Summary The fluoride complexation of the group-4 elements Zr, Hf, and Rf, and of the pseudo-homolog Th, was previously investigated in mixed HNO3/HF solutions by studying K d values on both cation-exchange resins (CIX) and anion-exchange resins (AIX) using the automated rapid chemistry apparatus ARCA. On the CIX, the fluoride complexation of Rf was found to be weaker than that of Zr and Hf but stronger than that of Th. On the AIX, the competition for the binding sites by the counter ion NO3 - was found to be stronger for the fluoride complexes of Rf than for those of Zr and Hf. The aim of the present work is to add independent evidence to the latter result by measuring K d values for Rf on the AIX in 0.1 M HNO3/0.5 M HF and in 0.01 M HF without any HNO3. The results are obtained via an activity ratio of the long-lived α-decay descendant of 261mRf, 20-d 253Es, using the multi-column technique (MCT). These experiments corroborate the seemingly much more pronounced competition of NO3 - for the exchanging sites of the AIX with respect to [RfF x ]( x -4)- than with [ZrF x ]( x -4)- and [HfF x ]( x -4)-.

Summary 27-s 263Db was produced in the 249Bk ( 18O, 4n) reaction at 93 MeV. The activity was transported by a He/KCl-jet to the laboratory where it was collected for 15 min and then subjected to a chemical separation specific for group-4 elements. The activity was dissolved in 0.5 M unbuffered α-HiB and eluted from a cation-exchange column. The effluent was made 9 M in HCl and group-4 tetrachlorides were extracted into TBP/Cyclohexane which was evaporated to dryness on a Ta disc. The Ta discs were assayed for α and SF activity. A SF activity with a half life on the order of 20 min was observed and assigned to the nuclide 263Rf. It is formed by electron-capture decay of 263Db with a decay branch of 3+4 -1%.

A. von Zweidorf1, R. Angert1, W. Brüchle1, S. Bürger2, K. Eberhardt2, R. Eichler1,3, H. Hummrich2, E. Jäger1, R. Jera2, H.-O. Kling2, J. V. Kratz2, U. Krille2, B. Kuczewski2, G. Langrock2, G. Lehr2, M. Mendel2, A. Nähler2, A. Peil2, V. Pershina1, U. Rieth2, M. Schädel1, B. Schausten1, E. Schimpf1, H.-J. Schött1, E. Stiel1, P. Thörle2, K. Tsukada4, N. Wiehl2, G. Wirth1 1Gesellschaft für Schwerionenforschung, Darmstadt, 2Institut für Kernchemie, Johannes Gutenberg-Universität Mainz, 3now at PSI, Villigen, 4JAERI, Tokai It has been predicted [1] and confirmed [2], that hassium forms a volatile tetroxide. The first attempt to study a chemical reaction of this compound, and to learn more about the chemical behaviour of Hs, is described in a companion contribution [3]. For this purpose, CALLISTO [4] has been developed in recent years. This system, which is in principle gas chemistry using reactive surfaces, was completely redesigned to integrate all the results of the many preliminary experiments. The volatile tetroxide is formed in-situ in the target chamber, where the recoils are stopped in the jet gas (a mixture of 1 l/min He and 0.1 l/min O2)[5]. At the exit of the target chamber, the gas flow passes a quartz glass tube containing a quartz wool plug, both heated to 500 °C in order to complete the oxidation of osmium and hassium to the tetroxide. The gas is transported via a 13 m long PTFE capillary to the detection system. Because water seems to influence the deposition of OsO4 on the NaOH surface [6], it was necessary to introduce it into the chemical system. As H2O cannot be added before the He passes the target chamber (it prohibits an accurate beam current measurement), it was added after the target chamber and before the detection system. For that reason, a special moisturizing unit was designed for CALLISTO. It consists of a large, thermostated moisturizer [7], which continuously adds at a defined temperature (30 °C) water to a second helium jet (0.1 l/min with the option to use 0.05 2 l/min). This humidified helium passes through a declusterizer at 200 °C to evaporate all remaining water aerosols. Thereafter, the humidity of the gas was monitored with a dewpoint transmitter (~20 g H2O per kg gas). This moisturized helium is added to the jet gas from the target chamber, containing only a few ppm of water and resulting in a humidity of about 2 g H2O per kg gas in the final gas jet. This jet is then distributed through a system of 4 computer-controlled valves to 4 detection arrays (Fig. 1). During an experiment, the He gas is flowing through 3 detection arrays, whereas 1 detection array is cut off from the gas flow; it is in a “service mode” to change the deposition material. We used a thin layer of NaOH as a deposition material, which was prepared by coating plates of stainless steel with 1M ethanolic NaOH and by drying these plates. Every 60 minutes, the valves were automatically switched and the deposition plate of the detection array, being in the “service mode”, was manually changed, cleaned and recoated. Thus, a continuously working detection and deposition system was realized. The surface of the deposition material looses reactivity with time [6]. One possible explanation is, that NaOH is partially neutralized by CO2, which is an impurity of the used gases and probably formed by a reaction of the carbon beam dump with the oxygen of the jet gas, too. The Na2CO3 has a decreased reactivity and shows only a yield of about 50%, compared to NaOH. After the volatile oxides (OsO4, HsO4) are deposited, their αdecay and spontaneous fission can be detected with the detection arrays, each consisting of four (10x10) mm2 large PINdiodes facing the deposition material (Fig. 2).

