Alpha radiation is a comm0n form of radiation energy with many applications. Seismic and oceanographic devices, smoke detectors, and static eliminators all use sources of alpha radiation.
A smoke detector in particular is a common household device. Using the alpha radiation of americium-241, electrons in the air molecules are knocked free and used to create an electrical current. When smoke particles disrupt this current, the alarm is triggered.
I was a bit skeptical if the the small amount of Americium 241 in a smoke detector is enough to receive obvious feedback from the oscillation program on my laptop, but luckily, I had access to other sources from a nearby military base if it did not work.
Radiation was in fair abundance, but devices used to detect alpha radiation are not. If you have a condenser microphone laying around, you may just have a detection device. Condenser microphones can in fact be used to detect alpha radiation, as demonstrated and explained by Senior Reactor Operator at the University of New Mexico, Carl Willis (his content is absolutely fantastic, I recommend checking him out!).
Using a condenser microphone as a radiation detector is what I am demonstrating through easy and accessible means for anyone to try. This experiment is simple, which opens many opportunities for other approaches and for it to be changed for different demonstrations in later experiments.
I first tried this experiment with an Americium 241 sample that came from a ionization smoke detector, and launched a visual analyzer program to document the input the microphone was receiving. In order to confirm this sample would be at least somewhat detectable, we measured its CPM. CPM, or counts per minute, indicates how many ionization events happen in a minute. For radioactive materials, ionization events will be high, as was our sample, sitting around 200k CPM when measured at an Air Force base. I then held the sample up to my FIFINE condenser microphone, and saw no results at all. I had then figured that the metal grill that surrounds the microphone likely had to be removed because I am using such a small source, and metal tends to absorb alpha radiation particles.
After removing the metal grill from around the actual microphone device itself, I tried the experiment again and held the source up to the microphone, and still saw no results. The microphone piece itself still had a small metal plate with holes that was encased with plastic, so I removed that too. There was also a remaining bit of plastic on the Americium that I went ahead and removed as well. Because alpha radiation particles carry such high mass, they have difficulty penetrating many materials like metal, plastic, and skin, which is why I have been handling the source using just a pair of pliers.
I decided to then go further and identify the actual audio input piece, and remove all obstructions from it. After trying the experiment once more, it was then that I was able to see identifiable feedback in the visual analyzer as the audio input piece received the alpha particles of the source directly. However, the output on the visual analyzer looked different than what I had expected. The source varied the oscillation by exaggerating the baseline background input and occasionally spiking, whereas this result was not seen when holding up a metal that was not radioactive like nickel.
Before I had totally resorted to deconstructing the microphone, I had reached out to Professor Carl Willis for his input about my failing results. He pointed me towards the idea that some condenser microphones may be condenser electret microphones, and therefore the experiment will vary due to the change in detection device.
I decided that the microphone I was working with was a condenser microphone after looking in to this, but simultaneously deducted it was just a poorly manufactured one. But why does experiment work, regardless of microphone quality?
When powering a condenser microphone, as shown in the diagram, the capsule becomes ionized, and the charge on the capacitor of the microphone system (detection piece) can be calculated. Radiation has an ionizing effect so when an alpha source is held up to the diaphragm, it creates a separation of charges in the space between the diaphragm and the backplate since the radiation creates a charge in neutral air molecules. So, when the ions move, the diaphragm detects this movement and sends signals to the amplifier, which then allows us to process this effect as sounds on an oscillator program.
Source: UCG Libraries
To conclude, this experiment primarily demonstrated the ionizing abilities of alpha radiation, and how basic technologies like microphones cam be used to aid radiation safety in areas without formal detection equipment. The abilities of alpha radiation are important in aiding our daily lives in the household and in the industries, as our main example being a smoke detector, and how it depends on a radioactive material to detect a change in air particles (just like the condenser microphone), which would be smoke. Static electricity can also be a major problem in manufacturing and industrial settings, and through the use of ionizing alpha particles, static can be safely eliminated in large areas. Overall, this phenomenon helps inspire many technologies able to be built or modified from pre-existing technologies or easy to access material, and can be used to create devices that can detect ionizing radiation for safety measures in regions that do not have access to formal detection equipment.
Below are the images and video demonstrations of what I saw and did in my experiment.
This is an image of all my mentioned materials, which include the microphone, the alpha source (the small white and metal piece), and pliers to hold the source up.
This video shows the alpha source reacting with the condenser microphone and producing a visible output on the visual analyzer. To compare, the video below shows the same demonstration, but with a very obviously not radioactive material.
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