[en] During the last years we have aimed at utilizing the high energy achievable at the Munich MP Tandem (TV=14 MV) for maximum sensitivity. One of our interests is the measurements of radionuclides around A=60 (⁵³Mn, ⁶⁰Fe, ⁶³Ni) because of their high scientific potentials. However, in this mass region there are usually strong limitations in sensitivity due to a large isobaric background. Its suppression is performed by means of a gas-filled magnet and a multi ΔE ionization chamber. A Wien filter and a time-of-flight path allow a further suppression of (non-isobaric) background. The optimization of the setup as a whole yielded detection limits of ⁵³Mn/Mn ∼2x10^-1463Ni/Ni ∼2x10^-14 and ⁶⁰Fe/Fe ∼2x10^-16, which presently cannot be achieved by any other detection method. The overall efficiency (including ion source) is typically 10^-5-10^-4. The gas-filled magnet allows an efficient reduction of the detector counting rate by more than three orders of magnitude. Therefore, relatively high negative ion currents and thus short times for the measurements are possible

[en] The high sensitivity of the accelerator mass spectrometry (AMS) method has been utilized to measure the extremely low yields for super asymmetric neutron-induced fission of uranium. From a high level radioactive waste concentrate (HAWC) of the reprocessing plant WAK in Karlsruhe, Germany, iron has been chemically extracted and investigated by means of AMS for possible ⁶⁰Fe from nuclear fission. The fission yield is masked due to the competing ⁶⁰Fe production via double neutron capture on ⁵⁸Fe. Therefore, only an upper limit for the A=60 fission chain yield of 1x10^-8% could be determined. To estimate this branch, the cross section for the ⁵⁹Fe(n, γ)⁶⁰Fe reaction has been measured to (6.0±1.3) barn

[en] The measurement of long-lived radionuclides, produced by neutrons originating from the atomic-bomb explosions, offers the possibility to reconstruct neutron fluences to which survivors in Hiroshima and Nagasaki were exposed. The long-lived radionuclide, ⁴¹Ca (T_1/2=103 000 years), is suggested here as a means for a retrospective determination of thermal neutron fluences, directly within the human body of a survivor. As proper material tooth enamel is proposed. The ⁴¹Ca signal in tooth enamel may be correlated with the exposure to A-bomb induced thermal neutron fluences, provided the natural background level of ⁴¹Ca/Ca is significantly lower. Therefore, tooth samples of unexposed survivors of the A-bomb explosions have been examined by means of accelerator mass spectrometry, in order to quantify the natural background level of ⁴¹Ca/Ca. Measured ⁴¹Ca/Ca ratios were confirmed to be as low as about 2 x 10^-15. Thus, the A-bomb induced additional signal should be detectable for survivors at epidemiological relevant distances. Since tooth enamel had already been used as a dosemeter for gamma radiation from the A-bomb explosion, the detection of ⁴¹Ca in tooth enamel would allow, for the first time, an assessment of both, γ-ray and neutron exposures in the same biological material

[en] Integral cross sections of the nuclear reactions ^natFe(p,x)⁵³Mn, ^natNi(p,x)⁵³Mn and ^natNi(p,x)⁶⁰Fe up to proton energies of 2.6 GeV were measured by means of accelerator mass spectrometry. Additionally, elemental production rates from targets placed in an isotropically irradiated iron sphere were determined. They provide the basis to calculate the corresponding neutron-induced cross sections. Both types of nuclear data are needed for the calculation of depth- and size-dependent production rates of the long-lived cosmogenic radionuclides, which gives us the possibility to discuss experimental abundances of ⁵³Mn and ⁶⁰Fe in extraterrestrial matter

[en] For a search of supernova-produced actinide atoms in terrestrial archives, techniques for measuring minute amounts of atoms of actinides with AMS have been developed at the Munich tandem accelerator laboratory. A large analyzing magnet has been installed, able to bend even the heavy transuranic ions at the high energies achievable with our MP tandem. The final detector is a time-of-flight and a multiple energy loss measurement which allows a nearly background-free detection of individual actinides like ²⁴⁴Pu. An efficient chemical preparation method has been developed for the extraction of small amounts of plutonium from samples up to nearly 1 kg. Furthermore, the preparation of sputter cathodes, containing the final sample material, was optimized for high yields of negative molecules in the Cs-sputter ion source. The first search for supernova-originated ²⁴⁴Pu in a deep sea ferromanganese crust has already been carried out

[en] Measuring the resonance strengths of the ²⁵Mg(p,γ)²⁶Al reaction at energies of astrophysical interest poses a very difficult task for the usual prompt γ-ray detection method. Here we describe an alternative method in which targets are first irradiated and the produced ²⁶Al nuclei are off-line counted by means of AMS. An overall efficiency of 4 x 10^-5 could be achieved extracting AlO^- from the ion source. For this purpose, a careful chemical treatment of the samples and the use of a gas filled magnet were necessary

[en] The detection of ⁶³Ni (T_1/2=100.1 yr) by means of accelerator mass spectrometry (AMS) using a gas-filled magnet (GFM) is described. The experimental setup includes a dedicated ion source, a 14 MV MP tandem, a GFM and a multi-anode ionization chamber. First results indicate a background level of ⁶³Ni/Ni ratios as low as 2x10^-14. This sensitivity will allow - for the first time ever - to detect ⁶³Ni induced by fast neutrons in copper samples from Hiroshima and Nagasaki, even for distances beyond 1500 m from the hypocenters. Thus, it will be possible to reconstruct experimentally the neutron doses of the A-bomb survivors from Hiroshima and Nagasaki

No abstract available

[en] Despite the emission of only low energy Auger electrons (ca. 3.6 keV) and the difficulty of obtaining a certified standard, Liquid scintillation counting (LSC) determinations are still reasonable options for a radioanalytical laboratory involved in nuclear installation decommission. Besides, accelerator mass spectrometry (AMS), being the most sensitive analytical technique not only for ⁴¹Ca, is gaining increasingly broader accessibility and applicability. Herein, we present a radiochemical separation procedure developed for ⁴¹Ca determination with LSC and AMS in varying materials (i.e. water, concrete, sediment, soil, and biota). The radioanalytical isolation consists of anion exchange and extraction chromatography as well as carbonate precipitation and recrystallization from organic solvents. Thereby, interfering radionuclides as ⁵⁵Fe, ⁶⁰Co, ¹⁵²Eu, U or actinides are removed with decontamination factors of 10²-10⁴. Quench curves for determining the measurement efficiency is generated with a ⁴¹Ca solution gained from the ⁴¹Ca/⁴⁰Ca certified reference material ERM-AE701. In routine application the procedure is characterized by chemical yields of 67-86 %, measurement efficiencies of 1-10 % and detection limits of 0.05 Bq g^-1 and 0.3 Bq L^-1. Aliquots of the digestion solutions of LSC can be easily converted into CaF₂-AMS targets by successive oxalate and fluoride precipitation. Pros and cons for both measurement techniques are addressed based on ⁴¹Ca results from LSC and AMS for the same material. (author)

[en] The discovery of naturally occurring long-lived isomeric states (t_1/2>10⁸ yr) in the neutron-deficient isotopes ^{211,213,217,218}Th[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