Ca-41 ultratrace determination by diode-laser-based resonance ionization mass spectrometry with extremely high isotopic selectivity is presented. Application to environmental dosimetry of nuclear reactor components, to cosmochemical investigations of production cross sections, and biomedical isotope-tracer studies of human calcium kinetics are discussed. Future investigations are possible use in Ca-41-radiodating. Depending on the application, Ca-41 isotopic abundances in the range of 10(-9) to 10(-15) relative to the dominant stable isotope Ca-40 must be determined. Either double- or triple-resonance optical excitation with narrow-band extended cavity diode lasers and subsequent non-resonant photoionization of calcium in a collimated atomic beam were used. The resulting photoions are detected with a quadrupole mass spectrometer optimized for background reduction and neighboring mass suppression. Applying the full triple-resonance scheme provides a selectivity of similar to 5 x 10(12) in the suppression of neighboring isotopes and > 10(8) for isobars, together with an overall detection efficiency of similar to 5 x 10(-5). Measurements on a variety of sample types are discussed; the accuracy and reproducibility of the resulting Ca-41/Ca-40 isotope ratios was better than 5%.

41Ca ultratrace determination by diode-laser-based resonance ionization mass spectrometry with extremely high isotopic selectivity is presented. Application to environmental dosimetry of nuclear reactor components, to cosmochemical investigations of production cross sections, and biomedical isotope-tracer studies of human calcium kinetics are discussed. Future investigations are possible use in 41Ca-radiodating. Depending on the application, 41Ca isotopic abundances in the range of 10–9 to 10–15 relative to the dominant stable isotope 40Ca must be determined. Either double- or triple-resonance optical excitation with narrow-band extended cavity diode lasers and subsequent non-resonant photoionization of calcium in a collimated atomic beam were used. The resulting photoions are detected with a quadrupole mass spectrometer optimized for background reduction and neighboring mass suppression. Applying the full triple-resonance scheme provides a selectivity of ∼ 5 × 1012 in the suppression of neighboring isotopes and > 108 for isobars, together with an overall detection efficiency of ∼ 5 × 10–5. Measurements on a variety of sample types are discussed; the accuracy and reproducibility of the resulting 41Ca/40Ca isotope ratios was better than 5%.

Subsecond 224 Pa (T 1/2 = 0.85 s) was produced via the 209 Bi(18 O,3n)224 Pa reaction at the 88 inch cyclotron at the Lawrence Berkeley National Laboratory. After production it was transported via a gas-jet system to the centrifuge system SISAK 3. Following on-line extraction with trioctylamine/scintillation solutions from 1M lactic acid, 224 Pa was detected applying on-line α-liquid scintillation counting. Unambiguous identification was achieved using time-correlated α-α-decay chain analysis. This constitutes the first chemical on-line separation and detection of a subsecond α-decaying nuclide, 0.85-s 224 Pa with the fast extraction system SISAK 3.

