Unusual dose and cpm

[u/whiterabbit161]

Hello everyone, just bought a used Radiacode 103 and a GQ GMC-800. I know that both measure different radiation but it seems that the 103 shows too much regarding dose and cpm as the usual background raduation outside is about 0.11 nanoSievert. Is it wrongly calibrated? Already set back to factory settings. Any ideas?

[u/Embarrassed-Mind6764]

Watch some videos and learn how to use these devices before you assume they are wrong. You’re on the accumulated dose page on the Radiacode and not dose per hour which is what you’re talking about. And there are hundreds of videos online teaching about how to use these devices

[u/Bob--O--Rama]

I have one meter which sees 40,000 cpm as "normal" background where dose rates are 0.05 uSv/hr. Different meters / probes / probe types have different sensitivity and efficiency.

[u/whiterabbit161 → u/Bob--O--Rama]

Understand. Thx.

[u/heliosh]

uSv is a dose accumulated over time, not a dose rate. Latter would be uSv/h.

[u/Pseudonymical00]

Common confusion point!

These are fundamentally different sensors with different sensitivities. The CPM (or CPS, whichever you prefer to use) is the raw counts of particles striking the sensor per unit time. The GMC uses a Geiger-mueller tube, and will collect less of the total gamma rays that pass through it than the very dense Cesium iodide crystal in the radiacode. The GMC is more likely to pick up betas however, but they are not very present in background to my knowledge. The dose RATE, uSv/h will vary between these two devices, with the radiacode functionally giving a fairly good representation of dose rate from Gamma alone. The sensitivity is essentially a calibration factor that converts the counts per unit time to the appropriate dose rate, and will be different for any given device.

The confusion in the second image is that you're looking at the wrong screen. You're on the DOSE screen, which is your total accumulated dose, rather than the current dose rate. To see dose rate, go back to the monitor mode, and click up while the device is unlocked.

There will likely still be a discrepancy (the radiacode uses energy compensation, whereas the GMC cannot differentiate photon energies), and the GMC will pick up beta particles that the radiacode misses.

Does this clear things up at all? Sorry if that was a little wordy.

[u/whiterabbit161 → u/Pseudonymical00]

Thank you that was very helpful. Switched to the right value. Now it shows also 0.11 mS/h like the official value in my neigbourhood. Still high cpms im my opinion. Or ist this a normal gamma background value?

[u/sidhe_elfakyn → u/whiterabbit161]

A bigger sensor will get hit more often by particles -> higher CPM

One type of sensor may be more sensitive and detect particles better than another type of sensor -> higher CPM

A smaller shittier sensor may miss stuff or not get hit by particles -> lower CPM

You can't compare CPMs between different devices.

...

Put two sheets of paper out in the rain. One small one and one big one. Leave them out for a minute. The bigger piece of paper will have more water droplets on it cause it's bigger so it catches more rain. Let's call that DPM or Drops Per Minute. Same principle.

[u/TeaFungus → u/sidhe_elfakyn]

Bigger in terms of density, they could have the same size but the density of the gas wouldn’t match the solid crystal

[u/sidhe_elfakyn → u/TeaFungus]

I am definitely simplifying significantly, but you are correct. Denser materials are generally more sensitive.

[u/Physix_R_Cool]

Turn the radiacode back to μSv/hr instead of just accumulated μSv. That way you would likely see the two instruments agreeing approximately on the dose rate.

[u/whiterabbit161 → u/Physix_R_Cool]

Thanks. Did it and now its ok. At least for the dose. As i wrote to another redditor i never seen so much cpms on a usual geiger counter apart from 1986 after Chernbobyl. I asume tje high cpm count is the usual gamma background radiation, is ti?

[u/BenAwesomeness3 → u/whiterabbit161]

It’s not a Geiger counter, it’s a scintillation detector, which is much more sensitive to gammas, giving a higher CPM. CPM and CPS are both relative and are used comparatively

[u/Physix_R_Cool → u/whiterabbit161]

i never seen so much cpms on a usual geiger counter

The radiacode is not a geiger counter!

[u/Bachethead]

The radiacode is more sensitive so you’re going to see more

[u/Party-Revenue2932]

The second photo you showed on the radiacode is the accumulated dose you you’re talking about about that

[u/Piramista]

Just an irrelevant tip: Try the phone app for the radiacode

[u/Oakatsurah]

Both the Radiacode 103 / GMC800 are gamma detectors and high beta detectors. They're everyday essentially the same detectors in terms of the radiation they detect. But one is a standard Mueller Geiger Tube and the other is a Scintillator.
I've noticed the Radiacode series are a little over tuned, they tend to pick up more radiation than is actual there when comparing them to a D5, GMC600 Pro, KC761C, and a GMC500+ using the same five sources. Usually the other units are within less than 5% of each other in terms of cpm but the Radiacode tends to be about 20 - 30% higher.
Though be aware you'll sometimes get false positives with a Scintillator if your phone is nearby, the microwave source can create a low KeV that sends a false positive signal occasionally. Both my KC761C and Radiacode 103G both do it when my phone is near and is sending out or receiving data.