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The radionuclide thorium-229 features an isomer with an exceptionally low excitation energy that enables direct laser manipulation of nuclear states. It constitutes one of the leading candidates for use in next-generation optical clocks 1 – 3 . This nuclear clock will be a unique tool for precise tests of fundamental physics 4 – 9 . Whereas indirect experimental evidence for the existence of such an extraordinary nuclear state is substantially older 10 , the proof of existence has been delivered only recently by observing the isomer’s electron conversion decay 11 . The isomer’s excitation energy, nuclear spin and electromagnetic moments, the electron conversion lifetime and a refined energy of the isomer have been measured 12 – 16 . In spite of recent progress, the isomer’s radiative decay, a key ingredient for the development of a nuclear clock, remained unobserved. Here, we report the detection of the radiative decay of this low-energy isomer in thorium-229 ( 229m Th). By performing vacuum-ultraviolet spectroscopy of 229m Th incorporated into large-bandgap CaF 2 and MgF 2 crystals at the ISOLDE facility at CERN, photons of 8.338(24) eV are measured, in agreement with recent measurements 14 – 16 and the uncertainty is decreased by a factor of seven. The half-life of 229m Th embedded in MgF 2 is determined to be 670(102) s. The observation of the radiative decay in a large-bandgap crystal has important consequences for the design of a future nuclear clock and the improved uncertainty of the energy eases the search for direct laser excitation of the atomic nucleus. The authors report on the radiative decay of a low-energy isomer in thorium-229 ( 229m Th), which has consequences for the design of a future nuclear clock and eases the search for direct laser excitation of the atomic nucleus.

225 Ac is a radio-isotope that can be linked to biological vector molecules to treat certain distributed cancers using targeted alpha therapy. However, developing 225 Ac-labelled radiopharmaceuticals remains a challenge due to the supply shortage of pure 225 Ac itself. Several techniques to obtain pure 225 Ac are being investigated, amongst which is the high-energy proton spallation of thorium or uranium combined with resonant laser ionization and mass separation. As a proof-of-principle, we perform off-line resonant ionization mass spectrometry on two samples of 225 Ac, each with a known activity, in different chemical environments. We report overall operational collection efficiencies of 10.1(2)% and 9.9(8)% for the cases in which the 225 Ac was deposited on a rhenium surface and a ThO 2 mimic target matrix respectively. The bottleneck of the technique was the laser ionization efficiency, which was deduced to be 15.1(6)%.

225 Ac is a promising candidate medical radionuclide for targeted alpha therapy of advanced stage cancers. One of the main production pathways is the high-energy proton spallation of thorium-based targets, that requires an efficient, nuclide-selective separation method to recover 225 Ac from hundreds of co-produced spallation and fission products. The main radioactive contaminant of concern is 227 Ac  (T 1/2 = 21.8 years), that could preclude extensive medical use if not significantly suppressed. In this work, 225 Ac samples were produced by mass separation of radioactive ion beams extracted from proton-irradiated thorium-based targets. The activity of 225 Ac and other possible contaminants of the samples were measured using complementary gamma- and alpha-decay spectrometry methods, while 227 Ac activity was calculated by performing alpha-decay spectrometry of recoiled progeny from the sample. Using this novel method, accurate measurement of trace 227 Ac activity in 225 Ac samples was performed much faster than with conventional spectrometry techniques, thanks to its 10,000-fold increase in relative sensitivity. The end of collection activity ratio of 227 Ac to 225 Ac in two samples from irradiated targets were determined to be and respectively, three orders of magnitude below the 227 Ac activity in 225 Ac products obtained through radiochemical separation. The high separation factor of 225 Ac over 227 Ac suggests the suitability of mass-separated accelerator-based 225 Ac for medical use.

