Short-lived Radioisotopes Research Articles

Investigation of the production routes of 81,82m,83,84 Rb isotopes through proton-induced nuclear reactions on 82,83,84,86 Kr

Investigations using nuclear reaction models are significant and have considerable consequences in terms of understanding nuclear reaction processes and their nature. The nuclear data on radionuclides created by the cyclotron find application in nuclear diagnostics and therapeutic treatments. The excitation function of proton-induced nuclear reactions on 82,83,84,86 Kr for the generation of medically beneficial short-lived radioisotopes 81,82m,83,84 Rb from threshold energy to 50 MeV has been investigated using Koning–Delaroche optical model potential with nuclear level density (NLD) from both the phenomenological and microscopic nuclear models incorporated in TALYS1.96 code. The phenomenological constant temperature + Fermi gas model, back-shifted Fermi gas model, generalised superfluid model, and microscopic NLD from the Skyrme–Hartree–Fock–Bogoliubov, Gogny–Hartree–Fock–Bogoliubov, and temperature-dependent Gogny–Hartree–Fock–Bogoliubov NLD tables have been used to calculate the excitation function. The calculated excitation functions are compared with the experimental data from EXFOR and the TALYS evaluated nuclear data library (TENDL2023). An analysis is carried out by estimating the mean deviation D-value between the theoretical and experimental cross-sections, and the NLD model corresponding to the best result is used for the estimation of activity and production yield for each reaction channel.

Sortase-Mediated Site-Specific Conjugation to Prepare Fluorine-18-Labeled Nanobodies.

Single-domain antibodies, or nanobodies (Nbs), are promising biomolecules for use in molecular imaging due to their excellent affinity, specificity, and fast clearance from the blood. Given their short blood half-life, pairing Nbs with short-lived imaging radioisotopes is desirable. Because fluorine-18 (18F) is routinely used for clinical imaging, it is an attractive radioisotope for Nbs. We report a novel sortase-based, site-specific 18F-labeling method applied to three nanobodies. Labeled nanobodies were synthesized either by a two-step indirect radiolabeling method in one pot or by a one-step direct labeling method using a sortase-mediated conjugation of either the radiolabeled chelator (H-GGGK((±)-Al[18F]FH3RESCA)-NH2) or the unlabeled chelator (H-GGGK((±)-H3RESCA)-NH2) followed by labeling with Al[18F]F, respectively. The overall radiochemical yields were 15-43% (n = 22, decay-corrected) in 70 min (indirect labeling) and 23-58% (n = 12, decay-corrected) in 50 min (direct labeling). The radiochemical purities of the labeled nanobodies prepared by both methods were >98% with a specific activity of 400-600 Ci/mmol (n = 22) for each of the three Nbs tested and exhibited excellent stability profiles under physiological conditions. This simple, site-specific, reproducible, and generalizable 18F-labeling method to prepare nanobodies (Nb-Al[18F]F-RESCA) or other low molecular weight biomolecules can easily be adopted in various settings for preclinical and clinical studies.

Devolatilization of extrasolar planetesimals by 60Fe and 26Al heating

ABSTRACT Whilst the formation of Solar system planets is constrained by meteoritic evidence, the geophysical history of low-mass exoplanets is much less clear. The bulk composition and climate states of rocky exoplanets may vary significantly based on the composition and properties of the planetesimals they form. An important factor influenced by planetesimal composition is water content, where the desiccation of accreting planetesimals impacts the final water content of the resultant planets. While the inner planets of the Solar system are comparatively water-poor, recent observational evidence from exoplanet bulk densities and planetary formation models suggests that rocky exoplanets engulfed by substantial layers of high-pressure ices or massive steam atmospheres could be widespread. Here, we quantify variations in planetesimal desiccation due to potential fractionation of the two short-lived radioisotopes 26Al and 60Fe relevant for internal heating on planetary formation time-scales. We focus on how order of magnitude variations in 60Fe can affect the water content of planetesimals, and how this may alter the formation of extrasolar ocean worlds. We find that heating by 26Al is the dominant cause of planetesimal heating in any Solar system analogue scenario, thus validating previous works focussing only on this radioisotope. However, 60Fe can become the primary heating source in the case of high levels of supernova enrichment in massive star-forming regions. These diverging scenarios can affect the formation pathways, bulk volatile budget, and climate diversity of low-mass exoplanets.

