Tri-Layered Neutron Filter for BNCT Beam Shaping
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Solution Overview
Problem
Current neutron beam sources for boron neutron capture therapy (BNCT) are often located in research reactors, making it inconvenient for medical applications, and there is a need for a more accessible and cost-effective accelerator-based neutron beam source that can produce a suitable epithermal neutron beam with a low fast neutron dose component.
Innovation Solution
A tri-layered filter structure comprising an iron layer, a layer of lithium fluoride, aluminum, and aluminum fluoride, and a layer of lithium fluoride and magnesium fluoride, used in conjunction with a beryllium target and an accelerator, to moderate neutrons and produce an epithermal neutron beam with optimal intensity and reduced fast neutron dose.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a research reactor is used as a neutron beam source, then a suitable epithermal neutron beam can be produced, but the location is fixed and inconvenient for medical applications
Solution Approach 1:
The patent changes the fundamental operating parameters by switching from a research reactor (thermal neutron source) to an accelerator-based system (proton beam incident on beryllium target). This parameter change enables the neutron beam source to be relocated from fixed research reactor facilities to hospital settings, dramatically improving accessibility while maintaining epithermal neutron beam quality through optimized filter design
Solution Approach 2:
The patent introduces a multi-layered filter as an intermediary component between the accelerator-based neutron source and the treatment area. This filter mediates the neutron spectrum by selectively moderating fast neutrons to epithermal energies while attenuating unwanted components, thereby enabling the use of simpler accelerator technology instead of complex research reactors
2Reliability
If thermal neutrons are used for BNCT of brain tumors, then treatment can be effective, but the skull must be opened requiring surgery and anesthesia
Solution Approach 1:
The patent changes the neutron energy parameter from thermal to epithermal range. Epithermal neutrons have higher energy and greater penetrating power, allowing them to pass through the skull and reach brain tumors without requiring surgical opening. The multi-layered filter is specifically designed to produce this epithermal spectrum, maintaining treatment effectiveness while eliminating invasive procedures
Solution Approach 2:
The patent applies preliminary energy modification to the neutron beam through the multi-layered filter before the neutrons enter the patient's body. The filter pre-moderates the neutrons to epithermal energies and shapes the spectrum optimally, so that when the neutrons reach the patient, they can penetrate the skull effectively without requiring surgical intervention
3Ease of manufacture
If an accelerator-based neutron beam source is used, then cost and accessibility are improved, but the fast neutron dose component increases
Solution Approach 1:
The patent optimizes the filter layer parameters (thickness, material composition) to change the neutron energy distribution. The first layer (polyethylene) moderates fast neutrons, the second layer (boron-containing material) absorbs thermal neutrons, and the third layer (lead) attenuates gamma rays. This parameter optimization reduces the fast neutron dose component to acceptable levels while maintaining the cost advantages of accelerator-based systems
Solution Approach 2:
The patent converts the harmful fast neutron radiation into beneficial epithermal neutrons through the moderating effect of the multi-layered filter. The fast neutrons produced by the accelerator would normally be harmful, but the filter transforms them into useful epithermal neutrons for treatment while absorbing the excess energy that would otherwise contribute to the harmful dose
4Object-affected harmful factors
If extensive shielding is used to reduce fast neutron dose, then radiation safety is improved, but the cost and complexity of the system increases
Solution Approach 1:
The patent merges the shielding function with the neutron beam shaping function in a single integrated multi-layered filter structure. The same layers that moderate and shape the neutron spectrum (polyethylene, boron-containing material, lead) also serve as radiation shielding, eliminating the need for separate shielding components and reducing overall system complexity while maintaining radiation safety
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 solution provides a neutron beam source that achieves a desirable epithermal neutron flux and low fast neutron dose rate, suitable for BNCT, reducing the need for extensive shielding and improving treatment efficiency while being cost-effective and accessible for hospital-based treatments.
Implementation Method 1
a first layer composed of iron... The first layer is used for moderating the fast neutrons into the neutrons with energy less than 1 MeV through the inelastic scattering
Implementation Method 2
a second layer composed of 1 part by volume of lithium fluoride, 20 to 50 parts by volume of aluminum, and 50 to 80 parts by volume of aluminum fluoride... the second layer is used for absorbing the thermal neutrons
Implementation Method 3
a third layer composed of 1 part by weight of lithium fluoride and 99 to 100 parts by weight of magnesium fluoride... the third layer is used for further moderating the neutrons
Data Source
AI summary
Disclosed is a filter including a second layer disposed between a first layer and a third layer. The first layer is composed of iron. The second layer is composed of 1 part by volume of lithium fluoride, 20 to 50 parts by volume of aluminum, and 50 to 80 parts by volume of aluminum fluoride. The third layer is composed of 1 part by weight of lithium fluoride and 99 to 100 parts by weight of magnesium fluoride.