<html><head></head><body><div dir="auto">I have no particular expertise, but this what I found in a quick trawl. It sounds an interesting project.<br><br>Although info is out there, much is ambiguous. The crystal appears to be sensitive to alpha, beta and gamma radiation. As you might expect a strike. causes a sharp rise in output with a decay that depends on what hit it. <br><br>I've seen decays mentioned of under 20nS that I assume refer to gamma. Elsewhere it was said particles gave delays of 680nS and 3340nS depending on type. My assumption is that a heavy alpha particle ploughs into the crystal atoms causing a cascade of particles giving the longest decay period. The lighter beta does much the same, but causes a lighter cascade whilst the gamma gives a minimal cascade. <br><br>In all cases the decay is followed by a longish (5ms+) of low level "afterglow". <br><br>Many comment that the crystal is hygroscopic i.e. absorbs water. Be aware also the non thallium doped version is noted as being temperature sensitive and works best when cooled. <br><br>The op amp seems designed for audio so I am not sure how it will fare with a pretty much instantaneous rise and 20nS decay. I suspect you may need to rethink the early stages.<br><br><br>Regards <br>Alan Gray <br><br></div><br><br><div class="gmail_quote"><div dir="auto">On 6 March 2025 16:33:23 GMT, Rhys Sage via Swlug <swlug@mailman.lug.org.uk> wrote:</div><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<pre class="k9mail"><div dir="auto">I'm in the middle of a project - to build a Geiger counter. It's a fun project so far.<br><br>I have all the bits I need (I think) but as with all projects there's a lot of experimentation and changes made on the fly. <br><br>I'm using a Thalium-doped Cesium Iodide crystal in combination with a BPX61 photo diode. For those that don't know- the BPX61 is slightly more sensitive to green light. The crystal emits blue/green light when struck by gamma radiation. Whether it emits light when struck by Alpha, Beta or X-Ray, I don't know. I do know there are other crystals more suited to those.<br><br>The BPX61 output will feed into an OPA134PA amplifier and then that will in turn feed into a microcontroller. Given that the events generated by radioactive decay are very brief, would microcontroller speed make much difference? I could use an ATTiny13/ATTiny85 or something small like a micro RP2040 or an ESP32 C3 Super Mini.<br><br>With a regular Geiger counter,does the system store the events somehow or does it just rely upon measuring maximum pulses when a pulse happens during a sampling period?<br><br>Rhys Sage<br><br></div></pre></blockquote></div></body></html>