(a) Micrograph of the alpha particle detector with the Sn absorber covering the TES. The Cu thermalization layer and the SiN isolation are clearly seen. The pads for electrical contact by wire bonding are shown at the bottom and the edge is patterned with gold so that gold wire bonds provide more thermal sinking. (b) Micrograph of same chip before the absorber is glued to the photoimagable posts. The TES is the square film in the middle of the chip and is connected by two fingers to the surrounding Cu film.
The bias and amplification chain for the TES detector. The TES thermometer, , is shunted by an approximately resistor, . All bias voltages are supplied by batteries that are unconnected to any external circuits. The current through the TES is amplified by a SQUID at 80 mK, labeled SQ1. The current from SQ1 is then amplified by an array of SQUIDs, labeled SQA. The output from SQA is used as the measured signal as well as the feedback to SQ1. Also shown in the circuit is the temperature where each component is maintained. The 80 mK stage is the ADR, while the 4 K stage is maintained by liquid helium, and 300 K is outside the cryostat.
Schematic sideview (not to scale) of the alpha detector. The aperture is a single Al piece that screws to the stage and has a hole above the Sn absorber. The stage is made of gold-plated copper. Surrounding the whole stage is an Al shield, thermally sunk to the stage. The alpha emitter is spontaneously deposited on a Pt planchet that is glued to the inside of the shield above the detector.
Microcalorimeter spectrum of alpha emission.
(a) Average current pulse from (log scale). Although the pulse shown is positive, physically it is a reduction in current through the TES. The baseline represents zero current reduction where an offset has been added to allow plotting on log scale. The initial pulse decay is exponential with a time constant of 10 ms. (b) The average pulse and average noise in the frequency domain.
Spectrum from a source. The detector resolution is 102.1 eV.
Plot of known gamma-ray photon and alpha particle energies vs their measured voltage. The line is a linear fit to all the points.
Fluctuations in cryostat temperature and corresponding energy fluctuations during spectrum acquisition. Each count corresponds to a 10 s interval.
(a) An optimally filtered noise trace taken just before the spectrum shown in Fig. 4. The average value has been offset to 0 V. (b) Plot of pulse height from vs time shift in noise record. A histogram of the plotted alpha energies has a FWHM of 340 eV.
Histogram of pulse height variation shown in Fig. 9.
Schematic potential energy curve. Two lattice sites are shown with energy relative to the vacuum energy. The energy barrier to leave a lattice site is and the energy cost for atoms that come to rest at an interstitial site is . The potential energy of a Frenkel pair, a vacancy and an interstitial, is . The formation of a Frenkel pair by an incoming alpha particle is shown schematically, although the vacancy-interstitial pairs are also formed by cascading Sn atoms.
(Main) Plot of ions vs number of vacancies created in Sn absorber. (Inset) Also shown is a plot of the resulting alpha particle spectrum assuming monoenergetic particles emitted from a source. The spectrum shown assumes a displacement energy of 28 eV, lattice energy of 3.14 eV, and surface binding energy of 3 eV. The spectrum yields a resolution of 0.3 keV FWHM.
Plot of expected microcalorimeter resolution from lattice damage vs Frenkel energy. The error bars correspond to the spread in published displacement energies.
Resolution degradation mechanisms.
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