# Low Temperature Microcalorimeters for Decay Energy Spectroscopy
## 4 Results
The Ta absorbers were measurements of ion-implanted \({}^{7}\)Be and achieved resolving powers on the order of 10, which is about a third lower than predicted from laser measurements [46; 47]. Other approaches under investigation include using bilayer absorbers to reduce the effect of bremsstrahlung [67]. The DES absorber is usually fabricated separately from the detector. Because of this, it must be thermally coupled to the detector for measurements. There are a variety of ways this has been done as shown in Figure 6. The most common ways are using an In bump bond or epoxy. The epoxies used included both Stycast 1266 and Stycast2850 FT. The best achieved resolving power for high energy DES measurements was done with an In bump bond. For low energy DES measurements, the best resolution achieved was accomplished with both the In bump bond and epoxy. Figure 5: Absorber materials used in Decay Energy Spectroscopy. The resolving power can be seen as a function of absorber material for both high energy DES and low energy DES measurements. Of the various deposition methods (see Figure 7), ion implantation has been shown to achieve excellent results (one of the best low energy measurements [17]), but requires dedicated facilities and high efficiency throughput can be a challenge, making it a less desirable option for source material that might be sparse or inhomogenous or unknown. Electroplating has shown to produce excellent results (the best low energy measurement [35]), but this is not possible for all materials and the electrodeposition process varies by element. Autodeposition or self-deposition is a subset where no electric current need be applied because the material will spontaneously deposit on the substrate. This is possible with Po and also produces superior results (the second best results with high energy measurements [55]). The preferred method for ease of mass-production and ability to deposit any radionuclide is the dried drop method. In this method, the radionuclide is usually a dissolved salt within the solution or an organic molecule with carrier. The liquid is deposited onto the substrate--usually a Au foil--and allowed to dry. Upon drying, it has been found that the salts within the solution have dried down along with the radionuclide and the mass of that salt is significantly more than the mass of just the radionuclide. The resultant residue degrades energy resolution as the energy from the decay is thermalized both within the residue and in the absorber matrix. The resolving power as a function of deposition method is given in Figure 7.  
Figure 6: (_Top_) Absorber attachment methods used in Decay Energy Spectroscopy. (_Bottom_) The resolving power can be seen as a function of absorber attachment method for both high energy DES and low energy DES measurements. The effects of improper deposition techniques are degraded energy resolution, shifts in peak energy [9; 16], long tailing [9], spectral distortion [68], and even peak splitting [9; 35]. Several different approaches are undertaken to address the problem of the crystalline deposits in the dried droplet method. One approach is to reduce the size of the crystalline deposits by using automatic microdrop dispensers [35; 67]. Reducing the thickness of the deposit improves energy resolution [69]. A second approach is to deposit the material into a nanoporous Au, so the pores control the size of the crystalline deposits. The challenge here is creating nanoporous Au with small enough pores. A third approach to control the size of the crystalline deposits is using a removable patterned latex pad to control where the material is dried and then removing the latex pad [64]. These methods have produced modest improvements. Other approaches to improve the results after the initial deposition are diffusion welding and mechanical alloying.