Instrumental neutron activation analysis of carbon containing micro-spheres from Jungfrau-Joch glacier ice

From about 700 kg old, high altitude glacier ice (age 400 y) more than 170 glassy spherical objects with a mean diameter of 100 m were isolated. Neutron activation analysis of individual transparent objects (each 10^–6 g) showed the presence of K, Sc, Cr, Fe, La, Eu, Au, etc., in varying concentrations. A detection limit of 10^–14 g/g was achieved by means of an anticompton circuit. A systematic study by mass spectrometry of positive and negative ions using a LASER microprobe disclosed that the main constituents of some of these smooth glacier spheres consisted of elemental carbon. The chemical composition of some spherules admits the possibility of extraterrestrial origin, e.g. ablation material from meteorites with high carbon contents, which entered the earth's atmosphere.     

Determination of227Ac in geological materials through neutron activation and alpha-spectrometric assay of induced228Th

A new route has been developed for the micro-determination of²²⁷Ac in geological materials by neutron activation. The method is based on intense neutron irradiation of the analysed samples followed by separation and α-spectrometric determination of²²⁸Th, the β-decay product of the 6.1 hrs²²⁸Ac isotope formed. Two alternatives are considered for analysis related to the origin of the analysed matrix. The high sensitivity of the method is documented by the determination of 10^?17 g²²⁷Ac/g sample. The method is successfully applied for age determination of five uranium containing materials and old uranium glass from Bohemia, CSSR.     

Computer assisted multielement analysis of terrestrial and extraterrestrial materials and studies on long-lived cosmogenic53Mn by neutron activation

In a large number of alpine rocks and respective mineral separates the beryllium distribution was studied via “non-destructive” photon activation. The detection limit of the assembly was ∼20 ppb. The existence of Be-rich areas was revealed. A selection of individual rocks was analysed by instrumental as well as by radiochemical neutron activation analysis for main and trace elements as: Na, K, Sc, Cr, Mn, Fe, Co, Rb, Cs, La, Eu, Yb, Ta, W, Au, and U. The latter was determined by counting the²³⁵U-fission tracks. The data supply an insight into the complex processes leading to the formation of metamorphic rocks. The hardware and the computer evaluation of the γ-spectra is described in some detail. A further application is the determination of traces of⁵³Mn (in the order of 10⁻¹² g/g) produced by the interaction of cosmic rays with stony meteorites. From a comparison of the²⁶Al- and⁵³Mn-values it is concluded that the depth dependent production of these two radionuclides differs slightly.     

Die Bestimmung von Submikromengen Kupfer in Reinstmetallen und Meteoriten Durch Ein Hochselektives γ,γ-Koinzidenzverfahren

Copper was determined non-destructively by neutron-activation analysis in the high purity metals Be, Bi, Pb, Se, Sn, Tl and in iron meteorite specimens down to concentrations of 40 ppb, while the minimum detectable mass for 1 g-samples as defined recently byCurrie ²⁵ was about 0.1 ppb Cu. γ,γ-coincidence counting of the annihilation radiation of⁶⁴Cu essentially improved suppression of interferences by other γ-cascade emitters. The latter was achieved by increasing the detector distances and by counting in centric and eccentric positions with respect to the detectors. Using the 180°-angle correlation of the annihilation γ-quants of⁶⁴Cu etc. an increase in selectivity—in relation to conventional coincidence methods—was achieved by a factor of about 10³. A goniometer arrangement proved to be very advantageous.      

Dynamic uncapacitated lot sizing with random demand under a fillrate constraint

This paper deals with the single-item dynamic uncapacitated lot sizing problem with random demand. We propose a model based on the “static uncertainty” strategy of Bookbinder and Tan (1988). In contrast to these authors, we use exact expressions for the inventory costs and we apply a fillrate constraint. We present an exact solution method and modify several well-known dynamic lot sizing heuristics such that they can be applied for the case of dynamic stochastic demands. A numerical experiment shows that there are significant differences in the performance of the heuristics whereat the ranking of the heuristics is different from that reported for the case of deterministic demand.     

Characteristics of a hybridly mode-locked cw dye laser

We present experimental and theoretical results on the characteristics and random variations of subpicosecond pulses generated by a synchronously pumped cw dye laser with saturable absorber. The analysis of the power spectra indicates rapid fluctuations of the pulse duration of 40–50%, energy fluctuations of 3%, and a jitter of the repetition time of 0.1% corresponding to an absolute jitter of 12 ps. The latter is caused mainly by the temporal jitter of the pump laser. A mismatch of the lengths of the dye and the pump-laser cavity can result in a nonstationary mode-locking regime with a periodic change of the pulse parameters. The interpretation of the experimental results are supported by computer simulations of the pulse evolution process.     

Die zerstörungsfreie,aktivierungsanalytische Bestimmung spezieller Spurenelemente mit hochselektiven 2fach- und 3fach-γ Koinzidenzanordnungen unter Berücksichtigung wichtiger Störfaktoren

Zusammenfassung Im Zusammenhang mit der Bestimmung von Kupferspurengehalten im ppm- und ppb-Bereich über die⁶⁴Cu-Vernichtungsstrahlung mit Hilfe einer verbesserten hochselektiven,-Koinzidenzanordnung wurde insbesondere die Störung durch Paarbildung an 22 in Frage kommenden Störnukliden untersucht. Das relative Paarbildungsvermögen dieser Nuklide wurde berechnet und eine spezielle Nachweismethode zur Erkennung, Verringerung und Berücksichtigung der Störung angegeben. Das Verfahren wurde zur Bestimmung des Kupfergehaltes von Standard-gesteinen, Steinmeteoriten und Molybdänglanzen angewandt.Für die Bestimmung einer Reihe anderer Nuklide, die drei oder mehr-Quanten entweder in Kaskade oder ein-Quant zusammen mit der Vernichtungsstrahlung emittieren, führt die Verwendung der Dreifach--Koinzidenz zu einer beachtlichen weiteren Erhöhung der Selektivität und einer Verbesserung hinsichtlich der störenden Zufallsimpulse. Eine wichtige Anwendung der Dreifachkoinzidenz wurde in der direkten Bestimmung von Iridiumspuren (bis herab zu 20 ppb) in Eisenmeteoriten gefunden.

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The interference-free, activation analytical determination of special trace elements with highly selective two-fold and three-fold--coincidence layouts with consideration of important interference factors

Summary Non-destructive neutron activation analysis of copper traces in the ppm- and ppb-range has been studied by means of an improved and highly selective,-coincidence, using the⁶⁴Cu-annihilation radiation, with particular reference to interfering pair production. For 22 interfering nuclides the relative pair production rate was calculated. A method for detection, reduction, and correction was developed and applied to the determination of copper contents in standard rocks, stony meteorites, and molybdenites. Especially the²⁴Na interference was succesfully overcome. For a number of nuclides, emitting three or more-quants either in cascade or one-quant together with the annihilation radiation, it has been shown that triple coincidence leads to a considerable further improvement in selectivity combined with a reduction of random coincidences. The triple coincidence has been applied to the direct determination of iridium traces (down to 20 ppb) in iron meteorites.

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Herrn Prof. W. Herr danken wir für wohlwollende Ratschläge bei der Verfassung und Durchsicht des Manuskripts.