Production and separation of 64Cu and 67Cu using 14 MeV neutrons

Production scheme for diagnostic-therapeutic radioisotopes by accelerator neutrons

Interest has been growing in the development of medical radioisotopes used for noninvasive nuclear medicine imaging of disease and cancer therapy. Especially the development of an alternative production scheme of ⁹⁹Mo, the mother radioisotope of ^99mTc used for imaging, is required, because the current supply chain of the reactor product ⁹⁹Mo is fragile worldwide. We have proposed a new production scheme of ⁹⁹Mo as well as therapeutic radioisotopes, such as ⁶⁴Cu and ⁶⁷Cu, using accelerator neutrons provided by the ^natC(d,n) reaction. Based on this scheme we have obtained high-quality ^99mTc, ⁶⁴Cu, and ⁶⁷Cu suitable for clinical use by developing both production and separation methods of the radioisotopes. We proposed a new facility to constantly and reliably produce a wide variety of high-quality, carrier-free radioisotopes, including ⁹⁹Mo, with accelerator neutrons. We report on the development of the proposed scheme and future prospects of the facility toward the domestic production of medical radioisotopes.

64Cu production by 14 MeV neutron beam

64Cu is an emerging radionuclide of great interest in personalized nuclear medicine. It is produced by a cyclotron via the reaction 64Ni(p,n)64Cu. This production method increased during the last decades, because small biomedical cyclotrons can be easily installed close to the nuclear medicine department of a hospital. As a matter of fact, 64Ni is a very expensive target material. For this reason, an alternative 64Cu production method was investigated at ENEA by using the quasi-monochromatic 14 MeV fusion neutron beam made available at the Frascati Neutron Generator (FNG) located at the ENEA – Frascati Research Center. In particular, two nuclear reactions were studied: 65Cu(n,2n)64Cu and 64Zn(n,p)64Cu. The radiochemical analysis of the activated samples was performed at the ENEA-NMLNWM laboratory located in ENEA-Casaccia Research Center. The activity measurements were carried out at the ENEA-INMRI, located in the ENEA-Casaccia Research Center, with high metrological level conditions and by assuring their traceability to the 64Cu primary activity standard here developed and maintained. A prediction of the 64Cu production by means of the high-brilliance 14 MeV neutron source named Sorgentina is also discussed.

Simple separation of 67Cu from bulk zinc by coprecipitation using hydrogen sulfide gas and silver nitrate

Copper-67 (67Cu), a feasible radionuclide for diagnosis and radiotherapy, is commercially generated from a bulk zinc (Zn) target using the 68Zn(p, 2p)67Cu and 68Zn(γ, p)67Cu nuclear reactions. Because it uses a large amount of zinc, the separation is complex – requiring a combination of three ion exchange columns – and is time-consuming (about 1 day). We developed a quick and easy separation method referred to as “double coprecipitation” using H2S gas and silver nitrate as coprecipitation agents in place of ion exchange columns. We compared this method with a conventional separation method using three ion exchange columns (AG50W-X8, AG1-X8, and Chelex-100) for a natural zinc (natZn) target irradiated by a proton beam. The product quality and the recovery rate with the new method were competitive with the conventional method, and the total operation time was reduced from 1 day to <3 h.

A novel approach to medical radioisotope production using inverse kinematics: A successful production test of the theranostic radionuclide 67Cu

A novel method for the production of important medical radioisotopes has been developed. The approach is based on performing the nuclear reaction in inverse kinematics, namely sending a heavy-ion beam of appropriate energy on a light target (e.g. H, d, He) and collecting the isotope of interest. In this work, as a proof-of-concept, we studied the production of the theranostic radionuclide ⁶⁷Cu (T_1/2 = 62 h) via the reaction of a ⁷⁰Zn beam at 15 MeV/nucleon with a hydrogen gas target. The ⁶⁷Cu radionuclide alongside other coproduced isotopes, was collected after the gas target on an aluminum catcher foil and their radioactivity was measured by off-line γ-ray analysis. After 36 h post irradiation, apart from the product of interest ⁶⁷Cu, the main radioimpurity coming from the ⁷⁰Zn + p reaction was ^69mZn (T_1/2 = 13.8 h), which can be reduced by further radio-cooling. Moreover, along with the radionuclide of interest produced in inverse kinematics, the production of additional radioisotopes is possible by making use of the forward-focused neutrons from the reaction and allowing them to interact with a secondary target. A preliminary successful test of this concept was realized in the present study. The main requirement to obtain activities appropriate for preclinical studies is the development of high-intensity heavy-ion primary beams.

Production, separation and supply prospects of 67Cu with the development of fast neutron sources and photonuclear technology

Experimental investigations have been carried out on the production of a promising therapeutic radionuclide 67Cu via the 67Zn(n,p)67Cu, 68Zn(n,x)67Cu, and 68Zn(γ,p)67Cu reaction routes. Natural zinc metal foils were irradiated with 14.1 MeV neutrons and bremsstrahlung of end-point energy 15 MeV. Radioactivity levels of 67Cu and other radioisotopes co-produced were determined by the quantification of photo-peaks by off-line γ-ray spectrometry. No carrier added 67Cu was separated from the irradiated zinc by solvent extraction. Yields >90% and high levels of radionuclidic purity were achieved. These studies indicate that the growth and development of intense fast neutron sources and photonuclear technology, will possibly aid in the sustained supply of 67Cu.

Theoretical estimation of 64Cu production with neutrons emitted during 18F production with a 30MeV medical cyclotron

PURPOSE

This work presents the theoretical estimation of a combined production of ¹⁸F and ⁶⁴Cu isotopes for PET applications. ⁶⁴Cu production is induced in a secondary target by neutrons emitted during a routine ¹⁸F production with a 30MeV cyclotron: protons are used to produce ¹⁸F by means of the ¹⁸O(p,n)¹⁸F reaction on a [¹⁸O]-H₂O target (primary target) and the emitted neutrons are used to produce ⁶⁴Cu by means of the ⁶⁴Zn(n,p)⁶⁴Cu reaction on enriched zinc target (secondary target).

METHODS

Monte Carlo simulations were carried out using Monte Carlo N Particle eXtended (MCNPX) code to evaluate flux and energy spectra of neutrons produced in the primary (Be+[¹⁸O]-H₂O) target by protons and the attenuation of neutron flux in the secondary target. ⁶⁴Cu yield was estimated using an analytical approach based on both TENDL-2015 data library and experimental data selected from EXFOR database.

RESULTS

Theoretical evaluations indicate that about 3.8 MBq/μA of ⁶⁴Cu can be obtained as a secondary, 'side' production with a 30MeV cyclotron, for 2h of irradiation of a proper designed zinc target. Irradiating for 2h with a proton current of 120 μA, a yield of about 457 MBq is expected. Moreover, the most relevant contaminants result to be ^63,65Zn, which can be chemically separated from ⁶⁴Cu contrarily to what happens with proton irradiation of an enriched ⁶⁴Ni target, which provides ⁶⁴Cu mixed to other copper isotopes as contaminants.

CONCLUSIONS

The theoretical study discussed in this paper evaluates the potential of the combined production of ¹⁸F and ⁶⁴Cu for medical purposes, irradiating a properly designed target with 30MeV protons. Interesting yields of ⁶⁴Cu are obtainable and the estimation of contaminants in the irradiated zinc target is discussed.