Peter Kunz

Atom-at-a-time laser resonance ionization spectroscopy of nobelium

Optical spectroscopy of a primordial isotope has traditionally formed the basis for understanding the atomic structure of an element. Such studies have been conducted for most elements and theoretical modelling can be performed to high precision, taking into account relativistic effects that scale approximately as the square of the atomic number. However, for the transfermium elements (those with atomic numbers greater than 100), the atomic structure is experimentally unknown. These radioactive elements are produced in nuclear fusion reactions at rates of only a few atoms per second at most and must be studied immediately following their production, which has so far precluded their optical spectroscopy. Here we report laser resonance ionization spectroscopy of nobelium (No; atomic number 102) in single-atom-at-a-time quantities, in which we identify the ground-state transition 1S0 1P1. By combining this result with data from an observed Rydberg series, we obtain an upper limit for the ionization potential of nobelium. These accurate results from direct laser excitations of outer-shell electrons cannot be achieved using state-of-the-art relativistic many-body calculations that include quantum electrodynamic effects, owing to large uncertainties in the modelled transition energies of the complex systems under consideration. Our work opens the door to high-precision measurements of various atomic and nuclear properties of elements heavier than nobelium, and motivates future theoretical work.

Ion source developments for the production of radioactive isotope beams at TRIUMFa)

At the ISAC facility at TRIUMF radioactive ions are produced by bombarding solid targets with up to 100 μA of 500 MeV protons. The reaction products have to diffuse out of the hot target into an ion source. Normally, singly charged ions are extracted. They can be transported either directly to experiments or via an ECR charge state breeder to a post accelerator. Several different types of ion sources have to be used in order to deliver a large variety of rare isotope beams. At ISAC those are surface ion sources, forced electron beam arc discharge (FEBIAD) ion sources and resonant laser ionization sources. Recent development activities concentrated on increasing the selectivity for the ionization to suppress isobaric contamination in the beam. Therefore, a surface ion rejecting resonant laser ionization source (SIRLIS) has been developed to suppress ions from surface ionization. For the FEBIAD ion source a cold transfer line has been introduced to prevent less volatile components from reaching the ion source.

An ion guide laser ion source for isobar-suppressed rare isotope beams

Modern experiments at isotope separator on-line (ISOL) facilities like ISAC at TRIUMF often depend critically on the purity of the delivered rare isotope beams. Therefore, highly selective ion sources are essential. This article presents the development and successful on-line operation of an ion guide laser ion source (IG-LIS) for the production of ion beams free of isobaric contamination. Thermionic ions from the hot ISOL target are suppressed by an electrostatic potential barrier, while neutral radio nuclides effusing out are resonantly ionized by laser radiation within a quadrupole ion guide behind this barrier. The IG-LIS was developed through detailed thermal and ion optics simulation studies and off-line tests with stable isotopes. In a first on-line run with a SiC target a suppression of surface-ionized Na contaminants in the ion beam of up to six orders of magnitude was demonstrated.

RIMS measurements for the determination of the first ionization potential of the actinides actinium up to einsteinium

The ionization potential is a fundamental property of an element. In order to determine the first ionization potential, a method based on the measurement of photoionization thresholds in the presence of a well-defined electrical field is used. By one or two step resonant laser excitation, the investigated atoms are promoted to a highly excited state. Ionization is obtained by scanning the wavelength of an additional tunable laser across the threshold Wth, which is detected by a sudden increase of the ion signal. Extrapolation of Wth to zero field strength yields directly the first ionization potential. Using this method the first ionization potentials of Ac, Am, Cm, Bk, Cf, and Es have been determined for the first time. Furthermore, the ionization potentials of Th, U, Np, and Pu were remeasured.

Nuclear and in-source laser spectroscopy with the ISAC yield station

A new decay station has been built for the ISAC facility at TRIUMF for the rapid and reliable characterization of radioactive ion beam (RIB) compositions and intensities with the capability of simultaneously collecting α, β, and γ decay data from RIB with intensities between a few and ≈10(11) ions per second. It features user-friendly control, data acquisition, and analysis software. The analysis of individual decay time structures allows the unambiguous assignment of α and γ lines even with substantial isobaric contamination present. The capability for accurate half-life measurements is demonstrated with the example of (46)K. The coupling of the yield station to the laser ion source, TRILIS, allows the correlation of radiometric data with automated laser frequency scans. First results of in-source laser spectroscopy measurements on astatine are discussed.

