The n-value is an important superconducting parameter, which represents the homogeneity of characterized superconductor as well as thermally activated depinning. In addition n-values are important for the evaluation of pinning mechanisms and pinning forces. n-values are crucial input parameters for the numerical simulations of superconducting tapes, coils and other complicated superconducting applications where E-J power law applies. In this publication, complex measurement data of n-values from different 2 nd generation of high temperature superconducting (2G HTS) tapes are presented and analysed. In addition, 2G HTS tapes were step by step irradiated by fast neutron fluences up to 1x10 22 m-2. n-values of the irradiated tapes, containing additional randomly distributed pinning centres, are presented, analysed and compared with unirradiated samples. Special attention is placed on the underlying physics resulting in power-law part of the I-V curve and on the correlation between critical currents and n-values. The measurements are performed within the temperature range of 50 K-85 K and magnetic fields up to 15 T. I Introduction Each I-V curve of a superconducting sample contains a power-law part close to the transition to the dissipative state. This part of the I-V curve can be described by a simple equation: V/V c =(I/I c) n (1)