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.

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

The Hi/Oh/Recombination Line Survey Of The Inner Milky Way (Thor) - Survey Overview And Data Release 1

The past decade has witnessed a large number of Galactic plane surveys at angular resolutions below 20 `\u27. However, no comparable high-resolution survey exists at long radio wavelengths around 21 cm in line and continuum emission. Aims. We remedy this situation by studying the northern Galactic plane at similar to 20 `\u27 resolution in emission of atomic, molecular, and ionized gas. Methods. Employing the Karl G. Jansky Very Large Array (VLA) in the C-array configuration and a large program, we observe the HI 21 cm line, four OH lines, nineteen Hn alpha radio recombination lines as well as the continuum emission from 1 to 2 GHz in full polarization over a large part of the first Galactic quadrant. Results. Covering Galactic longitudes from 14.5 to 67.4 deg and latitudes between +/- 1.25 deg, we image all of these lines and the continuum at similar to 20 `\u27 resolution. These data allow us to study the various components of the interstellar medium (ISM): from the atomic phase, traced by the HI line, to the molecular phase, observed by the OH transitions, to the ionized medium, revealed by the cm continuum and the Hn alpha radio recombination lines. Furthermore, the polarized continuum emission enables magnetic field studies. In this overview paper, we discuss the survey outline and present the first data release as well as early results from the different datasets. We now release the first half of the survey; the second half will follow later after the ongoing data processing has been completed. The data in fits format (continuum images and line data cubes) can be accessed through the project web-page. Conclusions. The HI/OH/Recombination line survey of the Milky Way (THOR) opens a new window to the different parts of the ISM. It enables detailed studies of molecular cloud formation, conversion of atomic to molecular gas, and feedback from HII regions as well as the magnetic field in the Milky Way. It is highly complementary to other surveys of our Galaxy, and comparing the different datasets will allow us to address many open questions

Galactic Supernova Remnant Candidates Discovered By Thor

There is a considerable deficiency in the number of known supernova remnants (SNRs) in the Galaxy compared to that expected. This deficiency is thought to be caused by a lack of sensitive radio continuum data. Searches for extended low-surface brightness radio sources may find new Galactic SNRs, but confusion with the much larger population of H II regions makes identifying such features challenging. SNRs can, however, be separated from H II regions using their significantly lower mid-infrared (MIR) to radio continuum intensity ratios. Aims: Our goal is to find missing SNR candidates in the Galactic disk by locating extended radio continuum sources that lack MIR counterparts. Methods: We use the combination of high-resolution 1-2 GHz continuum data from The HI, OH, Recombination line survey of the Milky Way (THOR) and lower-resolution VLA 1.4 GHz Galactic Plane Survey (VGPS) continuum data, together with MIR data from the Spitzer GLIMPSE, Spitzer MIPSGAL, and WISE surveys to identify SNR candidates. To ensure that the candidates are not being confused with H II regions, we exclude radio continuum sources from the WISE Catalog of Galactic H II Regions, which contains all known and candidate H II regions in the Galaxy. Results: We locate 76 new Galactic SNR candidates in the THOR and VGPS combined survey area of 67.4° \u3e ℓ \u3e 17.5°, | b | ≤ 1.25° and measure the radio flux density for 52 previously-known SNRs. The candidate SNRs have a similar spatial distribution to the known SNRs, although we note a large number of new candidates near ℓ ≃ 30°, the tangent point of the Scutum spiral arm. The candidates are on average smaller in angle compared to the known regions, 6.4\u27 ± 4.7\u27 versus 11.0\u27 ± 7.8\u27, and have lower integrated flux densities. Conclusions: The THOR survey shows that sensitive radio continuum data can discover a large number of SNR candidates, and that these candidates can be efficiently identified using the combination of radio and MIR data. If the 76 candidates are confirmed as true SNRs, for example using radio polarization measurements or by deriving radio spectral indices, this would more than double the number of known Galactic SNRs in the survey area. This large increase would still, however, leave a discrepancy between the known and expected SNR populations of about a factor of two

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

Inclusión de harina de Moringa oleifera en dietas para pollos de engorde

The purpose of the inclusion of M. oleifera leaf meal in diets for broilers was to determine its effect in relation to weight gain. Fifteen chickens of Broiler cobb 500 breed with an initial average weight of 45 g, were used. The methodology consisted in a completely randomized experimental design (DCR), distributed in three treatments with five repetitions. The treatments were T1: balanced commercial diet, T2: balanced diet with moringa flour at 7%, and T3: balanced diet with moringa flour at 15%. The weekly weights of each group were recorded, up to 42 days. The results showed that the addition of 7% M. oleifera flour is a viable supplement to implement in diets based on commercial balanced foods, well tolerated, achieving an increase in the final weight of the birds.El propósito de la inclusión de la harina de M. oleífera en dietas para pollos de engorde fue determinar su efecto en relación a la ganancia de peso. Se utilizaron 15 pollos Broiler cobb 500 con un peso promedio inicial de 45 g. La metodología empleada fue un diseño experimental completamente al azar (DCA), distribuido en tres tratamientos con cinco repeticiones. Los tratamientos fueron T1: balanceado comercial, T2: balanceado con harina de moringa al 7%, y T3: balanceado con harina de moringa al 15%. Se registraron los pesos semanales de cada grupo, hasta los 42 días. Los resultados evidenciaron que la adición de M. oleífera al 7% constituye una materia prima viable para implementarla en dietas basadas en balanceados comerciales, siendo bien tolerado y logrando un incremento significativo en el peso final de las aves

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

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 Científicas 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