41Ca ultratrace determination by diode-laser-based resonance ionization mass spectrometry with extremely high isotopic selectivity is presented. Application to environmental dosimetry of nuclear reactor components, to cosmochemical investigations of production cross sections, and biomedical isotope-tracer studies of human calcium kinetics are discussed. Future investigations are possible use in 41Ca-radiodating. Depending on the application, 41Ca isotopic abundances in the range of 10(-9) to 10(-15) relative to the dominant stable isotope 40Ca must be determined. Either double- or triple-resonance optical excitation with narrow-band extended cavity diode lasers and subsequent non-resonant photoionization of calcium in a collimated atomic beam were used. The resulting photoions are detected with a quadrupole mass spectrometer optimized for background reduction and neighboring mass suppression. Applying the full triple-resonance scheme provides a selectivity of approximately 5 x 10(12) in the suppression of neighboring isotopes and > 10(8) for isobars, together with an overall detection efficiency of approximately 5 x 10(-5). Measurements on a variety of sample types are discussed; the accuracy and reproducibility of the resulting 41Ca/40Ca isotope ratios was better than 5%.

We have studied the sorption of W on anion-exchange resins from HNO3/HF solutions under on-line conditions using continuous chromatography with the multi-column technique. Kd values and the charge of the W species were determined. In order to achieve an effective separation of mother (W) and daughter (Ta), also the sorption of Ta from HNO3/HF solutions on various anion exchange resins with different functional groups was studied. This investigation serves the purpose to select a suitable anion exchange resin for planned experiments with Sg.

The content of the long-lived isotope 41Ca in concrete samples obtained from the biological shield of a shut-down nuclear research reactor has been determined by diode-laser-based resonance ionization mass spectrometry (RIMS). Standard procedures were applied for the chemical separation of calcium. A radioactive tracer of 47Ca was used to determine the chemical yield. The total calcium concentration in the final nitric acid solution was measured by x-ray fluorescence (XRF) spectroscopy. The RIMS measurement yielded the abundance of 41Ca relative to the total calcium content with a detection limit of 5×10-10, limited by background effects at mass 41. The detection limit corresponds to a minimum detectable specific 41Ca activity of ~100 mBq/g in the concrete. Reproducibility and accuracy were determined with 41Ca spikes and found to be in the range of 15%, limited predominantly by ion counting statistics.

The fluoride complexation of the group-4 elements Zr, Hf and Rf, and of the pseudo-homolog Th, has been investigated in mixed HNO3/HF solutions by studying Kd values on both cation exchange resins (CIX) and anion exchange resins (AIX) using the automated rapid chemistry apparatus ARCA. On the CIX, the four elements are strongly retained as cations below 10-3 M HF. For Zr and Hf, the decrease of the Kd values due to the formation of fluoride complexes occurs between 10-3 M HF and 10-2 M HF. For Rf and Th, this decrease is observed at one order of magnitude higher HF concentrations. On the AIX, for Zr and Hf, a rise of the Kd values due to the formation of anionic fluoride complexes is observed between 10-3 M HF and 10-2 M HF, i.e. in the same range of HF concentrations where the decrease of the Kd values on the CIX is observed, yielding a consistent picture. For Rf and Th, on the AIX, no rise of the Kd values is observed even if the HF concentration is increased up to 1 M. By varying the concentration of the counter ion NO3- which is competing for the binding sites on the AIX resin, it could be shown, nevertheless, that Rf does form anionic fluoride complexes. Apparently, there is a more specific competition of NO3- with respect to [RfFx](x-4)- than with [ZrFy](y-4)- and [HfFz](z-4)-.

