Neutron Moderator Gamma Shielding for Hazardous Substance Detection

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Solution Overview

Problem

Conventional neutron moderators and detection systems face accuracy issues due to the presence of constituent elements like carbon, hydrogen, oxygen, and nitrogen, which interfere with the detection of hazardous substances by mixing gamma rays from the moderator and the substance, leading to reduced detection accuracy.

Innovation Solution

A neutron moderator system incorporating a gamma ray shielding material and a thermal neutron absorbing material to suppress secondary gamma rays and direct necessary fast and thermal neutrons for irradiation, while using a gamma ray detector to accurately detect hazardous substances regardless of their constituent elements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If fast neutron is moderated down to thermal neutron by allowing it to pass through a moderating material, then the amount of thermal neutron is increased, but the detected gamma ray amount includes gamma ray from the moderating material mixed with gamma ray from the explosive, reducing detection accuracy

Engineering Contradiction:

Improveamount of thermal neutronVSAvoiddetection accuracy

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The patent extracts and removes the harmful gamma rays produced by the moderating material using a gamma ray shielding material (lead or tungsten). This allows the system to maintain the beneficial thermal neutron production while eliminating the interfering gamma ray signal that reduces detection accuracy.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a gamma ray shielding material as an intermediary component between the moderating material and the detector. This intermediary blocks the harmful gamma rays from the moderating material while allowing the detection of gamma rays from the explosive, thereby resolving the contradiction between thermal neutron production and detection accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If gamma ray detector detects gamma ray from explosive irradiated with thermal neutron, then explosive detection is enabled, but gamma ray from carbon, hydrogen, oxygen, and nitrogen in the air is also detected, reducing accuracy

Engineering Contradiction:

Improveexplosive detection capabilityVSAvoiddetection accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent applies local quality by creating a localized low gamma-ray environment around the detector using shielding materials. The shielding is strategically positioned to block gamma rays from the moderating material and surrounding air, while maintaining the ability to detect gamma rays from the explosive. This localized protection improves detection accuracy without compromising detection capability.

Inventive Principle:

Principle #3Local quality

3Quantity of substance

If neutron moderating material is used to moderate fast neutron, then thermal neutron is produced, but secondary gamma ray is generated and leaks externally, causing interference

Engineering Contradiction:

Improvethermal neutron productionVSAvoidsecondary gamma ray leakage

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful secondary gamma rays produced by the moderating material into a manageable issue by using gamma ray shielding material (lead or tungsten) to absorb and block them. This approach maintains the beneficial thermal neutron production while transforming the harmful gamma ray leakage into a controlled shielding problem that can be effectively solved.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 system enhances detection accuracy by isolating and applying the necessary neutrons for irradiation, reducing external gamma ray leakage and interference, allowing for precise identification of hazardous substances based on gamma ray energy.

Implementation Method 1

a neutron moderating material arranged on one side of the neutron generator... Fast neutron is emitted from the neutron generator forward as well as backward and laterally. The fast neutron that is emitted backward and laterally is moderated down to intermediate neutron, epithermal neutron, and thermal neutron by way of the neutron moderating material

Methodology Applied

Scientific EffectNeutron moderation:

Implementation Method 2

a gamma ray shielding material covering an external surface of the neutron moderating material... The gamma ray shielding material prevents external leakage of secondary gamma ray that is generated when the fast neutron is moderated

Methodology Applied

Scientific EffectGamma ray shielding: Absorption (EM radiation)

Implementation Method 3

a thermal neutron absorbing material covering the external surface of the neutron moderating material except a side where the neutron generator is arranged... The remaining thermal neutron is absorbed by the thermal neutron absorbing material

Methodology Applied

Scientific EffectThermal neutron absorption: Absorption (physical)

Implementation Method 4

a gamma ray detector that detects gamma ray generated from the inspection target... by detecting energy of such gamma ray, an explosive can be detected based on the concentration of each of these constituent elements

Methodology Applied

Scientific EffectGamma ray detection:

Data Source

PatentUS8217360B2Neutron moderator, neutron irradiation method, and hazardous substance detection apparatus

Publication Date: 2012.07.10 MITSUBISHI HEAVY IND LTD

AI summary

A neutron moderator includes a neutron generator; a neutron moderating material arranged on one side of the neutron generator; a gamma ray shielding material covering an external surface of the neutron moderating material; and a thermal neutron absorbing material covering the external surface of the neutron moderating material except a side where the neutron generator is arranged.