Big-bang Nucleosynthesis on a bubble universe nucleated in Kerr-AdS5.

Modelling the Galactic chemical evolution (GCE) of short-lived radioisotopes (SLRs, with half-lives of the order of million years) can provide timing information on recent nucleosynthesis. The knowledge of their spatial distribution throughout the interstellar medium (ISM) is crucial. We are using a three-dimensional GCE model to investigate the evolution of four SLRs: \(^{53}\)Mn from supernovae of type Ia (SNeIa), \(^{60}\)Fe from core-collapse supernovae (CCSNe), \(^{182}\)Hf from stellar winds from intermediate mass stars (IMSs), and \(^{244}\)Pu from neutron star mergers (NSMs) to explain the recent (within the last $\approx 1 -- 20$ Myr) deposition of live SLRs into deep-sea reservoirs. We find that although these SLRs are produced at very different nucleosynthetic sites, they are deposited on Earth conjointly.

Development of an optical method for temperature measurements of the ISAC targets at TRIUMF

The temperatures of isotope separator on-line targets play an important role for the overall target performance, including the yield of the radioactive ion beams and the target lifetime. At TRIUMF an optical technique is being developed to obtain accurate real-time temperature feedback from ISAC and in the future ARIEL targets during beam delivery. The light emitted from within the hot tantalum target container is captured and transmitted into a spectrometer via an ionizer opening. For accurate results an absolute irradiance calibration of the spectrometer is performed to determine the spectral power density. Then, to analyze the light spectra and calculate the maximum temperature, two mathematical methods have been applied. These methods are first evaluated using the spectrum of a light source with a known colour temperature. One method is selected and applied to a tantalum target container heated off-line at nominal temperatures and cross-checked with a thermocouple. The results of the test are in close agreement with the temperatures read by the thermocouple. This paper describes the calibration of the optical system, the methods applied, along with their results and validations. This technique will be applied to the on-line targets and correlate isotope releases with target temperatures for optimizing the delivery of short-lived radioisotopes species.

Galactic Chemical Evolution with the short lived radioisotopes \(^{53}\textbf{Mn}\), \(^{60}\textbf{Fe}\), \(^{182}\textbf{Hf}\), and \(^{244}\textbf{Pu}\)

Modelling the Galactic chemical evolution (GCE) of short-lived radioisotopes (SLRs, with half-lives of the order of million years) can provide timing information on recent nucleosynthesis. The knowledge of their spatial distribution throughout the interstellar medium (ISM) is crucial. We are using a three-dimensional GCE model to investigate the evolution of four SLRs: \(^{53}\)Mn from supernovae of type Ia (SNeIa), \(^{60}\)Fe from core-collapse supernovae (CCSNe), \(^{182}\)Hf from stellar winds from intermediate mass stars (IMSs), and \(^{244}\)Pu from neutron star mergers (NSMs) to explain the recent (within the last $\approx 1 -- 20$ Myr) deposition of live SLRs into deep-sea reservoirs. We find that although these SLRs are produced at very different nucleosynthetic sites, they are deposited on Earth conjointly.

Photoevaporation versus enrichment in the cradle of the Sun

ABSTRACT The presence of short-lived radioisotopes (SLRs) 26Al and 60Fe in the Solar system places constraints on the initial conditions of our planetary system. Most theories posit that the origin of 26Al and 60Fe is in the interiors of massive stars, and they are either delivered directly to the protosolar disc from the winds and supernovae of the massive stars, or indirectly via a sequential star formation event. However, massive stars that produce SLRs also emit photoionizing far and extreme ultraviolet radiation, which can destroy the gas component of protoplanetary discs, possibly precluding the formation of gas giant planets like Jupiter and Saturn. Here, we perfom N-body simulations of star-forming regions and determine whether discs that are enriched in SLRs can retain enough gas to form Jovian planets. We find that discs are enriched and survive the photoionizing radiation only when the dust radius of the disc is fixed and not allowed to move inwards due to the photoevaporation, or outwards due to viscous spreading. Even in this optimal scenario, not enough discs survive until the supernovae of the massive stars and so have zero or very little enrichment in 60Fe. We therefore suggest that the delivery of SLRs to the Solar system may not come from the winds and supernovae of massive stars.

