Understanding Neutron Radiography

The film exposures can be reduced slightly by adding conversion screens of
paraffin, plastic, tantalum or lead. Fast neutron radiographs made by these
techniques display changes in metal specimen thickness in the range of 3 to
6 percent and have demonstrated a spatial resolution better than 1 mm.
Transfer detection is also used for fast neutrons. Some useful materials for
transfer conversion screens are summarized in Table 7.
It should be noted that the neutron reactions cited have threshold energies.
The reaction will not occur for energies lower than the threshold. This limits
the response of the detector to a portion of the neutrons that may be available,
thereby tending to increase the required exposure. On the other hand, since
scattered neutrons are oflower energy, the threshold response can be
valuable in eliminating radiographic detection of scattered neutrons.
Charlie Chong/ Fion Zhang