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

Pocket chambers were approximately 4 - 5" long and 0.5" in diameter. An
aluminum rod (ca. 0.0625” in diameter) running along the chamber axis
served as one electrode, while the outer wall of the chamber served as the
other electrode. The central electrode was suspended at each end with a
polystyrene insulator and at one end it penetrated the insulator to serve as
the charging contact. One problem with the early models involved the
threaded caps that were used to protect the charging contact - they would
wear and the metal fragments would get on the insulator. The graphite
coating on the inside of the chamber wall caused a similar type of problem
with some of the early models because it would sometimes flake off and short
out the chamber. The early models were also susceptible to discharge as a
result of mechanical shock because the central electrode would flex and
contact the chamber wall. To solve this problem, later versions used a thicker
central electrode and/or positioned a small insulating disk in the center of the
electrode. Because of these problems, it was usual for a worker to wear two
dosimeters and the lower of the two readings was considered the most
accurate.
Charlie Chong/ Fion Zhang
http://www.orau.org/ptp/collection/dosimeters/pocketchamdos.htm