Bolometric detectors as ion energy spectrometers

The response of a composite infrared bolometer to 5.4 MeV α particles from a ²⁴¹Am source is examined. The bolometer consists of a 1 mm × 3 mm × 0.3 mm thick germanium thermometric element bonded to a sapphire substrate 50 μm thick and 6 mm in diameter. It operates at a temperature near 0.35 K. Slow voltage signals from the bolometer were converted to pulses and pulse height spectra were recorded. Energy resolutions of 60 keV (fwhm) were observed for particles interacting with the sapphire absorber. Other structure arising from interactions with other bolometer components was also observed. A 100-fold improvement in resolution is theoretically possible with bolometers of this type.