Need feedback on my setup

4 years 11 months ago #4623 by g346342
I have this detector

There is some shared google drive folder in the description but it is not perfect documentation.

There is a J2 contact to calibrate the high voltage. However, the resistance is not 5*10 M ohms but 55.22M so using two multimeters (one 1M and one with 10M ohms internal resistance) I adjusted the voltage to around 355V (It is not possible to measure the tube voltage directly)

Everything seems fine. I use Arduino for now and send the reading with Radiation Logger software to this platform.

The average is around 20 CPM and for that tube j305, the index is 0.00812037. That converts to something like 200nSv/h

I compare that to the closest official station from (it is like max 5km from here) and I get a value that is two times higher. How can I get better results?

For testing I also got ttps://

That is not for testing but a real smoke sensor component. There was almost no difference if I move it close or away from the tube. I couldn't find some better documentation but from similar models, it seems like you need to apply voltage to two of the pins and get output that will indicate fire condition. Also, there was a note that no radiation leak out of the chamber I disassembled it:) Now it was much different. I got up to 150 CPM if it was very close and directed to the tube (like 3cm away). At least I know that it works. I couldn't assemble it back perfectly so now I need to find a way to store it (there are no effects if you are 15cm away from it) but it still sounds scary

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4 years 11 months ago #4624 by Bert490
Replied by Bert490 on topic Need feedback on my setup
Different tubes/technologies usually don't produce the same readings. I think the Eurdep/Remon detectors are specific for Gamma, while your tube senses both Gamma and Beta. GM tubes also have some amount of self-induced readings, producing non-zero values even inside a heavy lead box. Your test source from a Smoke detector likely contains Am 241, which produces primarily Alpha radiation, which is not detected by the j305 tube. A better test source that is easily obtained is Uranium glass beads or thorium lantern mantles.

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4 years 11 months ago - 4 years 11 months ago #4625 by Simomax
Replied by Simomax on topic Need feedback on my setup

How can I get better results?

It depends what you mean by 'better results'. Geiger counters are fickle devices. Much depends on how they are setup, the quality of the circuit and parts that are used. Especially the GM tube itself. Different tubes will give different counts with different radionuclides. Unlike say a volt meter, or an air quality sensor or carbon monoxide sensor, or other sensors Geiger Muller tubes of different models and manufacturers all tend to be very different. Two air quality sensors from two different manufacturers will (should) give the same result when testing the same air, the same goes for gas sensors or say UVA/UVB light sensors. Different GM tubes can give massively different results when testing the same radioactive source. There can be nearly an order of magnitude difference between one type of GM tube and another with the same source. So 'getting better results' should often be replaced with 'how do I best read the results I have got?'. In fact, I would akin a GM tube to that of a microphone. All microphones are able to pick up audio, but some are better than others and all, and I mean all, even the same makes and models will sound different. Maybe in the cases of the same makes and models this won't be detected by the human ear, but to the right analysis system there will be tiny differences in the frequency response and amplitude.

I think the tube that is in your counter is a J305by made by North Optic. The b and the y in the model number indicate the tube is sensitive to beta and gamma. I managed to track down the specs on this page:
It shows the gamma sensitivity for Cobalt-60 is 65cps, whereas an SBM-20 GM tube is only 22cps sensitive to Cobalt-60 making the J305 3x more sensitive to Cobalt-60. However the J305 may be more sensitive or less sensitive to different radionuclides. It is also important to note that when a Geiger counter is calibrated they are only calibrated to that particular radionuclide. So doing a comparison between the REMon database you state and your own counter; neither offer data on what radioniclides they are detecting, if any. Unless you know what you are detecting it is hard to make assumptions as to whether one counter is better than another, or whether one is better calibrated. When it comes to background level monitoring, again this is fickle. Different GM tubes have different background counts. The background count will also vary most of the time which is why averaging is important when measuring background radiation. There are also things that can distort the background count such as muons (cosmic rays) and inteference caused by near by electrical or electronic equipment. Sometimes cheap power supplies can interfere and show a higher background count than is actually present. Someone did a test where they placed a plasma ball near a Geiger counter and the counter went crazy. And, I'll always advise the use of a good quality power supply for a counter with preferably a linear regulator or even batteries. Batteries are so linear you can happily forget about any kind of noise or interference from them as it is a mere impossibility, unless using a step-down BUCK regulator after the batteries.

In the REMon database you show, I'm going to assume they are using top-notch equipment and to put it simply, you are not. There are going to be massive differences between a cheap Geiger counter and one that is made for monitoring purposes. So again this comes down to being able to read and understand your own counter. From what I can tell they are using a 24 hour average of the counts detected in the REMon database so in order for you to gain a better comparison you are going to have to leave your counter on for 24 hours, and then average the data respectively. If you are using an arduino you should be able to program it to simply count the number of clicks over a given time and generate an average from that. So say you get 30,000 counts in a 24 hour period, divide that by 1440 (the number of minutes in a day) and that will give you 20.83 cpm average over the 24 hour period.

