Quantitative molecular plating of large-area 242Pu targets with improved layer properties

For measurements of the neutron-induced fission cross section of 242Pu, large-area (42cm2) 242Pu targets were prepared onTi-coated Si wafers by means of constant current density molecular plating. Radiochemical separations were performed prior tothe platings. Quantitative deposition yields (>95%) were determined for all targets by means of alpha-particles pectroscopy. Layer densities in the range of 100–150 μg/cm2 were obtained. The homogeneity of the targets was studied by radiographic imaging. A comparative study between the quality of the layers produced on the Ti-coated Si wafers and the quality of layers grown on normal Ti foils was carried out by applying scanning electronmicroscopy and energy dispersive X-ray spectroscopy. Ti-coated Si wafers resulted clearly superior to Ti foils in the production of homogeneous 242Pu layers with minimum defectivity.JRC.E.3-Materials researc

Highly selective two-step laser ionization schemes for the analysis of actinide mixtures

Resonance ionization mass spectroscopy has proven to be a very efficient and selective method for the spatially resolved ultratrace determination of actinide contaminations, and the analysis of specific element and isotopic distributions on surfaces and environment particles. We report on the identification of highly element-selective optical excitation schemes identified for this purpose, with a particular focus on the precise determination of the isobaric ratios of 235U to 239Pu as well as 243Am to 241Pu. The chosen two-step ionization schemes were characterized with respect to their element selectivity on synthetic multi-element actinide mixtures, with an element ratio Pu : Am : U of 1 : 10 : 104, a composition which is typical, e.g., for spent nuclear reactor fuels. © 2020, The Author(s).Bundesministerium für Bildung und Forschung, BMBFBundesministerium für Bildung und Forschung, BMBF: 05P15UMCIAOpen Access funding provided by Projekt DEAL. Support by the Bundesministerium für Bildung und Forschung (BMBF, Germany) under project number 05P15UMCIA is acknowledged

Investigation of the atomic structure of curium and determination of its first ionization potential

We report on the investigation of the atomic structure of curium ($$Z=96$$) by resonance ionization spectroscopy. Three different excited energy levels were populated from the 5f^{7}6d7s^{2}\,^{9}D^{o}_{2} ground state as first excitation steps. Wide-range scans were performed for the search of second excitation steps around the literature value of the ionization potential. These spectra were analyzed to identify Rydberg levels and auto-ionizing resonances. The ionization potential was consistently determined as 48330.68(16)$$\hbox {cm} ^{-1}$$ through the evaluation of Rydberg convergences and the complementary approach of DC electric field ionization by evaluating the ionization threshold according to the saddle point model. The new result deviates by 6.7$$\hbox {cm} ^{-1}$$ from the literature value of 48324(2)$$\hbox {cm} ^{-1}$$ by Köhler et al. [15] and is about one order of magnitude more precise

Trapping and sympathetic cooling of single thorium ions for spectroscopy

Precision optical spectroscopy of exotic ions reveals accurate information about nuclear properties such as charge radii and magnetic and quadrupole moments. Thorium ions exhibit unique nuclear properties with high relevance for testing symmetries of nature. We report loading and trapping of single $^{232}$Th$^+$ ions in a linear Paul trap, embedded into and sympathetically cooled by small crystals of trapped $^{40}$Ca$^+$ ions. Trapped Th ions are identified in a non-destructive manner from the voids in the laser-induced Ca fluorescence pattern emitted by the crystal, and alternatively, by means of a time-of-flight signal when extracting ions from the Paul trap and steering them into an external detector. We have loaded and handled a total of 231 individual Th ions. We reach a time-of-flight detection efficiency of $\gtrsim 95\, \%$, consistent with the quantum efficiency of the detector. The sympathetic cooling technique is expected to be applicable for other isotopes and various charge states of Th e.g., for future studies of $^{229m}$Th.Comment: 5 pages, 4 figure

Direct detection of the 229^{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 the atomic shell transitions used so far. By today there is only one nuclear state known which could serve for a nuclear clock using currently available technology, which is the isomeric first excited state in $^{229}$Th. Here we report the direct detection of this nuclear state, which is a further confirmation of the isomer's existence and lays the foundation for precise studies of the isomer's decay parameters. Based on this direct detection the isomeric energy is constrained to lie between 6.3 and 18.3 eV, and the half-life is found to be longer than 60 s for $^{229\mathrm{m}}$Th$^{2+}$. More precise determinations appear in reach and will pave the way for the development of a nuclear frequency standard

Catching, trapping and in-situ-identification of thorium ions inside Coulomb crystals of 40^{40}Ca+^+ ions

Thorium ions exhibit unique nuclear properties with high relevance for testing symmetries of nature, and Paul traps feature an ideal experimental platform for performing high precision quantum logic spectroscopy. Loading of stable or long-lived isotopes is well-established and relies on ionization from an atomic beam. A different approach allows trapping short-lived isotopes available as alpha-decay daughters, which recoil from a thin sample of the precursor nuclide. A prominent example is the short-lived $^{229\text{m}}$Th, populated in a decay of long-lived $^{233}$U. Here, ions are provided by an external source and are decelerated to be available for trapping. Such setups offer the option to trap various isotopes and charge states of thorium. Investigating this complex procedure, we demonstrate the observation of single $^{232}$Th$^+$ ions trapped, embedded into and sympathetically cooled via Coulomb interactions by co-trapped $^{40}$Ca$^+$ ions. Furthermore, we discuss different options for a non-destructive identification of the sympathetically cooled thorium ions in the trap, and describe in detail our chosen experimental method, identifying mass and charge of thorium ions from the positions of calcium ions, as their fluorescence is imaged on a CCD camera. These findings are verified by means of a time-of-flight signal when extracting ions of different mass-to-charge ratio from the Paul trap and steering them into a detector

Probing the Atomic Structure of Californium by Resonance Ionization Spectroscopy

The atomic structure of californium is probed by two-step resonance ionization spectroscopy. Using samples with a total amount of about 2×1010 Cf atoms (ca. 8.3 pg), ground-state transitions as well as transitions to high-lying Rydberg states and auto-ionizing states above the ionization potential are investigated and the lifetimes of various atomic levels are measured. These investigations lead to the identification of efficient ionization schemes, important for trace analysis and nuclear structure investigations. Most of the measurements are conducted on 250Cf. In addition, the isotope shift of the isotopic chain 249−252Cf is measured for one transition. The identification and analysis of Rydberg series enables the determination of the first ionization potential of californium to EIP=50,666.76(5)cm−1. This is about a factor of 20 more precise than the current literature value

Probing the Atomic Structure of Californium by Resonance Ionization Spectroscopy

The atomic structure of californium is probed by two-step resonance ionization spectroscopy. Using samples with a total amount of about 2×1010 Cf atoms (ca. 8.3 pg), ground-state transitions as well as transitions to high-lying Rydberg states and auto-ionizing states above the ionization potential are investigated and the lifetimes of various atomic levels are measured. These investigations lead to the identification of efficient ionization schemes, important for trace analysis and nuclear structure investigations. Most of the measurements are conducted on 250Cf. In addition, the isotope shift of the isotopic chain 249−252Cf is measured for one transition. The identification and analysis of Rydberg series enables the determination of the first ionization potential of californium to EIP=50,666.76(5)cm−1. This is about a factor of 20 more precise than the current literature value