Development of Total Decay Energy Spectrometry of α-Emitting Radionuclides Using Metallic Magnetic Calorimeters

Low Temperature Microcalorimeters for Decay Energy Spectroscopy

“…The radionuclides of interest were dissolved in a solution and dried onto a gold foil, which was folded over, pressed, and diffusion-welded to encapsulate the material, then coupled to a Au:Er MMC [31,32]. In the first measurement [31], the spectral resolution allowed for differentiation between the K captures and L captures of 55 Fe, but was not sufficient to differentiate between the electronic subshells (i.e., capture from the L1 shell versus L2). Energy loss within the source (FeCl 3 crystals) contributed to spectral distortions in this measurement and there was a substantial difference in the detector response to X-rays versus Auger electrons.…”

“…There was some question with this measurement about whether other material co-deposited with the source (specifically a substance from the chemical separation of Pu and Am) contributed to spectral changes arising from different thermalization between electrons and photons. In 2017, a second measurement of 55 Fe featured an electroplated sample on a gold foil that was subsequently diffusion-welded at 400 • C [33]. This measurement was successful in both cleaning up the spectrum and lowering the energy threshold to 50 eV to include the M captures.…”

“…The former underwent the same mechanical kneading process as had prior samples. Despite this, poor resolution and different pulse shape from the electroplated 55 Fe sample within the same absorber prompted the team to pursue a Au nanofoam absorber. The nanofoam's small pore sizes (50-100 nm) limit the size of crystalline structures formed during the deposition of material.…”

“…ECHo is pursuing laser ion implantation within a Au absorber layer and then final encapsulation with a Au layer [37,38]. While stating that energy resolution was not degraded from the ion implantation technique, ECHo still reports energy resolutions worse than those of external 55 Fe X-ray measurements [39,40]. This is potentially due to lattice damage effects, increase in heat capacity due to the implantation process, or unequal operating parameters described in [39].…”

“…The KRISS team also encountered this problem with later measurements and modeling of 226 Ra [54]. Researchers from the French Atomic Energy Commission (CEA) also found that, while their 210 Po measurements did not exhibit peaksplitting, there was an unusually long tail associated with the peak [55]. A 'tail' is a non-Gaussian feature in the spectrum, usually on the low-energy side of a peak, that is often described by an exponential.…”