B. Biesmans | Searcharxiv

arXiv2026

Exploring $\alpha$- and $\beta$-decay-induced quenching of the $^{229}$Th nuclear-clock isomer in solid-state hosts

The radiative decay dynamics of an ensemble of $^{229\mathrm{m}}$Th nuclei embedded in CaF$_2$ and MgF$_2$ is investigated. The isomer is populated through $\beta$ decay of $^{229}$Ac following ion implantation, and its radiative decay is detected using vacuum-ultraviolet spectroscopy and measured as a function of time. This allows to identify and quantify the quenching of the radiative-decay signal induced by $\alpha$ or $\beta$ radiation. The quenching probability density is determined in different CaF$_2$ crystals and in a MgF$_2$ crystal, revealing differences up to two orders of magnitude between the investigated samples and a strong dependence on the host material and defect densities. The results support a microscopic mechanism mediated by charge carriers in which electronic excitations created by the decay radiation are captured near Th defects, thereby favoring non-radiative decay channels.

nucl-ex↗

arXiv2026

Lattice location of ion-implanted 6He in diamond

The properties of He in diamond are of interest with respect to geological dating and the creation of color centers with possible quantum applications. We report on the lattice location of the short-lived ion implanted nuclear probe 6He (t1/2=807 ms) in diamond, which was performed using the beta emission channeling method at CERN's ISOLDE facility. 6He was implanted with 30 keV into a single-crystalline artificial diamond sample kept at a temperature ranging from 30 deg C up to 800 deg C. By means of comparing the measured emission channeling patterns along different crystallographic directions with simulated yields for a variety of possible sites, we conclude that the implanted 6He occupies tetrahedral (T) interstitial sites, in agreement with theoretical predictions that T sites should be the preferred position of He in diamond. Implantation at 800 deg C resulted in a drop in the tetrahedral interstitial fraction by 20%, which we interpret as the onset of diffusion, 6He thus being able to change to lattice sites of low crystallographic symmetry, or reach the surface of the sample or escape to the bulk during its lifetime. We estimate the activation energy for interstitial migration of He to be around 1.63-2.89 eV, which agrees with theoretical predictions of 1.41-2.36 eV from the literature. Activation energies around 2 eV would mean that simple interstitial He cannot be stable in diamond on geological time scales, thus to remain inside, it should be bound to some defect in the material or exist in another form such as within inclusions of other minerals or liquids, or possibly small He bubbles.

cond-mat.mtrl-sci↗