Gamma ray irradiation tests of high-T/sub c/ SQUID

Gamma ray irradiation tests on high-T/sub c/ SQUIDs were carried out to examine their behavior under nuclear reactor environments. The SQUIDs were made of HoBa/sub 2/Cu/sub 3/O/sub 7-x/ superconducting thin films on SrTiO/sub 3/ substrates. Some were encapsulated in glass fiber reinforced epoxy resin. Gamma ray irradiation was performed with a Co-60 gamma ray source. Irradiation dose rates used were 8.1 to 12.2/spl times/10/sup 3/ Gy/h (1.0 to 1.5/spl times/10/sup 6/ R/h) and the maximum absorption dose was about 10.4 MGy. During and after the irradiation, the noise of the output of the SQUIDs was measured with a power spectrum analyzer. The modulation voltage did not change until a total irradiation dose of about 3 MGy, after which it decreased slightly. We conclude that high-T/sub c/ SQUIDs are resistant to gamma ray irradiation and thus the application of high-T/sub c/ SQUIDs as sensors for reactor component inspection is promising.