So with all that said, how do you get better results? You can change out the GM tube but that will only give you different results unless you are able to do the math. In order to do the math you need an understanding of the equipment you are using. I have been recording and learning about all things Geiger for about 3.5 years now and I reckon I have literally just got under the surface but there is still so much I don't understand and without the necessary tools (calibrated sources and mid-high end equipment) to experiment myself it is a very hard subject to contend with. As the sensitivity of your tube (assuming it is the J305) is 3x higher than say a SBM-20 then your background counts should be in order of at least double that of a SBM-20. Doing some crude (and I mean very crude) math if you are getting 40cpm background then I would say that is probably about right compared to that of a SBM-20. You cannot however compare your background count to that of a system you don't know. There is a possibility you are counting radiation that is on top of the actual background. I have seen a handful of cases where people experienced this and turns out they live in a high Radon emission area so they were actually detecting decay products from Radon gas decay and wasn't necessarily a high background count. It was an actual, be it small, event. It may also be possible they the voltage for your tube is slightly high and is causing the odd avalanche which may be distorting your background count.

My best advise to you, and other newcomers to radiation detection is simply to live with your counter for a while and learn as much as you can about both counters and radiation itself. Then apply your knowledge with the results you are getting. Maybe try one or two different tubes and see what the results are. Get a few different radioactive sources such as Uranium glass, fiesta ware pottery or other sources your tube is capable of detecting and play about with them. If you do experiment and are connected to Radlog then please do turn off the alerts whilst testing - this can be done on your Radmon profile.

The radioactive source you purchased is Americium-241 which is an Alpha emitter. But as the Americium decays it creates (transmutes?) other unstable radionuclides that are beta and gamma emitters which is why your tube detects it. Your tube is detecting the decay products of the Americium, not the Americium itself. I know, it is a mine field at first trying to understand everything.

With regards to your Americium-241 sample, be very careful with it. Very careful. Americium is extremely toxic if inhaled or ingested. Alpha emitters are about as bad as you can get for inhalation or ingestion. When you took it apart you probably found a little plastic disc inside. In the center of the disc there is a little metal part housing the americium itself, the very small round bit in the middle. The Americium is coated (only a few microns thick) onto a tiny disc that is held by the metal piece in the middle. Do not touch it, don't break it, don't take it apart more than you have already and keep it in a decent container. It is prudent to always either wear disposable gloves or wash your hands after handling it, even when you don't touch it. I really can not stress enough about the dangers of inhaling or ingesting microscopic particles of any radioactive source. I'm astonished you can just buy these right from Banggood and Ebay without massive safety warnings. They are dangerous. As dangerous as Asbestos IMHO, if not more so.

I also find it very interesting that you can buy your entire counter with the J305 tube for only £22! A quich search for that tube on Ebay shows the tube only for sale at £28, twice the cost of an SBM-20. I might buy one of those counters from Banggood if only for the tube itself.
Edit: I couldn't resist and have just bought the same counter and tube so I can have a play about with it. On spec the tube seems quite sensitive so will be interesting to play about with :woohoo:

I hope this helps.
Last edit: 4 years 11 months ago by Simomax.

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4 years 11 months ago #4626 by g346342
Replied by g346342 on topic Need feedback on my setup
Yes, it is using Am 241 but it also produces gamma ( scroll down). I am more interested in gamma only too. If I put it in plastic electrical box with a single layer of aluminim foil on the inside as beta filter... should I get good readings?

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4 years 11 months ago - 4 years 11 months ago #4627 by Simomax
Replied by Simomax on topic Need feedback on my setup

If I put it in plastic electrical box with a single layer of aluminim foil on the inside as beta filter... should I get good readings?

You will get whatever you was getting before less a small amount of beta. You will need around 5mm of amuminium around the entire tube (that's all of the tube, including the ends) to pretty much stop beta passing through. Putting aluminium over a window at one side won't stop gamma from entering the tube through the back or sides of the plastic box.
Edit: You will also get generally ever so slightly less counts with it being inside a plastic enclosure. Every material will reduce radiation when between the source and tube. The higher density the material will generally mean less radiation being passed through it. Except when it comes to beta and lead as beta will pass through lead much better than aluminium, whereas gamma passes through aluminium better than lead.
Last edit: 4 years 11 months ago by Simomax.

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4 years 10 months ago #4630 by FSM19
Replied by FSM19 on topic Need feedback on my setup
For a beta shield you need 3mm of aluminium, foil isn't thick enough, UK Civil Defence geiger counters and ionisation instruments, such as the Meter Doserate Portable No 1 Trainer, Meter Doserate Portable No 1 and the Meter Survey Radiac No 2 had diecast bodies about 1/8" thick to act as a beta shield - the latter two could be used to detect beta by removing the bottom of the case. For a few more details see my site .
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