Measurements of absolute gamma-ray energies using an ultra-high energy resolution magnetic microcalorimeter
We present new measurements of 27 gamma ray energies ranging from 14 keV to 136 keV, obtained using high-energy-resolution magnetic microcalorimeters for energy-dispersive spectrometry. The spectrometer has eight pixels and achieves an energy resolution between 15 and 30 eV across the entire energy range. It faces a cryogenic source sampler with four movable sources. Each source contains a mixture of radionuclides, including Yb-169 and Co-57 used to calibrate the spectrometer and correct its non-linearity. The gamma-ray energies, emitted through the decay of Co-57, Cd-109, Ba-133, Gd-153, Eu-154, Eu-155, Yb-169, Tm-170, Pb-210, Np-239, Am-241 and Am-243, have been reassessed. The lowest absolute uncertainty achieved is 0.13 eV at 105.3 keV, which corresponds to a relative uncertainty of 1.3 ppm. Of the 27 measured gamma rays, the uncertainties of 19 energies were improved with respect to the available literature: 10 by a factor of 5 and 4 by more than one order of magnitude. Good agreement is observed with energies obtained elsewhere by wavelength-dispersive spectrometry. This work significantly improves upon previously reported gamma energies obtained by energy-dispersive spectrometry using semiconductor detectors, thanks to the ultra-high energy resolution of magnetic microcalorimeters.