Refer to the Radiation Protection Dosimetry (December 2010) study of radon exposure in tombs carved from limestone in the Egyptian Valley of Kings, Exercise 6.30. The radon levels in the inner chambers of a sample of 12 tombs were determined, yielding the following summary statistics:  = 3,643 Bq/m3 and 5 = 4,487 Bq/m3. Use this information to estimate, with 95% confidence, the true standard deviation of radon levels in tombs in the Valley of Kings. Interpret the resulting interval.