158 research outputs found
Solving the stellar 62Ni problem with AMS
An accurate knowledge of the neutron capture cross sections of 62,63Ni is
crucial since both isotopes take key positions which affect the whole reaction
flow in the weak s process up to A=90. No experimental value for the
63Ni(n,gamma) cross section exists so far, and until recently the experimental
values for 62Ni(n,gamma) at stellar temperatures (kT=30 keV) ranged between 12
and 37 mb. This latter discrepancy could now be solved by two activations with
following AMS using the GAMS setup at the Munich tandem accelerator which are
also in perfect agreement with a recent time-of-flight measurement. The
resulting (preliminary) Maxwellian cross section at kT=30 keV was determined to
be 30keV = 23.4 +/- 4.6 mb. Additionally, we have measured the
64Ni(gamma,n)63Ni cross section close to threshold. Photoactivations at 13.5
MeV, 11.4 MeV and 10.3 MeV were carried out with the ELBE accelerator at
Forschungszentrum Dresden-Rossendorf. A first AMS measurement of the sample
activated at 13.5 MeV revealed a cross section smaller by more than a factor of
2 compared to NON-SMOKER predictions.Comment: Proceedings of the 11th International Conference on Accelerator Mass
Spectrometry in Rome, Sept. 14-19, 2008; to be published in Nucl. Instr.
Meth.
AMS measurements of cosmogenic and supernova-ejected radionuclides in deep-sea sediment cores
Samples of two deep-sea sediment cores from the Indian Ocean are analyzed
with accelerator mass spectrometry (AMS) to search for traces of recent
supernova activity around 2 Myr ago. Here, long-lived radionuclides, which are
synthesized in massive stars and ejected in supernova explosions, namely 26Al,
53Mn and 60Fe, are extracted from the sediment samples. The cosmogenic isotope
10Be, which is mainly produced in the Earths atmosphere, is analyzed for dating
purposes of the marine sediment cores. The first AMS measurement results for
10Be and 26Al are presented, which represent for the first time a detailed
study in the time period of 1.7-3.1 Myr with high time resolution. Our first
results do not support a significant extraterrestrial signal of 26Al above
terrestrial background. However, there is evidence that, like 10Be, 26Al might
be a valuable isotope for dating of deep-sea sediment cores for the past few
million years.Comment: 5 pages, 2 figures, Proceedings of the Heavy Ion Accelerator
Symposium on Fundamental and Applied Science, 2013, will be published by the
EPJ Web of conference
Highly Sensitive Gamma-Spectrometers of GERDA for Material Screening: Part 2
The previous article about material screening for GERDA points out the
importance of strict material screening and selection for radioimpurities as a
key to meet the aspired background levels of the GERDA experiment. This is
directly done using low-level gamma-spectroscopy. In order to provide
sufficient selective power in the mBq/kg range and below, the employed
gamma-spectrometers themselves have to meet strict material requirements, and
make use of an elaborate shielding system. This article gives an account of the
setup of two such spectrometers. Corrado is located in a depth of 15 m w.e. at
the MPI-K in Heidelberg (Germany), GeMPI III is situated at the Gran-Sasso
underground laboratory at 3500 m w.e. (Italy). The latter one aims at detecting
sample activities of the order ~0.01 mBq/kg, which is the current
state-of-the-art level. The applied techniques to meet the respective needs are
discussed and demonstrated by experimental results.Comment: Featured in: Proceedings of the XIV International Baksan School
"Particles and Cosmology" Baksan Valley, Kabardino-Balkaria, Russia, April
16-21,2007. INR RAS, Moscow 2008. ISBN 978-5-94274-055-9, pp. 233-238; (6
pages, 4 figures
Search for supernova-produced 60Fe in a marine sediment
An 60Fe peak in a deep-sea FeMn crust has been interpreted as due to the
signature left by the ejecta of a supernova explosion close to the solar system
2.8 +/- 0.4 Myr ago [Knie et al., Phys. Rev. Lett. 93, 171103 (2004)]. To
confirm this interpretation with better time resolution and obtain a more
direct flux estimate, we measured 60Fe concentrations along a dated marine
sediment. We find no 60Fe peak at the expected level from 1.7 to 3.2 Myr ago.
