[en] Systematic photon scattering experiments have been performed to investigate E1 and M1 excitations below 4 MeV. This paper reports on the results of the experiments on M1 excitations in deformed rare earth nuclei. The polarization measurements on ¹⁴⁴Nd completed the investigation of the transitional Nd chain, yielding a very good agreement with the previously derived δ² dependence of total M1 strength. The investigation of deformed nuclei with an unpaired nucleon shows pronounced differences between the neighbouring Dy and Gd isotopic chains. While in ^163,161Dy a concentration of dipole excitations in the region of the scissors mode around 3 MeV is seen, in ^157,155Gd an extreme fragmentation is observed. (author)

No abstract available

[en] Short communication

[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] The method of Nuclear Resonance Fluorescence presents a powerful tool for nuclear spectroscopy. Through the availability of intense photon sources like bremsstrahlung and highly efficient γ-spectrometers this method was used successfully in the systematic investigation of dipole excitations during the last decade. The progress in increasing the sensitivity and the still remaining problems in determining precise information also in odd-A nuclei are discussed. (author)

[en] The widths of the 3089 keV and the 3684 keV levels in ¹³C are precisely measured using nuclear self-absorption and employing amorphous ¹³C absorbers and scatterers. The role of the effective temperature of carbon is discussed in some detail. The result for the 3089 keV level was found to be larger by about 25% than the compiled value

[en] A nuclear self-absorption measurement was carried out on the nucleus ²⁷Al with a bremsstrahlung photon-beam endpoint energy of 4.2 MeV. For a number of states, commonly used as calibration standards in photon-scattering (NRF) experiments, the self absorption was measured. Thereby the level widths and lifetimes were determined absolutely. In addition it was found that the level energy of the 2212.01-keV level deviates from the literature value

[en] A tunable gamma-ray source in the MeV energy range can be obtained by Compton scattering of discrete gamma rays emitted after thermal neutron capture in an in-pile target. Here we report on the principle, on the results of Monte Carlo simulations for the photon flux and on the first realization of such a tunable gamma-ray source at the ILL high flux nuclear reactor in Grenoble (France). Two strong primary gamma rays, with energies of 6.7 and 6.4 MeV, respectively, are produced (among others) by the ⁴⁸Ti(n,γ)⁴⁹Ti reaction. Compton scattering of these photons on a graphite target (scatterer) yields gamma rays of lower energy. Their energy is tunable between about 300 keV and 6 MeV by choosing the appropriate scattering angle. This tunable gamma-ray source could be a very useful tool to investigate photoexcitations in nuclei, which require gamma rays of several MeV. This new source might overcome the background problems present with bremsstrahlung sources, since it is a quasi-discrete and not a continuous source. Therefore, considerably less background is produced in the lower energetic part of the spectra. (orig.)

[en] The width of 3841-keV level in ¹⁷O was precisely measured in nuclear resonance fluorescence experiments performed at the Stuttgart Dynamitron facility. The result of Γ(3841 keV)=(92±6) meV is compared with upper limits quoted in the literature. Possible particle-hole configurations of the 3841-keV level are discussed

[en] A photon scattering experiment was performed on the γ-soft nucleus ¹³⁴Ba with photon energies of E_γ<4.1. Around 3 MeV excitation energy a fragmented 1⁺ scissors mode as well as the (2⁺circle-times 3^-)_1^- two-phonon dipole state were identified. The dipole excitation strengths were measured. The excitation strength of the scissors mode in this γ-soft nucleus is well reproduced by an empirical M1 sum rule that generalizes the open-quote open-quote δ² law close-quote close-quote to nuclei without axial symmetry. The IBM-2 describes the mixed-symmetry states in ¹³⁴Ba and their decay pattern. A large E2/M1 mixing ratio for the 1⁺→2⁺₁ decay of the scissors mode to the 2⁺₁ state is predicted by the IBM-2. The new result from ¹³⁴Ba together with a similar previous observation in ¹⁹⁶Pt corroborates the scissors mode as a typical excitation mode of γ-soft nuclei. copyright 1996 The American Physical Society