Who gave birth to PAC ?
In 1940, D.R. Hamilton published a paper [1] in which he treated
the theory of the directional correlation of a gamma-gamma cascade.
It took seven years before Brady and Deutsch successfully measured
such a correlation [2]. They had to work with Geiger counters that
combine low detection efficiency with a very bad time resolution
and no energy resolution at all, and it is really amazing that a
positive result was obtained with such rather primitive equipment.
The experimental conditions improved considerably when scintillation
detectors became available. From then on gamma-gamma angular
correlation experiments became a standard technique to determine
spins and parities of nuclear states.
It was soon realized that extranuclear fields may perturb - and sometimes completely wipe out - the angular correlation [3]. As a matter of fact, this property permitted the determination of the nuclear g-factor [4] and of the nuclear quadrupole moment [5], and offered a tool to investigate solid state properties [6]. Theory as well as experimental approach were improved step by step, by many scientists, and before long the first report on a time-differential perturbed angular correlation (PAC) measurement was presented [7].
It was soon realized that extranuclear fields may perturb - and sometimes completely wipe out - the angular correlation [3]. As a matter of fact, this property permitted the determination of the nuclear g-factor [4] and of the nuclear quadrupole moment [5], and offered a tool to investigate solid state properties [6]. Theory as well as experimental approach were improved step by step, by many scientists, and before long the first report on a time-differential perturbed angular correlation (PAC) measurement was presented [7].