The Oxygen Isotopic Composition of Samples Returned from Asteroid Ryugu with Implications for the Nature of the Parent Planetesimal

We present oxygen isotopic analyses of fragments of the near-Earth Cb-type asteroid Ryugu returned by the Hayabusa2 spacecraft that reinforce the close correspondence between Ryugu and CI chondrites. Small differences between Ryugu samples and CI chondrites in can be explained at least in part by contamination of the latter by terrestrial water. The discovery that a randomly sampled C-complex asteroid is composed of CI-chondrite-like rock, combined with thermal models for formation prior to significant decay of the short-lived radioisotope 26Al, suggests that if lithified at the time of alteration, the parent body was small (≪50 km radius). If the parent planetesimal was large (>50 km in radius), it was likely composed of high-permeability, poorly lithified sediment rather than consolidated rock.

Intra-Arterial Delivery of Radiopharmaceuticals in Oncology: Current Trends and the Future of Alpha-Particle Therapeutics.

A paradigm shift is underway in cancer diagnosis and therapy using radioactivity-based agents called radiopharmaceuticals. In the new strategy, diagnostic imaging measures the tumor uptake of radioactive agent "X" in a patient's specific cancer, and if uptake metrics are realized, the patient can be selected for therapy with radioactive agent "Y". The X and Y represent different radioisotopes that are optimized for each application. X-Y pairs are known as radiotheranostics, with the currently approved route of therapy being intravenous administration. The field is now evaluating the potential of intra-arterial dosing of radiotheranostics. In this manner, a higher initial concentration can be achieved at the cancer site, which could potentially enhance tumor-to-background targeting and lead to improved imaging and therapy. Numerous clinical trials are underway to evaluate these new therapeutic approaches that can be performed via interventional radiology. Of further interest is changing the therapeutic radioisotope that provides radiation therapy by β- emission to radioisotopes that also decay by α-particle emissions. Alpha (α)-particle emissions provide high energy transfer to the tumors and have distinct advantages. This review discusses the current landscape of intra-arterially delivered radiopharmaceuticals and the future of α-particle therapy with short-lived radioisotopes.

Short-lived radioisotope enrichment in star-forming regions from stellar winds and supernovae

ABSTRACT The abundance of the short-lived radioisotopes 26Al and 60Fe in the early Solar system is usually explained by the Sun either forming from pre-enriched material, or the Sun’s protosolar disc being polluted by a nearby supernova explosion from a massive star. Both hypotheses suffer from significant drawbacks: the former does not account for the dynamical evolution of star-forming regions, while in the latter the time for massive stars to explode as supernovae can be similar to, or even longer than, the lifetime of protoplanetary discs. In this paper, we extend the disc enrichment scenario to include the contribution of 26Al from the winds of massive stars before they explode as supernovae. We use N-body simulations and a post-processing analysis to calculate the amount of enrichment in each disc, and we vary the stellar density of the star-forming regions. We find that stellar winds contribute to disc enrichment to such an extent that the Solar system’s 26Al/60Fe ratio is reproduced in up to 50 per cent of discs in dense ($\tilde{\rho } = 1000$ M⊙ pc−3) star-forming regions. When winds are a significant contributor to the SLR enrichment, we find that Solar system levels of enrichment can occur much earlier (before 2.5 Myr) than when enrichment occurs from supernovae, which start to explode at later ages (>4 Myr). We find that Solar system levels of enrichment all but disappear in low-density star-forming regions ($\tilde{\rho } \le 10$ M⊙ pc−3), implying that the Solar system must have formed in a dense, populous star-forming region if 26Al and 60Fe were delivered directly to the protosolar disc from massive-star winds and supernovae.

