Production of high specific activity copper -67

Details Production of high specific activity copper -67 Production of high specific activity copper -67

1994-04-12

2002-12-03

Behrend, Harvey E. (Department: 3641)

Induced nuclear reactions: processes, systems, and elements

Nuclear transmutation

By charged particle bombardment

Reexamination Certificate

active

06490330

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of selective production of various radioisotopes. More particularly, the present invention relates to the production and separation of high specific activity copper isotopes, e.g., Cu
67
, from irradiated enriched Zn
70
targets. This invention is the result of a contract with the Department of Energy(Contract No. W-7405-ENG-36).
BACKGROUND OF THE INVENTION
Copper-67 (Cu
67
) is a radioisotope with significant potential for application in diagnostic and therapeutic nuclear medicine. As it decays to stable Zn
67
, with a 2.6 day half-life, it emits beta particles with energy maxima ranging from about 0.4 MeV to about 0.6 MeV. It also emits a gamma photon of 185 keV. Excellent research has shown that the beta particles are effective in treating various tumor types when the radioisotope is delivered to the disease site. The gamma photon is well-suited for imaging applications using the conventional Anger Gamma Camera so that Cu
67
localized in a tumor, can be imaged using equipment typically available in a nuclear medicine facility. Despite its promise this radioisotope has failed to make significant impact in clinical nuclear medicine, primarily because the isotope is available only in a sporadic and limited supply. Current methods of production use high energy proton reactions on natural zinc targets at large accelerators operating only part of the year or in nuclear reactors on enriched Zn
67
using high energy neutrons.
The possibility of early lung cancer detection using porphyrin as described by Cole et al. (U.S. Pat. No. 5,162,231) and the development of labeling porphyrin with metal ions (see, e.g., Mercer-Smith et al., Vol. 1 of Targeted Diagnosis and Therapy Series, J. T. Rodwell, ed., Marcel Dekker, New York, p. 317, 1988) and research into the possibility of therapy using Cu
67
labeled monoclonal antibodies (see, e.g., de Nardo et al., J.Nucl. Med. 29, p.217, 1988) has generated increased interest in the availability of high specific activity Cu
67
on a more consistent basis. Presently, these efforts have been severely restricted as a result of the sporadic supply of the Cu
67
used for preparation of the porphyrin. Presently, accelerator-produced Cu
67
is only available from Los Alamos National Laboratory (LANL) and Brookhaven National Laboratory (BNL) in large quantities about 6 to 8 months of the year. The present production methods at LANL and BNL rely on nonspecific spallation reactions which co-produce stable copper isotopes. These stable copper isotopes dilute the specific activity to levels which are acceptable for porphyrin/monoclonal antibody labeling research but are barely adequate for therapy. Reactor production via the Zn
67
(n, p)Cu
67
reaction is possible but production rates are too low to be financially feasible for long range treatment protocols. A number of possible methods of production were examined using the Los Alamos National Laboratory Van de Graff accelerator.
It has now been found that Cu
67
can be produced at low energies, i.e., less than about 25 MeV. Thus, Cu
67
may be produced throughout the year. As reaction pathways for production of stable copper isotopes do not exist in this reaction process, Cu
67
with a higher specific activity may be produced than is currently possible with accelerator production.
Accordingly, it is an object of this invention to provide an improved method of producing Cu
67
with a higher specific activity than previously available.
It is a further object of this invention to provide a method to produce Cu
67
continuously throughout the year using a low energy proton induced (p, &agr;)reaction on enriched Zn
70
.
Still another object of this invention to provide a method of recovering and reusing the enriched Zn
70
target material.
A still further object of this invention to provide a method of producing Cu
67
essentially free of Cu
64
in a low energy proton accelerator.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a process of producing essentially copper
64
-free copper
67
including irradiating an enriched zinc
70
target with sufficient protons of an energy from about 10 MeV to about 25 MeV for time sufficient to produce copper
67
, and, separating copper
67
from the irradiated target to yield an essentially copper
64
-free copper
67
product. The present invention further provides a high specific activity copper
67
product produced by the above described process, the copper
67
product characterized as essentially free of copper
64
and as having a specific activity greater than about at least 5 percent of theoretical value. The present invention further provides a process including separating enriched zinc
70
from the irradiated target and recycling the separated enriched zinc
70
into an enriched zinc
70
target for subsequent irradiation.
In one embodiment of the invention, the separation of copper
67
from the irradiated target includes dissolution of the proton-irradiated enriched zinc target in an acid solution of appropriate type and strength to form a first ion-containing solution, contacting the first ion-containing solution with a first anionic exchange resin whereby ions from the group consisting of zinc, copper, gallium, aluminum, cobalt and iron are selectively removed from the solution and ions from the group consisting of beryllium, nickel, and germanium remain in the solution, contacting the first anionic exchange resin with a second acid solution of appropriate type and strength capable of stripping the absorbed ions of copper, gallium, aluminum, cobalt, and iron from the first anionic exchange resin to form a second ion-containing solution, evaporating the second ion-containing solution for time sufficient to remove substantially all of the acid and water from the second ion-containing solution whereby a residue remains, dissolving the residue from the second ion-containing solution in a concentrated acid to form a third ion-containing solution to permit said ions to be absorbed by a first cationic exchange resin, contacting the cationic exchange resin with concentrated acid to selectively remove copper ions while any gallium, aluminum, cobalt and iron ions present remain absorbed by the first cationic exchange resin. Alternatively, the residue from the second ion-containing solution can be dissolved in a concentrated acid to form a third ion-containing solution to permit said ions to be absorbed by an anion exchange resin, and the third-ion containing solution contacted with an anionic exchange resin followed by stripping with concentrated acid to selectively remove copper ion while any gallium, aluminum, cobalt and iron ions present remain absorbed by the anion exchange resin.
DETAILED DESCRIPTION
The present invention concerns the proton irradiation, selective recovery of radioisotopes of copper and the enriched zinc target material, and fabrication of new targets from such recovered target material. Such a process can produce multi-millicurie quantities of such radioisotopes for use in the fields on nuclear medicine and/or nuclear chemistry.
In the process of the present invention, a copper
67
product essentially free of any copper
64
can be produced as the reaction with enriched zinc
70
produces only copper
67
. This leads to a product that avoids the presence of a second radioisotope thus eliminating the unnecessary exposure to that radioisotope while using the targeted radioisotope. Further, as essentially only copper
67
is produced, the specific activity of the product is naturally greater. As the specific activity of radioisotopes is effected by co-production of other stable or radioactive isotopes, high specific activities cannot be achieved using previous methods. Prior copper
67
available had a specific activity of only about 1.5 percent of the theoretical maximum of about 755,000 curies per gram. The present process may achieve specif

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