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For the time period from 1.5 to 4 Myr before the present we found in deep ocean ferromanganese crusts a ^{53}Mn excess concentration in terms of ^{53}Mn/Mn of about 4×10^{-14} over that expected for cosmogenic production. We conclude that this ^{53}Mn is of supernova origin because it is detected in the same time window, about 2.5 Myr ago, where ^{60}Fe has been found earlier. This overabundance confirms the supernova origin of that ^{60}Fe. For the first time, supernova-formed ^{53}Mn has been detected and it is the second positively identified radioisotope from the same supernova. The ratio ^{53}Mn/^{60}Fe of about 14 is consistent with that expected for a SN with a 11-25 M_{⊙} progenitor mass and solar metallicity.

The $^{58}\mathrm{Ni}(n,\ensuremath{\gamma})^{59}\mathrm{Ni}$ cross section was measured with a combination of the activation technique and accelerator mass spectrometry (AMS). The neutron activations were performed at the Karlsruhe 3.7 MV Van de Graaff accelerator using the quasistellar neutron spectrum at $kT=25$ keV produced by the $^{7}\mathrm{Li}(p,n)^{7}\mathrm{Be}$ reaction. The subsequent AMS measurements were carried out at the 14 MV tandem accelerator of the Maier-Leibnitz Laboratory in Garching using the gas-filled analyzing magnet system (GAMS). Three individual samples were measured, yielding a Maxwellian-averaged cross section at $kT=30$ keV of ${\ensuremath{\langle}\ensuremath{\sigma}\ensuremath{\rangle}}_{30\phantom{\rule{0.16em}{0ex}}\text{keV}}$ = 30.4 (23)${}^{\mathrm{syst}}$(9)${}^{\mathrm{stat}}$ mbarn. This value is slightly lower than two recently published measurements using the time-of-flight (TOF) method, but agrees within the uncertainties. Our new results also resolve the large discrepancy between older TOF measurements and our previous value.

With a half-life of 81.1$\phantom{\rule{0.16em}{0ex}}$Myr, ${}^{244}$Pu could be both the heaviest and the shortest-lived nuclide present on Earth as a relic of the last supernova(e) that occurred before the formation of the Solar System. Hoffman et al. [Nature (London) 234, 132 (1971)] reported on the detection of this nuclide ($1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}$ g ${}^{244}$Pu/g) in the rare-earth mineral bastn\"asite with the use of a mass spectrometer. Up to now these findings were never reassessed. We describe the search for primordial ${}^{244}$Pu in a sample of bastn\"asite with the method of accelerator mass spectrometry (AMS). It was performed with a highly sensitive setup, identifying the ions by the determination of their time-of-flight and energy. Using AMS, the stripping to high charge states allows the suppression of any molecular interference. During our measurements we observed no event of ${}^{244}$Pu. Therefore, we can give an upper limit for the abundance of ${}^{244}$Pu in our sample of the mineral bastn\"asite of 370 atoms per gram ($1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}$ g ${}^{244}$Pu/g). The concentration of ${}^{244}$Pu in our sample of bastn\"asite is significantly lower than the previously determined value.

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. A

We have made a new determination of the half-life of the radioactive isotope $^{60}\mathrm{Fe}$ using high precision measurements of the number of $^{60}\mathrm{Fe}$ atoms and their activity in a sample containing over ${10}^{15}$ $^{60}\mathrm{Fe}$ atoms. Our new value for the half-life of $^{60}\mathrm{Fe}$ is $(2.62\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\mathrm{yr}$, significantly above the previously reported value of $(1.49\ifmmode\pm\else\textpm\fi{}0.27)\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\mathrm{yr}$. Our new measurement for the lifetime of $^{60}\mathrm{Fe}$ has significant implications for interpretations of galactic nucleosynthesis, for determinations of formation time scales of solids in the early Solar System, and for the interpretation of live $^{60}\mathrm{Fe}$ measurements from supernova-ejecta deposits on Earth.

The s process synthesizes the elements between Fe and Sr in massive stars during two major evolutionary stages, convective core He burning and C shell burning. This scenario implies fascinating consequences for the chemical evolution of the star. For instance, the neutron capture rate at each isotope can have a big influence on the production of many of the subsequent higher mass isotopes. Correspondingly, one needs to know the (n,γ) cross sections of the involved isotopes with high accuracy in order to determine the abundance pattern reliably and to obtain a consistent picture of this stage. This contribution gives an overview on recent and future experiments for the Fe/Ni nucleosynthesis in massive stars. New results on 60Fe, 62Ni and 64Ni are reported. 60Fe is mostly produced during the short convective C shell burning phase, where peak densities of ∼1011 cm−3 are reached, prior to the SN explosion. The stellar (n,γ) cross section of 60Fe could be measured with a 1 μg sample obtained at PSI (Switzerlan...

The discovery of naturally occurring long-lived isomeric states (t_1/2 > 10^8 yr) in the neutron-deficient isotopes 211,213,217,218Th [A. Marinov et al., Phys. Rev. C 76, 021303(R) (2007)] was reexamined using accelerator mass spectrometry (AMS). Because AMS does not suffer from molecular isobaric background in the detection system, it is an extremely sensitive technique. Despite our up to two orders of magnitude higher sensitivity we cannot confirm the discoveries of neutron-deficient thorium isotopes and provide upper limits for their abundances., 3 pages, 1 figure

The strengths of resonances located at center-of-mass energies of ${E}_{c.m.}=189$, 304, 374, and 418 keV for the $^{25}\mathrm{Mg}$($p$,$\ensuremath{\gamma})$ reaction have been measured for the first time with an off-line method: Mg targets were firstly activated with protons at the resonance energies and the produced $^{26}\mathrm{Al}$${}^{g}$ nuclei were counted by means of highly sensitive accelerator mass spectrometry (AMS). Thus, the production of $^{26}\mathrm{Al}$ in its ground state is determined independently from the \ensuremath{\gamma}-decay branching ratio. While the 304, 374, and 418 keV resonances show fair agreement with previous measurements, the 189 keV resonance yield a significantly less strength. In addition, an experimental upper limit for the ${E}_{c.m.}=92$ keV resonance was determined.