Pfeiffer requires a radiation survey of the pump. In our case we are looking for radiation from neutron activation.
I used the sparkfun USB geiger counter for this survey:
I started with a 10 minute background reading 9.7 Meters from the pump. 91 clicks or 0.1516 clicks per second:
The UBS geiger counter produces a digit for each click. You can actually hear the geiger counter make a sizzling sound with each click… it’s wild.
Next I did a reading at the exterior of the pump. 88 clicks in 10 minutes. 0.146 clicks per second.
Again with the geiger counter inside the pump. 83 clicks in 10 minutes. 0.138 clicks per second.
I’d say the pumping station is clean.
I put the pumping station back in its crate:
As a side note, this USB geiger counter produces high quality random numbers:
I asked P. Andrew Karam, Ph.D (radiological specialist) to comment on my survey approach. He says:
Looks good, Mark – the biggest thing you are looking for is a significant number of counts above background. You really don’t need to convert everything to CPS – the big thing is to make sure that the readings are all made using the same instrument and for the same amount of time.
In counting statistics we normally use a few concepts – LLD (lower level of detection) and Lc (Decision level). These are the levels at which we feel we can definitively say that there is contamination (or activation) present. The LLD is usually about 2 standard deviations higher than the average count rate – using Poisson statistics, one standard deviation is approximately equal to the square root of the total number of counts. So with a background count of 91 in 10 minutes one standard deviation is about 9.5 total counts. That means that anything less than about 19 counts above background (so less than about 110 counts total) is within the expected statistical variability of your instrument. The Lc is a somewhat more difficult calculation in that it depends on your survey speed as well as the size of the probe, counting time, and background counts. Having said all that, the fact that your highest reading was background and everything was within 1 standard deviation of background tells us that you don’t have any neutron activation that is detectable with a GM.
One question – 90 counts in 10 minutes is not very much for a GM – I am used to seeing about 50 cpm (or almost 1 cps) from my GM. I suspect that the reason for the low count rate is the relatively small size of the GM tube itself – the counts you get are a function of the cross-sectional area of the tube. Not disqualifying – just a comment!
The only other question that might come up is whether or not your GM is calibrated – if Pfeiffer were to find elevated rad levels (which I doubt they will find, by the way) they might ask for calibration documents on your meter.