5 )). Madagascan monazite and commercially available Th and U standard solutions were studied using different mass spectrometers, including an accelerator mass spectrometer. In the present paper we present the results obtained with pure Th standard solutions and also in one case with a monazite digest solution, using inductively coupled plasma-sector field mass spectrometer (ICP-SFMS).The instrument was an Element2 (Thermo-Electron, Bremen, Germany). The predefined medium resolution mode of m/∆m = 4000 (10% valley definition) was used throughout the experiments so as to separate atomic ions from interfering molecular ions with the same mass number. The sensitivityenhanced setup of the instrument was similar to that described in Ref.6 where a capacitive decoupling system and high-performance "X" skimmer were used, providing sensitivity for 232 16 O + peaks. Two 1000 mg l -1 Th stock solutions "A" and "B" from two manufacturers, Inorganic Venture and Customer Grade, were obtained from LGC Promochem AB (Borås, Sweden). Complete elemental screening was performed on both solutions to assess the impurity concentration levels PDF created with pdfFactory trial version www.pdffactory.com 2 The solutions were analyzed during three separate sessions: May 25, October 5, and November 6, 2005. A range of about 0.2 mass unit was scanned in each measured spectrum. This range was divided into approximately 60 channels. During the first session, masses from 210 to 269 were analyzed with an integration time per channel of 0.6 sec. During the second and third sessions, selected mass regions (where some indication of unidentified signals had been detected) were measured using an integration time per channel of 3 and 12 sec, respectively. Instrumental sensitivity varied significantly among runs as a result of matrix effects caused by the introduction of highly concentrated solutions into the ICP source. During the first session, the monazite digest (1000 mg monazite l -1 ) and Th solution A (diluted to 20 mg Th l -1 ) were scanned once. (The Th content in the monazite was approximately 2%. The contents of typical rare earth elements in it, like Ce, Dy and Er, were about 5%, 0.05% and 0.02%, respectively.) During the second session, 20 mg l -1 of Th A and B solutions spiked with 2 µg l -1 Bi were studied and eac...

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