Understanding Neutron Radiography Post Exam Reading VIII-Part 2a of 2A

Paralyzable Systems The top line of Fig. 12 illustrates a paralyzable system.
Resolving time τ follows each interaction, whether it is recorded or not.
Events that occur during resolving time τ are not recorded and further extend
the dead time by another period τ. The chart indicates only three recorded
events from the six interactions. In this case, τ increases with increased
number of interactions. It can be demonstrated that with a paralyzable system
(at increasingly higher interaction rates), the observed counting rates can
actually decrease with an increased number of events. When using a
counting system that may be paralyzable, extreme caution must be taken to
ensure that low observed counting rates correspond to low interaction rates,
rather than very high interaction rates with accompanying, long dead time. It
is possible for a paralyzable system to record the first interaction and then be
paralyzed, recording zero counts in high radiation fields.
Charlie Chong/ Fion Zhang