Gamma ray irradiation tests of high-Tc SQUID

Gamma ray irradiation tests on high-T_c SQUIDs were carried out to examine their behavior under nuclear reactor environments. The SQUIDs were made of HoBa₂Cu₃O_7-x superconducting thin films on SrTiO₃ 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 12.2×10³ Gy/h (1.0 to 1.5×10⁶ 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_c SQUIDs are resistant to gamma ray irradiation and thus the application of high-T_c SQUIDs as sensors for reactor component inspection is promising.