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[en] Preliminary measurements of the charge equilibrium fraction for the negative component are presented for a He⁺ beam traversing a 2 μ/cm² carbon foil. This fraction decreases with energy with a value of about 2.5 x 10^-4 at 60 keV and about 1 x 10^-4 at 250 keV

[en] We have measured, for nickel isotopes, several threshold reaction cross sections averaged over a ²³⁵U fission neutron spectrum. The measured reactions, and corresponding averaged cross sections found, are the following: ⁶⁰Ni(n,p)^60mCo, 1.499 ± 0.083 mb; ⁶¹Ni(n,p)⁶¹Co, 1.632 ± 0.096 mb; ⁵⁸Ni(n,2n)⁵⁷Ni, 4.72 ± 0.26 μb; ⁵⁸Ni(n, d+np+pn)⁵⁷Co, 275 ± 15 μb; ⁵⁸Ni(n,p)^58gCo, 74.8 ± 2.3 mb; and ⁵⁸Ni(n,p)^58mCo, 36.6 ± 1.2 mb; all referred to the well-known standard of 111 ± 3 mb for the ⁵⁸Ni(n,p)^58m+gCo-averaged cross section. The measured cross sections are of interest in nuclear engineering for the characterization of the fast neutron component in the energy distribution of reactor neutrons

[en] The ²³⁵U fission neutron spectrum averaged cross section for the ⁵⁰Ti(n,α)⁴⁷Ca reaction was experimentally determined by irradiation of titanium with reactor neutrons. A value of (9.7±1.1) μb was found for this cross section, using (307±11)μb for the ⁴⁸Ti(n,p)⁴⁸Sc spectrum-averaged cross section that was used as a standard. The ⁵⁰Ti(n,α)⁴⁷Ca spectrum-averaged cross section was also semiempirically evaluated by numerically integrating, through the ENDF/B-V representation of the ²³⁵U fission neutron spectrum, the available experimental differential cross section data. (author)

[en] The reaction cross sections averaged over a ²³⁵U fission neutron spectrum have been measured for the ⁴⁵Sc(n,α)⁴²K, ⁴⁵Sc(n,2n)⁴⁴Sc^g, and ⁴⁵Sc(n,2n)⁴⁴Sc^m threshold reactions. The values found for these cross sections are, respectively: 308 ± 16 μb, 27.3 ± 1.3 μb, and 22.0 ± 1.7 μb, using 111 ± 3 mb as the averaged cross section for the ⁵⁸Ni(n,p)⁵⁸Co^m+g reaction that was used as a standard. To the authors' knowledge, these are the first experimental determinations of the ⁴⁵Sc(n,2n)⁴⁴Sc^g and ⁴⁵Sc(n,2n)⁴⁴Sc^m spectrum-averaged cross sections, which were measured using a new method for the case when both the ground and an isomeric state are generated. By fitting with a suitable function the experimental differential cross sections found in the EXFOR data file for each of these reactions, the corresponding spectrum-averaged cross sections have been calculated for nine different analytical representations of the ²³⁵U fission neutron spectrum. This calculation was also performed for the representation based on the Madland-Nix model of prompt fission neutrons. The agreement between calculated and measured values is in general excellent for the ⁴⁵Sc(n, α)⁴²K low-threshold reaction. However, the agreement is rather poor for the ⁴⁵Sc(n,2n) high-threshold reactions, except for two, Maxwellian-type, representations tried

[en] One of the responsibilities of the Laboratory of Analysis by Neutronic Activation of the RA-6 reactor is to determine the burn-up in fuels of the MTR type. In order to gain experience, up to the arrival of the hyperpure Germanium detector (HPGe) to be used in normal operation, preliminary measurements with a crystal of INa(Tl) were made. The fuel elements used are originated in the RA-3 reactor, with a decay superior to the thirteen years. For this reason, the unique visible photoelectric peak is the one of Cs-137, owing to the low resolution of the INa(Tl). After preliminary measurements, the profiles of burn-up, rectified by attenuation, were measured. Once the efficiency of the detector was determined, the calculation of the burn-up was made; for the element No. 144, a value of 21.6 ± 2.9 g was obtained to be compared with the value 21.9 g which was the evaluation made by the operators. (Author)

[en] The reaction cross sections averaged over a ²³⁵U fission neutron spectrum have been measured for the ⁵⁴Fe(n, 2n)^53gFe and ⁵⁴Fe(n, 2n)^53mFe threshold reactions. The values found are, respectively: (1.14 ± 0.13) μb, and (0.52 ± 0.16) μb. The measured cross sections are referred to the (111± 3) mb standard cross section of the ⁵⁸Ni(n, p)^58m+gCo reaction. The (81.7 ± 2.2) mb standard cross section value for the ⁵⁴Fe(n, p)⁵⁴Mn reaction, was also used as a monitor to check the results obtained with the Ni standard, leading to an excellent agreement. (author)

[en] The fission neutron spectrum averaged cross-sections for the reactions ⁷⁰Ge(n,p) ⁷⁰Ga and ⁷⁴Ge (n,p) ⁷⁴Ga have been determined. The averages of four determinations are, respectively, (3.10±0.30) mb and (0.00938±0.00059) mb. The present values are, to the authors' knowledge, the first experimental data on the fission averaged cross-section for these reactions. (author). 6 refs., 2 tabs

[en] River bed sediment and suspended lead samples were collected from pristine and human disturbed areas at Nahuel Huapi National Park, North-Western Patagonia, Argentina. The present work aims to obtain baseline heavy metal concentration values in the region and to study the impact of human activities in the riverine systems. The identification of the sediments origin was achieved by studying the rare earth and other immobile elements behavior. The elemental concentration determinations were performed by means of Instrumental Neutron Activation Analysis (INAA) at RA-6 research reactor, complemented by Atomic Absorption Spectrophotometry. A leaching study with HCl 0.5 N and 3.5 N was performed to discriminate the total non residual (TN-R) of the following heavy metals: Cu, Pb, Ni, Zn, Mn and Fe. Speciation procedures were applied for fluvial sediments determining the adsorbed metals associated with the organic matter and with Fe and Mn oxides. Cu an Pb are mainly associated to Fe and Mn oxides, although Pb maintains this behaviour along the river (except in one association with organic matter while approximating to the river mouth in the urban areas. Heavy metal enrichment factors were calculated for rivers and streams flowing in urban and peri urban areas, showing values of Cr, Cu, Pb and Zn factors above the baseline. (author). 17 refs., 3 figs., 1 tabs

[en] Two 200-hour irradiations were programmed for a certain experiment in the RA-6 Reactor in Bariloche, Argentina. Taking advantage of these long irradiations, several commercial wires of high purity materials were also irradiated and analysed. The wires analyzed, which are frequently used in different applications in the nuclear area, were: Ti, Nb, Mo, and the alloys Mn-Cu (80.2%). Co-Al (0.116%) and Au-Al (0.112%). This long-irradiation instrumental-neutron-activation-analysis made possible a determination, with low detection limits, of the concentration of long lived isotope impurities. These measurements were complemented with short irradiations of the same wires to determine the concentration of short lived isotope impurities. The results show, on the one hand, differences with the concentrations given by the supplier for some elements in the Material Data Sheet supplied with each material, and on the other hand, the existence of some impurities not report by the supplier. (author). 1 ref, 7 tabs