Determination of90Sr in environmental samples with resonance ionization spectroscopy in collinear geometry

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…

Die experimentelle Bestimmung der Ionisationsenergien von Berkelium und Californium

ATTEMPTS TO PRODUCE SUPERHEAVY ELEMENTS IN REACTIONS BETWEEN HEAVY NUCLEI

A system for rapid radiochemical separations from aqueous solutions

Abstract For the study of short-lived fission products, an automatic system has been developed that allows to irradiate aqueous solutions sealed in polystyrene capsules, to separate chemically the radioactive products formed, and to start counting, all within a few seconds. Irradiations are performed in a pneumatic tube system installed in a horizontal beam hole of a reactor. The capsule is projected into a separation apparatus where it breaks by impact. Its content is then sucked through a thin reactive layer that takes up the desired product. The whole sequence of irradiation, transportation, chemical separation, and counting is controlled by automatic timers. The adaption of this techniq…

Delayed-Neutron Spectra Following Decay ofAs85andSb135

Trennung von Spaltprodukten durch Extraktionschromatographie

The possibilities for the separation of a complex fission product mixture by extraction chromatography have been investigated. Here the partition coefficients between three solvents and hydrochloric acid are reported for the following elements: Zn(II), Ge(IV), As(III), As(V), Se(IV), Zr(IV), Nb(V), Mo(VI), Tc(IV) Ru(III), Ru(IV), Rh(III), Ag(I), Cd(II), In(III), Sn(IV), Sb(III), Sb(V), Te(IV), I(oxidized), Cs(I), Ce(III), Tb(III), Tm(III), Ac(III), Th(IV), Pa(V), U(VI), Np(IV), Np(VI). As solvents tri-n-butylphosphate (TBP), tri-n-octylamine (TOA) and di-(2-ethylhexyl)-orthophosphoric acid (HDEHP) have been used. The partition coefficients have been measured by batch-experiments in which th…

Verfl�chtigung von Spaltprodukten aus festem Uran(IV)-fluorid und anderen Fluoriden

In der Kernehemie sueht man nach temperaturund strahlenresistenten Targetsystemen, aus denen naeh Kernreaktionen kurzlebige Nuklide kontinu: ierlich abgetrennt werden kSnne n. Dies ist insbesondere im Hinblick auf die yon der Gesellschaft fiir Sehwerionenforsehung in Darmstadt geplanten Experimente interessan~, bei denen die Synthese neuer, iibersehwerer Elemente versucht wird. Als Modell fiir Verdampfungsstudien aus festen Targets wurde die tr~gerfreie Verfliichtigung yon Spaltprodukten aus festem Uran(IV)-fluorid gew~hlt [1--3]. Im fliiehtigen Anteil konnten folgende Elemente identifiziert werden: Se, Kr, Zr, Iqb, Me, Te, Ru, Sn, Sb, Te, J und Xe. In einem Rohr mit Temperaturgradienten l~…

ABC Geschichte der Chemie. Herausgegeben von einem Autorenkollektiv, federführende Herausgeber: S.Engels und R.Stolz. VEB Deutscher Verlag für Grundstoffindustrie, Leipzig 1989. 496 S. + 15 S. Anhang, geb. (Leinen) DM 60.00.—ISBN 3–342–00118–6

Search for Superheavy Elements in theU238+U238Reaction

A search was made for spontaneously fissioning superheavy elements in damped collisions of two uranium nuclei. Different techniques were applied covering the elements 108 to 118 and approx. =126, and a half-life range from 1 ms to more than 1 yr. No evidence for superheavy elements was found at upper cross-section limits of 10/sup -32/, 10/sup -33/, and 10/sup -35/ cm/sup 2/ for half-lives from 1 to 100 ms, 100 ms to 1 d, and 1 d to 1 yr, respectively.

From Nuclear Fission to Superheavy Elements

(1998). From Nuclear Fission to Superheavy Elements. Nuclear Physics News: Vol. 8, No. 2, pp. 7-21.

Delayed-neutron spectroscopy with 3He spectrometers

Abstract The characteristics of a 3 He ionization chamber for high-resolution spectroscopy of β-delayed neutrons have been examined. The detector response function is given in the energy range 0.019–2.77 MeV. A considerably improved energy resolution has been achieved by minimizing effects due to pulse summing, detection of scattered neutrons, and microphonics, and is most evident in the low-energy part of the spectra.

Trace Analysis of Plutonium and Technetium by Resonance Ionization Mass Spectrometry Using an Atomic Beam and a Laser Ion Source

A method for low level detection of plutonium and technetium is described with a detection limit of less than 107 atoms. Plutonium is a very toxic element due to its radioactive decay as well as its chemical behaviour. It was released to the environment in large amounts during the fifties and sixties of his century, principally by nuclear-weapon tests and some accidents. As a result about 0.4 − 4 mBq per gram 239Pu(T1/2 = 24390 y), corresponding to 4 × 108 − 4 × 109 atoms, can be found in the Northern Hemisphere in soil samples.

