which (inexpensive) Geiger counter for lenses?

You can probably dispense with a Geiger counter and or dosage meter.

Simply mount the lens on a camera cover the lens and take as long an exposure as you can, with as high an ISO value as your can. The camera will take the frame and them take another to subtract the dark current but ionized particles that get to the sensor will leave a spot and this will happen on both frames. the spots will be in different places so you get two exposures, one with bright spots for hits and one with holes.

Compare this with a known not radioactive lens to get an idea of the difference.

When Shutterbug showed that a Takumar was "hot" they did it by putting the lens over a covered Polaroid film and then processed it after two days and the lens had produced a dark spot.

Dr JLW said:

You can probably dispense with a Geiger counter and or dosage meter.

Simply mount the lens on a camera cover the lens and take as long an exposure as you can, with as high an ISO value as your can. The camera will take the frame and them take another to subtract the dark current but ionized particles that get to the sensor will leave a spot and this will happen on both frames. the spots will be in different places so you get two exposures, one with bright spots for hits and one with holes.

Compare this with a known not radioactive lens to get an idea of the difference.

When Shutterbug showed that a Takumar was "hot" they did it by putting the lens over a covered Polaroid film and then processed it after two days and the lens had produced a dark spot.

Click to expand...

Interesting idea. Thanks.

Does this kind of exposure to the sensor cause (minor) damage to the sensor as it has been reported that regular airplane flights can do because the sensor is exposed to more cosmic rays higher up in the atmosphere? If so, can I use your camera to do the testing?

Just get a roll of Reynolds wrap. Aluminum foil stop 100% of alpha particles.

A hot lens is not going to do any more damage than cosmic rays your camera sensor gets all the time.

An ionization event first puts charge into device which looks like light exposure. If it does permanent damage, it will be a change in dark current in the affected pixels. For most photography, dark current is too small to be worth removing. For long exposures the camera takes a second frame with shutter closed and subtracts it from the exposure. Dark current changes are removed. There is damage but it is not visible and it happens all the time.

The damage depends on the type of sensor. For a long time the state of art was SIT vidicon tubes, They operated but having 10KV electrons bombard the silicon sensor. This did not damage the device.

Livermore Labs once made a special sensor by diffusing a dopant into a silicon sensor and then bombarded it to convert the dopant into an element harder to infuse.

Any ionizating radiation is going to have some lasting effect but its highly doubtful that a hot lens is going to do any permanent damage you will notice.

I have flown my digital cameras a lot and not seen any sensor damage. The airport X-Ray is a larger dose.

I once did damage a line scanner by exposing it to a high energy electron beam. This put a high energy current into a small spot. That was almost 50 years ago.

That is lot different from the sporadic and dispersed events from a gamma emitter. It probably less exposure than a camera gets from an airport X ray machine. BTW my cameras survive this just fine but an airport X-ray did erase my EZ-pass transponder.

In any event if you are nervous you can buy a cheap used digital camera and it will cost less than a decent Geiger counter. In worst case, it's good excuse to buy yourself a new camera!

Yes, if $80 or $300 is too much. If I have 150 lenses a counter is easier and works for the front and sides.

If you have 150 lenses, the cost of a Geiger counter should be very minor for you.

To me the only real hazard of old radioactive lenses is that they can fog your long exposure. When these lenses were in use for film, the fogging issue was more serious because the film stayed in the camera and was exposed from then the film was wound into place until the next frame was shot, which could be a very long time, months sometimes. To deal with this at least one camera of that era had a second set of shutter blades that open on a partial press of the shutter.

The hazard is less severe with silicon sensors because they get cleared before and after exposure. Any remaining damage is fully compensated in long exposures by frame subtraction.

I checked eBay and found that working old DSLRs go for about $30. If sensor damage is a concern , buy one of these and try test suspect lenses with it.. The lens does not have to mount fully it just has to be put in front of the sensor and light sealed. This test will directly tell whether a lens is "hot' enough to interfere with long time exposures. If the lens does not fog a frame it is also not going to cause injury either.

Dr JLW said:

You can probably dispense with a Geiger counter and or dosage meter.

Simply mount the lens on a camera cover the lens and take as long an exposure as you can, with as high an ISO value as your can. The camera will take the frame and them take another to subtract the dark current but ionized particles that get to the sensor will leave a spot and this will happen on both frames. the spots will be in different places so you get two exposures, one with bright spots for hits and one with holes.

Compare this with a known not radioactive lens to get an idea of the difference.

When Shutterbug showed that a Takumar was "hot" they did it by putting the lens over a covered Polaroid film and then processed it after two days and the lens had produced a dark spot.

Click to expand...

We're talking orders of magnitude longer exposure time than you'd get with a sensor to get the fogging mentioned with film -- and that's also from 0 distance (direct contact of radioactive element with the film).

I'd be very surprised if any of the lenses as mounted would be hot enough to show fogging that would be distinguishable from noise or even from light leakage through a typical adapter.

Any evidence this is actually feasible?

I measured 17,000 CPM in the rear (counter was still climbing. Another tester measured 27,000. Even with aluminum foil it was way over 3000 CPM. I let the Meyer and the Killfit stay were they are but the Takumar really is quarantined. Even while focusing it was 3100 CPMa few MM away from the thick barrel. I just did not feel comfortable.

Now I know, 35 to 50 CPM is normal. And the safety of that is based on estimates that all parts of a user body is absorbing at this rate. In the lens case, it’s some smaller body mass, as it goes to down with distance fast.



