Geiger Counter Question

[worriedsick79]

TL;DR

Possibly contaminated device

Hi,

I’ve recently purchased two geiger counters from Amazon, GQ GMC-800 and GQ GMC-300S, because someone in my life was supposed to receive RAI. Ended up my relative didn’t need the treatment. I’ve heard about granite countertops being potentially radioactive, so decided to open the devices and test things around the house. I opened both on my bed… without thinking anything of it.

One appeared used and didn’t have the protective screen film. I used the GQ GMC-800 to measure things around the house. I got anywhere from 3-31 CPM. I measured an item which showed 11 the first time and went up to 26 later, the second time I measured. I touched the meter directly to items, such as my sofa, countertop, pillow, etc. Then I started worrying that if this product was used maybe it was contaminated with radioactive materials. I also took it outside, and the readings of concrete and a brick were like 14 cpm.

If the device was actually contaminated, would the readings be so low? I am terrified as I have a small child at home. Is there anything I could do now?

 

[.Scott]

According to the GQ GMC-800 Geiger Counter User Guide:

Background Safe Levels Suggested background readings levels: 1. Safe level. Less than 50CPM or 0.25uSv/h. Nothing to worry about 2. Attention level. 51CPM – 99CPM. OR 0.26uSv/h – 0.39uSv/h. Unnaturally high, time to figure out what is wrong 3. Warning level. More than 100CPM or more than 0.40uSv/h. Dangerous to stay in this area for long.

So, all of the reading you have taken are considered by the manufacturer to be "safe background levels".

The other issue is "integration time". "CPM" stands for "counts per minute". If your CPM is less than 30, don't expect "30" to show up every second. The device is integrating over time (apparently, over a rolling 30 second period). So, if you put this on the sidewalk and only wait 5 seconds, you won't get a "sidewalk" reading - you'll get a path-to-the-sidewalk reading.

Here's another excerpt from the manual:

After GMC-800 is turned on, it will show the background radiation reading. The background radiation reading (in CPM) indicates the nature radiation detected at that minute. This reading may change from time to time and location to location. To get an accurate reading, user may need to get an average value over a longer time period.

All that said, if you think that you have soiled your sidewalk with this level of radiation and you want to clean it up, then put your garden hose on it's fast tight stream setting and rinse the area away onto permeable ground.

 

[worriedsick79]

According to the GQ GMC-800 Geiger Counter User Guide:

Background Safe Levels Suggested background readings levels: 1. Safe level. Less than 50CPM or 0.25uSv/h. Nothing to worry about 2. Attention level. 51CPM – 99CPM. OR 0.26uSv/h – 0.39uSv/h. Unnaturally high, time to figure out what is wrong 3. Warning level. More than 100CPM or more than 0.40uSv/h. Dangerous to stay in this area for long.

So, all of the reading you have taken are considered by the manufacturer to be "safe background levels".

The other issue is "integration time". "CPM" stands for "counts per minute". If your CPM is less than 30, don't expect "30" to show up every second. The device is integrating over time (apparently, over a rolling 30 second period). So, if you put this on the sidewalk and only wait 5 seconds, you won't get a "sidewalk" reading - you'll get a path-to-the-sidewalk reading.

Here's another excerpt from the manual:

After GMC-800 is turned on, it will show the background radiation reading. The background radiation reading (in CPM) indicates the nature radiation detected at that minute. This reading may change from time to time and location to location. To get an accurate reading, user may need to get an average value over a longer time period.

All that said, if you think that you have soiled your sidewalk with this level of radiation and you want to clean it up, then put your garden hose on it's fast tight stream setting and rinse the area away onto permeable ground.

Thanks. I’m obviously not worried about the sidewalk, just included that detail since that’s another thing I tested. I’m worried about my house. So if the readings were background level, does that mean the counter itself didn’t arrive contaminated? I’m very new to this.

 

[.Scott]

Thanks. I’m obviously not worried about the sidewalk, just included that detail since that’s another thing I tested. I’m worried about my house. So if the readings were background level, does that mean the counter itself didn’t arrive contaminated? I’m very new to this.

It means that if it was contaminated, the contamination is not being picked up by the counter - so (assuming the counter works) it's not very radioactive.

 

[worriedsick79]

It means that if it was contaminated, the contamination is not being picked up by the counter - so (assuming the counter works) it's not very radioactive.

Ok, thanks!

 

[gleem]

It is understandable why one would want to determine the radiation dose level. The Problem is that it is not simple to do so, especially with a GM-style radiation meter. Part of the problem is the nature of radioactive decay, part is the nature of the instrument, and part is the manufacturer.

Digital instruments must sample for a specified amount of time. This manufacturer of this instrument does not say what it is. GM meters are usually used for detecting variations in radiation levels, so this time must be long enough to get a decent average, but not too long so as to average over too much area, as pointed out by @.Scott. Some instruments let the user change this time. This time is important for low count rates, but less so as the rates increase. In general, one must linger for a while at a point to record enough counts to get a good average before moving on. Low count rates can vary as much as +/- 50% of the average, e.g., on average, 20 readings may vary from 10 cpm to 35 cpm with an average of 25 cpm. Any reading in this range is associated with that average.

To get a good background reading for your instrument, take it outside in your yard, at least 10 ft away from any concrete or rocks, and watch the meter's readings so you know the range of variations. Now go back into your house. The reading in the house should be the same, but could be a bit more if it is of brick or concrete construction. Keeping in mind that the natural background could vary from about 0.005mRem/hr to 0.01 mRem/hr, depending on where you live.

 

[worriedsick79]

It is understandable why one would want to determine the radiation dose level. The Problem is that it is not simple to do so, especially with a GM-style radiation meter. Part of the problem is the nature of radioactive decay, part is the nature of the instrument, and part is the manufacturer.

