Posted by **Beth** on Friday, August 3, 2012 at 12:05pm.

One kilogram of dry air at STP conditions is exposed to 1.00 R of X-rays. One roentgen is defined by Equation 32.1 in Section 32.1. An equivalent definition can be based on the fact that an exposure of one roentgen deposits 8.30 x 10-3 J of energy per kilogram of dry air. Using the two definitions and assuming that all ions produced are singly charged, determine the average energy (in eV) needed to produce one ion in air.