Recent Program-Supported Publications

An experiment was performed at the National Superconducting Cyclotron Laboratory using a 140 MeV/nucleon ⁴⁸Ca beam and a flowing-water target to produce ⁴⁷Ca for the first time with this production route. A production rate of 0.020 ± 0.004 ⁴⁷Ca nuclei per incoming beam particle was measured. An isotope harvesting system attached to the target was used to collect radioactive cationic products, including ⁴⁷Ca, from the water on a cation-exchange resin. The ⁴⁷Ca collected was purified using three separation methods optimized for this work: (1) DGA extraction chromatography resin with HNO₃ and HCl, (2) AG MP-50 cation-exchange resin with an increasing concentration gradient of HCl, and (3) AG MP-50 cation-exchange resin with a methanolic HCl gradient. These methods resulted in ≥99 ± 2% separation yield of ⁴⁷Ca with 100% radionuclidic purity within the limits of detection for HPGe measurements. Inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to identify low levels of stable ions in the water of the isotope harvesting system during the irradiation and in the final purified solution of ⁴⁷Ca. For the first time, this experiment demonstrated the feasibility of the production, collection, and purification of ⁴⁷Ca through isotope harvesting for the generation of ⁴⁷Sc for nuclear medicine applications.

A high-intensity proton irradiation was performed with the flowing-water isotope harvesting target at the University of Wisconsin-Madison Cyclotron Laboratory to measure the rate of degradation of the target shell during irradiation conditions. The beam reached an intensity of 34 µA by the end of the irradiation and covered an area of 0.7 cm² on the target. Radiolysis products, such as H₂O₂, H₂, and O₂, were measured in the bulk water of the system and found to be present at much lower levels than predicted by literature escape yields. Radionuclides formed in the target shell were measured in the system water as a radiotracer for target degradation. Using a simple, beam intensity-dependent model, a corrosion rate of 1.5E-6 μm/(μA*s) was found to match the measured radiotracer activities at various points in the irradiation. This rate was used to extrapolate the lifetime of future isotope harvesting targets at the NSCL and FRIB, using the areal power density of different ion beams to scale the corrosion rate.

The Nuclear Medicine Global Initiative (NMGI) was formed in 2012 by 13 international organizations to promote human health by advancing the field of nuclear medicine and molecular imaging by supporting the practice and application of nuclear medicine. The first project focused on standardization of administered activities in pediatric nuclear medicine and resulted in two manuscripts. For its second project the NMGI chose to explore issues impacting on access and availability of radiopharmaceuticals around the world. Methods: Information was obtained by survey responses from 35 countries on available radioisotopes, radiopharmaceuticals and kits for diagnostic and therapeutic use. Issues impacting on access and availability of radiopharmaceuticals in individual countries were also identified. Results: Detailed information on radiopharmaceuticals utilized in each country, and sources of supply, was evaluated. Responses highlighted problems in access particularly due to the reliance on a sole provider, regulatory issues and reimbursement, as well as issues of facilities and workforce particularly in low- and middle-income countries. Conclusion: Strategies to address access and availability of radiopharmaceuticals are outlined, to enable timely and equitable patient access to nuclear medicine procedures worldwide. In the face of disruptions to global supply chains by the COVID-19 outbreak, renewed focus on ensuring reliable supply of radiopharmaceuticals is a major priority for nuclear medicine practice globally.

Harvesting isotopes from beam stops and other activated materials at accelerator facilities is a promising source of environmentally, scientifically and socially important radionuclides. At the Facility for Rare Isotope Beams (FRIB), a multitude of short- and long-lived radionuclides will be collected in a synergistic manner by dumping unused beams into a flowing-water beam stop. Ongoing exploratory research at the National Superconducting Cyclotron Laboratory (NSCL) with an analogous beam blocker aims towards obtaining the necessary radiochemical expertise for this endeavor.

Herein we present a beam blocker and an isotope harvesting system which allows collection of a wide variety of aqueous and gaseous radionuclides. The water which flows through the beam blocker functions as an isotope production target and concurrently transports the newly formed radionuclides to collection sites. The system includes analytical instruments for online measurements of conductivity, dissolved oxygen, temperature, pressure and for detection of radiolytic products. To limit the levels of radiolytically produced hydrogen peroxide, a stainless-steel based degradation system was designed and implemented. The suitability of the constructed system for the anticipated radionuclide harvesting project was demonstrated by offline tests and under irradiation with 140 MeV/u ⁴⁸Ca^20＋ ions at the NSCL Coupled Cyclotron Facility.

