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EP-4736196-A2 - CONVERTERLESS CONVERSION OF RADIUM-226 TO ACTINIUM-225

EP4736196A2EP 4736196 A2EP4736196 A2EP 4736196A2EP-4736196-A2

Abstract

A converterless method for converting 226 Ra to 225 Ac by direct electron beam bombardment with high energy electron beam having an average effective beam power of about 20 to about 250 kW at a beam energy of about 25 to about 100 MeV to impact the 226 Ra is disclosed. Contrary to other electron-based bombardment methods, the present method is carried out without a converter that slows the electrons and transforms their kinetic energy into Bremsstrahlung photons, but rather into the production of virtual photons that transmute the target 226 Ra to 225 Ra that decays to 225 Ac.

Inventors

  • NUSAIR, Omar

Assignees

  • NORTHSTAR MEDICAL TECHNOLOGIES, LLC

Dates

Publication Date
20260506
Application Date
20240628

Claims (14)

  1. 1. A method for converting 226 Ra to 225 Ac by electron beam bombardment with high energy electrons without the use of a converter that comprises the steps of : a) bombarding a target comprised of 226 Ra present within a hermetically sealed capsule with an electron beam having an average effective beam power of about 20 to about 250 kW at a beam energy of about 25 to about 100 MeV, said capsule having a capsule lid through which said beam of electrons passes prior to impacting said 226 Ra, the capsule lid optionally having a high-Z material coating having a thickness of about 120 to about 220 microns (p) on its internal capsular surface through which said beam of electrons also passes prior to impacting said 226 Ra target; and b) maintaining said bombardment for a time period sufficient to remove a neutron and or a proton from said 226 Ra target and form 225 Ac in a commercial scale .
  2. 2. The method according to claim 1, wherein the formed 225 Ac is recovered.
  3. 3. The method according to claim 1, wherein said high-Z material coating is present.
  4. 4. The method according to claim 1, wherein said capsule is comprised of aluminum or titanium .
  5. 5. The method according to claim 4, wherein said capsule is provided in the form of a hollow cylinder with generally rounded ends, a hollow cone, or a hollow truncated cone.
  6. 6. The method according to claim 5, wherein said capsule lid is positioned at an end along an axis of the capsule that is different from a long axis of the capsule.
  7. 7. The method according to claim 5, wherein said capsule lid is positioned at the end of the capsule that is along a long axis of the capsule.
  8. 8. The method according to claim 1, wherein said time period for bombardment is maintained for about 4 days to about 30 days.
  9. 9. The method according to claim 1, wherein said average electron beam power is at about 60 to about 200 kW .
  10. 10. The method according to claim 1, wherein said beam energy is at about 25 to about 65 MeV electrons .
  11. 11. A method for converting a 226 Ra target to 225 Ac by electron beam bombardment of said 226 Ra target with high energy electrons without the use of a converter that comprises the steps of: a) bombarding a target comprised of 226 Ra present within a hermetically sealed capsule with an electron beam having an average effective beam power of about 60 to about 200 kW at a beam energy of about 25 to about 65 MeV, said capsule having a capsule lid through which said beam of electrons passes prior to impacting said 226 Ra, the capsule lid optionally having a high-Z material coating having a thickness of about 120 to about 220 microns (p) on its internal capsular surface through which said beam of electrons also passes prior to impacting said 226 Ra target; and b) maintaining said 226 Ra target bombardment for a time period of about 4 days to about 30 days to form 225 Ac in a commercial scale.
  12. 12. The method according to claim 11, wherein said 226 Ra target is present as a halide or nitrate salt.
  13. 13. The method according to claim 11, wherein the formed 225 Ac is recovered.
  14. 14. The method according to claim 11, wherein said capsule is comprised of aluminum.

