Neutron source with beam shaping apparatus for radiography
A neutron generator has a neutron source generating an ion beam bombarding a Titanium target having a first diameter, the target embedded in a pre-moderator, emitting fast neutrons isotropically, a portion of the fast neutrons moderated in passing through the pre-moderator and exiting through a lowermost surface of the pre-moderator, and a plate of moderating material abutting the lowermost surface of the pre-moderator, the plate having an opening therethrough in a shape of a truncated cone with an axis aligning with direction of the ion beam, a depth, a major diameter of at the upper surface of the plate and a minor diameter at the lower surface of the plate, the opening forming a funnel through which neutrons pass. Neutrons enter the funnel and are to exit through the minor diameter of the funnel, providing a neutron beam with a spot size useful for neutron radiography.
1. A neutron radiography generator, comprising:
a modular neutron source generating an ion beam in a first direction, the ion beam bombarding a Titanium target having a surface comprising a first diameter, the target embedded in a pre-moderator having a lowermost surface, emitting fast neutrons isotropically, a portion of the fast neutrons moderated in passing through the pre-moderator and exiting through the lowermost surface of the pre-moderator; and
a plate of moderating material abutting the lowermost surface of the pre-moderator, the plate having an upper surface, a lower surface, a thickness, and an opening therethrough in a shape of a truncated cone with an axis aligning with the first direction of the ion beam, a depth, a major diameter of at the upper surface of the plate and a minor diameter at the lower surface of the plate, the opening forming a funnel through which neutrons pass;
wherein neutrons exiting the pre-moderator through the lowermost surface thereof enter the funnel and are collimated through the funnel to exit through the minor diameter of the funnel, providing a neutron beam with a spot size useful for neutron radiography.
2. The neutron radiography generator of claim 1 wherein the thickness of the plate of moderating material is greater than the depth of the funnel, further comprising a sleeve of high-density neutron reflecting material having in inside diameter equal to the major diameter of the truncated cone shape of the funnel, the sleeve lining a circular hole in the plate of moderating material, the hole having a first depth from the upper surface to the major diameter of the truncated cone shape of the funnel, such that the depth of the circular hole and the depth of the funnel equals the thickness of the plate, and the inside diameter of the sleeve of reflecting material meets the major diameter of the truncated cone shape of the funnel.
3. The neutron radiography generator of claim 2 further comprising a disk of Bismuth having a diameter equal to the inside diameter of the sleeve and a length less than the first depth of the hole, and a solid cylinder of sapphire crystal having a diameter equal to the inside diameter of the sleeve and a length such that the length of the bismuth disk and the sapphire cylinder equal the length of the hole from the upper surface of the plate of moderating material to the major diameter of the funnel, the bismuth disk and sapphire crystal attenuating gamma radiation and attenuating fast neutrons.
4. The neutron radiography generator of claim 1 further comprising a layer of shielding material cladding the outer surfaces of the generator including the lower surface of the plate of moderating material, with a hole through the shielding material at and equal in diameter to the minor diameter of the funnel.