Nuclei display many diverse modes of excitation. It is sometimes possible to interpret the behaviour of the nuclear system in terms of the motion of individual particles while in other cases it shows correlated collective behaviour such as rotations or vibrations of the nucleus as a whole or the movement of surface waves around it. As a consequence there are different models needed to describe the many features observed in nuclei.
The interplay between the different degrees of freedom in a nucleus can be studied by investigating the processes of either its excitation or de-excitation as characterized via the measurement of the gamma transitions involved. The most crucial information is thereby obtained from absolute transition rates which are related to the knowledge of the state lifetimes. Measured lifetimes provide a sensitive test of the validity of different theoretical approaches.
The GRID method can be applied to all nuclei which can be reached by thermal neutron capture. In exceptional cases nuclei with up to 2 neutrons beyond stability have been studied. Examples for lifetime studies concern for instance the observation of mixed symmetry states in ⁵⁴Cr, the investigation of multiphonon excitations in medium heavy nuclei like ¹¹⁴Cd, the determination of quadrupole-octupole coupled states in ¹⁴⁴Nd and the search for multiphonon excitations in heavy deformed nuclei like ¹⁶⁸Er.

The main difficulty of the method concerns the often sparsely know feeding of a given level (needed to describe the initial recoil velocities). This can be overcome by simulating it with statistical models or by extracting upper and lower lifetime limits which depend on extreme feeding assumptions about the population routes and intensities.

Ref.: Genilloud L., Jolie J., Boerner H.G., Lehmann H., Becvar F., Krticka M., Zamfir N.V., Casten R.F.; Physical Review C 62, 034313-1-034313-8 (2000)