Description

CONVERTERLESS CONVERSION OF RADIUM-226 TO ACTINIUM-225 Description CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to US application Serial No. 63/523992, filed on June 29, 2023, whose disclosures are incorporated herein by reference . TECHNICAL FIELD The present invention relates to the preparation of 225Ac from 226Ra target by the bombardment of that radium isotope with a high energy electron beam to produce virtual photons electromagnetic radiation that transmutes the 226Ra to 225Ra and 225Fr both of which decay to 225 Ac . This photonuclear reaction is carried out without the use of an intervening Brems strahlung- converter between the electron beam and the target 226Ra. BACKGROUND ART The quest for bridging the gap between the severely constrained 225Ac (which has a half-life T2/2= 9.92 days) supply and the large worldwide demand for that isotope is a key factor in nuclear medicine. The demand for 225Ac stems from the use of that isotope in targeted alpha therapy (TAT) . Radioisotope 225Ac and its daughter 213Bi (T2/2= 45.61 minutes) are used in medicine for the treatment of several cancers, including prostate, brain, and neuroendocrine cancers. In one of the usual methods of production, 225Ac is produced via the p“-decay of 225Ra (T2/2= 14.9 days) , which is itself produced by the (y,n) reaction on a high-purity 226Ra (T2/2= 1600 years) target. The photons are produced by a solid converter of high atomic number (high-Z) material, such as tantalum, via the braking-radiation (Bremsstrahlung) mechanism that can result from slowing down very energetic accelerated electrons impinging on the converter material. The Bremsstrahlung thereby produced are high energy photons that impinge upon the target 226Ra and cause the 226Ra to transmute into another radioisotope, 225Ra that decays via the p~-decay to 225Ac. However, the typical photon spectrum generated using a converter is widely dispersed in terms of energy (see Fig. 1) and also to an extent in terms of the emission angle (see Fig. 2) . Moreover, around 80% of the photon flux spectrum is below the neutron separation energy (e.g. , Sn) of 226Ra (Sn= 6.39 MeV) , which makes those photons sterile, but can catastrophically overheat the target and its surrounding materials. Such overheating requires enhanced cooling and, consequently enhanced radiowaste removal systems. Two tantalum disk converters were used previously to enhance cooling and heat removal. They are shown in Figs. 1 and 2 as illustrative of difficulties found when using converters. The use of more than a single converter was proposed by Diamond et al., J Appl Phys 129:104901 (March 09, 2021) . In addition, with the use of converters, the proton-removal channel that produces an important precursor of the 225Ra, i.e., 225Fr (T2/2= 3.95 m) , via photon bombardment (irradiation) of the 226Ra target is not feasible. The deficiency stems from the anticipated very low yield due to the very low photon flux level at the energy where the (y, p) reaction cross- section has its peak value omax(30 MeV)= 0.2 mb. Alternatively, without a converter, and as a result of the electrons traveling with an ultra- relativistic speed (Energy »M») and hitting the high-Z target, a new class of interaction with the time-varying Coulomb field takes place. This interaction, named Coulomb Dissociation (CD) , can be interpreted as an absorption of a virtual photon [Bertulani et al., Physics Reports 163:299-408, 1988; and International Atomic Energy Agency, Handbook on Photonuclear Data for Applications : Cross sections and Spectra, I.A.E.A TECDOC 1178 (2000) , Sections 3.1.4 and 4.4] . The absorption probability can be translated into (y,n) and (y,p) cross-sections, which can be experimentally measured using several techniques. One of these techniques is the activation and delayed counting method. Many measurements were performed in the past using this technique on a variety of different beam-target systems. The work reported in [Gerab et al., Phys Rev C, 48 (1) : 105-108 (1993) ; Martins et al; ., Phys. Rev. C, 16: 613 (1977) ; and Shotter et al., Nucl Phys A330:325 (1979) ] for accelerated electrons incident on 238U are of special interest due to their seeming similarity to the reactions here for the production of 225Ra/225Ac via (e~,n) and (e~,p) on 226Ra. The similarity in the nuclear structures between both target nuclear systems, i.e. , 238U and 226Ra, suggests using the same optical model potential (OPM) parameters for the distorted-wave Born approximation (DWBA) calculation as the reaction model for both systems when interacting with El and E2 virtual photons generated from the ultra- relativistic electrons. As noted in Fig. 3, which is adopted from Gerab et al., above, and replotted here using the JANIS database [JANIS Database (Nuclear Energy Agency (NEA) - JANIS (oecd-nea.org) ] , the cross- section for removing a neutron from a 238U nucleus at 40 MeV of beam energy is about 2.5 mb.