Digital instruments must sample for a specified amount of time. This manufacturer of this instrument does not say what it is. GM meters are usually used for detecting variations in radiation levels, so this time must be long enough to get a decent average, but not too long so as to average over too much area, as pointed out by @.Scott. Some instruments let the user change this time. This time is important for low count rates, but less so as the rates increase. In general, one must linger for a while at a point to record enough counts to get a good average before moving on. Low count rates can vary as much as +/- 50% of the average, e.g., on average, 20 readings may vary from 10 cpm to 35 cpm with an average of 25 cpm. Any reading in this range is associated with that average.

To get a good background reading for your instrument, take it outside in your yard, at least 10 ft away from any concrete or rocks, and watch the meter's readings so you know the range of variations. Now go back into your house. The reading in the house should be the same, but could be a bit more if it is of brick or concrete construction. Keeping in mind that the natural background could vary from about 0.005mRem/hr to 0.01 mRem/hr, depending on where you live.

Thank you for the tips. Would you worry about the instrument being possibly contaminated if it was in fact sent to me used? That’s my biggest worry now. I’m not a professional and I really wish I didn’t play around with it once I found out that my relative doesn’t need RAI. I’m worried about my baby since I touched ordinary things such as our sofa, counter top, etc. With the device.

 

[phyzguy]

Why would you worry that the instrument might be contaminated? It sounds like the count rates you got were normal background levels.

 

[gleem]

Thank you for the tips. Would you worry about the instrument being possibly contaminated if it was in fact sent to me used?

That would depend on who was selling it. If it came from a radiation instrument manufacturer, I would not worry. If it came from eBay, maybe. To determine definitively, you would need another detector with the required sensitivity to detect the contamination. Usually, when an instrument is used in a high contamination area, it is wrapped with protective material, such as plastic, to prevent its contamination. Your instruments are not of the type that are most likely not used in industry, where high-contamination areas are most likely, so I wouldn't worry.

I really wish I didn’t play around with it once I found out that my relative doesn’t need RAI.

I really don't like to see people buying these instruments without sufficient instruction on their use. Even then, unusual circumstances might not be addressed, which can lead to misinterpretations of reading. Their use in low-dose situations is especially a problem for the uninitiated, since there is a lot of confusion about the meaning of these readings.

If I may ask, is the relative living with you, and what was the treatment for (Diagnosis), since this information determines the severity of the possible radiation exposure? Typically, the usual instruction from the practitioner for those given radioiodine and immediately sent home, when followed, provides very adequate protection from excessive radiation exposure. The only exception might be a cognitively compromised patient. Patients treated with large quantities are kept in the hospital for up to three days, allowing much of the radiodine to be excreted and stored for decay. Generally, the exposure to any member of the patient's family is expected to be less than 100 mrem/yr (1 mSv/yr) above background.

I’m worried about my baby since I touched ordinary things such as our sofa, counter top, etc. With the device.

As well you should. If your relative did receive the treatment, any excess exposure would have been due to not following the instructions for the patient's care.

It may be of interest to know that the main source of radiation exposure above background to the general public will be from medical imaging that uses radiation, and that is by a large margin over a lifetime.

 

[worriedsick79]

Why would you worry that the instrument might be contaminated? It sounds like the count rates you got were normal background levels.

Just because it looked like it might’ve been used and I touched household items with it to test them. I’m not an expert on this and bought the instrument because someone was supposed to have RAI and didn’t, so I decided to check it out. I didn’t think about the possibility of contamination at the time. I have a small child so I’m worried about it.

 

[worriedsick79]

That would depend on who was selling it. If it came from a radiation instrument manufacturer, I would not worry. If it came from eBay, maybe. To determine definitively, you would need another detector with the required sensitivity to detect the contamination. Usually, when an instrument is used in a high contamination area, it is wrapped with protective material, such as plastic, to prevent its contamination. Your instruments are not of the type that are most likely not used in industry, where high-contamination areas are most likely, so I wouldn't worry.


I really don't like to see people buying these instruments without sufficient instruction on their use. Even then, unusual circumstances might not be addressed, which can lead to misinterpretations of reading. Their use in low-dose situations is especially a problem for the uninitiated, since there is a lot of confusion about the meaning of these readings.

If I may ask, is the relative living with you, and what was the treatment for (Diagnosis), since this information determines the severity of the possible radiation exposure? Typically, the usual instruction from the practitioner for those given radioiodine and immediately sent home, when followed, provides very adequate protection from excessive radiation exposure. The only exception might be a cognitively compromised patient. Patients treated with large quantities are kept in the hospital for up to three days, allowing much of the radiodine to be excreted and stored for decay. Generally, the exposure to any member of the patient's family is expected to be less than 100 mrem/yr (1 mSv/yr) above background.

As well you should. If your relative did receive the treatment, any excess exposure would have been due to not following the instructions for the patient's care.

It may be of interest to know that the main source of radiation exposure above background to the general public will be from medical imaging that uses radiation, and that is by a large margin over a lifetime.

Thank you so much for taking the time to advise me.
So the relative was supposed to have radioactive iodine treatment after thyroid surgery. However, it ended up that she didn’t need it. I bought the Geiger counter before I knew that she won’t be needing treatment. The counter was purchased on Amazon and I measured ordinary items around the house with it. So I’m worried about the fact that I touched items with the possibly used counter. I am worried that the counter itself came to me contaminated, if that makes sense.

 

[gleem]

So I’m worried about the fact that I touched items with the possibly used counter. I am worried that the counter itself came to me contaminated, if that makes sense.

You have two detectors; use one to check the other.