Draft:Pulse Shape Discrimination

Pulse Shape Discrimination (PSD) is a technique which is used to differentiate between the type of radiation by analyzing the shape of the pulse/signal that is detected.[1].

When a radiation is exposed to a scintillator, the radiation excites the molecules in the scintillating material of the detector to a higher energy state. These molecules return to the stable ground state by emitting a photon whose energy level is equal to the difference in energy between those states. The detected scintillation signal consists of two parts, the predominant part of the signal is from prompt fluorescence (returns directly to the ground energy state) while the remaining part is from delayed fluorescence (returns to the ground state through intermediate energy states, triplet states). Generally, the delayed fluorescence is higher in the heavier radiations like alpha, neutron and etc.

The decay time for delayed fluorescence is around a few hundred nanoseconds relatively longer than the decay time of the prompt fluorescence which is in a few nanoseconds. This causes an extended tail in the signals. This property can be used to differentiate the heavier particles from radiations like gamma, x-rays and beta rays. A study [2] was conducted using stillbene to understand the signal shapes for different radiation exposure, which concludes that the heavier the radiation in terms of mass, the larger the tail of the signal [3]

References

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  1. ^ Roush, M.L.; Wilson, M.A.; Hornyak, W.F. (December 1964). "Pulse shape discrimination". Nuclear Instruments and Methods. 31 (1): 112–124. Bibcode:1964NucIM..31..112R. doi:10.1016/0029-554X(64)90333-7.
  2. ^ Bollinger, L. M.; Thomas, G. E. (1 September 1961). "Measurement of the Time Dependence of Scintillation Intensity by a Delayed-Coincidence Method". Review of Scientific Instruments. 32 (9): 1044–1050. Bibcode:1961RScI...32.1044B. doi:10.1063/1.1717610.
  3. ^ Knoll, Glenn F. (2010). Radiation detection and measurement (4th ed.). Hoboken, NJ: Wiley. ISBN 978-0-470-13148-0.