Isotope Distributions in the Reaction ofU238withU238

Radiochemically determined cross sections $\ensuremath{\sigma}(Z, A)$ were used to construct charge and mass distributions for the reaction of 1785-MeV $^{238}\mathrm{U}$ ions with thick $^{238}\mathrm{U}$ targets. Fission of the colliding nuclei is found to dominate. For the surviving uraniumlike fragments an enhancement of yields compared to the Kr + U and Xe + U reactions is observed. The formation of heavy actinides is shown to be associated with the low-energy tails of the broad excitation energy distributions in damped collisions.

Georg de Hevesy. 1885–1966. Festschrift. Herausgegeben vonG. Marx. Akadémiai Kiadó, Budapest 1988. 165 S., geb., DM 34.00 – ISBN 963-05-5230-2

Trace detection of plutonium by three-step photoionization with a laser system pumped by a copper vapor laser

Laser photoionization has been used to detect trace amounts of plutonium. A high sensitivity and selectivity has been achieved by applying three-step excitation and ionization of the plutonium atoms with high pulse-repetition rates and additional mass determination by time-of-flight measurements. A laser system was developed which consists of a copper vapor laser pumping three dye lasers simultaneously. Samples containing between 1010 and 1012 atoms of239Pu on Re filaments were measured yielding strong resonance signals with maximum ion count rates of several kHz at a vanishingly low background. A detection efficiency of 10−7 was determined allowing the detection of about 108 plutonium atom…

Fast, low-level detection of strontium-90 and strontium-89 in environmental samples by collinear resonance ionization spectroscopy

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 exc…

Resonance ionization mass spectroscopy for trace analysis of neptunium

Resonance ionization mass spectroscopic (RIMS) measurements for trace analysis and spectroscopy of 237Np, the ecologically most important isotope of neptunium, are described. The chemical procedure for the separation of neptunium from aqueous samples as well as the preparation of filaments for RIMS are outlined. Several two- and three-step excitation schemes have been investigated in order to find suitable conditions for the sensitive detection of 237Np. Using a three-step, three-color excitation and ionization scheme an overall detection efficiency of 3×10−8 was obtained, resulting in a detection limit of 4×108 atoms (160 fg) of 237Np. The hyperfine structure splittings of the levels under…

First Experimental Determination of the Ionization Potentials of Berkelium and Californium

Search for superheavy elements in monazites using chemical enrichment

Evidence for the existence of superheavy elements in monazite inclusions embedded in Madagascan mica and surrounded by giant radioactive haloes was given by Gentry et al.1 who observed photons with energies corresponding to predicted Lα1 X-ray energies of element 126 (at 27.25 keV) and also of elements 116, 124 and 127 in irradiations of such crystals with collimated proton beams. For an unambiguous identification, the detection of further members of the L X-ray series would be most important. In X-ray spectra of monazite samples these transitions are buried under the strong K X-ray peaks of the lanthanide elements. They should, however, become visible after chemical enrichment of the super…

New nuclides: Neptunium-243 and neptunium-244

We have observedγ-rays following the β−-decay of243Np and244Np after chemical isolation of neptunium isotopes from the products of the reaction of 835 MeV136Xe with244Pu. The ground-state of 1.85-min243Np hasJ=5/2. The decay of 2.29-min244Np (probableJπ=7−) populates high-spin members of the ground state rotational band in244Pu.

Beta-decay of148,150,152Pr into levels of148,150,152Nd

Theβ−-decay of148,150,152Pr into levels of148,150,152Nd has been studied byγ-singles,γγ-coincidence and for148Pr also byγγ-angular correlation measurements. The praseodymium activities have been obtained by thermal neutron-induced fission of235U followed by on-line mass separation with the helium-jet coupled mass separator HELIOS. Decay schemes for these heaviest praseodymium nuclides are proposed. From the angular correlation measurements spin values for the seven lowest levels of148Nd are deduced. Spin and parity assignments for the lower levels in150,152Nd have been extrapolated from level systematics.

Actinide Production in Collisions ofU238withCm248

Cross sections for the production of heavy actinides in damped collisions of $^{238}\mathrm{U}$ ions with $^{248}\mathrm{Cm}$ targets are reported and compared with similar data for other projectiles. The relatively small differences in the formation rates of a given isotope made by different projectiles indicate a balance between increased mass transfer probability with increasing projectile mass and a concurrent decrease in survivability because of an increase in excitation energy.

Search for supermassive nuclei in nature

We report on a search for supermassive nuclei in nature with masses up to 107 amu. Such exotic nuclei might consist, for example, of stable strange matter, which comprises a mixture of up, down, and strange quarks, or of relic particles from the early Universe. The experiments are based on Rutherford backscattering of heavy ions, preferably238U, from various target samples. The measured parameters of a detected particle are its time-of-flight, scattering angle, and specific ionization. From this information the mass of the target nucleus can be inferred. Upper limits for the abundance of strange supermassive nuclei with massesA−4·102 to 107 amu relative to the number of nucleons were found …

Erste Messung der Ionisationsenergie von Americium und Curium

Principle and analytical applications of resonance lonization mass spectrometry

Resonance ionization mass spectrometry (RIMS) is a very sensitive analytical technique for the detection of trace elements. This method is based on the excitation and ionization of atoms with resonant laser light followed by mass analysis. It allows element and, in some cases, isotope selective ionization and is applicable to most of the elements of the periodic table. A high selectivity can be achieved by applying three step photoionization of the elements under investigation and an additional mass separation for an unambiguous isotope assignment. An effective facility for resonance ionization mass spectrometry consists of three dye lasers which are pumped by two copper vapor lasers and of…

