Section 325.5493. Measurements.

Rule 493. (1) Compliance with the exposure rate limit specified in rule 492

(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 any point on the external surface of the enclosure under 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 any 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 such enclosure in the  position  which would maximize external exposure levels.

History: 1979 AC.