Summary of BPW34 GAMMA RAY DETECTOR
Summary: Stefan Wagner’s portable detector replaces a Geiger-Müller tube with three BPW34 silicon PIN photodiodes in parallel to sense gamma radiation. Gamma photons generate electron-hole pairs in the diodes’ depletion regions, producing small current pulses that are amplified by an instrumentation amplifier and processed by an LM311 comparator to trigger a buzzer. The design favors readily available low-voltage components and a small sensitive area to reduce background counts and simplify construction.
Parts used in the BPW34 Gamma Ray Detector:
- BPW34 PIN photodiode (x3, connected in parallel)
- Instrumentation amplifier
- LM311 comparator (operation amplifier used for comparison and triggering)
- Buzzer (alert output)
- Enclosure (device housing, implied)
- Supporting passive components (resistors, capacitors, implied for biasing and filtering)
- Power supply (low-voltage source for op amp and amplifier, implied)
The usual approach to radiation detection is the use of a Geiger-Müller tube and its high voltage circuit requirements, but during a quick surf through the internet today, I came across this portable and “accurate looking” solution developed by Stefan Wagner, on EasyEDA.
Rather than the Geiger Muller tube and its complex circuitry, the project uses a miniature Silicon PIN Photodiode, the 3x BPW34 (which were connected in parallel to improve sensitivity), as the primary sensing component. The BPW34 is a PIN photodiode with high speed and high radiant sensitivity in miniature, flat, top view, clear plastic package. It is sensitive to visible and near-infrared radiation and has a small sensitive area, which is an advantage in radiation detection, as the background rate due to cosmic rays is very low, and signals from small samples will be easier to detect than when a counter tube is used.
The behavior of the BPW34 PIN photodiode used in the project is similar to that of a low-cost counter tube in the sense that, while alpha particles may be stopped by the enclosure of the device, gamma rays due to their high penetration ability will pass through and create electron-hole pairs in the depletion layer of the diode. This will lead to the charge carriers in the diode being drawn away and a small current pulse being created. The small current pulse can then be amplified and processed to determine radiation levels.
For the amplification, the project featured an instrumentation amplifier and the processing is done with an LM3111 operation amplifier which is used to compare the values and trigger a buzzer when radiation is detected.
With the Geiger-Muller tube becoming hard to find and the high voltage circuitry adding another layer of complexity, this accurate approach by Stefan using relatively, readily available components might be the best way to build your next radiation detection device.
Read more: BPW34 GAMMA RAY DETECTOR
- What sensing component does this detector use instead of a Geiger-Müller tube?
The project uses BPW34 silicon PIN photodiodes (three in parallel) as the primary sensing components. - Can this detector detect gamma rays?
Yes, gamma rays can pass through and create electron-hole pairs in the diode depletion layer, producing detectable pulses. - How are the small current pulses from the diodes processed?
Pulses are amplified by an instrumentation amplifier and then processed by an LM311 comparator to trigger a buzzer. - Does the design use high-voltage circuitry like a Geiger-Müller tube?
No, the design uses low-voltage silicon photodiodes and amplifiers, avoiding the high-voltage circuitry of Geiger-Müller tubes. - Why is a small sensitive area advantageous in this detector?
A small sensitive area reduces background counts from cosmic rays and makes signals from small samples easier to detect. - Are alpha particles detected by this device?
Alpha particles may be stopped by the enclosure and thus are less likely to be detected by this design. - What output indicates detected radiation?
An LM311 comparator triggers a buzzer when radiation is detected. - Is this approach presented as easier to build than a Geiger-Müller-based detector?
Yes, the project is presented as a simpler and more readily built alternative due to available low-voltage components and no high-voltage requirements.