Book Review: Table of Isotopes. 8th Edition, Volumes 1 and 2. Edited by R. B. Firestone and V. S. Shirley

Trace Analysis of the Radionuclides90Sr and89Sr in Environmental Samples I: Laser Mass Spectrometry

Electrolytic preparation of actinide filaments for laser resonance ionization spectroscopy

Abstract For the determination of trace amounts of actinide elements by resonance ionization mass spectroscopy, atomic beams of these elements are produced by evaporation from rhenium substrates. The actinides are deposited by electrolysis as hydroxides in a 2 mm spot on a rhenium foil and covered electrolytically with a thin layer of rhenium or platinum. During heating of such a sandwich reduction occurs to the metallic state while diffusing through the overplated layers and the actinides are evaporated as atoms from the surface. With lead-doped platinum, efficient release is observed already at 1700°C in contrast to rhenium where 2100°C is required and a higher background is produced.

Criteria for the Discovery of Chemical Elements

The availability of suitable heavy-ion accelerators should make it possible to synthesize and identify additional heavy transuranium elements. Criteria for adequate proof that a new element has been synthesized or found in nature and identified are suggested. The basic criterion must be the proof that the atomic number of the new element is different from the atomic numbers of all previously known elements. Chemical identification constitutes an ideal proof; the procedure must be valid for application to individual atoms in an unequivocal manner. Also satisfactory is the identification of characteristic x rays in connection with the decay of the isotope of the new element. This is likely to…

Superheavy-element research

The existence of an island of relatively stable elements beyond the present Periodic Table has been predicted by theoretical extrapolations of nuclear properties. During the past 12 years vigorous efforts have been made to discover these superheavy elements in nature and to produce them by nuclear reactions.

Heavy isotopes of actinium: 229Ac, 230Ac, 231Ac and 232Ac

Abstract By irradiation of 232Th with 150-MeV bremsstrahlung and with 14-MeV neutrons, three new neutron-rich isotopes of actinium, 230Ac, 231Ac and 232Ac, were produced and identified and the previously reported isotope, 229Ac, was confirmed. The actinium isotopes were chemically isolated by a fast procedure based on elution with α-hydroxyisobutyric acid from cation exchange resins. For 229Ac, a half-life of 62·7 ± 0·5 min and a β-ray energy of 1·14 ± 0·15 MeV were found; 35 γ-rays were observed, the strongest ones with the following energies and relative intensities: 135·3(34), 146·4(35), 164·6(100), 252·2(24), 261·9(39), 317·0(23), 539·9(20), 569·1(91), and 605·2 keV(23). For 230Ac, a ha…

A heavy-ion identification system for the detection of rare events

Abstract A large area detection system is described which consists of twelve low-pressure multi-wire proportional counters and is used in the search for exotic super-massive nuclei. The experiments are based on Rutherford backscattering of heavy ions, preferably 208Pb or 238U, from various target samples. The measured parameters of a detected particle are its time-of-flight, scattering angle, and specific ionization. From this information the mass of the target nucleus can be inferred. The present experimental sensitivity for the detection of exotic nuclei with at least twice the mass of the projectile is about 10−12 relative to the number of nucleons.

Continuous separation and identification of neutronrich neptunium isotopes from heavy-ion reactions by means of the centrifuge system “sisak”

Abstract Neutron-rich neptunium isotopes formed in direct transfer reactions between 136 Xe projectiles and targets of 244 Pu have been separated from other reaction products with the on-line liquid-liquid extraction system SISAK. A four-detector delay method was used to determine the half-lives of the previously unknown isotopes 243 Np and 244 Np. From the decay of the 287.4 keV γ-line a half-life of 1.8 ± 0.3 min was determined for 243 Np. From the decay curves of the γ-lines at 162.7 and 216.7 keV, which fit into the known level scheme of 244 Pu, a half-life of 2.5 ± 0.3 min results for 244 Np.

Rapid continous radiochemical separations by thermochromatography in connection with a gas-jet recoil-transport system

Abstract A combination of a gas-jet recoil-transport system with a thermochromatographic system has been studied as a technique for rapid, continuous radiochemical separations. Fission products were used as a model for complex mixtures of elements. A nitrogen gas-jet containing potassium chloride clusters was applied to transport nuclides produced in a reactor from the target area to the thermochromatographic column. Conversion of the reaction products carried by the gas-jet volatile species was achieved by stopping the clusters in a quartz-wool plug located in the column and kept at high temperatures and feeding a reactive gas into the column. Several reactive gases producing volatile chlo…

Quantitative Detection of Strontium-90 and Strontium-89 in Environmental Samples by Laser Mass Spectrometry

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.

Decay properties of 114Ag

Fast volatilization of some lanthanide and actinide elements from titanium surfaces

The ad- and desorption of trace quantities of the lanthanide elements lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, dysprosium, and ytterbium and of the actinide elements americium and curium were investigated by thermochromatographic and isothermal measurements with hot titanium columns. The adsorption enthalpies deduced from the experimental data are in reasonable agreement with calculated values which indicate considerable variations in volatility under such conditions. More volatile elements can quickly be separated from less volatile elements by heating the mixture on titanium in high vacuum.

