A four-detector time differential perturbed angular correlation spectrometer is built based on the original rotating three-detector spectrometer in order to improve the accuracy and reliability of the measurement and to increase the coincidence efficiency. The spectrometer possesses the advantages of high coincidence efficiency

good differential non-linearity and independance of the measurement upon detector efficiencies. It has a time resolution better than 1.5 ns

a differential non-linearity of less than ± 2.5% and a good stability for a long time operation. The spectrometer has been used in the study of quadrupole interaction and the study of structure and phase transition in materials. Satisfactory results have been obtained.