Feasibility of Isotope Harvesting at a Projectile Fragmentation Facility: 67Cu

There are many isotopes that could be useful in a range of disciplines from medicine to stockpile stewardship, geology, nuclear astrophysics and biology that are not available in the quantities needed from conventional production methods based on small medical cyclotrons or reactors1,2,3,4,5,6,7. The construction of the Facility for Rare Isotope Beams (FRIB) will allow “harvesting” usable quantities of many of these isotopes, concurrent with secondary-beam operations for basic nuclear science experiments. The FRIB design has provisions for delivering research quantities (μCi to Ci) of radioisotopes as an ancillary service to the on-line experimental program by collecting radioisotopes produced or stopped in an aqueous beam dump8,9 in the primary target facility while secondary beams are produced for on-line experiments. Ideally this collection or “harvesting” of isotopes at FRIB could provide isotopic material for which there is currently no comparable source. One such radioisotope is 67Cu which can be used in medicine as a therapeutic isotope6,10,11. Its relatively long 2.58 day half-life is ideal for labeling antibodies that also have several-day biological half-lives. Obtaining therapeutic doses that are typically on the order of hundreds of mCi/patient12 has proved to be quite difficult due to inconsistent production and no reliable continuous supply6,12,13,14. 67Cu can be made via several nuclear reactions: 68Zn(p,2p)67Cu, 70Zn(p,α)67Cu, 67Zn(n,p)67Cu, and 68Zn(γ,p)67Cu; however each reaction has practical drawbacks. For example, 68Zn(p,2p)67Cu has a low but broad (in energy) cross section and in order to efficiently produce the large quantities needed for therapeutic doses thick targets and high-energy proton accelerators such as those at Brookhaven15,16 or Los Alamos National Laboratories17 need to be employed. These are multiuser facilities that cannot routinely dedicate proton beam to produce a continuous supply of 67Cu12. Studies at several facilities of the 70Zn(p,α)67Cu reaction have obtained varying yields and the production of the large quantities needed for therapeutic studies are challenging with this method18,19,20. Production via the 67Zn(n,p)67Cu and 68Zn(γ,p)67Cu reactions have undesirable side reactions and concerns about waste products create challenges for their large scale use12. It is estimated that FRIB will be able to produce a saturated activity of 67Cu as high as ~2 Ci depending on the primary beam21 so that weekly harvesting of 67Cu could provide a more consistent supply of this isotope. Therefore, given the difficulty of other production methods, the favorable half-life and well-understood chemistry of 67Cu, this isotope was selected for a proof-of-principle test of isotope harvesting from an aqueous beam stop for projectile fragments. The work reported here can be extended to other projectile fragments collected in an aqueous beam stop. Previously, a liquid-water target system/beam stop was designed and tested at the NSCL for a first attempt to harvest useful radioisotopes from a beam dump similar to what will exist at FRIB22. This system was used successfully to collect several samples of 24Na from a projectile fragment beam at ~85 MeV/u and an intensity of ~2 × 106 pps. In the present work, the liquid water target system described in ref [8] was used to collect several samples of 67Cu that were also produced as a secondary beam at the NSCL. The aqueous samples were then transported to Washington University in St Louis, MO and Hope College in Holland, MI for chemical separation, antibody labeling, and offline counting. We report here the results of these studies and the observation of relatively high chemical extraction efficiency.