Release Studies of Atomic Technetium

Application of a laser ion source (LIS) is a promising new technique for trace analysis with high efficiency and selectivity. One of the problems which can limit its efficiency attained in practice is the adsorption of sample atoms on the hot walls of the LIS cavity. We have studied the release of atomic technetium from different wall materials at temperatures up to 2500 K. For these investigations resonance ionization of technetium atoms applying a copper vapour pumped dye laser system and γ-spectrometry of 6-h 99mTc have been used. Theoretical calculations of the heat of desorption for technetium on different wall materials are presented and compared with experimental data. Though the res…

Search for strange matter by Rutherford backscattering

According to a number of suggestions, stable strange matter could exist in the form of supermassive nuclei (or 'strange nuggets')1,2. In contrast to ordinary nuclei, which contain only 'up' and 'down' quarks, a piece of strange matter should comprise a mixture of 'up', 'down' and 'strange' quarks in roughly equal proportions. Small amounts of strange matter could have survived from the early stages of the Universe1. Alternatively, strange matter might reach the Earth as a flux of strange nuggets produced in collisions of neutron stars3. Limits to the cosmic flux of strange nuggets with masses in the range from 10−4 to 250 g have been obtained in a search for light produced by the nuggets in…

Search for superheavy elements in damped collisions betweenU238andCm248

Negative results for the production of superheavy elements in damped collisions between $^{238}\mathrm{U}$ projectiles and $^{248}\mathrm{Cm}$ targets are reported. This reaction was believed to permit a closer and more widespread approach to the predicted island of stability near Z=114 and N=184 than any practical fusion reaction. Aqueous and gas phase chemistry techniques were used to isolate superheavy element fractions. The fractions were counted for spontaneous fission activity, fragment kinetic energies, and neutron multiplicities. Cross-section limits for half-lives from hours to several years are g4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}35}$ ${\mathrm{cm}}^{…

Excitation functions for production of heavy actinides from interactions ofCa40andCa48ions withCm248

Excitation functions have been measured for production of isotopes of Bk through Fm in bombardments of /sup 248/Cm with 234- to 294-MeV /sup 40/Ca ions and with 239- to 318-MeV /sup 48/Ca ions. The maxima of the isotopic distributions for these elements occur at only 2 to 3 mass numbers larger for /sup 48/Ca than for /sup 40/Ca reactions. The shapes of the distributions and the half-widths of about 2.5 mass numbers are quite similar to those observed previously for reactions of /sup 16/O, /sup 18/O, /sup 20/Ne, and /sup 22/Ne with /sup 248/Cm. In general, the excitation functions for /sup 40/Ca show maxima near the Coulomb barrier while those for /sup 48/Ca are about 20 MeV above the barrie…

Resonance ionization mass spectroscopy for trace determination of plutonium in environmental samples

Resonance ionization mass spectroscopy (RIMS) is a sensitive and isotope selective method and well suited for trace analysis of plutonium in the environment. After the chemical isolation of plutonium from soil, air filters or urine, e.g., it is electrolytically deposited as hydroxide on a tantalum backing and covered with a thin titanium layer. By heating such a sandwich filament in the RIMS-apparatus under vacuum an atomic beam of plutonium is produced. The atoms are ionized by a three-step resonant excitation using pulsed dye lasers, and the ions are mass-selectively detected with a time-of-flight (TOF) spectrometer and a multi channel plate detector. RIMS yields a low detection limit of …

Trennung von spaltprodukten durch Extraktionschromatographie

The separation of fission products which form anionic species in mineral acids and of uranium and neptunium from samples of neutron-irradiated uranium is described. The method used is extraction chromatography with tri-n-butylphosphate (TBP) and di-(2-ethylhexyl)-orthophosphoric acid (HDEHP) as extractants and polytrifluoromonochloroethylene powder as the solid support. In the first column Zr, U and Np are extracted with TBP from 8N HNO3/NaClO3. In the second column, HDEHP is applied as extractant and 9N HCl/NaClO3 as the mobile phase for the isolation of Nb, Sb, and I, and in the third column (HDEHP), the rare earths and Mo are extracted from 0.1N HCl. Finally with the fourth column (TBP),…

Chemische Überwachung der Verbreitung radioaktiver Substanzen

Radioaktive Isotope werden durch Kernwaffenversuche, die Fortschritte der Reaktortechnik und ihre vielfaltigen Anwendungen in Wissenschaft und Technik in immer groserem Mase verbreitet. Eine Uberwachung, etwa von Wasser, Luft, Boden und Nahrung, ist daher notwendig. Neben physikalischen Bestimmungs-Verfahren spielen chemische Untersuchungen eine entscheidende Rolle besonders dann, wenn das meist vorliegende Isotopen-Gemisch aufzutrennen ist. Die Bestimmung der aus physiologischen Grunden wichtigen Isotope wird eingehend beschrieben.

