Walter Kutschera

The Age of Olfactory Bulb Neurons in Humans

Continuous turnover of neurons in the olfactory bulb is implicated in several key aspects of olfaction. There is a dramatic decline postnatally in the number of migratory neuroblasts en route to the olfactory bulb in humans, and it has been unclear to what extent the small number of neuroblasts at later stages contributes new neurons to the olfactory bulb. We have assessed the age of olfactory bulb neurons in humans by measuring the levels of nuclear bomb test-derived (14)C in genomic DNA. We report that (14)C concentrations correspond to the atmospheric levels at the time of birth of the individuals, establishing that there is very limited, if any, postnatal neurogenesis in the human olfactory bulb. This identifies a fundamental difference in the plasticity of the human brain compared to other mammals.

14C dating with the bomb peak: An application to forensic medicine

Abstract Samples originating from the time period after 1950 can be radiocarbon dated utilising the 14C bomb peak as a calibration curve. The applicability of “radiocarbon dating” of recent organic human material for the determination of the time of death of humans was tested. The radiocarbon results from hair and lipid samples from individuals with known date of death were compared with the results from two individuals with unknown time of death. An estimate of the year of death for the unknowns could be derived by this way. Due to the long turnover time of collagen in human bones it is not possible to use the radiocarbon content of bone collagen for a reliable estimate. In order to study the time dependence of the collagen turnover we tested “soft” chemical methods for the isolation of collagen from the bone matrix. First radiocarbon results of this investigation are presented.

A comparison of groundwater dating with 81Kr, 36Cl and 4He in four wells of the Great Artesian Basin, Australia

The isotopic ratios 81 Kr/Kr and 36 Cl/Cl and the 4 He concentrations measured in groundwater from four artesian wells in the western part of the Great Artesian Basin (GAB) in Australia are discussed. Based on radioactive decay along a water flow path the 81 Kr/Kr ratios are directly converted to groundwater residence times. Results are in a range of 225^400 kyr with error bars in the order of 15% primarily due to counting statistics in the cyclotron accelerator mass spectrometer measurement. Additional uncertainties from subsurface production and/or exchange with stagnant porewaters in the confining shales appear to be of the same order of magnitude. These 81 Kr ages are then used to calibrate the 36 Cl and the 4 He dating methods. Based on elemental analyses of rock samples from the sandstone aquifer as well as from the confining Bulldog shale the in situ flux of thermal neutrons and the corresponding 3 He/ 4 He and 36 Cl/Cl ratios are calculated. From a comparison of: (i) the 3 He/ 4 He ratios measured in the groundwater samples with the calculated in situ ratios in rocks and (ii) the measured N 37 Cl ratios with the 4 He concentrations measured in groundwater it is concluded that both helium and chloride are most likely added to the aquifer from sources in the stagnant porewaters of the confining shale by diffusion and/or mixing. Based on this ‘working hypothesis’ the 36 Cl transport equation in groundwater is solved taking into account: (i) radioactive decay, (ii) subsurface production in the sandstone aquifer (with an in situ 36 Cl/Cl ratio of 6U10 315 ) and (iii) addition of chloride from a source in the confining shale (with a 36 Cl/Cl ratio of 13U10 315 ). Lacking better information it is assumed that the chloride concentration increased linearly with time from an (unknown) initial value Ci to its

Accelerator mass spectrometry of heavy long-lived radionuclides

Abstract This paper describes the upgrade of the Vienna Environmental Research Accelerator (VERA) to a universal facility for accelerator mass spectrometry (AMS). As a result, it is now possible to measure many long-lived radionuclides at natural abundances across the nuclear chart, from the lightest ( 10 Be ) to the heaviest ( 244 Pu ). Particular emphasis is placed on measurements to understand the ion optics and the origin of background ions, which ultimately limit the sensitivity. VERA is now ready to venture into the realm of actinides (e.g., 236 U , 244 Pu ), and other heavy radionuclides (e.g., 182 Hf ), which promise interesting applications in astrophysics and other fields.

81Kr in the Great Artesian Basin, Australia: a new method for dating very old groundwater

