Regensburg 2019 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 67: Cryogenic Particle Detectors and Other Superconducting Electronics
TT 67.3: Talk
Friday, April 5, 2019, 10:00–10:15, H4
Gamma spectroscopy to measure the 229Th isomer energy using a 2-dimensional array of metallic magnetic microcalorimeters — •Jeschua Geist1, Daniel Hengstler1, Christian Schötz1, Sebastian Kempf1, Loredana Gastaldo1, Andreas Fleischmann1, Christian Enss1, Georgy A. Kazakov2, Simon Stellmer2, and Thorsten Schumm2 — 1Heidelberg University — 2Vienna University of Technology
The isotope 229Th has a nuclear isomer state with the lowest presently known excitation energy, which possibly allows to connect the fields of nuclear and atomic physic with a potential application in a nuclear clock. In order to verify and improve the accuracy of the currently most accepted energy value for this isomere energy, (7.8±0.5) eV, we plan to resolve the 29.18 keV doublet in the γ-spectrum following the α-decay of 233U, corresponding to the decay into the ground and isomer state, to measure the isomer transition energy without additional theoretical input parameters.
We developed the detector array maXs-30 consisting of 8x8 metallic magnetic calorimeters with an expected energy resolution below 6 eV, providing a large detection area of 16 mm2 to face the low rate of the 29.18 keV transitions. We present a new value for the isomere energy with a detector performance of 11 eV FWHM for photons up to 60 keV, show latest recorded 229Th spectra and discuss different ways to derive the isomer energy from these spectra.