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), anda 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.

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 emitted along a beam axis, the proton beam having an energy comprised between 16 MeV and 100 MeVr and a beam intensity up to 1 mA, the neutron activator comprising:
 a neutron source comprising a metallic target presenting a longitudinal axis intended to be arranged parallel to the beam axis, wherein the metallic target has a hollow conical shape, the longitudinal axis of said conical shape being aligned with the proton beam, and   a Beryllium first reflector-moderator peripheral to the neutron source and comprising a neutron activation area configured to accommodate the neutron source and the material to be activated, the neutron activation area of the first reflector-moderator 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 of the first reflector-moderator further includes at least one activation channel extending along a channel axis parallel to the bore axis at the vicinity of the bore, the activation channel being configured to load the material to be activated. 
     
     
         3 . The neutron activator according to  claim 2 , wherein the neutron activation area comprises a plurality of activation channels distributed, around the bore. 
     
     
         4 . The neutron activator of  claim 1 , further comprising a cooling area in direct contact with an 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 1 , wherein the aperture of the hollow conical target and the thickness of its lateral walls are optimized so that
 (i) part of the protons received from the proton beam have sufficient energy to release the fraction of the thermal energy corresponding to the Bragg peak outside the metallic target,   (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 release their thermal energy inside the target, and,   (iii) the number of generated neutrons in the target is at least 70% equal to the number of neutrons generated in a target having a thickness where all the protons received from the proton beam release their thermal energy inside the target.   
     
     
         6 . The neutron activator according to  claim 1 , wherein the aperture of the hollow conical target and the thickness of its lateral walls is optimized so that
 (i) the protons received from the proton beam lose all their energy within the metallic target, and   (ii) the stresses generated by the temperature gradients in the target remain within the elastic limit of the metallic target, while still keeping the cooling liquid temperature below the boiling point.   
     
     
         7 . The neutron activator according to  claim 4 , further comprising, housed in the first reflector-moderator:
 an inlet channel conveying the cooling fluid to a flow guide,   a flow guide delimiting the cooling area for guiding the cooling fluid along the outer surface of the target as a flow from the inlet channel to the outlet channel,   an outlet channel for removing the cooling fluid from the flow guide.   
     
     
         8 . The neutron activator according to  claim 7 , wherein the flow guide is at least partly conical so that said conical flow guide covers the outer surface of the conical target thereby delimiting a cooling area surrounding the outer surface of the conical target. 
     
     
         9 . The neutron activator according to  claim 1 , wherein an aperture of the conical target is comprised between 20° and 45°. 
     
     
         10 . The neutron activator according to  claim 1 , wherein the metallic target is made of Beryllium or Tantalum. 
     
     
         11 . The neutron activator according to  claim 1 , wherein said first reflector-moderator is cylindrical along the bore axis. 
     
     
         12 . The neutron activator according to  claim 1 , presenting an overall dimension that does not exceed a volume of a cube of 1 meter side. 
     
     
         13 . The neutron activator according to  claim 1 , further comprising a second reflector-moderator embedding said first reflector-moderator ( 4 ). 
     
     
         14 . A neutron activation system for neutron activation of a material, comprising:
 a generator configured to produce a proton beam along a beam axis, the proton beam having an energy comprised between 16 MeV and 100 MeV, and a beam intensity up to 1 mA,   a neutron activator according to  claim 1  arranged so that the longitudinal axis of the target is parallel to the beam axis.   
     
     
         15 . The neutron activation system according to  claim 14 , wherein the neutron activation area of the first reflector-moderator further includes at least one activation channel extending along a channel axis parallel to the bore axis at the vicinity of the bore, the activation channel being configured to load the material to be activated, and further comprising a supplying device for loading the material to be activated, the supplying device being connected to the activation channel and configured to move samples of material to be activated along the activation channel. 
     
     
         16 . Use of the neutron activation system of  claim 14  for producing β −  emitting radioisotope suitable for Nuclear Medicine applications. 
     
     
         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 at an energy suitable for neutron activation of said material, and having for example an intensity up to 1 mA thereby activating said material.   
     
     
         18 . The method of  claim 17 , wherein the target is cooled by a flow of cooling liquid 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. 
     
     
         19 . The method of  claim 17 , wherein said material to be activated is contained within or in the form of a microparticle or nanoparticle. 
     
     
         20 . The neutron activator according to  claim 12 , wherein the overall dimension that does not exceed the volume of a cube of 0.75 meter side. 
     
     
         21 . The neutron activator according to  claim 12 , wherein the overall dimension that does not exceed the volume of a cube of 0.50 meter side. 
     
     
         22 . The neutron activation system according to  claim 14 , wherein the generator is configured to produce the proton beam having an energy comprised between 30 MeV and 70 MeV. 
     
     
         23 . The neutron activation system according to  claim 14 , wherein the generator is configured to produce the proton beam having a beam intensity up to 350 μA for 70 MeV. 
     
     
         24 . The neutron activation system according to  claim 14 , wherein the generator is configured to produce the proton beam having a beam intensity up to 1 mA for 30 MeV. 
     
     
         25 . Use according to  claim 16  for producing  166 Ho,  186 Re,  188 Re,  177 Lu,  198 Au,  90 Y,  227 Ra and  161 Tb. 
     
     
         26 . The method of  claim 18 , wherein the cooling liquid is water. 
     
     
         27 . The method of  claim 17 , wherein the proton beam has an energy between 16 MeV and 100 MeV. 
     
     
         28 . The method of  claim 17 , wherein the proton beam has an energy between 30 MeV and 70 MeV. 
     
     
         29 . The method of  claim 17 , wherein the proton beam has an intensity up to 350 μA for 70 MeV. 
     
     
         30 . The method of  claim 17 , wherein the proton beam has an intensity up to 1 mA for 30 MeV. 
     
     
         31 . The neutron activator according to  claim 3 , wherein the activation channels are equally distributed around the bore. 
     
     
         32 . The method of  claim 19 , wherein said material is in the form of Holmium-oxide microparticles or nanoparticles.