Abstract The measurement of cosmogenic 81Kr (t1/2=(2.29±0.11)×105 yr) has been proposed for many years as a reliable tool for groundwater dating in the range from 105 to 106 yr. In this paper, we report on the first use of 81Kr to determine the age of groundwater from four wells in the Great Artesian Basin in Australia. As the concentration of 81Kr in old groundwater is only a few hundred atoms per liter, krypton was extracted from large (16 000 l) groundwater samples and was analyzed for the isotopic abundance of 81Kr by accelerator mass spectrometry (AMS) with a cyclotron. 81Kr/Kr isotope ratios of (1.54±0.22)×10−13, (1.78±0.26)×10−13, (2.19±0.28)×10−13 and (2.63±0.32)×10−13, respectively, were measured for these samples. It is reasonable to assume that krypton dissolved in surface water in contact with the atmosphere has the known atmospheric 81Kr/Kr ratio of (5.20±0.40)×10−13. The observed reduction of isotope ratios in the groundwater samples can then be interpreted as being due to radioactive decay since recharge. This results in respective groundwater ages of: (4.02±0.51)×105 yr, (3.54±0.50)×105 yr, (2.87±0.38)×105 yr and (2.25±0.42)×105 yr. The main emphasis of this paper lies on the description of the analytic procedure to extract a reliable 81Kr signal from large groundwater samples. Although the uncertainties are still relatively large (primarily due to counting statistics caused by the low cyclotron AMS efficiency), the new technique enabled for the first time a definite determination of residence times for old groundwater with 81Kr. It thus confirms the hope that this radionuclide may become a very valuable tool for groundwater dating.

Tracing noble gas radionuclides in the environment

▪ Abstract Trace analysis of radionuclides is an essential and versatile tool in modern science and technology. Because of their ideal geophysical and geochemical properties, long-lived noble gas radionuclides—particularly 39Ar (t1/2 = 269 y), 81Kr (t1/2 = 2.3 × 105 y), and 85Kr (t1/2 = 10.8 y)—have long been recognized to have a wide range of important applications in Earth sciences. In recent years, significant progress in the development of practical analytical methods has led to applications of these isotopes in the hydrosphere (tracing the flow of groundwater and ocean water). In this article, we introduce the applications of these isotopes and review three leading analytical methods: low-level counting (LLC), accelerator mass spectrometry (AMS) and atom trap trace analysis (ATTA).

“Isotope language” of the Alpine Iceman investigated with AMS and MS

This paper reviews the use of stable and radioactive isotopes to elucidate an extraordinary archaeological find, the

Disentangling Geomagnetic and Precipitation Signals in an 80-kyr Chinese Loess Record of 10Be

The cosmogenic radionuclide 10 Be is produced by cosmic-ray spallation in Earths atmosphere. Its production rate is regulated by the geomagnetic field intensity, so that its accumulation rate in aeolian sediments can, in principle, be used to derive high-resolution records of geomagnetic field changes. However, 10 Be atmospheric fallout rate also varies locally depending on rainfall rate. The accumulation rate of 10 Be in sediments is further complicated by overprinting of the geomagnetic and precipitation signals by 10 Be attached to remobilized dust, which fell from the atmosphere at some time in the past. Here, we demonstrate that these signals can be deconvoluted to derive both geomagnetic field intensity and paleoprecipitation records of Asian Monsoon intensity in an 80,000-yr-long 10 Be record from Chinese loess. The strong similarity between our derived paleomagnetic intensity record and the SINT 200 (Guyodo and Valet 1996) and NAPIS 75 (Laj et al. 2002) stacked-marine records suggests that this method might be used to produce multimillion-yr-long records of paleomagnetic intensity from loess. This technique also reveals a new method for extracting quantitative paleoprecipitation records from continental interior regions. Our derived precipitation record is broadly similar to the speleothem δ 18 O-based records of paleo-Asian Monsoon intensity from Dongge (Yuan et al. 2004) and Hulu (Wang et al. 2001) caves, and suggests that the paleo-Asian Monsoon intensity may be responding to a combination of both Northern and Southern Hemisphere insolation forcing.

Pushing the precision limit of 14C AMS

High precision for radiocarbon cannot be reached without profound insight into the various sources of uncertainty which only can be obtained from systematic investigations. In this paper, we present a whole series of investigations where in some cases (super 16) O: (super 17) O: (super 18) O served as a substitute for (super 12) C: (super 13) C: (super 14) C. This circumvents the disadvantages of event counting, providing more precise results in a much shorter time. As expected, not a single effect but a combination of many effects of similar importance were found to be limiting the precision. We will discuss the influence of machine tuning and stability, isotope fractionation, beam current, space charge effects, sputter target geometry, and cratering. Refined measurement and data evaluation procedures allow one to overcome several of these limitations. Systematic measurements on FIRI-D wood show that a measurement precision of + or -20 (super 14) C yr (1 sigma ) can be achieved for single-sputter targets.

Measurement of 81Kr in the atmosphere

Abstract We present the first AMS measurement of the 81Kr concentration in atmospheric krypton. The measurement was performed by combining positive-ion production in an electron cyclotron resonance source with acceleration to high energy in a cyclotron and subsequent full stripping for 81Br81Kr separation. The result, 81 Kr Kr = (5.3 ± 1.2) × 10 −13 , agrees well with two previous low-level decay counting measurements.