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Using an ultra-sensitive single-channel SQUID system an upper limit of 80 aT Hz−1/2 for the body noise contribution of the human head in ultra-low-field SQUID-based MRI or MEG is determined. We discuss in detail the various noise contributions which need to be taken into account. Simulations and measurements of conducting phantoms show that presumably residual radio frequency interference cause an increase in the sensor noise at the aT Hz−1/2-level and need to be considered. Using a phenomenological approach, the body noise contribution of the human head is determined to 55 aT Hz−1/2 for our setup. We also provide simulations of the expected body noise for other sensor geometries.

We describe a self-contained 3He melting curve thermometer (MCT), which is compact and easy to operate and makes a reliable tool for the direct dissemination of the new provisional low-temperature scale, PLTS-2000. It is based on a cylindrical pressure gauge and uses a tunnel diode oscillator circuit for capacitive read-out. The gas-handling system uses a set of relief valves and an electronic pressure sensor, enabling the thermometer to be fully automated, including the calibration procedure. The performance of the MCT was evaluated by comparison with a current-sensing noise thermometer in the temperature range from 20 to 700 mK.