We discuss possible evidence for a dilution of 14C caused by the Tunguska impact event, proposed by Rasmussen et al. ( 1 999). The results presented in that paper and other available information do not support this hypothesis.

Usually neutron activation analyses are performed in point-source geometry. However, specially designed irradiation positions and carefully planned measuring conditions enabled the activation and analysis of samples with weights up to several tens of kilograms. A dedicated character of irradiation and of measuring conditions was the main reason for a very limited application of such activation analysis. The use of routine irradiation facilities and standard conditions for analytical gamma-spectrometric measurements is described. Starting with samples of some hundred milligrams usually used in activation, through multi-gram samples to several hundred gram samples, irradiation and measuring conditions were studied and tested for development of the method. This work began in 1991 in Denmark, using the Danish DR-3 reactor. Since then different aspects of the method have been investigated on 6 reactors; in Denmark on DR-3, in Austria on Triga-MkII (in Vienna), and Astra (in Seibersdorf), in the German Federal Republic on FRG-1 in Geesthacht, in Norway on Jeep II (in Kjeller), and in Kazakhstan on VVR-K (in Alatau). Altogether more than 1000 samples have been irradiated and measured. In total, the roughly 30 kg of irradiated materials included almost 300 large samples of more than 30 gram weight. The following theoretical and practical aspects were investigated during the work: theoretical problems concerning neutron self-absorption in common organic and inorganic materials, as well as gamma-attenuation during the measurement. From a more practical point of view: health physics and radiation hazards during irradiation, measurement, transportation and storage of samples with several hundred grams weight. Special requirements to irradiation containers were formulated and various containers were tested. Main advantages and drawbacks of the method are discussed.

For the practical application of large sample activation analysis, an extensive characterization of the irradiation facility and of the measurement system — of sample size, flux-gradient, maximum count rate, size of irradiation and counting containers, estimation of created activity after irradiation and dose rate — is required.The term, “large samples” is not unequivocal. Here the consideration is restricted to samples from several grams to 100 or 200 grams, which can be irradiated in existing irradiation facilities. Calculations were performed for about 1200 organic samples divided into 18 groups. The results are in about 400 tables. The effective Z number, Z/A ratio, mass attenuation for several gamma lines, the relative contribution of the main absorbing elements in the sample for effective cross sections and for gamma transmission are calculated for each sample. All these data have been calculated for various sizes of irradiation and measuring containers. Macroscopic thermal, epithermal, scattering and transport cross sections were used for calculation of self-shielding by five different methods. Owing to the limited space only a selection of the most pertinent values characterizing each group of samples is presented and discussed.The main differences of Large Sample NAA to other nuclear analytical methods are self-shielding and gamma attenuation in the sample. The main object of this paper is to show up problems that may arise in LS-NAA through self-shielding and gamma attenuation.

Anthropogenic activity is one of the causes of contamination in the human environment: contamination of air, water, top soils, plants and food products has complex effects on human health problems. Wear and abrasion of various surfaces are constant processes in daily life, and commonly include interaction between human fingers and surfaces of every conceivable material. New methods for investigation of trace transfer processes by human fingers are described. Results of transfer for commonly used metals such as gold, silver, zinc, cadmium, tin, cobalt, nickel, chromium and iron are presented. Relationship between transfer of metals by touch and the general problem of purity in analytical activities is briefly discussed.

Instrumental neutron activation analysis was utilized for the multielemental determination of elements in the roots of Ageratum conyzoides , a tropical medicinal plant that is used locally for the cure of various diseases in Nigeria. The concentrations of Al, Ba, Br, Ca, Co, Cr, Fe, K, Mg, Mn, Na, Rb, Sc, Sr, V and Zn were analyzed with the 250 kW Triga Reactor at the Atominstitut, Vienna. The essential elements K, Na, Ca, Fe, Mg, Mn and Zn and the non-essential elements Al, Ba, Sr and Rb are present in significant concentrations. Other elements including Co, Cr, Sc and V are present at trace levels. The likely implication of these elements in restoring and maintaining good health is discussed. Quality control on the measurements was carried out by analyzing standard reference materials alongside the samples.

The environmental remediation programs in Kazakhstan require fast, viable and relatively cheap analytical control of thousands of samples of soils, plants, food products and materials from geological prospecting. The WWR-K reactor of the Institute of Nuclear Physics in Almaty, operated at low thermal power mode, is an excellent tool for use of nuclear methods of elemental analysis for a wide range of environmental materials. The recent adaptation of the reactor, enabling irradiation of large organic samples, gives a unique opportunity to apply the WWR-K reactor for neutron activation analysis in the vast remediation and phytoremediation research programs. First results of investigation of systems consisting of plants and soils to their roots are described and discussed.

Jull et al. propose an alternative interpretation of our depth vs. C-14 data measured on a peat core from the central Tunguska impact site (Rasmussen et al., 1999). We find that the proposed alternative is untenable.

Based on a Preloaded Digital Filter operating on a 20% n-type HpGe detector with transistor reset preamplifier, and on a software implementation of a loss-free counting MCA, storing immediately into the multi-megabyte main memory of a low-cost 486-type PC, the new system enables the collection of up to 120 pairs of simultaneously recorded loss-corrected and non-corrected spectra of 16 k channels each, in a true sequence without time gaps in between, at a throughput rate of up to 140 kc/s. Intended for activation analysis of short-lived isomeric transitions, the system for the first time makes possible peak to background optimizations and even separations of lines with different half-lives without an a priori knowledge of sample composition by summing up appropriate numbers of spectra over appropriate intervals of time. The speed of this programmable system also made possible the direct comparison of two methods of real-time correction of counting loss. by simultaneous recording of LFC-corrected, ZDT(tm)-corrected and non-corrected spectra together with their corresponding weighting factor distributions.

