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Magnetic Resonance Imaging (MRI) usually relies on magnetization of hydrogen nuclei (protons) in water or molecules in tissue as source of the signal. Biological environments with low proton content, notably the lungs, are difficult to image. Inhaling of hyperpolarized 3He gas opens the possibility to investigate ventilated spaces by MRI. To overcome the loss in signal due to the low density of the gas the nuclear polarization of the 3He spins is greatly enhanced by laser Optical Pumping. For more than three decades Optical Pumping of noble gases has been investigated, using spin exchange scattering (SE) or metastability exchange scattering (ME). Since powerful resonant laser light is available for Optical Pumping, large quantities of 3He gas can be operated. The original interest was the development of dense spin polarized targets for fundamental research in physics. As a spin off, the possibility of MRI of lung tissue filled with hyperpolarized 129Xenon was demonstrated in 1994. Later 3He was used for M...

The application of Collinear Resonance Ionization Spectroscopy for the determination of 89,90Sr contaminations in various environmental samples is presented, demonstrating the versatility of this highly specialized and isotope‐selective ultra‐trace determination technique. Additionally to these studies we have analysed the different processes, which lead to nonselective ionization and hence cause background. Optimization of the experimental conditions resulted in a significant lowering of the detection limit to a value of 3×106 atoms of 90Sr (corresponding to an activity of 2mBq) in the presence of up to 1017 atoms of stable 88Sr. In a parallel measurement trace determination of both isotopes 89Sr and 90Sr is possible with a detection limit for 89Sr of 108 atoms. Measurements on different samples, ranging from air filter samples of 1958 up to today, soil, vegetation, milk and human urine samples as well as cooling water from nuclear power plants document the applicability and the specifications of the tec...

Collinear resonance ionization spectroscopy has been developed as a sensitive technique for fast trace detection of 90Sr and 89Sr in the environment. A detection limit for 90Sr of 107 atoms in the presence of 1017 atoms in the presence of 1017 atoms of stable Strontium has been achieved, while the applicability of the method has been demonstrated on real world samples. After collection and chemical separation, strontium is surface ionized, accelerated to 33keV and mass separated. The ions are neutralized and the emerging fast atoms interact with an argon ion laser beam (γ=364 nm) in a quasi‐collinear geometry. Optical excitation starts from the long‐lived 5s4d3 D2 state of strontium, which is populated in the charge exchange process, and the fast atoms are selectively excited into the high‐lying 5s23f3F3 Rydberg state. The Rydberg‐atoms are subsequently field‐ionized and detected by a channeltron detector after energy selection. The described method was successfully used to determine the 90Sr‐content in a...

A resonant ionization mass spectrometer has been developed as an analytical tool for the detection of trace elements, especially of plutonium and other radionuclides. The sample, deposited on a rhenium filament, is evaporated by electrical heating and the atoms of the element under investigation are selectively ionized by laser light delivered from three dye lasers pumped by a copper vapour laser. The resulting photoions are detected in a time-of-flight spectrometer with a channelplate detector. For plutonium a mass resolution of M/δM=1500 was obtained and an overall detection efficiency of 4×10−6 was determined for stepwise excitation and ionization via autoionizing states. With a laser light bandwidth of 3–5 GHz neighbouring isotopes could be suppressed by a factor of 20 due to isotope shifts in the excitation transitions. The isotope composition of synthetic samples was measured and good agreement was found with mass spectroscopic results. The influence of the hyperfine structure on the isotope ratios is discussed.

The possibilities of determining nuclear spin, moments and variation in charge volume by optical pumping of on line masseparated isotopes are described for the example of the isotopic chain lY1Hg-205Hg. The variation in nuclear charge volume (6 ) along this chain and in particular its abrupt change for the lightest Hg-isotopes, indicating a phase transition in nuclear structure, are discussed. 1. Introduction. - This talk is based on expe- riments (I), (2), (3) performed recently by a visiting team (*) at the ISOLDE facility at CERN with the members : J. Bonn, G. Huber, H.-J. Kluge, U. Kopf, L. Kugler, J. Rodriguez, and E. W. Otten. The investigation of the hyperfine structure (hfs) and isotopic shift (IS) of optical spectra allows the determination of the basic nuclear ground state properties : spin (I), magnetic moment (p,), electric quadrupole moment (Q,), and change of the mean squared radius of the nuclear charge distribution between different isotopes (6 ). The subject has therefore widely been explored in the past for stable and long lived isotopes (4), (5) and contributed substantially to the systematic topography of nuclear structure in the valley of stability which could be established within the last two decades. Still basical and quantitative questions are open in understanding nuclear matter. In this situation it makes from first principles is missing. In this situation it makes sense to enlarge the scope of investigations principally. In particular we should be in a position to choose and change systematically the parameters N and Z of a nucleus independently and free from the boun- dary condition of being close to the stable valley. With other words, a systematic investigation of nuclear properties along lines of constant Z or N across the full array of nuclei which we can reach in our days, would give us a much wider and more reliable view on the topography of nuclear structure (*) In the course of the experiments the team changed its home university from Heidelberg to Mainz.

The nuclear Zeeman levels of the ground state of Barium (6s21S0, F=I=3/2) were polarized by means of optical pumping with the resonance line (6s21S0−6s 6p1P1, λ=5535 A). The magnetic field was calibrated by means of optical pumping of sodium. The magnetic moments, calculated from the nuclear Hf-Zeeman-transitions at 228 Gauss are μ135=0,83651 (6) μN μ137=0,93573 (6) μN (with diamagnetic correction).

Laser resonance ionization mass spectrometry has been investigated as a method for the determination of trace amounts of actinides and technetium. A high sensitivity and selectivity have been achieved by three-step photoionization of the elements in the atomic state followed by time-of-flight measurement for mass analysis. The system for photoionization consists of three dye lasers which are pumped simultaneously by a copper vapour laser of 30 W average power at a pulse repetition rate of 6.5 kHz. The time-of-flight spectrometer has a mass resolution better than 2500. By ionization via autoionization states and by saturation in each excitation step a detection limit of less than 108 atoms of actinides or of technetium in the sample can be reached.

The excited 7/sup 2/P/sub 3/2/ term of the neutral atom was investigated in Cs/sup 135/ and Cs/sup 137/ by the Doppler resonance method. An isotopic mixture containing 39.4% Cs /sup 133/, 30% Cs/sup 135/, and 30.6% Cs/sup 137/ was used in the measurements. The nuclear quadrupole moments were calculated to be Q(Cs/sup 135/) = +(0.049 plus or minus O.0l) x 10/sup -24/ and Q(Cs/sup 137/) = +(0.050 plus or minus 0.01) x 10/sup -24/ cm/sup 2/. (J.S.R.)