Delayed-neutrons from arsenic isotopes 84As, 85As and 86As

Abstract Short-lived arsenic isotopes were produced by thermal-neutron fission of 235U and isolated within 2·5 sec by volatilization of arsenic hydride. The existence of a strong delayed-neutron precursor of 2·05±0·05 sec half-life among the arsenic isotopes is confirmed and its assignment to 85As ascertained by milking of the daughter product 33 sec 85Se and 3·1 min 84Se, which is the final nucleus in the neutron decay branch of 85As. A delayed-neutron yield of 7·8 ± 1·2 neutrons/104 fissions was obtained for 85As. A new isotope, 0·9 ± 0·2 sec 86As, was detected by delayed-neutron counting and by following the decay of its most prominent γ-ray. The mass assignment was verified by milking o…

Absolutzählung von radionukliden durch die beta-gamma-koinzidenzmethode mit einem flüssigen szintillator als innerem beta-detektor

Zusammenfassung Fehlerquellen und Genauigkeit der Methode wurden untersucht. Die Ortsabhangigkeit der Zahlausbeuten im β- und γ-Detektor bedingt trotz des grossen Probenvolumens keinen wesentlichen Fehler, wenn die Detektoren symmetrisch angeordnet sind. Dagegen mussen Fehler korrigiert werden, die durch unvollkommenen Nachweis energiearmer Zerfallszweige im β-Detector und durch die γ-Empfindlichkeit des β-Detektors entstehen; dies kann entweder durch graphische Extrapolation oder—allgemeiner—durch Berechnen eines Korrekturfaktors geschehen. Die rechnerische Korrektur wird an typischen Zerfallsschemata erlautert. Fur den statistischen Fehler der Zerfallsrate wird eine Formel angegeben, welc…

Spurenbestimmung der Radionuclide90Sr und89Sr in Umweltproben I: Laser-Massenspektrometrie

Acetic acid-guided biopsies after magnifying endoscopy compared with random biopsies in the detection of Barrett's esophagus: a prospective randomized trial with crossover design.

Background In contrast to standard video endoscopy, magnifying endoscopy after local acetic acid application enables recognition of mucosal surface architecture. Objective To investigate the diagnostic yield of magnifying endoscopy with acetic acid–targeted biopsies compared to random, 4-quadrant biopsies. Design Prospective randomized trial (ratio 1:1) with crossover design. Setting Two referral hospitals in Germany. Patients Thirty-one patients with Barrett's esophagus or visible columnar-lined lower esophagus. Interventions Patients were randomized to undergo either standard video endoscopy with 4-quadrant biopsies or magnifying endoscopy in conjunction with acetic acid application. All …

Determination of trace elements by resonant ionization mass spectrometry (RIMS)

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 li…

Decay of the 4.2-min152Pm into levels of152Sm

After bombardments of enriched152Sm with 14-MeV neutrons, three isomers of125Pm reaction, have been observed with half-lives of 4.2±0.2 min, 7.5±0.2 min and 15.0±1.0 min. Sources of pure 4.2-min152Pm were obtained by separating the promethium from its parent 11-min152Nd produced by thermal-neutron induced fission of235U. The beta and gamma radiations of the 4.2-min152Pm have been investigated using semiconductor and scintillation spectrometers. Most of theγ-ray transitions could be placed in a level scheme for 152Sm. Especially interesting is a level at 1083 keV for which the assignmentI π=0+ is proposed. In a 4πβγ experiment, the ground state feeding of152Sm in theβ −-decay of the 4.2-min1…

Book Review: Georg de Hevesy. 1885-1966. Festschrift. Edited by G. Marx

Verdampfung von Uranspaltprodukten in Wasserstoff, Stickstoff und Sauerstoff

Die Verdampfung der Spaltprodukte Germanium, Arsen, Molybdan, Ruthenium, Cadmium, Zinn, Antimon und Tellur aus bestrahltem U3O8 im Wasserstoff-, Stickstoff- und Sauerstoffstrom wurde zwischen 900 und 1500° C untersucht. Bei 1500° C verdampfen die meisten dieser Elemente innerhalb 1 Std mit hoher Ausbeute.

Über die Adsorption von Tellur (IV), Jodid und Jodat an Anionenaustauschern

Direct identification of 103–107Mo by a rapid chemical separation procedure

Abstract The nuclides 103–107Mo have been identified by means of γ-ray spectroscopy after the separation of molybdenum from fission products of 235U and 239Pu by a rapid chemical procedure. Half-lives of 67.5 ± 1.5 s for 103Mo, 59.4 ± 0.8 s for 104Mo, 36.7 ± 1.0 s for 105Mo, 8.4 ± 0.5 s for 106Mo and 3.5 ± 0.5 s for 107Mo have been determined and the main γ-lines were assigned to the decay of these isotopes. Some evidence for 108Mo with a half-life ≤2 s has also been obtained.

