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We measured the O-17(n,alpha) C-14 reaction cross section from subthermal up to about 350 keV neutron energy. Two distinct resonances were observed at 178 and 253 keV, respectively, and a bump in our data near 2 keV could be explained by the presence of a negative-energy p-wave resonance. In the lower energy region, the cross section was shown to have a 1/v shape. The O-17(n, alpha) C-14 reaction is of importance in two different applications: it is one of the major reactions responsible for the C-14 pollution in nuclear reactors. Also, this reaction plays a role in primordial and nucleosynthesis in various astrophysical scenarios. For this application, the reaction rate at astrophysically relevant temperatures was calculated.

Suitable O-17 samples are required for the study of the O-17(n,alpha)C-14 reaction with various detectors, The electrospraying of metal oxides enriched in O-17 onto an Al substrate yielded negative results: no O-17(n(th),alpha) reactions were observed when irradiating these samples with thermal neutrons, These tests demonstrated the need to minimize the B-10 content in sample and backing, since the B-10(n(th),alpha(1)) reaction causes a strongly disturbing background. Good results were obtained in the reactor experiments using gaseous samples (O-17 enrichments of 58.2%, 72.1% and 85.5%) with a dedicated experimental setup. The experimental conditions being quite different at accelerators, an alternative method was developed to prepare samples suited for use in ionization chambers, For this purpose, O-17 ions were implanted in ultra-pure Al foils. The thickest sample prepared in this way contains 8 x 10(18) atoms of O-17, with a B-10/O-17 ratio of 10(-4). (C) 2001 Elsevier Science B.V. All rights reserved.

A first experimental study of the neutron induced charged particle reactions on (37)A and Ar-39 as a function of the neutron energy has been made. Therefore, complementary measurements were performed with thermal neutrons at the High Flux Reactor of the ILL (Grenoble, France) and with resonance neutrons at the GELINA neutron spectrometer of the IRMM (Geel, Belgium). The stellar cross sections, which were calculated from the obtained data, show important discrepancies with the theoretical values used in recent network calculations.

The Ar-37(n, p)Cl-37 and Ar-37(n, alpha)S-34 reactions were studied for the first time as a function of the neutron energy at the neutron spectrometer GELINA at the IRMM in Geel (Belgium). For the Ar-37(n, alpha)S-34 reaction, cross section data were obtained covering the neutron energy region from 10 meV up to 100 keV, but the sensitivity was too low to observe the Ar-37(n, p)Cl-37 reaction. In the low energy region, the (n, alpha) cross-section was shown to have a 1/v shape, while in the keV region several resonances were determined and subsequently analysed. Finally, the Maxwellian averaged cross section value was calculated at astrophysically relevant temperatures. (C) 2000 Elsevier Science B.V. All rights reserved.

Item does not contain fulltext, When solid objects are viewed from only one direction, some parts are necessarily occluded. Expectations about possible completions of novel objects (cubes with indentations) were measured by the response times to determine whether two images could be two depth-rotated views from the same object. Completions are considered global if the completed indentations are identical to the visible indentations (i.e., they are globally simple because of the repetitions) and are considered local if they are locally simple (e.g., straight contours with a minimal number of additional surfaces). The results of three experiments show that local and global completion tendencies which were well-established for two-dimensional surfaces appear valid for three-dimensional objects as well. Additionally, it is shown that structural object aspects play an important role in object completion.

The 37Ar(n_th,alpha)34S and 37Ar(n_th,p)37Cl reactions were studied at the high flux reactor of the ILL in Grenoble. For the 37Ar(n_th,alpha_0) and 37Ar(n_th,p) reaction cross sections, values of (1070+/-80)b and (37+/-4)b, respectively, were obtained. Both values are about a factor 2 smaller than results of older measurements. The observed suppression of the 37(n_th,alpha_1) transition could be verified from theoretical considerations. Finally, evidence was found for the two-step 37Ar(n_th,gamma-alpha) process. Comment: 11 pages, 5 figures, accepted for publication in Nuclear Physics A