Anomalous effects on radiation detectors and capacitance measurements inside a modified Faraday cage

• Background counts and decay rates changes of different nuclides are described.
• Those changes are observed inside a multilayer modified Faraday cage.
• Noise in a multichannel analyzer increases inside the multilayer enclosure.
• Capacitance of a class-I multilayer ceramic capacitor varies inside the enclosure.
• Capacitance changes depend on the used frequency.

We present experimental results showing certain anomalies in the measurements performed inside a modified Faraday cage of decay rates of Ra-226, Tl-204 and Sr-90/I-90, of the gamma spectrum of a Cs-137 preparation, and of the capacitance of both a class-I multilayer ceramic capacitor and of the interconnection cable between the radiation detector and the scaler. Decay rates fluctuate significantly up to 5% around the initial value and differently depending on the type of nuclide, and the spectrum photopeak increases in 4.4%. In the case of the capacitor, direct capacitance measurements at 100 Hz, 10 kHz and 100 kHz show variations up to 0.7%, the most significant taking place at 100 Hz. In the case of the interconnection cable, the capacitance varies up to 1%. Dispersion also tends to increase inside the enclosure. However, the measured capacitance variations do not explain the variations observed in decay rates.