Preclinical PET Imaging and Toxicity Study of a 68Ga-Functionalized Polymeric Cardiac Blood Pool Agent

Cardiac blood pool imaging is currently performed almost exclusively with 99mTc-based compounds and SPECT/CT imaging. Using a generator-based PET radioisotope has a few advantages, including not needing nuclear reactors to produce it, obtaining better resolution in humans, and potentially reducing the radiation dose to the patient. When the shortlived radioisotope 68Ga is used, it can be applied repeatedly on the same day-for example, for the detection of bleeding. Our objective was to prepare and evaluate a long-circulating polymer functionalized with gallium for its biodistribution, toxicity, and dosimetric properties. A 500 kDa hyperbranched polyglycerol was conjugated to the chelator NOTA and radiolabeled rapidly at room temperature with 68Ga. It was then injected intravenously into a rat, and gated imaging allowed us to easily observe wall motion and cardiac contractility, confirming the suitability of this radiopharmaceutical for cardiac blood pool imaging. Internal radiation dose calculations showed that the radiation doses that patients would receive from the PET agent would be 2.5× lower than those from the 99mTc agent. A complete 14-day toxicology study in rats concluded that there were no gross pathology findings, changes in body or organ weights, or histopathological events. This radioactive-metal-functionalized polymer might be a suitable non-toxic agent to advance for clinical application.

Hybridised production of technetium-99m and technetium-101 with fluorine-18 on a low-energy biomedical cyclotron

New modes of production and supply of short-lived radioisotopes using accelerators are becoming attractive alternatives to the use of nuclear reactors. In this study, the use of a compact accelerator neutron source (CANS) was implemented to explore the production of 99mTc and 101Tc. Irradiations were performed with neutrons generated from a 16.5 MeV cyclotron utilising the 18O(p, n)18F reaction during routine 18F-fluorodeoxyglucose (FDG) production in a commercial radiopharmacy. Natural molybdenum targets in metal form were employed for the production of several Tc isotopes interest via (n, γ) reactions on 98Mo and 100Mo. The production of 99mTc and 101Tc under these conditions is considered and discussed.

Inhomogeneous Enrichment of Radioactive Nuclei in the Galaxy: Deposition of Live 53Mn, 60Fe, 182Hf, and 244Pu into Deep-sea Archives. Surfing the Wave?

While modeling the galactic chemical evolution (GCE) of stable elements provides insights to the formation history of the Galaxy and the relative contributions of nucleosynthesis sites, modeling the evolution of short-lived radioisotopes (SLRs) can provide supplementary timing information on recent nucleosynthesis. To study the evolution of SLRs, we need to understand their spatial distribution. Using a three-dimensional GCE model, we investigated the evolution of four SLRs: 53Mn, 60Fe, 182Hf, and 244Pu with the aim of explaining detections of recent (within the last ≈1–20 Myr) deposition of live 53Mn, 60Fe, and 244Pu of extrasolar origin into deep-sea reservoirs. We find that core-collapse supernovae are the dominant propagation mechanism of SLRs in the Galaxy. This results in the simultaneous arrival of these four SLRs on Earth, although they could have been produced in different astrophysical sites, which can explain why live extrasolar 53Mn, 60Fe, and 244Pu are found within the same, or similar, layers of deep-sea sediments. We predict that 182Hf should also be found in such sediments at similar depths.

Aβ-Targeting Bifunctional Chelators (BFCs) for Potential Therapeutic and PET Imaging Applications

Currently, more than 55 million people live with dementia worldwide, and there are nearly 10 million new cases every year. Alzheimer's disease (AD) is the most common neurodegenerative disease resulting in personality changes, cognitive impairment, memory loss, and physical disability. Diagnosis of AD is often missed or delayed in clinical practice due to the fact that cognitive deterioration occurs already in the later stages of the disease. Thus, methods to improve early detection would provide opportunities for early treatment of disease. All FDA-approved PET imaging agents for Aβ plaques use short-lived radioisotopes such as 11C (t1/2 = 20.4 min) and 18F (t1/2 = 109.8 min), which limit their widespread use. Thus, a novel metal-based imaging agent for visualization of Aβ plaques is of interest, due to the simplicity of its synthesis and the longer lifetimes of its constituent isotopes. We have previously summarized a metal-containing drug for positron emission tomography (PET), magnetic resonance imaging (MRI), and single-photon emission computed tomography (SPECT) imaging of Alzheimer's disease. In this review, we have summarized a recent advance in design of Aβ-targeting bifunctional chelators for potential therapeutic and PET imaging applications, reported after our previous review.

