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Abstract: Ultra-weak resonances in nuclear reactions impose a challenge on experimentalists. The present work describes the setup used in the first direct measurement of extremely weak low energy resonances of the 18O(α, γ)22Ne reaction. A Clover HPGe detector in coincidence with specified energy windows in BGO counters covering a large solid angle, and combined with large plastic veto counters led to a significantly improved sensitivity, thus allowing for the clear identification of specific γ-transitions. Different modes of operation have been tested for optimizing the final experimental setup. [Copyright &y& Elsevier]

The neutron-capture cross sections of64Zn, 68Zn, and 70Zn have been measured with the activation technique in a quasistellar neutron spectrum corresponding to a thermal energy of kT = 25 keV. By a series of repeated irradiations with different experimental conditions, an uncertainty of 3% could be achieved for the 64Zn(n,&ggr;)65Zn cross section and for the partial cross section 68Zn(n,&ggr;)69Znm feeding the isomeric state in 69Zn. For the partial cross sections 70Zn(n,&ggr;)71Znm and 70Zn(n, &ggr;)71Zng, which had not been measured so far, uncertainties of only 16% and 6% could be reached because of limited counting statistics and decay intensities. Compared to previous measurements on 64,68Zn, the uncertainties could be significantly improved, while the 70Zn cross section was found to be two times smaller than existing model calculations. From these results Maxwellian average cross sections were determined between 5 and 100 keV. Additionally, the β-decay half-life of 71Znm could be determined with significantly improved accuracy. The consequences of these data have been studied by network calculations for convective core He burning and convective shell C burning in massive stars. [ABSTRACT FROM AUTHOR]

Since 1980 the 7Li(p,n)7Be reaction was intensively used for activation measurements. With a proton energy of the resulting neutron spectrum resembles a Maxwell-Boltzmann distribution with a thermal energy of . Therefore, this neutron source is ideal to determine Maxwellian-averaged neutron capture cross sections (MACS) close to a temperature of 250 million Kelvin () which is typical for the s process in red giant stars. Meanwhile, detailed stellar models indicate that the dominant neutron exposure of the main s-process component in low mass AGB stars occurs at a lower temperature of 90 million Kelvin (). Hence, the necessary stellar reaction rates had to be extrapolated from 25 keV to the lower thermal energy. In order to avoid the corresponding additional uncertainties, we report on the 18O(p,n)18F neutron source, which allows one to produce a Maxwell-Boltzmann spectrum close to the lower thermal energy of kT=8 keV. First results of activation measurements for 138Ba(n,γ)139Ba, 139La(n,γ)140La, and 175Lu(n,γ)176Lu m will be presented. [Copyright &y& Elsevier]

A gamma spectrometer composed of two Clover Ge detectors in close geometry is described. The advantages and drawbacks of the different modes of operation are investigated. The use of offline coincidence analysis for substantial background reduction is presented and an experimental approach for the determination of the summing correction factor is formulated. [Copyright &y& Elsevier]

An activation technique was used to investigate relative yields of fission products from the reaction 232Th(n, f ) for neutron energies between 1.3 and 1.8MeV covering the region around the first hyperdeformed resonances. Intensities of characteristic γ-ray transitions were analyzed to search for changes in the mass distribution for neutron energies corresponding to the resonances and below the resonances. Relative increases in yield between 7 and 23% are observed for A ≈ 100 and 132 in the resonance region around 1.6MeV. It is proposed that the yield enhancement of daughter nuclei of the preformed fragments 132Sn and 101Zr arises from cold fission of a di-cluster configuration. The experimental results support theoretical predictions for the existence of hyperdeformed octupole shapes based on the di-nuclear configuration 132Sn + 101Zr. [ABSTRACT FROM AUTHOR]

We report on new measurements of the 14C(n,γ)15C cross section with averaged neutron energies of 30, 150, and 500 keV using the fast cyclic activation technique. [Copyright &y& Elsevier]

The radiological safety of red meat irradiated with 7.5 MeV X-rays (bremsstrahlung) has been investigated theoretically and verified by dedicated experiments. Samples of meat and meat ash were located in a large volume of fresh meat at the position of the highest photoneutron fluence and irradiated to an X-ray dose of 15 kGy, twice the maximum dose allowed by the US FDA for meat irradiation. In order to evaluate the safety of treatment with any kind of electron accelerators, two experiments have been performed with different accelerators delivering electrons with a narrow and a broad energy spread.The measured activities and theoretical estimates are of the same order of magnitude. An evaluation of the corresponding radiation exposure from ingestion of the irradiated product has been compared to natural background radiation. The paper concludes that the risk to individuals from intake of food irradiated with X-rays from 7.5 MeV electrons, even with a broad energy spectrum, would be trivial. [Copyright &y& Elsevier]

Luminosity is a measure of the colliding frequency between beam and target and it is a crucial parameter for the measurement of absolute values, such as reaction cross sections. In this paper, we make use of experimental data from the ESR storage ring to demonstrate that the luminosity can be precisely determined by modelling the measured Rutherford scattering distribution. The obtained results are in good agreement with an independent measurement based on the x-ray normalization method. Our new method provides an alternative way to precisely measure the luminosity in low-energy stored-beam configurations. This can be of great value in particular in dedicated low-energy storage rings where established methods are difficult or impossible to apply. [ABSTRACT FROM AUTHOR]