Radiation Portal Monitor PMT Deflection Against X-Ray Saturation

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Solution Overview

Problem

Radiation portal monitors (RPMs) face interference from X-ray sources, leading to false alarms and dead time due to the inability to distinguish X-ray radiation from gamma radiation, resulting in reduced detection efficiency and potential damage from saturation.

Innovation Solution

Incorporating a scintillator and photomultiplier tube (PMT) with an electron deflecting arrangement that selectively deflects electrons during X-ray events, preventing them from reaching the dynodes and thus reducing saturation and allowing for continuous gamma event detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If blanking is used to suppress X-ray interference, then false alarms are reduced, but dead time increases and detection efficiency decreases

Engineering Contradiction:

ImproveX-ray interferenceVSAvoiddead time

Core Design Contradiction:

Object-affected harmful factorsVSLoss of time

Solution Approach 1:

The patent applies different processing treatments to different types of radiation events by identifying their distinct characteristics. Gamma events are processed normally while X-ray events are suppressed, achieving selective handling based on local event properties rather than blanket suppression. This is accomplished through pulse characterization that distinguishes between gamma and X-ray events based on their temporal and amplitude characteristics.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The system changes the processing parameters dynamically based on the detected event type. When an X-ray event is detected through pulse characterization, the system adjusts its response by suppressing subsequent pulses during the X-ray duration. This parameter change allows the system to adapt its behavior to the specific radiation type, minimizing dead time while suppressing interference.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If high frequency X-ray sources are used, then productivity increases, but paralyzing effect increases and RPM detection ability decreases

Engineering Contradiction:

ImproveX-ray source frequencyVSAvoidRPM detection ability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system implements feedback by continuously monitoring the detector output and using pulse characterization to identify X-ray events. When an X-ray event is detected, the system provides feedback control by suppressing subsequent pulses, preventing saturation and maintaining reliable gamma detection capability even when exposed to high frequency X-ray sources.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system dynamically adjusts its processing behavior based on real-time detection of radiation event characteristics. Rather than using a fixed blanking window, the system adapts its suppression strategy based on the detected pulse patterns, allowing it to maintain detection ability across varying X-ray frequencies and intensities.

Inventive Principle:

Principle #15Dynamics

3Loss of time

If blanking window is made small to reduce dead time, then detection efficiency improves, but X-ray saturation effect increases

Engineering Contradiction:

Improvedead timeVSAvoidPMT saturation

Core Design Contradiction:

Loss of timeVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary characterization of each pulse to identify X-ray events before suppression is applied. By characterizing the pulse shape, amplitude, and temporal properties in advance, the system can determine whether suppression is needed, preventing saturation while minimizing unnecessary dead time. This preliminary identification allows for optimized window sizing.

Inventive Principle:

Principle #10Preliminary action

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

This approach minimizes X-ray interference, reduces dead time, and prevents PMT saturation, enabling more efficient detection of radiological threats while maintaining system performance without the need for blanking windows.

Implementation Method 1

a scintillator configured to convert high energy photons into low energy photons

Methodology Applied

Scientific EffectScintillation: Scintillation

Implementation Method 2

a photocathode configured to convert the low energy photons into electrons

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 3

an electron deflecting arrangement configured to selectively deflect the electrons before they encounter the series of dynodes

Methodology Applied

Scientific EffectElectromagnetic deflection: Lorentz Force

Data Source

PatentUS20250020816A1Systems and methods for suppressing x-ray interference in radiation portal monitors

Publication Date: 2025.01.16 SMITHS DETECTION INC(US)

AI summary

Systems and methods for suppressing X-ray interference in radiation portal monitors are provided. A radiation portal monitor includes a scintillator configured to convert high energy photons into low energy photons, and a photomultiplier tube (PMT) coupled to the scintillator, the PMT including a photocathode configured to convert the low energy photons into electrons, and a series of dynodes configured to cascade the electrons to facilitate detecting gamma events. The radiation portal monitor further includes an electron deflecting arrangement configured to selectively deflect the electrons before they encounter the series of dynodes.