The effect of waterproofing sleeves on ionization chamber response

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Abstract
The principal objective of the authors' measurements was to determine the effect on ionization chamber response of a 0.3 mm thick nylon sleeve (as used at the NRC) and of a 1 mm Lucite sleeve (as used at the PTB). They estimated that with 60Co, the nylon sleeve increases the response by 0.01(+or-0.03)%, while the Lucite sleeve increases it by 0.06(+or-0.03)%. At 20 MV, the 0.3 mm nylon sleeve decreases the response by 0.10(+or-0.07)%, while the 1 mm Lucite sleeve decreases it by 0.19(+or-0.10)%. An unexpected result is the large effect that the thin rubber sleeve obtained from Capintec has on ionization chamber response. With 60Co, a single sleeve (as would normally be used) causes the response to increase by 0.2% to 0.4%, depending on the thimble material. Additional layers cause a small additional increase in response. At 20 MV, a single layer causes the response to increase by 0.5% to 0.6%. The response continues to increase as additional layers are added, with three layers giving an increase of 1.15% for the PR-06C and 1.35% for the NE 2571.