Air filter to catch radioactive particles - suggestions please

mw0uzo wrote:

Modify the filter so the tube is inside it and connect to a kit geiger counter. Initially, it could provide a warning for when anything is drawn in or detected.
I wonder if a feature could be added to RadLog to output a signal to start the fan every 15 minutes for 5 minutes... perhaps by the serial port/usb. Then count over 10 minutes for accurate reading. RPi might be good for that with a modified Pyradmon.

My next project....

At the moment I'm checking the filters first thing in the morning and last thing at night using AtomicDave's Geiger Pal (SBT-9 alpha, beta, gamma, x-ray Russian tube).

Success!

Tonight when I tested the filters I found a little "hotspot" on the top right hand corner of the outer part of the HEPA-type filter.

Background reading was 0.12 micro-sieverts, but the hotspot was reading 0.46. I repeated the testing and this remained a consistent finding.

The air purifier works!

Last night I marked the "hotspot" with a little piece of blutack so I would know if there were any new areas of activity since last night. This morning the reading has dropped to 0.36 microsieverts with the background averaging out at 0.16 microsieverts using the GeigerPal. I will check again late this evening.

The hotspot seems to have disappeared, but the front face of the HEPA-type filter is reading on average after 5 minutes, 0.41 microsieverts.

When resetting the GeigerPal and leaving it on the desk the reading drops to 0.14 microsieverts averaged over 5 minutes.

There is a definite difference in the audible number of clicks when I put the GeigerPal on the desk and then move it to the filter.

I've not been looking at any unsealed radioactive sources in the room where the purifier is just in case any dust from these might be the culprit, so I wonder if this is down to naturally occuring radon and daughter nuclides? (I'll forget about the two nuclear power stations upwind of me for the moment, Asco and Vandellos, or the mothballed uranium mine about 2 hours drive downwind of me )

I'll start averaging over a longer period of 10 minutes for better accuracy, starting from tomorrow morning.

I think I'm picking up something above background as there was nothing above background when I tested these filters each morning and evening of the first few days I was using the machine.