Particle therapy relies on the advantageous dose deposition which permits to highly conform the dose to the target and better spare the surrounding healthy tissues and organs at risk with respect to conventional radiotherapy. In the case of treatments with heavier ions (like carbon ions already clinically used), another advantage is the enhanced radiobiological effectiveness due to high linear energy transfer radiation. These particle therapy advantages are unfortunately not thoroughly exploited due to particle range uncertainties. The possibility to monitor the compliance between the ongoing and prescribed dose distribution is a crucial step toward new optimizations in treatment planning and adaptive therapy. The Positron Emission Tomography (PET) is an established quantitative 3D imaging technique for particle treatment verification and, among the isotopes used for PET imaging, the 11 C has gained more attention from the scientific and clinical communities for its application as new radioactive projectile for particle therapy. This is an interesting option clinically because of an enhanced imaging potential, without dosimetry drawbacks; technically, because the stable isotope 12 C is successfully already in use in clinics. The MEDICIS-Promed network led an initiative to study the possible technical solutions for the implementation of 11 C radioisotopes in an accelerator-based particle therapy center. We present here the result of this study, consisting in a Technical Design Report for a 11 C Treatment Facility. The clinical usefulness is reviewed based on existing experimental data, complemented by Monte Carlo simulations using the FLUKA code. The technical analysis starts from reviewing the layout and results of the facilities which produced 11 C beams in the past, for testing purposes. It then focuses on the elaboration of the feasible upgrades of an existing 12 C particle therapy center, to accommodate the production of 11 C beams for therapy. The analysis covers the options to produce the 11 C atoms in sufficient amounts (as required for therapy), to ionize them as required by the existing accelerator layouts, to accelerate and transport them to the irradiation rooms. The results of the analysis and the identified challenges define the possible implementation scenario and timeline.

Terbium features four clinically interesting radionuclides for application in nuclear medicine: terbium-149, terbium-152, terbium-155, and terbium-161. Their identical chemical properties enable the synthesis of radiopharmaceuticals with the same pharmacokinetic character, while their distinctive decay characteristics make them valuable for both imaging and therapeutic applications. In particular, terbium-152 and terbium-155 are useful candidates for positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging, respectively; whereas terbium-149 and terbium-161 find application in α- and β -/Auger electron therapy, respectively. This unique characteristic makes the terbium family ideal for the \"matched-pair\" principle of theranostics. In this review, the advantages and challenges of terbium-based radiopharmaceuticals are discussed, covering the entire chain from radionuclide production to bedside administration. It elaborates on the fundamental properties of terbium, the production routes of the four interesting radionuclides and gives an overview of the available bifunctional chelators. Finally, we discuss the preclinical and clinical studies as well as the prospects of this promising development in nuclear medicine.

Thulium-167 is a promising radionuclide for nuclear medicine applications with potential use for both diagnosis and therapy (“theragnostics”) in disseminated tumor cells and small metastases, due to suitable gamma-line as well as conversion/Auger electron energies. However, adequate delivery methods are yet to be developed and accompanying radiobiological effects to be investigated, demanding the availability of 167 Tm in appropriate activities and quality. We report herein on the production of radionuclidically pure 167 Tm from proton-irradiated natural erbium oxide targets at a cyclotron and subsequent ion beam mass separation at the CERN-MEDICIS facility, with a particular focus on the process efficiency. Development of the mass separation process with studies on stable 169 Tm yielded 65 and 60% for pure and erbium-excess samples. An enhancement factor of thulium ion beam over that of erbium of up to several 10 4 was shown by utilizing laser resonance ionization and exploiting differences in their vapor pressures. Three 167 Tm samples produced at the IP2 irradiation station, receiving 22.8 MeV protons from Injector II at Paul Scherrer Institute (PSI), were mass separated with collected radionuclide efficiencies between 11 and 20%. Ion beam sputtering from the collection foils was identified as a limiting factor. In-situ gamma-measurements showed that up to 45% separation efficiency could be fully collected if these limits are overcome. Comparative analyses show possible neighboring mass suppression factors of more than 1,000, and overall 167 Tm/Er purity increase in the same range. Both the actual achieved collection and separation efficiencies present the highest values for the mass separation of external radionuclide sources at MEDICIS to date.

CERN-MEDICIS is an off-line isotope separator facility for the extraction of radioisotopes from irradiated targets of interest to medical applications. The beamline, between the ion source and the collection chamber, consists of ion extraction and focusing elements, and a dipole magnet mass spectrometer recovered from the LISOL facility in Louvain-la-Neuve. The latter has been modified for compatibility with MEDICIS, including the installation of a window for injecting laser light into the ion source for resonance photo-ionization. Ion beam optics and magnetic field modeling using SIMION and OPERA respectively were performed for the design and characterization of the beamline. The individual components and their optimal configuration in terms of ion beam extraction, mass separation, and ion transport efficiency is described, along with details of the commissioning and initial performance assessment with stable ion beams.