Simulation studies of a 30-keV MR-ToF device for highly sensitive collinear laser spectroscopy

The Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS) seeks to extend the reach of high-resolution collinear laser spectroscopy (CLS) to more exotic radionuclides. In this novel technique, ion bunches of short-lived radioisotopes are trapped between two electrostatic mirrors of a Multi-Reflection Time-of-Flight (MR-ToF) device at 30-keV kinetic energy. The same ion bunch can be probed by a spectroscopy laser for thousands of times compared to a single probing in the traditional CLS measurement scheme. Thus, the experimental sensitivity is increased by more than one to two orders of magnitude. Extensive simulations are presented, demonstrating the feasibility of high-resolution collinear laser spectroscopy (CLS) in the newly envisioned MR-ToF apparatus operating at ion energies of 30 keV. Once the mechanical design and operational parameters are optimized for the requirements of CLS, the spectral line is neither significantly broadened nor distorted by the combination of CLS and MR-ToF operation. According to the simulations, the storage efficiency and the ion–laser overlap are suitable for laser excitation of the majority of the trapped ions. In summary, >90% injection and storage efficiency, >75% ion–laser overlap and a line width approaching the natural line width of the transition of interest are reached in the simulation.

Prevalence of short-lived radioactive isotopes across exoplanetary systems inferred from polluted white dwarfs

ABSTRACT In the Solar system, short-lived radioisotopes, such as 26Al, played a crucial role during the formation of planetary bodies by providing a significant additional source of heat. Notably, this led to early and large-scale melting and iron core formation in planetesimals and their loss of volatile elements, such as hydrogen and carbon. In the context of exoplanetary systems therefore the prevalence of short-lived radioisotopes is key to interpreting the observed bulk volatile budget and atmospheric diversity among low-mass exoplanets. White dwarfs that have accreted planetary material provide a unique means to infer the frequency of iron core formation in extrasolar planetesimals, and hence the ubiquity of planetary systems forming with high short-lived radioisotope abundances. Here, we devise a quantitative method to infer the fraction of planetary systems enriched with short-lived radionuclides upon planetesimal formation from white dwarf data. We argue that the current evidence from white dwarfs point towards a significant fraction of exoplanetesimals having formed an iron core. Although the data may be explained by the accretion of exomoon or Pluto-sized bodies that were able to differentiate due to gravitational potential energy release, our results suggest that the most likely explanation for the prevalence of differentiated material among polluted white dwarfs is that the Solar system is not unusual in being enriched in 26Al. The models presented here suggest a ubiquitous pathway for the enrichment of exoplanetary systems by short-lived radioisotopes, disfavouring short-lived radioisotope enrichment scenarios relying on statistically rare chance encounters with single nearby supernovae, Wolf–Rayet, or AGB stars.

Optimized Methodology for Reference Region and Image-Derived Input Function Kinetic Modeling in Preclinical PET.

PET imaging of small animals is often used for assessing biodistribution of a novel radioligand and pharmacology in small animal models of disease. PET acquisition and processing settings may affect reference region or image-derived input function (IDIF) kinetic modeling estimates. We examined four different factors in comparing quantitative results: 1) effect of reconstruction algorithm, 2) number of MAP iterations, 3) strength of the MAP prior, and 4) Attenuation and scatter. The effect of these parameters has not been explored for small-animal reference region and IDIF kinetic modeling approaches. Dynamic PET/CT scans were performed in 3 species with 3 different tracers: house sparrows with [11C]raclopride, rats with [18F]AS2471907 (11βHSD1) and mice with [11C]UCB-J (SV2A). FBP yielded lower kinetic modeling estimates compared to 3D-OSEM-MAP reconstructions, in sparrow and rat studies. Target resolutions (MAP prior strength) of 1.5 and 3.0mm demonstrated reduced VT in rats but only 3.0mm reduced BP ND in sparrows. Therefore, use of the highest target resolution (0.8mm) is warranted. We demonstrated using kinetic modeling that forgoing CT-based attenuation and scatter correction may be appropriate to improve animal throughput when using short-lived radioisotopes in sparrows and mice. This work provides recommendations and a framework for future optimization of kinetic modeling for preclinical PET methodology with novel radioligands.

