Induced nuclear reactions: processes – systems – and elements – Nuclear transmutation – By neutron bombardment
Patent
1992-08-10
1994-10-11
Harvey, Behrend E.
Induced nuclear reactions: processes, systems, and elements
Nuclear transmutation
By neutron bombardment
376170, 423 3, 423249, G21G 102
Patent
active
053553942
DESCRIPTION:
BRIEF SUMMARY
The invention refers to a method for producing actinium-225 and bismuth-213.
Radiotherapeutic methods for locally fighting against cancer (metastases) become more and more important in view of progresses obtained in the molecular biology field. Generally speaking, alpha-radiating nuclides of a short half-lifetime are thereby integrated into monoclonal antibodies which, after having been inserted into the body of a patient, tend to be incorporated into malign cells and destruct these cells due to an intensive irration of very short range. The radionuclide must in this case reply to particular requirements: It must be apt to be linked for conjugation to a convenient antibody, it must have a short half-lifetime (in the range of some hours) and its decay products must show a rather low chemical and radiological impact.
Among the possible candidates for such radionuclides actinium-225 and bismuth are particularly important, the relevant bismuth isotopes being either the isotope Bi-212 (half-lifetime 60,6 minutes) or the isotope Bi-213 (half-lifetime 47 minutes). The production of Bi-212 for medical use has been described in the periodical Ing. J.Nucl.Med.Biol. 9(1982), page 83. However, this isotope suffers from producing as a decay product a thallium isotope which is gamma-active and which causes an undesired radiation strain for the patient.
This does not apply to Bi-213, but this isotope is not available in sufficient quantities and cannot, until now, be produced in such quantities from U-233 at a reasonable expenditure. This uranium isotope U-233 is transformed via several decay steps into actinium-225 and the latter finally into Bi-213.
The decisive drawback of this decay chain resides in the small available quantity of Th-229 which is derived by decay from U-233. Since, for a significant hospital supply, between 10 and 100 g of Th-229 is required, U-233 should be available in a quantity of about 1 ton and with a storage time of 20 to 30 years in view of the separation. But such quantities of U-233 do not even exist on a world-wide scale.
The invention thus aims to indicate a method allowing to produce at a reasonable price sufficient quantities of actinium-225 and bismuth-213 for therapeutical use.
The method according to the invention consists in irradiating radium in the thermal neutron flux of a nuclear reactor, in chemically separating the thorium content from the irradiated product and in chemically separating therefrom the radio nuclides radium-225 and actinium-225 obtained in a continuous way by decay from thorium-229, said radio nuclides radium-225 and actinium-225 serving as basic substance ("cow") for the nuclides actinium-225 and bismuth-213.
Preferably, the radium is submitted to a high thermal neutron flux of about 5.times.10.sup.14 /cm.sup.2 sec.
The invention will now be described in detail by means of an example.
FIG. 1 shows the natural decay chain leading to bismuth-213.
FIG. 2 shows the formation of thorium-229 (in grams) as a function of time (in years) by irradiating 1 kg radium-226 in a thermal flux of 4.7.times.10.sup.14 neutrons/cm.sup.2 sec.
FIG. 3 shows schematically the entire method according to the invention.
FIG. 1 indicates the decay chain from thorium-229 to bismuth-213. At the upper end of this decay chain, there is also indicated with the atomic number 92 the isotope U-233 from which the desired thorium-229 is derived by natural decay, but, as said above, in an insufficient quantity. The key for producing Ac-225 and Bi-213 in significant quantities would be found if the isotope Th-229 could be produced in another way than by decay of U-233.
As it is shown in FIG. 3, according to the invention, the basic product is not U-233, but radium-226 having an atomic number of 88. For producing 100 g of thorium Th-229, about 1 kg of radium 226 is needed. This basic product is exposed for some years, e. g. three years, a high flux reactor, to a thermal neutral flux, which is as intense as possible, of about 4.7.times.10.sup.14 neutrons/cm.sup.2 sec. This is indicated in FIG. 3 by an
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Fuger Jean J.
Koch Lothar
van Geel Jacobus N. C.
European Atomic Energy Community (EURATOM)
Harvey Behrend E.
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