This work presents the production cross-sections of Ce, Tb and Dy radionuclides produced by 300 MeV to 1.7 GeV proton-induced spallation reactions in thin tantalum targets as well as the related Thick Target production Yield (TTY) values and ratios. The motivation is to optimise the production of terbium radionuclides for medical applications and to find out at which energy the purity of the collection by mass separation would be highest. For that purpose, activation experiments were performed using the COSY synchrotron at FZ Jülich utilising the stacked-foils technique and γ spectrometry with high-purity germanium detectors. The Al-27(p,x)Na-24 reaction has been used as monitor reaction. All experimental data have been systematically compared with the existing literature.

Ac is a promising candidate medical radionuclide for targeted alpha therapy of advanced stage cancers. One of the main production pathways is the high-energy proton spallation of thorium-based targets, that requires an efficient, nuclide-selective separation method to recover Ac from hundreds of co-produced spallation and fission products. The main radioactive contaminant of concern is Ac  (T = 21.8 years), that could preclude extensive medical use if not significantly suppressed. In this work, Ac samples were produced by mass separation of radioactive ion beams extracted from proton-irradiated thorium-based targets. The activity of Ac and other possible contaminants of the samples were measured using complementary gamma- and alpha-decay spectrometry methods, while Ac activity was calculated by performing alpha-decay spectrometry of recoiled progeny from the sample. Using this novel method, accurate measurement of trace Ac activity in Ac samples was performed much faster than with conventional spectrometry techniques, thanks to its 10,000-fold increase in relative sensitivity. The end of collection activity ratio of Ac to Ac in two samples from irradiated targets were determined to be [Formula: see text] and [Formula: see text] respectively, three orders of magnitude below the Ac activity in Ac products obtained through radiochemical separation. The high separation factor of Ac over Ac suggests the suitability of mass-separated accelerator-based Ac for medical use.

The CERN-MEDICIS (MEDical Isotopes Collected from ISolde) facility has delivered its first radioactive ion beam at CERN (Switzerland) in December 2017 to support the research and development in nuclear medicine using non-conventional radionuclides. Since then, fourteen institutes, including CERN, have joined the collaboration to drive the scientific program of this unique installation and evaluate the needs of the community to improve the research in imaging, diagnostics, radiation therapy and personalized medicine. The facility has been built as an extension of the ISOLDE (Isotope Separator On Line DEvice) facility at CERN. Handling of open radioisotope sources is made possible thanks to its Radiological Controlled Area and laboratory. Targets are being irradiated by the 1.4 GeV proton beam delivered by the CERN Proton Synchrotron Booster (PSB) on a station placed between the High Resolution Separator (HRS) ISOLDE target station and its beam dump. Irradiated target materials are also received from external institutes to undergo mass separation at CERN-MEDICIS. All targets are handled via a remote handling system and exploited on a dedicated isotope separator beamline. To allow for the release and collection of a specific radionuclide of medical interest, each target is heated to temperatures of up to 2,300°C. The created ions are extracted and accelerated to an energy up to 60 kV, and the beam steered through an off-line sector field magnet mass separator. This is followed by the extraction of the radionuclide of interest through mass separation and its subsequent implantation into a collection foil. In addition, the MELISSA (MEDICIS Laser Ion Source Setup At CERN) laser laboratory, in service since April 2019, helps to increase the separation efficiency and the selectivity. After collection, the implanted radionuclides are dispatched to the biomedical research centers, participating in the CERN-MEDICIS collaboration, for Research & Development in imaging or treatment. Since its commissioning, the CERN-MEDICIS facility has provided its partner institutes with non-conventional medical radionuclides such as Tb-149, Tb-152, Tb-155, Sm-153, Tm-165, Tm-167, Er-169, Yb-175, and Ac-225 with a high specific activity. This article provides a review of the achievements and milestones of CERN-MEDICIS since it has produced its first radioactive isotope in December 2017, with a special focus on its most recent operation in 2020.