Strassmann in the shadow

Rutherford - Scientist Supreme. Von John Campbell

Reactions of40Ar with233U,235U, and238U at the barrier

Production cross sections for target-like transfer products in reactions of40Ar with233,235,238U at the barrier were determined using radiochemical techniques. The heaviest products detected are isotopes of californium (Z=98). In addition to the quasi-elastic component of the isotopic distributions observed in the vicinity of uranium, there are also relaxed contributions throughout the entire region. The peak positions of the isotope distributions of this component for fixed atomic number, after the transfer of > 3 charges, approach closely the minimum of the potential energy surfaces (PES). The experimental results thus indicate the cold formation of the reaction products. A search for lon…

Search for long-lived superheavy elements in the reaction of136Xe with238U

A search with radiochemical methods for long-lived superheavy elements in 238U targets bombarded with intense beams of136Xe ions produced negative results. A formation cross section of ≤1×10−35 cm2 is deduced at 95% confidence level for nuclides with half-lives between 1 and 200 d.

Determination of the first ionization potential of actinide elements by resonance ionization mass spectroscopy

Abstract Resonance ionization mass spectroscopy (RIMS) in the presence of an external static electric field has been used for the determination of photoionization thresholds. Extrapolation of the thresholds obtained with different electric field strengths to zero field strength directly leads to the first ionization potential (IP). The ionization potentials of the transplutonium elements americium, curium, berkelium and californium could be measured for the first time. Due to the high sensitivity of RIMS, samples of only 1012 atoms have been used. The results are: IPAm = 5.9738(2)eV, IPCm = 5.9915(2)eV, IPBk = 6.1979(2)eV and IPCf = 6.2817(2)eV. The same technique was applied to thorium, ne…

Investigation of beta strength functions by neutron and gamma-ray spectroscopy

Abstract Neutron spectra from the decay of the β− delayed neutron precursors 55.6 sec 87Br, 24.5 sec 137I, 2.05 sec 85As and 1.71 sec 135Sb have been studied with high resolution 3He ionization chambers. By γ-ray measurements, the partial neutron emission probabilities to excited states in 84Se and 134Te have been determined independently. For the neutron-emitter nuclei 87Kr and 137Xe, from which neutron decay proceeds only to the ground states of the final nuclei, 86Kr and 136Xe, unique information on the shape of the β− strength function Sβ(E) is obtained. For the emitter nuclei 85Se and 135Te, correlations between neutron transition energies and differences in level energies in 84Se and …

Vom Radiothor zur Uranspaltung. Eine wissenschaftliche Selbstbiographie. (Nachdruck der 1. Auflage). Von O. Hahn. Friedr. Vieweg & Sohn, Braunschweig/Wiesbaden 1988. XVI, 160 S., geb. DM 78.00. - ISBN 3-528-08413-8

VERFLÜCHTIGUNG VON SPALTPRODUKTEN AUS FESTEM URAN(IV)-FLUORID UND ANDEREN FLUORIDEN

In der Kernehemie sueht man nach temperaturund strahlenresistenten Targetsystemen, aus denen naeh Kernreaktionen kurzlebige Nuklide kontinu: ierlich abgetrennt werden kSnne n. Dies ist insbesondere im Hinblick auf die yon der Gesellschaft fiir Sehwerionenforsehung in Darmstadt geplanten Experimente interessan~, bei denen die Synthese neuer, iibersehwerer Elemente versucht wird. Als Modell fiir Verdampfungsstudien aus festen Targets wurde die tr~gerfreie Verfliichtigung yon Spaltprodukten aus festem Uran(IV)-fluorid gew~hlt [1--3]. Im fliiehtigen Anteil konnten folgende Elemente identifiziert werden: Se, Kr, Zr, Iqb, Me, Te, Ru, Sn, Sb, Te, J und Xe. In einem Rohr mit Temperaturgradienten l~…

Decay of the heaviest isotope of neodymium:154Nd

The neutron-rich isotope154Nd has been separated from235U fission products with the HELIum-jet On-line mass Separator HELIOS and investigated by γ-singles, γγ- and γX-coincidence measurements. The Z- and A-assignment have been confirmed by the observation of promethium KX-rays and by the genetic relationship to the daughter product 1.7-min154Pm. A half-life of 26±2 s has been obtained for154Nd, and a partial decay scheme is proposed. A 40 s activity previously assigned to154Nd could not be confirmed.

The decay of 31 sec98Zr, 2.9 sec98Nb and 51 min98Nb

TheΒ- andγ-radiations of98Zr and98m, g Nb have been investigated employing scintillation and semiconductor spectrometers and coincidence techniques. Sources of98Nb were produced by the98Mo(n, p)98Nb reaction, sources of98Zr by fission of235U with thermal neutrons applying chemical separations. For98Zr, a half-life of 30.7±0.4 sec and aQ β-value of 2.3±0.2 MeV were obtained, for the98Nb isomers, half-lives of 2.86±0.06 sec and 51.3±0.4 min, andQ β-values of 4.8±0.2 MeV and 4.5±0.2 MeV, respectively. Noγ-rays were observed in the decay of98Zr. The decay of 2.9 sec98Nb was found to involve 11γ-ray transitions. In the decay of 51 min98Nb, 54γ-transitions were detected. Spin and parity of 1+ and…

J. Robert Oppenheimer. Schöpfer der ersten Atombombe. VonK. Hoffmann. Springer, Berlin, 1995. 307 S., geb. 48.00 DM. – ISBN 3–540–59330–6

