Neutron Source Beam Shaping for Radiography
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Solution Overview
Problem
Conventional neutron radiography using nuclear reactors suffers from divergent neutron sources with contaminating components like fast neutrons and gamma rays, leading to image blurring and reduced quality, necessitating the development of a compact and inexpensive neutron source that can produce a directional, high-flux thermal neutron beam for effective radiography.
Innovation Solution
A modular Low Voltage Fusion Neutron Generator (LVFG) with a pre-moderator and Beam Shaping Assembly (BSA) comprising a convergent funnel and neutron filters to produce a focused beam of thermal neutrons, minimizing unwanted radiation and enhancing neutron flux and image resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional nuclear reactors are used as neutron sources, then neutron flux is high, but the neutron beam is highly divergent and contains contaminating components (fast neutrons and gamma rays) that blur and deteriorate image quality
Solution Approach 1:
The patent extracts only the useful thermal neutron component from the reactor neutron spectrum by using energy filters (such as boron-loaded polyethylene or cadmium filters) that selectively absorb fast neutrons and gamma rays while transmitting thermal neutrons. This extraction of the harmful components resolves the contradiction by maintaining high neutron flux while eliminating image-deteriorating radiation.
Solution Approach 2:
The patent applies local quality by using spatial filters and collimators with specific geometries (such as pinhole apertures or channel-shaped collimators) that create a directional neutron beam with localized properties. These filters provide different levels of filtering in different spatial regions, allowing high flux in the desired direction while blocking divergent and contaminating neutrons elsewhere.
2Manufacturing precision
If neutron collimators and spatial filters are used to improve image quality, then image resolution improves, but neutron flux is significantly reduced
Solution Approach 1:
The patent performs preliminary moderation of fast neutrons to thermal energies using a moderator (such as polyethylene or water) positioned close to the neutron source. This preliminary action converts the high-energy divergent neutrons into thermal neutrons before they enter the collimator, increasing the efficiency of subsequent filtering and reducing neutron flux loss while maintaining image resolution.
Solution Approach 2:
The patent introduces an intermediary moderator material between the neutron source and the collimator. This intermediary converts fast neutrons to thermal neutrons through scattering, creating a more suitable neutron spectrum for the subsequent filtering stages. The moderator acts as a bridge that transforms the neutron properties to optimize both flux and image quality.
3Quantity of substance
If a compact LVFG neutron source is used, then source size is small and neutron brightness is high, but the neutron emission is isotropic and not directional, making it difficult to focus the beam
Solution Approach 1:
The patent employs asymmetric collimator geometries (such as conical or parabolic shapes) that are optimized for directional neutron transport. These asymmetric structures preferentially guide neutrons in the desired direction while blocking isotropic emission in other directions, converting the LVFG's isotropic output into a directional beam without significant flux loss.
Solution Approach 2:
The patent uses reflective surfaces (such as grazing-angle reflectors or neutron mirrors) to redirect neutrons from isotropic emission into a focused directional beam. By adding spatial dimensionality through reflection and focusing geometries, the system transforms the LVFG's omnidirectional output into a collimated beam suitable for radiography.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The modular LVFG system achieves high thermal neutron flux and purity, reducing image blur and improving resolution, enabling efficient and effective radiography with a compact, cost-effective neutron source.
Implementation Method 1
the LVFG has qualities that can compensate for this issue, such as small source size, high neutron brightness, and low fast neutron energy (2.5MeV). Small source size allows for easier collection and moderation of fast neutrons into either thermal or epithermal neutrons
Implementation Method 2
Beam Shaping Assembly (BSA) comprising a convergent funnel and neutron filters to produce a focused beam of thermal neutrons
Implementation Method 3
neutron filters to produce a focused beam of thermal neutrons, minimizing unwanted radiation and enhancing neutron flux and image resolution
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
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.