Silicon Drift Detector Shielding for Secondary X-Ray Noise
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Solution Overview
Problem
The silicon drift X-ray detector (SDD) experiences increased background noise due to secondary X-rays produced by the Peltier cooling device, and its magnetic field interferes with the electron beam in TEM and SEM instruments, affecting the performance of these microscopes.
Innovation Solution
The implementation of a two-layer shielding system, with a first shield made of a light-element material and a second shield made of a heavy-element material, positioned between the X-ray detection device and the Peltier device, reduces secondary X-rays and minimizes the magnetic field's impact on the electron beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a Peltier cooling device is used to cool the X-ray detection device, then electronic cooling is achieved and liquid nitrogen is not required, but secondary X-rays are produced by the Peltier device which increase background noise
Solution Approach 1:
A first shield made of light-element material is introduced as an intermediary between the X-ray detection device and the Peltier cooling device. This shield absorbs secondary X-rays generated by the Peltier device before they can reach the detector, thereby reducing background noise while maintaining the cooling function.
Solution Approach 2:
A two-layer shielding system is employed: a first shield of light-element material (such as aluminum or plastic) to absorb low-energy secondary X-rays, and a second shield of heavy-element material (such as lead or tungsten) to absorb higher-energy secondary X-rays. This composite structure effectively reduces background noise across a broad energy range.
2Temperature
If the Peltier cooling device is positioned close to the X-ray detection device, then effective cooling is achieved, but the magnetic field generated by the Peltier device interferes with the electron beam in TEM and SEM instruments
Solution Approach 1:
A non-magnetic thermal conductor is introduced as an intermediary between the Peltier cooling device and the X-ray detection device. This thermal conductor provides a path for heat transfer while blocking the magnetic field generated by the Peltier device, thereby preventing interference with the electron beam in TEM and SEM instruments.
3Measurement precision
If the thickness of the X-ray detection device is increased to improve detection performance, then higher reverse bias voltage is required, but stringent protective conditions are needed which compromise the design
Solution Approach 1:
The patent employs thin-film shielding materials that can be easily deposited on the X-ray detection device. These thin shields provide effective protection against secondary X-rays and magnetic fields without requiring excessive thickness in the detection device itself, thereby maintaining detection performance while reducing complexity.
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 shielding system effectively reduces background noise and prevents the magnetic field from interfering with the electron beam, enhancing the sensitivity and accuracy of X-ray detection in TEM and SEM instruments.
Implementation Method 1
a Peltier device in thermal contact with the X-ray detection device via the electrode terminal subassembly to cool the X-ray detection device
Implementation Method 2
A first shield made of a material consisting mainly of a chemical element having an atomic number smaller than the average atomic number of the chemical elements included in the material of the Peltier device is formed between the X-ray detection device and the Peltier device. The dose of X-rays reaching the Peltier device after being transmitted through the X-ray detection device is reduced by the first shield.
Implementation Method 3
A second shield made of a material consisting mainly of a chemical element having an atomic number greater than the atomic numbers of the chemical elements included in the material of the Peltier device is formed between the first shield and the Peltier device. The amount of secondary X-rays entering the X-ray detection device after being produced from the Peltier device is reduced
Data Source
AI summary
A silicon drift detector used in an energy-dispersive X-ray spectrometer and having a background lower than heretofore. The detector has an X-ray detection device (1), an electrode terminal subassembly (2) for electrical connection, a Peltier device (3), and first and second shields (5,6) formed between the electrode terminal subassembly (2) and the Peltier device (3). The first shield (5) is made of a material consisting chiefly of an element having an atomic number smaller than the average atomic number of the elements included in the material of the Peltier device (3). The second shield (6) is made of a material consisting chiefly of an element having an atomic number greater than the atomic numbers of the elements included in the material of the Peltier device (3). The shields (5, 6) reduce the amount of secondary X-rays entering the X-ray detection device (1) after being produced from the Peltier device (3), the secondary X-rays being induced by X-rays transmitted through the detection device (1).