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REACTOR START-UP FISSION CHAMBERS
W. Dabek, Joanna Jabłońska, A. Janikowski, J. Topa
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Abstract
Two fission chambers, RAM-501 and RAMU-501, were designed, tested, and put to use in the reactor EVA and in the critical assemblies ANNA and MARYLA. The two types of chambers are identical except that RAM- 501 has an electrode coated with natural uranium and RAM-501 with 10% U/sup 235/. The sensitive volume of the counter is defined by several concentric cylinders of which three cylindrical surfaces are coated with uranium to a thickness of about 1 mg/cm/sup 2/. With an active area of about 500 cm/sup 2/, the counting rate at the plateau is about 3 x 10/sup -3/ neutron/cm/sup 2/-sec with natural uranium and about 4 x 10/sup -2/ neutron/cm/sup 2/-sec with uranium enriched 10% in U/sup 235/. The rise time of the pulses is about 0.08 mu sec, allowing for counting rates of up to 10/sup 6//sec before significant count-loss occurs due to chance coincidences. The filling-gas is a 2.5 atmosphere charge of 99.99% pure argon with 2% nitrogen added. (CTT)