Development of a preclinical 211Rn/211At generator system for targeted alpha therapy research with 211At

INTRODUCTIONnThe availability of 211At for targeted alpha therapy research can be increased by the 211Rn/211At generator system, whereby 211At is produced by 211Rn electron capture decay. This study demonstrated the feasibility of using generator-produced 211At to label monoclonal antibody (BC8, anti-human CD45) for preclinical use, following isolation from the 207Po contamination also produced by these generators (by 211Rn α-decay).nnnMETHODSn211Rn was produced by 211Fr electron capture decay following mass separated ion beam implantation and chemically isolated in liquid alkane hydrocarbon (dodecane). 211At produced by the resulting 211Rn source was extracted in strong base (2N NaOH) and purified by granular Te columns. BC8-B10 (antibody conjugated with closo-decaborate(2-)) was labeled with generator-produced 211At and purified by PD-10 columns.nnnRESULTSnAqueous solutions extracted from the generator were found to contain 211At and 207Po, isolated from 211Rn. High radionuclidic purity was obtained for 211At eluted from Te columns, from which BC8-B10 monoclonal antibody was successfully labeled. If not removed, 207Po was found to significantly contaminate the final 211At-BC8-B10 product. High yield efficiencies (decay-corrected, n=3) were achieved for 211At extraction from the generator (86%±7%), Te column purification (70%±10%), and antibody labeling (76%±2%).nnnCONCLUSIONSnThe experimental 211Rn/211At generator was shown to be well-suited for preclinical 211At-based research.nnnADVANCES IN KNOWLEDGEnWe believe that these experiments have furthered the knowledge-base for expanding accessibility to 211At using the 211Rn/211At generator system.nnnIMPLICATIONS FOR PATIENT CAREnAs established by this work, the 211Rn/211At generator has the capability of facilitating preclinical evaluations of 211At-based therapies.

Multi-isotope SPECT imaging of the 225Ac decay chain: feasibility studies

Effective use of the [Formula: see text] decay chain in targeted internal radioimmunotherapy requires the retention of both [Formula: see text] and progeny isotopes at the target site. Imaging-based pharmacokinetic tests of these pharmaceuticals must therefore separately yet simultaneously image multiple isotopes that may not be colocalized despite being part of the same decay chain. This work presents feasibility studies demonstrating the ability of a microSPECT/CT scanner equipped with a high energy collimator to simultaneously image two components of the [Formula: see text] decay chain: [Formula: see text] (218u2009keV) and [Formula: see text] (440u2009keV). Image quality phantoms were used to assess the performance of two collimators for simultaneous [Formula: see text] and [Formula: see text] imaging in terms of contrast and noise. A hotrod resolution phantom containing clusters of thin rods with diameters ranging between 0.85 and 1.70u2009mm was used to assess resolution. To demonstrate ability to simultaneously image dynamic [Formula: see text] and [Formula: see text] activity distributions, a phantom containing a [Formula: see text] generator from [Formula: see text] was imaged. These tests were performed with two collimators, a high-energy ultra-high resolution (HEUHR) collimator and an ultra-high sensitivity (UHS) collimator. Values consistent with activity concentrations determined independently via gamma spectroscopy were observed in high activity regions of the images. In hotrod phantom images, the HEUHR collimator resolved all rods for both [Formula: see text] and [Formula: see text] images. With the UHS collimator, no rods were resolvable in [Formula: see text] images and only rodsu2009u2009⩾1.3u2009mm were resolved in [Formula: see text] images. After eluting the [Formula: see text] generator, images accurately visualized the reestablishment of transient equilibrium of the [Formula: see text] decay chain. The feasibility of evaluating the pharmacokinetics of the [Formula: see text] decay chain in vivo has been demonstrated. This presented method requires the use of a high-performance high-energy collimator.

