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6. a Trial to Detect the Aberration O F Ru Isotopic Ratios Due To No. 2] Proc. Japan Acad., 70, Ser. B (1994) 25 6. A Trial to Detect the Aberration of Ru Isotopic Ratios Due to Radioactive Decay of Technetium By Akimasa MASUDA and Min HUANG Department of Chemistry, University of Electro-Communications, Chofu, Tokyo 182 (Communicated by Syun-iti AKIMOTO, M. J. A., Feb. 14, 1994) Abstract: As our basic work to establish precisely the reference isotopic abundance ratios of ruthenium, we examined carefully the isotopic abundance ratios of seven stable isotopes of ruthenium using its solution prepared by Aldrich Chemical Co., Inc., Milwaukee, WI, USA. Prior to our examination, Poths, Schmitt-Strecker and Begemann (1987) at Max-Planck-Institut fur Chemie, Mainz, also determined precisely the corres- ponding ratios using Ru of Ventron-Alpha Co. Our 98Ru/99Ruratio is about 11 higher than that reported by Poths et al., while our 104Ru199Ruratio is about 10 e lower than that by them. As regards 96Ru, 100Ru, lo1Ru and potentially 99Ru, there are little if any re- markable differences between us and them. The difference in 104RuI99Ruis judged to reflect the interference from (88Sr160)+ion in their measurement. However, it is difficult to account for the difference in 98Ru/99Ruratio. One cannot rule out the possibility that this has resulted from the difference in nuclear-decay contribution from 98Tc. Key words: Technetium; primeval technetium; ruthenium; isotopic ratio; tech- netium-98; ruthenium-98; isotopic inhomogeneity. In spite of laborious attemptsl),2> to discover the real presence of element 43, its "reality" was not recognized until the production of technetium radio -isotopes by bombardment of 94Mo and 96Mo by deuteron3~ (Perrier and Segre, 1937). A subsequent surprising news was an observation of spectra of neutral technetium in S-type stars4~ (Merrill, 1952), the first finding of Tc in "nature". Of course, however, the spectral observation cannot identify the nuclide species. In 1961, Kenna and Kuroda5~ could find out 99Tc which was formed transiently from the spontaneous fission in a terrestrial uranium mineral. A few attempts to search for primeval technetium in the earth around the period 1955-1956 are reviewed by Kuroda.6~ According to a calculation by Cowan and Haxton7~ based on nuclear physics, 97Tc and 98Tc can be produced by reaction of solar neutrino with molybdenum isotopes. But the effects of these productions are estimated to be far lower than recognizable by the ordinary techniques, for the usual natural systems. In the result, the spectral lines of Tc in S-type stars are the only case indicative of reality of primeval Tc. Thus far, it is known that three species of Tc isotopes, i.e., 97Tc, 98Tc and 99Tc have considerably long half-lives, 2.6x 106 y, 4.2x 106 y and 2.l x 105 y, respectively (cf. Table I). (It intrigues us that the isotopic abundance for 99Ru (see Table II) is higher than either of neighboring isotopes 98Ru and 100Ru, because such a case is known only for 129Xe and the fact observed for an even-odd nuclide 99Ru can be interpreted to suggest a contribution from 99Tc.) Masuda and Qi-Lu8~suspected that the mass spectra for 97 and 99 emitted from unloaded Re filament might be 97Tc and 99Tc. But these strange mass spectra were ascribed° to a cluster ion (K2F)+ which had not been known. The last remaining possible access to the primeval technetium would be to look for the variation of isotopic ratios of 97Mo , 98Ru and 99Ru based on the precise mass spectrometric measurement of Mo and Ru. 26 A. MASUDA and M. HVANG [Vol. 70(B), Table I. Three technetium isotopes with long half-lives Table II. Isobaric effects on ruthenium isotopes Mass Spectrometry. Poths et al. 10) presented the very precise data on Ru isotopes employing the chemical reagent (Ventron-Alpha solution). As shown in Table II, the Ru isotopes can be affected by isotopes of Zr, Mo and Pd. Accordingly, we measured the mass spectra for 94, 95, 96, 97, 98, 99, 100, 101, 102, 104 and 105. Furthermore, caution was also taken against the possible formation of K2F+ ion. As a result, it was noticed that the most serious problem arises from the Mo+ ion emitted from the Re filament which is used for thermal ionization of Ru. Any words are not given about this effect in their paper. Their measurement, however, was made between 15001600°C, while ours between 1950.2050°C. The lower temperature is favorable in suppressing the emission of impurity Mo ion. In our work, in order to reduce the impurity Mo effect, a zone-refined Re filament was adopted after careful preheating at 5A for 3 hours. It should be noted that 98Ru is a key nuclide for the purpose under consideration and that this nuclide