However, applying the same chemistry used for the sediment, we confirm the 60Fe
signal in the FeMn crust. The cause of the discrepancy is discussed.Comment: 15 pages, 5 figures, submitted to PR
The Search for Supernova-produced Radionuclides in Terrestrial Deep-sea Archives
An enhanced concentration of 60Fe was found in a deep ocean's crust in 2004
in a layer corresponding to an age of ~2 Myr. The confirmation of this signal
in terrestrial archives as supernova-induced and detection of other
supernova-produced radionuclides is of great interest. We have identified two
suitable marine sediment cores from the South Australian Basin and estimated
the intensity of a possible signal of the supernova-produced radionuclides
26Al, 53Mn, 60Fe and the pure r-process element 244Pu in these cores. A finding
of these radionuclides in a sediment core might allow to improve the time
resolution of the signal and thus to link the signal to a supernova event in
the solar vicinity ~2 Myr ago. Furthermore, it gives an insight on
nucleosynthesis scenarios in massive stars, the condensation into dust grains
and transport mechanisms from the supernova shell into the solar system
41Ca in tooth enamel. part I: A biological signature of neutron exposure in atomic bomb survivors
The detection of 41Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima and Nagasaki. In general, 41Ca atoms are produced via thermal neutron capture by stable 40Ca. Thus any 41Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both natural sources and radiation from the bomb. Tooth samples from five survivors in a control group with negligible neutron exposure were used to investigate the natural 41Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bomb-related neutron exposure. The results showed that the mean 41Ca/Ca isotope ratio was (0.17 ± 0.05) × 10-14 in the control samples and increased to 2 × 10-14 for survivors who were proximally exposed to the bomb. The 41Ca/Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values that have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that γ-ray doses were determined earlier for the same tooth samples by means of electron spin resonance (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures that were calculated individually for the survivors but that had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).Fil: Wallner, A.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; Alemania. Universidad de Viena; AustriaFil: Ruhm, W.. Helmholtz Center Munich German Research Center For Environmental Health; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Rugel, G.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; AlemaniaFil: Nakamura, N.. Radiation Effects Research Foundation; JapónFil: Arazi, Andres. Universitat Technical Zu Munich; Alemania. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Faestermann, T.. Universitat Technical Zu Munich; AlemaniaFil: Knie, K.. Universitat Technical Zu Munich; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Maier, H. J.. Ludwig Maximilians Universitat; AlemaniaFil: Korschinek, G.. Universitat Technical Zu Munich; Alemani
First Measurement of the 64Ni(gamma,n)63Ni Cross Section
Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-ShareAlike LicenceIn the past 10 years new and more accurate stellar neutron capture cross section measurements have changed and improved the abundance predictions of the weak s process. Among other elements in the region between iron and strontium, most of the copper abundance observed today in the solar system distribution was produced by the s process in massive stars. However, experimental data for the stellar 63Ni(n,gamma)64Ni cross section are still missing, but is strongly required for a reliable prediction of the copper abundances. 63Ni (t1/2 =101.2 a) is a branching point and also bottleneck in the weak s process flow, and abehaves differently during core He and shell C burning. During core He burning the reaction flow proceeds via beta-decay to 63Cu, and a change of the 63Ni(n,gamma)64Ni cross section would have no influence. However, this behavior changes at higher temperatures and neutron densities during the shell C burning phase. Under these conditions, a significant amount of the s process nucleosynthesis flow is passing through the channel 62Ni(n,gamma)63Ni(n,gamma)64Ni. At present only theoretical estimates are available for the 63Ni(n,gamma)64Ni cross section. The corresponding uncertainty affects the production of 63Cu in present s process nucleosynthesis calculations and propagates to the abundances of the heavier species up to A=70. So far, experimental information is also missing for the inverse 64Ni(gamma,n) channel. We have measured for the first time the 64Ni(gamma,n)63Ni cross section and also combined for the first time successfully the photoactivation technique with subsequent Accelerator Mass Spectrometry (AMS). The activations at the ELBE facility in Dresden-Rossendorf were followed by the 63Ni/64Ni determination with AMS at the MLL accelerator laboratory in Garching. First results indicate that theoretical predictions have overestimated this cross section up to now. If this also holds for the inverse channel 63Ni(n,gamma)64Ni, more 63Ni is accumulated during the high neutron density regime of the C shell that will contribute to the final abundance of 63Cu by radiogenic decay. In this case, also a lower s process efficiency is expected for the heavier species along the neutron capture path up to the Ga-Ge regio
Condiciones de la fauna silvestre de tráfico ilegal en un centro de rescate en la ciudad de Guayaquil, Ecuador
The aim of the study was to identify the species affected by the illegal trafficking of wildlife received in a rescue center in the city of Guayaquil. For this, the records from 2018 to 2020 were collected, from which data were obtained on the origin of the rescue, the presence of injuries and their severity, and the percentage of mortality. Additionally, with the identification of the specimen, it was categorized according to the species, and its situation according to the red list of threatened species of the IUCN (International Union for the Conservation of Nature) and the red books of Ecuador. A total of 743 animals of different species were registered, the juvenile stage being the most frequent. These animals were received by confiscation and voluntary surrender. During this period there was a 10% mortality, with mammals showing the highest rate. According to the IUCN, most of the specimens are in the category of Least Concern, and according to the red books of Ecuador, birds and mammals were located in those of Least Concern and reptiles were registered Vulnerable in a higher proportion.El objetivo del estudio fue identificar las especies afectadas por el tráfico ilegal de fauna silvestre receptadas en un centro de rescate en la ciudad de Guayaquil. Para ello se recopilaron los registros del 2018 al 2020, de los que se obtuvieron datos de procedencia de rescate, presencia de lesiones y gravedad de las mismas, y el porcentaje de mortalidad. Adicionalmente, con la identificación del ejemplar, se categorizó según la especie, y su situación de acuerdo a la lista roja de especies amenazadas de la UICN (Unión Internacional para la Conservación de la Naturaleza) y los libros rojos del Ecuador.   Fueron registradas un total de 743 animales de diferentes especies, siendo el estadÃo juvenil el más frecuente.  Estos animales fueron receptados por decomiso y entregas voluntarias. Durante este perÃodo se presentó un 10% de mortalidad, siendo los mamÃferos los que presentaron dicha tasa más elevada. De acuerdo a la UICN, la mayorÃa de los ejemplares están en la categorÃa de Preocupación menor, y según los libros rojos del Ecuador, las aves y mamÃferos estuvieron situadas en los de Preocupación menor y los reptiles se registraron Vulnerables en mayor proporción
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