A flowing-water target was irradiated with a 140 MeV/u, 8 nA 40Ca20+ beam to test the feasibility of isotope harvesting at the upcoming Facility for Rare Isotope Beams. Among other radionuclides, 2.6(2)E-6 48Cr and 5.6(5)E-6 28 Mg nuclei were formed for every impingent 40Ca and were collected through ion exchange. Radiolysis-induced molecular hydrogen evolved from the target at an initial rate of 0.91(9) H2 molecules per 100 eV of beam energy deposited. No radiation-accelerated corrosion of the target material was observed.

The Isotope Production Facility (IPF) at Los Alamos National Laboratory (LANL) is used to produce an array of isotopes for medical, global security, and research applications with an intense beam of protons supplied by the linear accelerator at the Los Alamos Neutron Science Center (LANSCE). An Accelerator Improvement Project (AIP) was recently conducted at IPF to improve facility reliability and reduce programmatic risk while increasing general isotope production capacity and flexibility. This was accomplished through the installation of an improved beam window assembly, more robust beam diagnostics, an active and adjustable collimator, and a new beam rastering system. This paper will highlight the four exciting innovations and how they were designed, validated, and installed in parallel as well as the significant operational advantages they provide to IPF. Key experiments and the increased currents achieved in routine production runs demonstrating the enhanced capability from the AIP will be presented. The most notable capability enhancements include irradiations with beam currents ranging from 100 nA experimental runs up to 300 μA on routine production targets and utilization of a range of cylindrical target diameters.

The upcoming Facility for Rare Isotope Beams (FRIB) at Michigan State University provides a new opportunity to access some of the world's most specialized scientific resources: radioisotopes. An excess of useful radioisotopes will be formed as FRIB fulfills its basic science mission of providing rare isotope beams. In order for the FRIB beams to reach high-purity, many of the isotopes are discarded and go unused. If harvested, the unused isotopes could enable new research for diverse applications ranging from medical therapy and diagnosis to nuclear security. Given that FRIB will have the capability to create about 80% of all possible atomic nuclei, harvesting at FRIB will provide a fast path for access to a vast array of isotopes of interest in basic and applied science investigations. To fully realize this opportunity, infrastructure investment is required to enable harvesting and purification of otherwise unused isotopes. An investment in isotope harvesting at FRIB will provide a powerful resource for development of crucial isotope applications. In 2010, the United States Department of Energy Office of Science, Nuclear Physics, sponsored the first 'Workshop on Isotope Harvesting at FRIB', convening researchers from diverse fields to discuss the scientific impact and technical feasibility of isotope harvesting. Following the initial meeting, a series of biennial workshops was organized. At the fourth workshop, at Michigan State University in 2016, the community elected to prepare a formal document to present their findings. This report is the output of the working group, drawing on contributions and discussions with a broad range of scientific experts.

Abstract

Actinium-225 (225Ac) can be produced with a linear accelerator by proton irradiation of a thorium (Th) target, but the Th also underdoes fission and produces 400 other radioisotopes. No research exists on optimization of the cation step for the purification. The research herein examines the optimization of the cation exchange step for the purification of 225Ac. The following variables were tested: pH of load solution (1.5–4.6); rinse steps with various concentrations of HCl, HNO3, H2SO4, and combinations of HCl and HNO3; various thorium chelators to block retention; MP50 and AG50 resins; and retention of 20–45 elements with different rinse sequences. The research indicated that HCl removes more isotopes earlier than HNO3, but that some elements, such as barium and radium, could be eluted with ≥2.5 M HNO3. The optimal pH of the load solution was 1.5–2.0, and the optimized rinse sequence was five bed volumes (BV) of 1 M citric acid pH 2.0, 3 BV of water, 3 BV of 2 M HNO3, 6 BV of 2.5 M HNO3 and 20 BV of 6 M HNO3. The sequence recovered >90% of 225Ac with minimal 223Ra and thorium present.

Abstract

The degradation of proton beam energy within a target stack was monitored via product nuclide ratios at the Los Alamos Isotope Production Facility (LANL-IPF). Nuclear reaction channels employed as energy monitors included NatNi(p,x)57Co and NatNi(p,x)57Ni. Natural nickel foils (thicknesses 0.025 mm) were used to determine proton beam energies ranging from 15 to 30 MeV. Energy values were estimated from a fitted 57Ni/57Co production activity ratio curve, which, in turn, was calculated from formation cross section data. Isotope production yields in the low energy “C” slot at LANL-IPF are very sensitive to beam energy, and differences of several MeV can translate into a drastic effect on overall production yields and radiochemical purity. Proton energies determined in this target stack position using nickel foils will serve as a basis to optimize radionuclide production in terms of product yield maximization and by-product minimization.