can be affected most seriously by the Mo impurity (see Table II). It was found out that the effects from Zr, Pd and K2F+ were ordinarily almost negligible so long as our chemical reagent solution (Aldrich solution) was employed. (But one should be cautious about the fortuitous impurity trouble.) For the purpose of increasing the intensity, Poths et al. 10) employed the V-shaped filament and an activating reagent composed of boric acid and silica gel. In our experiment, however, the keenest attention was placed on high precision rather than on the sensitivity enhancement. Accordingly, the measurement was made with a simple filament using a relatively large amount (1015 µg) of Ru. Comparison between the mass spectrometric abundance data. Three sets (Table III) of our data for Aldrich sample are presented as relative difference in abundance ratio of data of Poths et al, from the values obtained by us for Aldrich. The values obtained are No. 2] A Trial to Detect Ru Isotope Aberration due to Tc 27 Table III. Relative difference (parts per 104) in abundance ratio of data of Poths et al. (1987) (Ventron-Alpha solution) from our data (Aldrich solution) Nos. 1-3 Fig. 1. Plot of difference (cf. Table III) in relative isotopic abundance ratio between Poths et al.10~ and the measurement No. 2 for Aldrich against mass number. A solid line refers to the collimation based on 102Ru over 99Ru (Table III), while a broken line to that based on levelling between 99Ru and 101Ru (see text). normalized against 102Ru/99Ru=2.47404. It is easily seen that the 104Ruh9Ru ratio presented by those authors is about +10 e (r=part per 104 parts) higher than ours. This can be understood to indicate that their data can be subject to interference from (88Sr16O)+ ion. It is suggested by themselves in their paper10~ that their data can be subject to such an interference. Another remarkable difference (-11---15 r) for 98Ru/99Ru draws our attention. So long as our careful scrutiny was made, the 98Ru/99Ru ratios secured by both groups are free from any sizable interference by interfering ions accountable for this difference. 28 A. MASUDA and M. HUANG [Vol. 70(B), It should be noted that the SrO+ can cause an interference not only for 104 but also 102 owing to (86Sr16O)+ion. Accordingly, this interference can have some perturbations in the results of calculation shown in Table III. If the apparent deviation for 104Ru/99Ru normalized against 102Ruf9Ru without considering the effects by 88Sr16O and 86Sr16Ois assumed to be +11 E, such a perturbation gives rise to an artifact error of -0.61 e for 101Ru/-9Ru. This result of estimation is in agreement especially with the value of No. 2 (see Table III). Poths et al. suggested that their data might be subject to an interference from (40Ca28Si16O2)+ion corresponding to m/e=100, which effect is observed for Nos. 2 and 3. Thus, judging from the consistency of numerical values in precise checking, the results for No. 2 seem to be the best in quality. If the measurement for No. 2 is adopted as the most reliable and the 99Ru/101Ruis taken as a bais for normalization or collimation (see a broken line in Fig. 1), the data by Poths et al. are evaluated to have the differences (in t) of -0.43, -15 .91, +0.57, +0.91 and +12.62, respectively, for 96Ru/99Ru, 98Ru/99Ru, 100Ru/99Ru, 1o2Ruj99Ruand 104Ru/99Ru , relative to the measurement No. 2 for Aldrich. Assuming that the deviation of -0.43 Efor 96Ru/99Ru can be interpreted to be an over-subtraction for Mo+ in their experiment or an under-subtraction in ours , the corresponding corrected deviation for 98Ru/99Ru turns out to be -14.1 ~. Summary. One should be very cautious in concluding definitely that the observed difference in 98Ru/99Ru ratio between two samples is due to the difference in contribution from technetium-98 (see below), because its significance is far-reaching. According to our examination, however, the measurements by Poths et al. and by us are free from any molecular ions and interfering isobaric effects. At present, on this basis, we are led to a judgment that the observed difference in 98Ru/99Ru is dependable, which can be explained in terms of difference in contribution originating from the radioactive decay of 98Tc. Following this line of interpretation, one can infer that there was primeval technetium and a kind of chemical fractionation had taken place between technetium and ruthenium an indefinable long time ago. In connection with this chemical fractionation, it is worth while to note that the valency of Tc under the condition of the earth is inferred" to be +4 and its geochemical behavior is supposed to be lithophile in contrast with that of Ru, one of platinum-group elements which are siderophile.
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