[en] A system for the standartization of radioisotopes activity using liquid scintillator detector was developed. The system was set up at Nuclear Metrology Laboratory - L.M.N. (Nuclear Physics Division - IEA). The system performance was checked by absolute activity measurements for two radioisotopes, ⁶⁰Co and ²⁴¹Am. The activities were determined by the 4π(α, β-γ) coincidence method. An accuracy of the order of 99,8% was obtained. The results for ⁶⁰Co were compared with those obtained by 4πβ-γ coincidence method using a proportional counter at L.M.N., while the results for ²⁴¹Am were compared with those obtained through the linear extrapolation method using the same liquid scintillator. Compared to other systems, the advantages of this one are the simplicity and the short time spent in the sample preparation, and the negligible self-absorption. (Author)

[en] The hydrogen diffusion in the storage material Ti sub(0.8) Zr sub(0.2)CrMnH₃ has been studied in the temperature range of 260 to 360K, by means of the quasi-elastic neutron scattering technique. The experimental measurements have been performed using a high resolution backscattering spectrometer. The half widths at half maximum of the quasi-elastic line have been determined for momentum transfers in the range 0.24 to 1.85 A^-1. The data, corrected for multiple scattering effect, have been analysed in term of simple diffusion and jump diffusion models. From the diffusion coefficients determined at different temperatures, the following Arrhenius equation was obtained: D= (3+-1) x 10^-8 m²/s exp [-(220+-20 meV/kT] yielding a diffusion coefficient at room temperature of 6.0 x 10^-12 m²/s. This comparatively fast hydrogen diffusion is not the rate determining step in the absorption and desorption kinetics. The results at large momentum transfers show evidence for the existence of more than one component in the quasi-elastic spectra. This fact has been explained considering the diffusion governed by the existence of energetically different interstitial sites and by blocking effects due to the high hydrogen concentration. (Author)

[en] Published in summary form only

[en] By means of the neutron diffraction technique the texture of a maraging steel rolled sheet have been determined. The measurements were performed by using a neutron diffractometer installed at the IEA-PI Nuclear Research Reactor, in the beam-hole n⁰ 6. To avoid corrections such as neutron absorption and sample luminosity the geometric form of the sample was approximated to spheric and its dimensions do not exceed that of neutron beam. The texture of the sample was analysed with help of a computer programm that analyses the intensity of the diffracted neutron beam and plot the pole figure. (author)

[en] The study of dynamic behaviour of the crystalline structure is one of the most important applications of neutron inelastic scattering technique. As part of the neutron inelastic scattering program of IPEN Nuclear Physics Division, a triple axis crystal neutron spectrometer is built and, in order to verify operational conditions and performance of the instrument, measurements of the known dispersion relations of copper are performed. In connection with these recent improvements, it deals with focusing conditions in coherent neutron inelastic process in which a single quantum of vibrational energy (phonon) is exchanged between the neutron and the crystal. For the instrument focusing conditions attainment mathematical expressions were deduced taking into account the finite collimation, incident and scattered wave vectors, and interplanar spacing of the monochromator and the analyser crystals. The focusing conditions were graphically represented in order to have a practical and adequate routine procedure for the focusing of the spectrometer. An experimental test is made by measuring acoustic phonon peaks propagating in the /00xi/ symmetry direction of a copper crystal. The measurements were performed in focusing conditions such as: optimum, good and defocused; the agreement between experimental results and theoretical predictions shows the usefulness of the adopted graphical method. (Author)

[en] The track etching method has been employed for neutron radiography purposes, by making use of a cold neutron beam obtained at the IEA-R1 Nuclear Research Reactor. The films used were the Solid State Nuclear Track Detectors CN-85, CR-39, MAKROFOL-E and LR-115, with a natural Boron converter screen. In order to obtain mean track diameter about 3 μ with a minimum overlapping between them, adequate conditions for etching and exposure times about 30 minutes and 3 hours respectively were evaluated. For such conditions exposures of 10⁹ n/cm² that corresponds to 10⁷ track/cm² are achieved. Neutron radioagraphs of several materials were performed and the best results in terms of optical contrast, were obtained for the films CN-85 and CR-39. (author)

[en] The solid state nuclear track detectors technique has been used for determination of boron in aqueous solutions, using a filtered neutron beam. The particles tracks from the ¹⁰B(n,α)Li⁷ reaction were registered in the CR-39 film, chemically etched in a (30%) KOH solution 70⁰C during 90 minutes. The obtained results showed the usefulness of this technique for boron determination in the ppm range. The inferior detectable limit was 9 ppm. The combined track registration efficiency factor K has been evaluated in the solutions, for the CR-39 detector and its values is K= (4,60 -⁺ 0,06). 10 ^-4 cm. (Author)

[en] The gamma spectrometry technique has been used for masses determinations of uranium-233 and plutonium-239, granted by AERE-HARWELL. A high purity Ge semicondutor detector was used and the total efficiency curve was obtained for the counting system in the energy range 13 KeV to 135 KeV. The calculated values for the masses compared with that obtained by means of gravimetry technique. (author)

[en] Neutronradiography of several materials have been obtained at the IEA-R1 Nuclear Research Reactor (IPEN-CNEN/SP), by means of two conversion techniques: a) (n, α) at the beam-hole n⁰3 where a collimated thermal neutron beam, exposure area 4 cm x 8cm and flux at the sample 10⁵ n/s cm² is obtained. The film used was the CN-85 cellulose nitrate coated with lithium tetraborate (conversor). The time irradiation of the film was 15 minutes and in following was eteched during 30 minutes in a NaOH(10%) aqueous solution at a constant temperature of 60⁰C.; b) (n,γ) by using an experimental arrangement installed in the botton of the pool of the reactor. The flux of the collimated neutron beam is 10⁵ n/s/cm² at the sample and the conversion is made by means of a dysprozium sheet. The film used was Kodak T-5. The irradiation and the transfering time was 2 hours and 20 hours respectively. (author)

[en] By means of the neutron diffraction technique the texture of 5% and 98% rolled-aluminium and of iron-silicon steel used in the core of electric transformers, have been determined. The measurements were performed by using a neutron diffractometer installed at the IEA-R1 Nuclear Research Reactor, in the Beam-Hole N⁰6. To avoid corrections such as neutron absorption and sample luminosity the geometric form of the samples were approximated to spheric or octagonal prism, and its dimensions do not exceed that of the neutron beam. The texture of the samples were analysed with the help of a computer programme that analyses the intensity of the diffracted neutron beam and plot the pole figures. (author)