211Rn/211At and 209At production with intense mass separated Fr ion beams for preclinical 211At-based α-therapy research

Mass-separated francium beams (211Fr or 213Fr) were implanted into solid targets for producing 211Rn (14.6h half-life) or 209At (5.41h), in situ. 211Rn was transferred to dodecane and isolated from contaminants, providing sources for 211At (7.21h) production by 211Rn decay (73%). 209At was recovered with high radionuclidic purity in aqueous solutions, directly. These experiments demonstrated Fr beam implantations as a novel method for producing preclinical quantities of 211Rn/211At (for therapy) and 209At (for imaging).

Evaluation of 209At as a theranostic isotope for 209At-radiopharmaceutical development using high-energy SPECT

The development of alpha-emitting radiopharmaceuticals using ²¹¹At requires quantitative determination of the time-dependent nature of the ²¹¹At biodistribution. However, imaging-based methods for acquiring this information with ²¹¹At have not found wide-spread use because of its low abundance of decay emissions suitable for external detection. In this publication we demonstrate the theranostic abilities of the ²¹¹At/²⁰⁹At isotope pair and present the first-ever ²⁰⁹At SPECT Images. <b>Methods:</b> The VECTor microSPECT/PET/CT scanner was used to image ²⁰⁹At with a collimator suitable for the 511 keV annihilation photons of PET isotopes. Data from distinct photopeaks of the ²⁰⁹At energy spectrum (195 keV (22.6%), 239 keV (12.4%), 545 keV (91.0%), a combined 782/790 keV peak (147%), and ²⁰⁹Po x-rays (139.0%)) were independently evaluated for use in image reconstructions using Monte Carlo (GATE) simulations and phantom studies. ²⁰⁹At-imaging <i>in vivo</i> was demonstrated in a healthy mouse injected with 10 MBq of free [²⁰⁹At]astatide. Image-based measurements of ²⁰⁹At uptake in organs of interest - acquired in 5-minute intervals - were compared to <i>ex vivo</i> gamma counter measurements of the same organs. <b>Results:</b> Simulated and measured data indicated that - due to the large amount of scatter from high energy (>750 keV) gammas - reconstructed images using the x-ray peak outperformed those obtained from other peaks in terms of uniformity and spatial resolution, determined to be <0.85 mm. ²⁰⁹At imaging using the x-ray peak revealed a biodistribution that matched the known distribution of free astatide, and <i>in vivo</i> image-based measurements of ²⁰⁹At uptake in organs of interest matched <i>ex vivo</i> measurements within 10%. <b>Conclusion:</b> We have acquired the first ²⁰⁹At SPECT images and demonstrated the ability of quantitative SPECT imaging with ²⁰⁹At to accurately determine astatine biodistributions with high spatial and temporal resolution.The development of alpha-emitting radiopharmaceuticals using 211At requires quantitative determination of the time-dependent nature of the 211At biodistribution. However, imaging-based methods for acquiring this information with 211At have not found wide-spread use because of its low abundance of decay emissions suitable for external detection. In this publication we demonstrate the theranostic abilities of the 211At/209At isotope pair and present the first-ever 209At SPECT images. The VECTor microSPECT/PET/CT scanner was used to image 209At with a collimator suitable for the 511u2009keV annihilation photons of PET isotopes. Data from distinct photopeaks of the 209At energy spectrum (195u2009keV (22.6%), 239u2009keV (12.4 %), 545u2009keV (91.0 %), a combined 782/790u2009keV peak (147 %), and 209Po x-rays (139.0 %)) were independently evaluated for use in image reconstructions using Monte Carlo (GATE) simulations and phantom studies. 209At-imaging in vivo was demonstrated in a healthy mouse injected with 10 MBq of free [209At]astatide. Image-based measurements of 209At uptake in organs of interest-acquired in 5u2009min intervals-were compared to ex vivo gamma counter measurements of the same organs. Simulated and measured data indicated that-due to the large amount of scatter from high energy (>750u2009keV) gammas-reconstructed images using the x-ray peak outperformed those obtained from other peaks in terms of image uniformity and spatial resolution, determined to beu2009u2009<0.85u2009mm. 209At imaging using the x-ray peak revealed a biodistribution that matched the known distribution of free astatide, and in vivo image-based measurements of 209At uptake in organs of interest matched ex vivo measurements within 10%. We have acquired the first 209At SPECT images and demonstrated the ability of quantitative SPECT imaging with 209At to accurately determine astatine biodistributions with high spatial and temporal resolution.