[[File:Pacshowoff.png|thumb|right|upright=2|Nuclear probe in a lattice.]]
[[File:PAC-Spectroscopy-Schema.png|thumb|right|upright=2|Schema of PAC-Spectroscopy]]
The '''perturbed γ-γ angular correlation''', '''PAC''' for short or '''PAC-Spectroscopy''', is a method of nuclear solid-state physics with which [[magnetic field|magnetic]] and [[electric fieldsfield]]s in [[crystal structuresstructure]]s can be measured. In doing so, electrical field gradients and the [[Larmor frequency]] in magnetic fields as well as dynamic effects are determined. With this very sensitive method, which requires only about 10-100010–1000 billion atoms of a radioactive [[isotope]] per measurement, material properties in the [[local structure]], phase transitions, magnetism and diffusion can be investigated. The PAC method is related to [[nuclear magnetic resonance]] and the [[Mössbauer effect]], but shows no signal attenuation at very high temperatures.
Today only the time-differential perturbed angular correlation ('''TDPAC''') is used.