Methoden der Kern- und Radiochemie. VonP. Hoffmann undK. H. Lieser. VCH Verlagsgesellschaft, Weinheim, 1991. XII, 241 S., geb. DM 88.00. — ISBN 3-527-28256-4

Schnelle Extraktion durch quasi-feste Extraktionsmittel

Losungsmittelextraktionen lassen sich erheblich beschleunigen, indem man das Extraktionsmittel an einen feinkornigen TrAger adsorbiert und die zu extrahierende Losung rasch durch eine dunne Schicht dieses Materials saugt. Funfwertiges Antimon und Protactinium werden durch Diisobutylcarbinol und Di-2-Athylhexyl-orthophosphorsAure, gebunden an PolytrifluormonochlorAthylen, selbst bei maximaler Sauggeschwindigkeit von 2–3 ml/sec nahezu quantitativ extrahiert. Die Anwendung dieser Technik bei kernchemischen Studien wird an folgenden schnellen Trennungen demonstriert: Protactinium-234 m aus Uran, Antimon aus Tellur nach (n, p)-Proze\, Antimon aus Spaltprodukten und wiederholtes Abmelken von Tell…

Historical Reminiscences: The Pioneering Years of Superheavy Element Research

This chapter deals with the pioneering years of superheavy element research, from the mid 1960s to the mid 1980s. The prediction that superheavy nuclides could form an island around element 114 with half-lives long enough to have survived in Nature since nucleosynthesis led to intensive searches—not unlike “gold fever”—for such relic nuclei in all sorts of natural environments. Positive claims were raised from time to time but could not stand up under further scrutiny. Numerous attempts to synthesize superheavy nuclei by large leaps from the mainland of elemental stability to the island of superheavy elements went without success as well. The discovery of three more transactinide elements, …

Development of new centrifuges for fast solvent extraction of transactinide elements

The H-0.3 liquid-liquid centrifuge applied for rapid and efficient separation of two liquid phases, and the HG-0.1 gas-liquid centrifuge used to separate the gas phase stemming from a gas jet transportation system and the liquid phase, have been further improved. New centrifuges have been produced of PEEK, a plastic material, which makes them resistant to most aqueous and organic solutions. The performance with respect to time behavior and phase purity is comparable to the titanium centrifuges used so far. The H-0.3 centrifuge has been applied to solvent extraction studies of Zr, Nb, Mo, Hf, Ta, W and Pa from HF solutions into tri-n-octylamine.

Die schwersten chemischen Elemente

Vor hundert Jahren beschrieb Mendeleev [1] zum ersten Mal das Periodensystem chemischer Elemente: Ordnet man die Elemente nach ihrem Atomgewicht - heute ihrer Kernladungszahl -, so kehren chemische wie physikalische Eigenschaften periodisch wieder. Allerdings musten damals viele Lucken fur unbekannte Elemente gelassen werden, denn ein Drittel der naturlichen Elemente fehlte noch. Gerade das Schliesen dieser Lucken mit Elementen, deren Eigenschaften oft bis ins Detail richtig vorausgesagt werden waren, bestatigte iiberzeugend die Konzeption des Systems. Dennoch dauerte es nahezu achtzig Jahre, bis 1945 mit dem Element 61, Promethium, der letzte freie Platz besetzt werden konnte [2]; denn ein…

First Determination of the Ionization Potential of Americium and Curium

Schnelle radiochemische Trennungen durch Isotopen-und Ionenaustausch an vorgeformten Niederschlägen

Kurzlebige Nuklide konnen durch schnellen Isotopen-oder Ionenaustausch zwischen ihren Losungen und vorgeformten Niederschlagen isoliert werden. Dazu wird die Losung rasch durch eine dunne Niederschlagsschicht gesaugt. An Silberhalogeniden, Caesium-, Barium-und Thalliumverbindungen wird gezeigt, wie sich Herstellung, Menge und Loslichkeit des Niederschlags sowie Zusammensetzung und Kontaktzeit der Losung auf den Austausch auswirken. In einigen Systemen tragen nicht nur Oberflachenschichten, sondern der gesamte Niederschlag oder der groste Teil davon zum schnellen Austausch bei. Als Anwendung wird eine automatisierte Abtrennung von Brom-und Jodnukliden aus Spaltprodukten durch Austausch an Si…

Decay properties of neutron-rich niobium isotopes

The decay of neutron-rich niobium isotopes in the mass region $A\ensuremath{\simeq}100$ has been investigated by $\ensuremath{\gamma}$-ray singles and $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidence measurements. The isotopes were produced by thermal-neutron induced fission of $^{235}\mathrm{U}$, $^{239}\mathrm{Pu}$, and $^{249}\mathrm{Cf}$, and niobium was separated from fission-product mixtures with an automated chemical procedure. Isomerism was found in the even-mass niobium isotopes with the following half-lives: 1.5 and 3.1 sec for $^{100}\mathrm{Nb}$, 1.3 and 4.3 sec for $^{102}\mathrm{Nb}$, and 0.8 and 4.8 sec for $^{104}\mathrm{Nb}$. Half-lives and $\ensuremath{\gamma}$ rays…

Trace determination of 90Sr and 89Sr in environmental samples by collinear resonance ionization spectroscopy

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 …

Chemical reactions in a gas-jet recoil-transport system: Continuous separation procedure for selenium and tellurium from fission products

Abstract Chemical selectivity in a gas-jet recoil-transport system can be achieved by chemical reactions with the carrier gas. This is demonstrated for an ethylene-nitrogen jet in which volatile species of selenium and tellurium are formed by passing the gas through a reaction zone heated to 860°C. Rapid continuous separation procedures for selenium and tellurium from fission products based on this effect are described and some decay data of the neutron-rich nuclides 85–88Se and 135–137Te obtained with these methods are given.

