Accelerator-driven neutron activator for brachytherapy

Abstract

A neutron activator for neutron activation of a material, the neutron activator being configured to produce neutrons from an interaction with a proton beam ( 7 ), the neutron activator comprising: a neutron source comprising a metallic target ( 1 ), and a Beryllium first reflector-moderator ( 4 ) peripheral to the neutron source and comprising a neutron activation area ( 10 ) configured to accommodate the neutron source and the material to be activated, the neutron activation area ( 10 ) of the first reflector-moderator ( 4 ) comprising a bore configured to accommodate the neutron source. FIG. 1

1 . A neutron activator for neutron activation of a material, the neutron activator being configured to produce neutrons from an interaction with a proton beam ( 7 ) emitted along a beam axis, the proton beam ( 7 ) having an energy comprised between 16 MeV and 100 MeV, preferably 30 MeV and 70 MeV and a beam intensity up to 1 mA, preferably up to 350 μA for 70 MeV and up to 1 mA for 30 MeV, the neutron activator comprising:
 a neutron source comprising a metallic target ( 1 ) presenting a longitudinal axis intended to be arranged parallel to the beam axis, and 
 a Beryllium first reflector-moderator ( 4 ) peripheral to the neutron source and comprising a neutron activation area ( 10 ) configured to accommodate the neutron source and the material to be activated, the neutron activation area ( 10 ) of the first reflector-moderator ( 4 ) comprising a bore extending along a bore axis and configured to accommodate the neutron source so that the bore axis and the longitudinal axis are coaxial. 
 
     
     
         2 . The neutron activator according to  claim 1 , wherein the neutron activation area ( 10 ) of the first reflector-moderator ( 4 ) further includes at least one activation channel ( 5 ) extending along a channel axis parallel to the bore axis at the vicinity of the bore, the activation channel ( 5 ) being configured to load the material to be activated. 
     
     
         3 . The neutron activator according to  claim 2 , wherein the neutron activation area ( 10 ) comprises a plurality of activation channels ( 5 ) distributed, especially equally distributed, around the bore. 
     
     
         4 . The neutron activator of  claim 1 , wherein the metallic target ( 1 ) has a hollow conical shape, the longitudinal axis of said conical shape being aligned with the proton beam, and further comprising a cooling area in direct contact with the outer surface of the target ( 1 ) for receiving a flow of fluid for cooling the target ( 1 ) during neutron generation. 
     
     
         5 . The neutron activator according to  claim 4 , wherein the aperture of the hollow conical target ( 1 ) and the thickness of its lateral walls are optimized so that
 (i) part of the protons received from the proton beam ( 7 ) have sufficient energy to release the fraction of the thermal energy corresponding to the Bragg peak outside the metallic target ( 1 ),   (ii) the power density inside the target is reduced to at least 50% as compared to the power density in a target where all the protons received from the proton beam ( 7 ) release their thermal energy inside the target ( 1 ), and,   (iii) the number of generated neutrons in the target is at least 70% equal to the number of neutrons generated in a target ( 1 ) having a thickness where all the protons received from the proton beam ( 7 ) release their thermal energy inside the target ( 1 ).   
     
     
         6 . The neutron activator according to  claim 4 , wherein the aperture of the is hollow conical target ( 1 ) and the thickness of its lateral walls is optimized so that
 (i) the protons received from the proton beam ( 7 ) lose all their energy within the metallic target ( 1 ), and   (ii) the stresses generated by the temperature gradients in the target ( 1 ) remain within the elastic limit of the metallic target ( 1 ), while still keeping the cooling liquid temperature below the boiling point.   
     
     
         7 . The neutron activator according to  claim 4 , further comprising, housed in the reflector-moderator ( 4 ):
 an inlet channel ( 8 ) conveying the cooling fluid to a flow guide ( 2 ),   a flow guide ( 2 ) delimiting the cooling area for guiding the cooling fluid along the outer surface of the target ( 1 ) as a flow from the inlet channel ( 8 ) to the outlet channel ( 9 ),   an outlet channel ( 9 ) for removing the cooling fluid from the flow guide ( 2 ).   
     
     
         8 . The neutron activator according to  claim 7 , wherein the flow guide ( 2 ) is at least partly conical so that said conical flow guide covers the outer surface of the conical target ( 1 ) thereby delimiting a cooling area surrounding the outer surface of the conical target ( 1 ). 
     
     
         9 . The neutron activator according to  claim 4 , wherein the aperture of the conical target ( 1 ) is comprised between 20° and 45°. 
     
     
         10 . The neutron activator according to  claim 1 , wherein the metallic target ( 1 ) is made of Beryllium or Tantalum. 
     
     
         11 . The neutron activator according to  claim 1 , wherein said Beryllium reflector-moderator ( 4 ) is cylindrical along the bore axis. 
     
     
         12 . The neutron activator according to  claim 1 , presenting an overall dimension that does not exceed the volume of a cube of 1 meter side, preferably 0.75 meter side, and for example 0.50 meter side. 
     
     
         13 . The neutron activator according to  claim 1 , further comprising a second reflector-moderator ( 6 ) embedding said Beryllium reflector-moderator ( 4 ). 
     
     
         14 . A neutron activation system for neutron activation of a material, comprising:
 a generator ( 13 ) configured to produce a proton beam ( 7 ) along a beam axis, the proton beam ( 7 ) having an energy comprised between 16 MeV and 100 MeV, preferably 30 MeV and 70 MeV and a beam intensity up to 1 mA, preferably up to 350 μA for 70 MeV and up to 1 mA for 30 MeV,   a neutron activator according to  claim 1  arranged so that the longitudinal axis of the target ( 1 ) is parallel to the beam axis.   
     
     
         15 . The neutron activation system according to  claim 14 , wherein the neutron activation area ( 10 ) of the first reflector-moderator ( 4 ) further includes at least one activation channel ( 5 ) extending along a channel axis parallel to the bore axis at the vicinity of the bore, the activation channel ( 5 ) being configured to load the material to be activated, the neutron activation system further comprising a supplying device ( 14 ,  16 ) for loading the material to be activated, the supplying device ( 14 ,  16 ) being connected to the activation channel ( 5 ) and configured to move samples of material ( 15 ) to be activated along the activation channel ( 5 ). 
     
     
         16 . Use of the neutron activation system of  claim 14  for producing β −  emitting radioisotope suitable for Nuclear Medicine applications, preferably  166 Ho,  186 Re,  188 Re,  177 Lu,  198 Au,  90 Y,  227 Ra and  161 Tb. 
     
     
         17 . A method for neutron activation of a material, said method comprising:
 a) providing the material to be activated,   b) placing the material at the activation area of the neutron activator as defined in  claim 1 ,   c) generating a proton beam ( 7 ) at an energy suitable for neutron activation of said material, for example comprised between 16 MeV and 100 MeV, preferably between 30 MeV and 70 MeV, and having for example an intensity up to 1 mA, for example up to 350 μA for 70 MeV and up to 1 mA for 30 MeV,   
       thereby activating said material. 
     
     
         18 . The method of  claim 17 , wherein the target is cooled by a flow of cooling liquid, preferably water, at a static pressure comprised between 1 and 20 bar and reaching velocity comprised between 8 m/s and 24 m/s at the target surface. 
     
     
         17 . The method of  claim 17 , wherein said material to be activated is contained within or in the form of a microparticle or nanoparticle, for example of Holmium-oxide microparticles or nanoparticles.