R 333.5493 Measurements.

Rule 493. (1) Compliance with the exposure rate limit specified in R 333.5492 (1) shall be determined by measurements averaged over an area of 100 square centimeters with no linear dimension exceeding 20 centimeters. (2) Measurements of exposure rates from tubes in enclosures from which the tubes cannot be removed without destroying the function of the tube may be made at a distance of 30 centimeters from a point on the external surface of the enclosure under either of the following conditions: (a) In the case of enclosures containing tubes designed primarily to demonstrate the production of x-radiation, measurements shall be made with a beam blocking device in the beam blocking position. (b) In the case of enclosures containing tubes designed primarily to demonstrate the effects of a flow of electrons, measurements shall be made with all movable or removable parts of the enclosure in the position which would maximize external exposure levels.