Measurement of the

We present a measurement of the low-energy (0-60 keV) γ-ray spectrum produced in the α decay of ^{233}U using a dedicated cryogenic magnetic microcalorimeter. The energy resolution of ∼10 eV, together with exceptional gain linearity, allows us to determine the energy of the low-lying isomeric state in ^{229}Th using four complementary evaluation schemes. The most precise scheme determines the ^{229}Th isomer energy to be 8.10(17) eV, corresponding to 153.1(32) nm, superseding in precision previous values based on γ spectroscopy, and agreeing with a recent measurement based on internal conversion electrons. We also measure branching ratios of the relevant excited states to be b_{29}=9.3(6)% and b_{42}<0.7%.

Application of Resonance Ionization Mass Spectrometry for Ultratrace Analysis of Technetium.

This work shows the ability of resonance ionization mass spectrometry (RIMS) to determine 99gTc at the ultratrace level. The characterization of the prepared samples by X-ray photoelectron spectroscopy (XPS) and optimization of the RIMS setup for this purpose, as well as the application of the RIMS method to a soil sample, are presented in this article. 97Tc was used as a tracer isotope to determine the amount of 99gTc in a soil sample with RIMS. With 8.8 × 1010 atoms of 97Tc as the tracer, the concentration of 99gTc was found to be 1.5 × 109 atoms per gram of dried sample material, demonstrating the sensitivity of the method. Furthermore, it could be shown that the 97Tc solution contained 98Tc as well. This is the first time that 97,98,99gTc have been simultaneously measured with RIMS.

Direct detection of the (229)Th nuclear clock transition.

Today's most precise time and frequency measurements are performed with optical atomic clocks. However, it has been proposed that they could potentially be outperformed by a nuclear clock, which employs a nuclear transition instead of an atomic shell transition. There is only one known nuclear state that could serve as a nuclear clock using currently available technology, namely, the isomeric first excited state of (229)Th (denoted (229m)Th). Here we report the direct detection of this nuclear state, which is further confirmation of the existence of the isomer and lays the foundation for precise studies of its decay parameters. On the basis of this direct detection, the isomeric energy is constrained to between 6.3 and 18.3 electronvolts, and the half-life is found to be longer than 60 seconds for (229m)Th(2+). More precise determinations appear to be within reach, and would pave the way to the development of a nuclear frequency standard.