High-resolution gamma-ray spectroscopy

To obtain the highest possible resolution in a measurement has always been one of the major challenges for experimental physicists because increased resolution generally results in progress. At the Institut Laue-Langevin, gamma rays emitted after neutron capture can be recorded with parts-permillion resolution. This is achieved by diffracting the gamma rays on highly perfect Sior Ge crystals. Precise measurement of the Bragg angles and the crystal lattice spacings permits the determination of wavelengths or energies. This outstanding resolving power allows the measurement of extremely small Doppler effects caused by the emission of primary gamma rays. These so-called gamma-ray-induced Doppler broadening measurements have given rise to applications in both nuclear and condensed matter physics.