Fast solvent extraction is a chemical separation method, which can be applied to study exotic nuclides. Since about 1970 the SISAK technique, which is an on-line method based on multi-stage solvent extraction separations, has been successfully used to investigate the nuclear properties of β-decaying nuclides with half-lives down to about one second. During the last decade it has become possible to produce transactinide elements in high enough yields to investigate their chemical properties on a one-atom-at-a-time scale. For this purpose it was necessary to improve and change the detection part of the SISAK system in order to be capable to detect spontaneously fissioning and α-decaying nuclides in a flowing organic solution. This technique is based on liquid scintillation counting with pulse-shape discrimination and pile-up rejection

: The decay of 111 Ru obtained from fast on-line chemical and mass separation has been investigated by β-γ- t and γ-γ coincidence techniques. Earlier spin and parity assignments of 111 Rh levels based on extrapolations of level systematics are confirmed. In particular, the K=1/2 intruder band is supported by the hindrance of E2 transitions between deformed and spherical states and enhancement of intraband E2 transitions. The excitation energies of intruder band members in Rh isotopes show a minimum at 109 Rh 64 , with two neutrons less than 111 Rh at the N=66 midshell. This trend, which differs from the one in the higher-Z neighbouring elements Ag and Cd with minima at N=66, follows the evolution of deformation observed in the lower-Z elements Ru and Mo.

The performance of the SISAK(1) liquid-liquid extraction system applied in transactinide experiments has been improved with respect to the equipment itself and the way it is operated. The improvements were checked in on-line experiments, under conditions similar to those during transactinide experiments. As a result, the yield of the separation system was increased by a factor >5. Furthermore, a cleaner organic scintillation phase was obtained due to a better phase separation. This reduced the beta-background, which disturbs the alpha-measurements. The sensitivity of the SISAK apparatus, including the gasjet and the detection system has been improved by more than one order of magnitude. (C) 1998 Elsevier Science S.A.

Resonance ionization mass spectroscopy (RIMS) is used for the precise determination of the first ionization potential (IP) of transuranium elements. Small amounts of material (approximate to 0.4 ng) are sufficient for these measurements due to the high sensitivity of RIMS enabling the investigation of the actinides beyond plutonium, which are accessible only in limited amounts and difficult to handle due to their high radioactivity. The method presented takes advantage of the dependence of the ionization threshold on an external static electric field. With samples of 10(12) atoms of Bk-249 and Cf-249 experimental values for the first ionization potentials of IPBk = 49989(2) cm(-1) and IPCf = 50665(2) cm(-1) were obtained.

A liquid-scintillation counting system has been developed for the internal measurement of α-particle energies and the detection of spontaneous fission events on-line in flowing organic solutions resulting from continuous rapid chemical separations by liquid-liquid extraction. The scintillator, dimethyl-POPOP and naphthalene dissolved in toluene, contains the extracting agent, di-(2-ethylhexyl-)-phosphoric acid or dibutylphosphate. An average α-energy resolution of 4,8% FWHM was measured in the energy range 4.78 to 7.69 MeV in stationary as well as flowing organic solutions. Additional features of they system are: (1) detection of spontaneous fission events by larger pulses than produced by α-particles; (2) suppression of interfering β- and γ-radiation by pulse shape discrimination and pile-up rejection; (3) identification of parent-daughter α-α- or α-fission-correlations in decay chains; (4) on-line α-energy calibration by spiking the organic phase with 3.96-s 219Rn-1.78-ms 215Po milked from a 227Ac source. In order to increase the detection efficiency, a unit with three detector cells in series was built and tested with 219Rn and 220Rn. An on-line model experiment for element 104 was carried out using the α-emitter 17-s 161Hf produced by nuclear fusion of samarium with neon and chemically separated by liquid-liquid extraction.

Resonance ionization mass spectroscopy (RIMS) is used for the determination of plutonium in environmental samples. A chemical procedure based on an ion‐exchange technique for the separation of plutonium from a polycarbonate filter is described. The overall yield is about 60% as determined by α‐particle spectroscopy. A technique for the subsequent preparation of samples for RIMS measurements is developed. Plutonium is electrode‐posited as hydroxide and covered with a thin metallic layer. While heating such a sandwich filament the plutonium hydroxide is reduced to the metal and an atomic beam is evaporated from the surface, as required for RIMS.