[en] When a nucleus undergoes beta decay via the electron capture reaction, it emits an electron neutrino. The neutrino emission gives a small recoil to the atom, which can be experimentally observed as a Doppler broadening on subsequently emitted gamma rays. Using the two-axis flat-crystal spectrometer GAMS4 and the electron capture reaction in ¹⁵²Eu, the motion of atoms having an excess kinetic energy of 3 eV in the solid state was studied. It is shown how the motion of the atom during the first hundreds of femtoseconds can be reconstructed. The relevance of this knowledge for a new neutrino helicity experiment is discussed

[en] The Crystal-GRID method is used to study interatomic collisions at low energy in metals and such to probe the repulsive interatomic potential. Line shapes of gamma rays, emitted by the recoiling ⁵⁹Ni isotope after thermal neutron capture in Ni single crystals, were measured and compared to results obtained by molecular dynamics simulations of the slowing down. The same procedure is also used for recoiling ⁵⁷Fe and ⁵⁴Cr atoms in Fe and Cr single crystals, respectively. Different potentials (including several from the embedded atom method) are investigated using the observed fine structure of the line shape which depends on the crystal orientations. From the detailed study of the lineshapes measured in two different orientations, a new potential is then derived for each element. Nuclear state lifetimes for the excited isotopes are also deduced with a higher precision than obtained with standard nuclear techniques

[en] Prompt gamma-ray activation analysis (PGAA) is a nuclear analytical technique for the determination of trace and other elements in solid, liquid or gaseous samples. The method consists in observing gamma rays emitted by a sample during neutron irradiation. Of particular importance for PGAA is the measurement of boron. Indeed, this technique gives the opportunity to detect boron concentration down to the ppm or ppb level depending on the sample matrix. Furthermore, boron cannot be easily measured by other methods without risks of contamination. Trace analysis of boron in liquids has been performed and characterized at the PGA facility of the neutron spallation source SINQ (Paul Scherrer Institute, Switzerland). First, a calibration curve was determined with standard boron solutions. Then, the PGAA was applied for the determination of boron in geological water samples. The results were compared with ICP-MS measurements. Finally, the method yielded promising results to measure the concentration of boron taken up by cells in a new treatment for rheumatoid arthritis

[en] The goal of this study was to develop a method to quantitatively assess the structural shielding performance of computed tomography (CT) rooms in Switzerland. The method was based on the comparison between calculated maximum allowed ambient dose rate (DR) and measured ambient DR in adjacent spaces. If the measured DR exceeds the calculated maximum allowed value, additional shielding is required; otherwise the shielding is sufficient. The maximum allowed ambient DR was calculated using two different shielding concepts either based on the tube loading of the scanner or on the accumulated dose length product of the scans. The method was validated for 36 spiral CT head protocols. The average ratio of the maximum allowed ambient DR between both concepts was 1.11 (range 0.57-2.14). Among 36 CT rooms, 7 room boundaries were insufficiently shielded. In conclusion, this method allows the authority to check on-site the compliance of the structural shielding with legal requirements. (authors)

[en] The international recommendations the Swiss legislation on radiation protection in force is based on are outdated and have been replaced in 2007. The new recommendations should be transposed into national law, also in Switzerland, since legislation on radiation protection in Switzerland is supposed to base on current scientific evidence. Since 2011 eleven ordinances are being revised and adapted to international recommendations in a revision project. The consultations should be conducted in 2014. (orig.)

[en] The motion of atoms in single-crystal metals is studied by the observation of the Doppler-broadened line-structure formed when the nuclei decay while recoiling. The recoil is imparted to the nucleus by the emission of gamma rays following thermal neutron capture. The high resolution gamma-ray spectrometer GAMS4 and molecular dynamics simulations of the slowing down of atoms in oriented crystals provide information on interatomic potentials. Three transition metals (Ni, Fe, Cr) were studied and two nuclear levels in each element were analyzed. (authors)

[en] Ten years ago it was proposed that the Gamma Ray Induced Doppler broadening (GRID) method could be used to study interatomic potentials in solids. Recently, this possibility was developed into a powerful technique due to the combination of Molecular Dynamics simulation techniques with the use of oriented single crystal targets. A systematic study of interatomic potentials in metals will be presented. High quality Crystal-GRID data on pure Ni, Fe and Cr were obtained using the GAMS4 spectrometer at the High Flux Beam reactor of the Institut Laue Langevin in Grenoble (France). Fits of the pronounced fine structures on the measured lineprofiles permitted the verification of several interatomic potentials proposed for these metals as well as the extraction of a new interatomic potential. An outlook to further applications in solid state physics of this technique is also presented

[en] The possibility to create a tunable gamma-ray source using two different approaches has been investigated. The first source relies on crystal diffraction and uses bremsstrahlung produced by electrons from the 15 MeV linear accelerator of the university of Ghent. It delivers very well defined monochromatic gamma-ray beams with energies between 80 and 1000 keV. The second approach uses Compton scattering of gamma-rays with a poorer energy resolution but a higher intensity. Some applications of these sources are described. (author)

[en] A direct measurement of a tantalum/graphite bremsstrahlung source, observed under three different angles, was realised with a germanium detector. This experiment was conducted using the 15 MeV linear electron accelerator of the University of Ghent and a full energy spectrum was obtained. This kind of data, which is fairly important in many fields such as dosimetry, medicine, etc., has been rarely analysed by means of a direct measurement. The results are compared with a Monte Carlo simulation to verify their exactness. (orig.)

[en] The motion of atoms caused by neutrino emission following electron capture is observed in EuO crystals by measuring the Doppler shift of subsequently emitted gamma rays. The slowing down of the recoiling atom, which depends on the forces exerted by other atoms in the crystal, is calculated by molecular dynamics simulations using different interatomic potentials. The comparison between measured and simulated gamma-ray line shapes opens the way to a precise determination of the interatomic potential and of the lifetime of the nuclear state. copyright 1997 The American Physical Society