Development of gamma compensated boron lined ionisation chambers for reactor safety and control applications

A gamma compensated boron lined ionisation chamber with parallel plate electrode geometry has been developed for reactor safety and control applications. The chamber has overall dia of 50 mm and overall length of 500 mm. The electrode spacing is 1.5 mm and the sensitive volume is filled with nitrogen gas at 10 psi pressure of Hg. The neutron sensitivity of the chamber was measured as 15.7 fA/nv. Tests conducted at KAMINI reactor at 2.68 x 1010 nv neutron flux showed that the chamber required less than 200 V to achieve 90 % saturation. The linearity of the chamber response was measured to be within 10 % from 1.44 x 104 nv to 2.68 x 1010 nv. For negative HT bias of -350 V and positive bias voltage of 400 V the gamma compensation factor varies from 1.7 to 8.1 % for gamma fields varying from 0.3 MR/h to 0.2 kR/h. (author)