Rapid chemical separation procedures

Fast, discontinuous separation procedures are described for zirconium, niobium, technetium and antimony from fission products. Other rapid separation methods from aqueous solutions are summarized. The combination of a gas jet recoil transport system with a continuous solvent extraction technique and with a thermochromatographic separation method is presented. The application of such procedures to the investigation of new and already known short-lived nuclides is illustrated by some examples.

Attempts to Produce Superheavy Elements by Fusion ofCa48withCm248in the Bombarding Energy Range of 4.5-5.2 MeV/u

A search for superheavy elements was made in bombardments of $^{248}\mathrm{Cm}$ with $^{48}\mathrm{Ca}$ ions performed at projectile energies close to the interaction barrier in order to keep the excitation energy of the compound nucleus $Z=116$, $A=296$ as low as possible. No evidence for superheavy nuclei was obtained in a half-life region from 1 \ensuremath{\mu}s to 10 yr with a production cross section greater than ${10}^{\ensuremath{-}34}$ to ${10}^{\ensuremath{-}35}$ ${\mathrm{cm}}^{2}$.

Fast preparation and gas-chromatographic separation of lanthanide and actinide hexafluoroacetylacetonates

A fast method for the separation of lanthanide elements by gas chromatography of their hexafluoroacetylacetonates is described. Individual lanthanides can be isolated within a few minutes, and the whole group can be separated in less than 10 min. The hexafluoroacetylacetonates are applied in form of mixed complexes with tri-n-butyl phosphate or trioctylphosphine oxide prepared by fast extraction into quasi-solid solvents. The applicability of this method for the separation of trivalent actinide elements is shown, including the fast preparation of thin counting samples.

Determination of the first ionization potential of nine actinide elements by resonance ionization mass spectroscopy (RIMS)

The high sensitivity of RIMS enables the precise determination of the first ionization potential of actinide elements with a sample size of ≤1012 atoms. By multiple resonant laser excitation, the actinide atoms under investigation are ionized in the presence of an electric field, and the ions are mass-selectively detected in a time-of-flight spectrometer. The first ionization potential is obtained by scanning the wavelength of the laser used for the last excitation step across the ionization threshold Wth—indicated by a sudden increase of the ion count rate—at various electric field strengths. Extrapolation of Wth to electric field strength zero leads directly to the first ionization potent…

Educational programs in nuclear and radiochemistry at the University of Mainz and in Germany

A survey is given of the educational programs at German universities and research institutions. The program at the University of Mainz is outlined in some detail.

Ermittlung von Einzelheiten bei Reaktionsabläufen

Die Verwendung isotopenmarkierter Verbindungen bei Stoffwechseluntersuchungen gestattet ganz allgemein folgende Aussagen: 1. Die Verteilung innerhalb des Organismus und die Ausscheidung kann bestimmt werden. 2. Es last sich feststellen, ob eine Verbindung an dem betreffenden Stoffwechselvorgang beteiligt ist. 3. Durch eine Lokalisation des Isotops kann weiterhin gepruft werden, in welcher Weise die markierte Verbindung in das Stoffwechselprodukt eingebaut wird, ob wahrend des Stoffwechsels eine Veranderung in der Reihenfolge von Atomen eintritt und ob bestimmte Atome oder Atomgruppierungen abgespalten werden.

über die polarographische Bestimmung des Urans und seine Abtrennung durch Lösungsmittelextraktion in Gegenwart von Phosphat

Es wurde versucht, das Verfahren von Hecht u. Mitarb. zur polarographischen Uranbestimmung unter Ausnutzung der katalytischen Nitratwelle zu reproduzieren. Unter den von uns angewandten Versuchsbedingungen verliefen diese Versuche negativ. Durch Versuche wurde eine Grundlosung aus SalpetersAure, SchwefelsAure und Methylrot ermittelt, die es gestattet, 0,05–5 ΜgU/ml polarographisch zu bestimmen. Die katalytische Nitratwelle wird jedoch leicht gestort und eignet sich kaum zur Serienbestimmung kleiner Uranmengen.

A rotating wheel system for the detection of spontaneously fissioning nuclides from heavy ion reactions

Abstract A rotating wheel system for the detection of spontaneously fissioning reaction products from heavy ion reactions was developed. In this system products recoiling from a rotating target wheel are stopped in a catcher foil stack which can be rotated at various velocities up to 80 rotations per second. All products emitted within a wide emission cone are stopped in the catcher foils and are rotated into shielded positions with stationary fission-track detectors positioned on both sides of each rotating foil. This technique allows a sensitive detection of spontaneously fissioning nuclides over a broad range of half-lives from 1 ms to about 1 d. By post-bombardment exposure of the catch…