Effects of back shield albedo on imagery with a photodiode array using a 9MV bremsstrahlung spectrum

We use a photodiode array with a mammography screen to measure the relative albedo from concrete and lead radiation shielding placed behind the imagin g detector. When illuminated by radiation from a 9 MV electron linac, the m easured level of radiation backscattered from the concrete shield is 3.33 /- 0.24 that from the lead shield. This result is consistent with Monte Car lo simulations. The measured backscatter intensity shows the expected inver se distance squared behavior. When the shields are 3 m (10 ft) from the det ector, the measured backscatter intensity is at the background level in the detector (eight percent for the given experimental arrangement and for the given energy range).