The collapse of a section of the cliff at Stevns Klint, Denmark in 1986 provided a unique opportunity to collect about 50 kg of Fish Clay representing the Cretaceous‐Tertiary (K‐T) boundary layer. In this paper, details of the preparation of this sample are presented, together with preliminary analytical results to support the development of this sample as a reference material, particularly for the determination of iridium and the other platinum‐group elements in clays and sediments associated with K‐T boundary studies and in other environmental samples collected to study the effects of automobile exhaust catalysts.

The new measurement system for high-resolution, high-rate gamma -spectrometry consists of a 20% n-HPGe detector with a transistor reset preamplifier, a PLDF-system, and a software implementation of an LFC-multichannel analyzer allowing the continuous registration of 120 pairs of 16k channel gamma -spectra, pile-up and dead-time corrected, and uncorrected [3, 4]. Thus, it is possible to obtain the total information contained in the gamma -spectra of short- and medium-lived radionuclides after a short neutron irradiation. The new gamma -spectrometry system was tested by activation of a mixture of In, Se, and Ba. This enables the optimal analysis of radionuclides by selecting the optimal summation range simultaneously with a quality assurance of the data by plotting the decay curves of the respective radionuclides.

The usual mass of samples for activation analysis is in the range of several milligrams to several hundred milligrams. An improvement of the detection limit by three orders of magnitude is attainable by use of a larger sample size. Limitations of the method due to thermal effects, neutron self-shielding and gamma-ray attenuation during activation and measuring of large organic samples are discussed.

Abstract— Precise radiometric age determination of the Kaalijärv meteorite craters on the island of Saaremaa in Estonia have so far proved inconclusive. Here we present trace element analyses of peat cores taken several kilometers away from the Kaalijärv craters that reveal a distinct Ir‐enriched layer produced by the meteorite impact. By radiocarbon dating the peat cores, we have determined for the first time the precise age of the impact that generated the Kaalijärv craters. The calibrated date of the impact is 400–370 B.C. at ± 1σ.

The irradiation of large samples of biological material in a high neutron flux enables the extention of trace element analysis into the ng to pg range, but raises several problems as gamma heating and radiolysis degrade the samples. Gamma heating increases the pressure to a point where either a very large irradiation container is necessary or a container which can endure the high pressure. Several methods to overcome these problems have been published. The irradiation of open samples was performed as an alternative to these methods. Temperature effects on biological material during irradiation in a high and in a low neutron flux were compared. As an example, wheat was irradiated in open containers allowing simultaneous temperature measurement in the sample during irradiation.

Fields in which progress has been achieved at the Atomic Institute Vienna are discussed briefly. The use of short and medium lived nuclides for activation analysis (AA). Construction of out-core parts of a fast transfer system. Combined sample catcher sample-changer for AA allowing cyclic and pseudocyclic AA. A system for discontinuous or continuous irradiation of liquid samples. Counting with an anticompton shield and quantitative correction of random coincidences. Screening analyses with the fast irradiation and measurement system. Improved peak-evaluation of gamma-spectra, Epithermal AA by a neutron converter. Following short-lived nuclide measurement, automatic sample transfer into a well-type detector enabling sensitive counting of nuclides with short half-lives. Use of large samples to increase the detection limits of ng to pg at activation with moderate neutron flux. Flux determination by liquid scintillation counting.

In the process of transferring stable and radioactive isotopes from soil to plants, a soil solution is the intermediate phase. A transfer coefficient from soil to plants can be divided into two separate distribution coefficients-one between a soil and a soil solution and the other between a soil solution and a plant. A new method, the so-called large-sample activation analysis, has been applied to determine stable species in plants and extractant solutions, simulating soil solutions.

A geometrical configuration is described where the counting of varying amounts of analytical samples is carried out in 1 to 13 identical counting containers placed radially around the detector. As the response of the detector does not differ for each of these containers, the calibration is required for only one of them. The counting of transmitted gamma-rays of radioisotope radiation sources in a collimated geometry was performed for various environmental materials. Measurement of IAEA and CCRMP standards for Cs-137, uranium, thorium and potassium in quantities from 6 to 300 mi was done. A short description is given of results of numerical experiment comprising the calculation of the attenuation coefficient for selected gamma energy in more than 400 geological, environmental and biological standards and samples with known composition.

We have measured excess Ir and depletion of C-14, two independent indicators of cosmic material, in peat cores from the central Tunguska impact site. Both Ir and 14C show pronounced anomalies in the same stratigraphical depth interval. We have estimated an integral deposition of nonradioactive cosmogenic C of 6.8 +/- 1.0 mg C cm(-2), and an integrated Ir deposition of 5.9 +/- 1.2 pg Ir cm(-2). The very high C/Ir ratio and a deduced delta(13)C value of +55 +/- 10 parts per thousand relative to V Pee Dee Belemnite (VPDB) of the impactor material found in this study points towards a cometary type impactor, rather than a chondritic or achondritic asteroidal type impactor.