Strontium‐90 is one of the most poisonous radionuclides. Its toxicity results from its long half‐life of 28.5 years and permanent deposition in the blood‐forming bone system. Strontium‐90 is formed in high yields during the nuclear fission of uranium‐235 and plutonium‐239. The classic analytical procedure for the determination of 90Sr, which relies on the β−‐radiation of the daughter nuclide yttrium‐90, necessitates the chemical removal of all accompanying nuclides. This method requires the Sr/Y ratio to be at equilibrium which takes about two to three weeks to achieve—far too long for the analysis of acute contaminations. Three communications deal with new procedures for ultra‐trace analysis using complex physical detection methods (resonance ionization and accelerator mass spectrometry) and high‐performance separation techniques (high‐performance ion chromatography, HPIC) are presented. In accordance with the strategies of the German Federal Ministry of the Environment, Nature Conservation, and Nuclear Safety, precision methods are described for the determination of the strontium‐90 content in aerosols. These techniques yield data for calculations of the spread of contaminants, which in turn yield results that can be verified in various samples with the aid of the novel fast detection method (HPIC with on‐line detectors). The three analytical procedures are set up in a modular manner and can therefore be utilized in variable combinations. They also indicate the high level of refinement achieved by modern ultra‐trace analyses.

The hyperfine structure splitting and the isotope shift of the neutron-deficient gold isotopes 194−191Au in the optical transition 5d9 6s2 2D32 → 5d10 6p 2P12 (627.8 nm) have been determined by collinear laser spectroscopy at the on-line isotope separator ISOLDE. The nuclear magnetic moments, spectroscopic quadrupole moments and changes in the mean square charge radii are deduced. Experimental electromagnetic moments and deformation parameters are compared with results of a particle-triaxial-rotor model calculation for both odd-A and odd-odd gold nuclei. Very good overall agreement between calculation and experimental data has been achieved. We find, for the first time, consistent evidence for a relatively large contribution from hexadecapole deformation (ϵ4 = 0.06, β4 = −0.05) to odd-A gold isotopes ground states in the region of 183 ≤A ≤ 197. Calculated values of quadrupole deformation are consistent with the prolate-to-oblate shape change between ground states of 186Au and 187Au. In addition, our results suggest another shape change between 190Au (oblate) and 191Au (triaxial). The former change is accompanied by a considerable change in quadrupole deformation, the latter occurs at almost constant deformation.

A new, fast technique for trace analysis of the radioactive isotopes89Sr and90Sr in environmental samples has been developed. Conventional mass separation is combined with resonance ionization spectroscopy in collinear geometry, which provides high selectivity and sensitivity. In addition, a chemical separation procedure for sample preparation has been developed. The described technique was used to determine the90Sr content in ≈ 870 m3 air samples collected near Munich during and shortly after the Chernobyl reactor accident in April 1986. The content of90Sr was measured to be 1.4 mBq per m3, corresponding to 1.6 × 109 atoms of90Sr per sample. This value is in good agreement with the results of radiochemical measurements.

The design of a novel electrode structure for electric-field ionization of Rydberg atoms in a fast atomic beam is described. It allows the resolution of the ion signal from Rydberg atoms with adjacent effective principal quantum numbers n* in the range of 14≤n*≤40 and minimizes the volume where field ionization takes place. These features drastically reduce the number of background events arising from collisions of fast atoms with residual gas molecules and thus are essential for trace analysis applications of the technique of resonance ionization spectroscopy in collinear geometry.

Environmental assessment in the wake of a nuclear accident requires the rapid determination of the radiotoxic isotopes 89Sr and 90Sr. Useful measurements must be able to detect 108 atoms in the presence of about 1018 atoms of the stable, naturally occurring isotopes. This paper describes a new approach to this problem using resonance ionization spectroscopy in collinear geometry, combined with classical mass separation. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an isotopic selectivity of about 106. The ions are then neutralized by charge exchange and the resulting fast strontium atoms are selectively excited into high-lying atomic Rydberg states by narrow-band cw laser light in collinear geometry. The Rydberg atoms are then field-ionized and detected. Thus far, a total isotopic selectivity of S > 1010 and an overall efficiency of ξ = 5 × 10−6 have been achieved. The desired detection limit of 108 atoms 90Sr has been demonstrated with synthetic samples.

Lifetimes of Rydberg states of the triplet-series 5s ns3S1 withn = 19–23, 35 and 5s nd3D3 withn = 18–20, 23–28 in the spectrum of neutral strontium have been determined. Observation of the exponential decay after excitation by a pulsed laser in a fast atomic beam and subsequent state-selective field ionization was employed. The lifetimes of the states of the3S1-series show the expectedn*3 dependence on the effective principal quantum number, while the3D3-series is disturbed by configuration mixing. Furthermore, state re-populations induced by black-body radiation have been observed.

An experimental method for the sensitive and selective detection of the radionuclides Sr-90 and Sr-89 in environmental samples has been worked out. The technique allows the quantitative detection pf about 10(8) atoms of these isotopes in the presence of 10(18) atoms of stable strontium. The sample is ionized and the ions are accelerated to an energy of 50 keV. In a conventional mass spectrometer the isotope under investigation is enriched by a factor of > 10(5). The ions are neutralized and the resulting atoms are selectively excited to a Rydberg state by narrow-band cw laser light in collinear geometry and detected after field ionization. A total isotopic selectivity of S > 10(11), an overall efficiency of epsilon almost-equal-to 10(-6) and a detection limit for Sr-90 of 5 . 10(8) atoms have presently been achieved.

The combination of collinear fast-beam laser excitation with particle detection via resonance ionization offers rather unique possibilities for the study of high lying atomic Rydberg states and provide high spectral resolution. Precise results for term energies, fine and hyperfine structures as well as configuration interaction parameters can be obtained. In addition life time measurements in the musec range can be carried out by pulsed laser excitation and time resolved detection. Results on a number of 5sns S-3(1) and 5snd 3D3 Rydberg states of Sr I in the range 17<n<35 are reported; they form the experimental basis for ultra-sensitive trace analysis.

A set-up is presently under construction for the fast and quantitative trace detection of the radioisotopes Sr-89 and Sr-90 in environmental samples. For this purpose the strontium atoms are chemically extracted from the sample, surface ionized and accelerated to 50 keV for mass separation. The resulting fast ion beam is neutralized and resonance ionization in collinear geometry is realized via excitation into Rydberg states and subsequent field ionization. The extremely high selectivity and efficiency of this technique forms the basis for trace detection of Sr-89, Sr-90 contaminations as low as 10(8) atoms in a surplus of more than 10(18) stable strontium atoms.

Parallel to the strongly growing public concern about environmental problems, new ideas for trace detection and analysis of toxic and radioactive material are being developed. One of these new and outstanding experimental techniques is the application of analytical laser spectroscopy. Most interesting in this context is the method of resonance ionization spectroscopy (RIS), as proposed1 already in 1972 combining very high sensitivity in the detection of the element or isotope under investigation with high selectivity in the suppression of contaminants2–4.