Films made from cellulose nitrate LR-115 (Pathé Kodak) and CR-39 have been used for long-term measurements of the radon-222 emanation from building materials and the resultant activity inside houses. The emanation from crushed granite bricks is found to be produced from within the brick while in the clay bricks it originates in the surface layers only. The airborne radon activity inside houses constructed from clay brick is found on average to be 22 mBq 1-1 (0.57 pCi 1-1) while inside a closed vessel sealed to the brick the average equilibrium activity is 40 mBq 1-1 pCi 1-1).

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