Assessment of internal exposure to 131I and short-lived radioiodine isotopes and associated uncertainties in the Ukrainian cohort of persons exposed in utero.

This study revised the thyroid doses for 2582 Ukrainian in utero cohort members exposed to Chornobyl fallout (the Ukrainian in utero cohort) based on revision of: (i) 131I thyroid activity measured in the Ukrainian population, (ii) thyroid dosimetry system for entire Ukraine, and (iii) 131I ground deposition densities in Ukraine. Other major improvements included: (i) assessment of uncertainties in the thyroid doses considering shared and unshared error, and (ii) accounting for intake of short-lived radioisotopes of tellurium and iodine (132Te+132I and 133I). Intake of 131I was the major pathway for thyroid exposure, its median contribution to the thyroid dose was 97.4%. The mean prenatal and postnatal thyroid dose from 131I was 87mGy (median = 17mGy), higher than previous deterministic dose of 72mGy (median = 12mGy). For 39 individuals (1.5%) the dose exceeded 1.0Gy, while the highest dose among the cohort members was 2.7Gy. The geometric standard deviation (GSD) of 1000 individual stochastic doses varied from 1.9 to 5.2 with a mean of 3.1 and a median of 3.2. The lowest uncertainty (mean GSD = 2.3, median GSD = 2.2) was found for the subjects whose mothers were measured for 131I thyroid activity, while for individuals, whose mothers were not measured, the mean and median GSDs were 3.4. Uncertainties in thyroid doses were driven by shared errors associated with the parameters of the ecological model.

A novel technique for measuring diffusivities of short-lived radioisotopes in solids

Abstract After reminding the reader of the major techniques for measuring diffusion coefficients in solids, a detailed description of the conventional radiotracer techniques is presented. These allow to measure solid-state diffusivities in the regime 10– 8–10– 24 m2s– 1 and therefore, and for other reasons to be discussed, are superior to all competing methods. However, the conventional radiotracer techniques suffer from the restriction that they are not applicable to radio-tracer atoms with half-lives t 1/2 ≲ 1 d. The main objective of this paper is to introduce a novel experimental set-up which enables us to perform radiotracer-type diffusivity measurements with short-lived radioisotopes (1 d ≳ t ≳ 10 min). First results on the diffusion of 31Si (t 1/2 = 2.6 h) and 11C (t 1/2 = 20.38 min) in Si–Ge alloys and Si –C–N-based ceramics measured in this set-up are presented.

The use of the short-lived radioisotope <sup>188</sup>Re in the analytical practice of rhenium determination

The possibility of using the short-lived radioisotope 188Re (16.9 h) in the radioactive-tracer technique for estimation of the losses occurred during sample preparation and for analysis of the solutions with a low rhenium content is shown. The radioisotope was obtained in an 188Re generator, which is a glass column filled with aluminum oxide with a pre-adsorbed parent isotope 188W (69.4 days) that forms 188Re during β-decay. The latter in the form of a perrhenate ion was selectively washed into an aqueous solution, which was used to obtain a labeled solution. The values of rhenium losses and their distribution over the stages of sample preparation of carbon-containing raw materials (e.g., high-viscosity oil) including sintering, leaching, filtration and evaporation are estimated. It is shown that the greatest amount of rhenium is lost at the stage of sintering. However, the use of MgO + KMnO4 mixture minimize the losses occurred at this stage and, hence, the total losses of rhenium. A rapid procedure of rhenium determination using the method of radiometric correction with substoichiometric separation is described. The method is based on the quantitative extraction of a stable complex of tetraphenylphosphonium cation (TPhPh) with the perrhenate ion by dichloroethane. The extraction constant of (C6H5)4PReO4 complex is (3.03 ± 0.75) × 106. The extraction of the perrhenate ion not complexing with TPhPh does not exceed 1 – 2 %. The developed method provides rhenium determination in the sample at a level of 1 – 100 μg. A 10-fold excess of Zn2+ and Ni2+ present in a chloride-containing medium affects the determination of rhenium. The anions , , and have the most pronounced interfering effect whereas , , and Cl– do not interfere with the determination.