Remmy
New member
Hi guys 
I've got a bit of an unusual one here, but some may find it interesting so I thought I'd share what I've been doing for the last few weeks in my 3rd year physics group project at uni. We're in the last week of the project now, and we've been working on it once or twice a week for about 5 weeks, including the planning.
The project initially began as us trying to replicate a paper we had read which was about detecting alpha particles from a radioactive 241Am source. 241Am emits alpha, beta, and gamma radiation, so one of the first decisions was how to differentiate between the three; as it turned out just achieving detection of any of the particles is not an easy task (surprise, surprise), so we are more than happy to just detect any of the radioactive particles emitted
Alphas only travel a few centimetres in air, so we designed a small brass vacuum chamber to house the radioactive source and the silicon detector diode. The diode is also sensitive to light, so the chamber was also useful to block out as much light as possible.
Now that we had a way of mounting the source and detector in the chamber, we needed a way of seeing an output, which requires a great amount of amplification because the current produced by the particles in the diode is so miniscule. To do this, the department's electrical engineer helped us (a lot) to develop this circuit:
I only understand about half of what is going on here; I like electronics as a hobby, but I'm no electrical engineer If anybody has some knowledge on this, feel free to try explain to me what the use of L1, C1, C5, C6, C8, or C9 are
The key things I understand about the circuit is that IC1 converts the current produced in the diode into an AC voltage, and IC2 amplifies that voltage to give us a usable output. I understand that the op amp negative feedback loops make the op amp force the inputs to be equal potential by raising the potential of the output, thereby amplifying the voltage. I think the silicon diode D1 is in reverse bias so that the depletion layer in the semiconductor is free of charge carriers, so the detected particles are the only current producers; or something like that
Here is the PCB of the circuit
Here is a picture of our whole setup
The photo includes the vacuum chamber and pump, the amplifier circuit, and the oscilloscope. The breadboard shown is just being used to provide power to the amplification circuit; the circuit was previously tested on the breadboard. The radioactive source is mounted in one end of the brass chamber.
Today was the first day we had everything we needed together and complete, and us and the lecturers working with us in the lab are quite convinced that this was the first particle we've detected:
We don't know which it is, but we were so excited just seeing this peak appear on the screen after so much fiddling about trying to get everything to work
The mechanical engineers who made us the vacuum chamber, and the electrical engineer will be so glad that this is our last week of bugging them with all of our problems! They're really busy all the time without us nagging them, so they deserve praise Hopefully on Thursday we can get some more of these detections with a bit more perseverence This has been a really fun project for us despite many difficulties in trying to get everything working correctly, and it's reignited my electronics hobby I used to have during GCSE
I've got a bit of an unusual one here, but some may find it interesting so I thought I'd share what I've been doing for the last few weeks in my 3rd year physics group project at uni. We're in the last week of the project now, and we've been working on it once or twice a week for about 5 weeks, including the planning.
The project initially began as us trying to replicate a paper we had read which was about detecting alpha particles from a radioactive 241Am source. 241Am emits alpha, beta, and gamma radiation, so one of the first decisions was how to differentiate between the three; as it turned out just achieving detection of any of the particles is not an easy task (surprise, surprise), so we are more than happy to just detect any of the radioactive particles emitted
Alphas only travel a few centimetres in air, so we designed a small brass vacuum chamber to house the radioactive source and the silicon detector diode. The diode is also sensitive to light, so the chamber was also useful to block out as much light as possible.
Now that we had a way of mounting the source and detector in the chamber, we needed a way of seeing an output, which requires a great amount of amplification because the current produced by the particles in the diode is so miniscule. To do this, the department's electrical engineer helped us (a lot) to develop this circuit:
I only understand about half of what is going on here; I like electronics as a hobby, but I'm no electrical engineer
If anybody has some knowledge on this, feel free to try explain to me what the use of L1, C1, C5, C6, C8, or C9 are The key things I understand about the circuit is that IC1 converts the current produced in the diode into an AC voltage, and IC2 amplifies that voltage to give us a usable output. I understand that the op amp negative feedback loops make the op amp force the inputs to be equal potential by raising the potential of the output, thereby amplifying the voltage. I think the silicon diode D1 is in reverse bias so that the depletion layer in the semiconductor is free of charge carriers, so the detected particles are the only current producers; or something like that
Here is the PCB of the circuit
Here is a picture of our whole setup
The photo includes the vacuum chamber and pump, the amplifier circuit, and the oscilloscope. The breadboard shown is just being used to provide power to the amplification circuit; the circuit was previously tested on the breadboard. The radioactive source is mounted in one end of the brass chamber.
Today was the first day we had everything we needed together and complete, and us and the lecturers working with us in the lab are quite convinced that this was the first particle we've detected:
We don't know which it is, but we were so excited just seeing this peak appear on the screen after so much fiddling about trying to get everything to work
The mechanical engineers who made us the vacuum chamber, and the electrical engineer will be so glad that this is our last week of bugging them with all of our problems! They're really busy all the time without us nagging them, so they deserve praise
Hopefully on Thursday we can get some more of these detections with a bit more perseverence This has been a really fun project for us despite many difficulties in trying to get everything working correctly, and it's reignited my electronics hobby I used to have during GCSE 
thats my problem