I draw a line about 2000 CPM in rear. Subjective and I am not an expert in any way. But I have to draw a line I feel comfortable with.

Don't get suckered in like those sheep in California did after Fukushima, buying old Victoreen rate meters off Ebay that weren't worth $20, thinking they were geiger counters. Anyone actually getting a measurable reading using one should have run away at high speed since their ion chambers only read "post-nuclear attack" radiation levels!

SiFu said:

sensiblename99 said:

Which (inexpensive) Geiger counter for lenses?

I'm looking to buy a fairly cheap (the cheaper the better) Geiger counter for measuring the radiation from lenses but not sure what I should be looking at.

What kind of radiation do you need to consider with lenses (Alpha, Beta, Gamma, obviously not electromagnetic)?

There are plenty of inexpensive options on eBay but not sure if they will be useful.
Any suggestions or experience to share?

Click to expand...

Hello!

I bought this one (via Amazon):

https://www.gqelectronicsllc.com/comersus/store/comersus_viewItem.asp?idProduct=5629

It does not show alpha though, but this is fine with me, since this is the one I am not concerned about.

Best,

Alex

Click to expand...

All counters will show gamma (most penetrating) and beta (electrons). Many counters do not detect alpha since alpha (helium nucleus) will only penetrate saran wrap, not skin or a sheet of paper. For that, the geiger counter must have an "alpha window" which is usually seen as a screen or grid on an opening in the counter allowing the alpha particles access to the geiger tube interior. If the counter has an exposed alpha window (no screen protection) do NOT touch it as it will shatter, it is very thin and brittle. Also, alpha particles will only travel about 1 inch in air and be stopped so no alpha will be detected beyond that no matter what geiger counter you use.

MHshooter said:

Don't get suckered in like those sheep in California did after Fukushima, buying old Victoreen rate meters off Ebay that weren't worth $20, thinking they were geiger counters. Anyone actually getting a measurable reading using one should have run away at high speed since their ion chambers only read "post-nuclear attack" radiation levels!

Click to expand...

I am about to buy this fine measuring device from eBay -


Do you think I will be able to detect evil dose in my radioactive lenses with it?

So far we are running dish washer, TV and the air purifier with the radioactive power generated from my lenses, but I would like to include the spiritual VR and am a little bit afraid of opening the gate to the evil ghost...

FWIW I have over 50 radioactive lenses and within 15 years I can only notice positive effects. My third hand and fourth eye are a great addition to my superhero intelect.

MHshooter said:

SiFu said:

sensiblename99 said:

Which (inexpensive) Geiger counter for lenses?

I'm looking to buy a fairly cheap (the cheaper the better) Geiger counter for measuring the radiation from lenses but not sure what I should be looking at.

What kind of radiation do you need to consider with lenses (Alpha, Beta, Gamma, obviously not electromagnetic)?

There are plenty of inexpensive options on eBay but not sure if they will be useful.
Any suggestions or experience to share?

Click to expand...

Hello!

I bought this one (via Amazon):

https://www.gqelectronicsllc.com/comersus/store/comersus_viewItem.asp?idProduct=5629

It does not show alpha though, but this is fine with me, since this is the one I am not concerned about.

Best,

Alex

Click to expand...

All counters will show gamma (most penetrating) and beta (electrons). Many counters do not detect alpha since alpha (helium nucleus) will only penetrate saran wrap, not skin or a sheet of paper. For that, the geiger counter must have an "alpha window" which is usually seen as a screen or grid on an opening in the counter allowing the alpha particles access to the geiger tube interior. If the counter has an exposed alpha window (no screen protection) do NOT touch it as it will shatter, it is very thin and brittle. Also, alpha particles will only travel about 1 inch in air and be stopped so no alpha will be detected beyond that no matter what geiger counter you use.

Click to expand...

Actually the pancake G-M tube used is our contamination monitors as work have very little sensitivity to gamma. They are sensitive to alpha (our main issue) & beta.

For ultra budget radiation detection I suspect a solid state type will be the answer. Buying cheap used GM tubes you'll probably end up with one with a cracked window...

SiFu said:

sensiblename99 said:

fferreres said:

ProfHankD said:

fferreres said:

My doubt has been, what if one has a cabinet about 3 meter away from a desk/chair used randomly (20 mins to 4 hours per day), that has a few shelves with 80 of them. I am considering testing. The cabinet has mostly glass, the lenses face up and often have caps.

I am not worried about one, but not sure what multiple many old lenses would add to when one has more lenses, many are 1950s to early 1970s. Has anyone wondered about multiple lenses in storage?

Click to expand...

The Alphas are not an issue. Betas will be blocked by the lens barrels, especially by metal barrels. Gammas will not be stopped by any of that, but 3m distance is quite significant in that the Gammas will be at a much lower density 3m away than within a few cm.

I'm not worried about this.

Click to expand...

Yes, but these are in a bedroom, 3 meters from the bed, so it's completely unlike the typical case where we are considering using it maybe 1 full day or 5 days a year. This is about 1.3 a year, and I am concerned because as there are old lenses, I don't need the average to be high, just a few elements really hot may not be a good idea at that distance for prolonged periods.

I ordered is A/B/G/X...I will try to separate each, A with paper in front of counter, B with Alu foil (likely innacurate but a reference, I don't even know the thickness of the kitchen foil), and then the rest. I assume X will be none or background.

If at 7.5 cm a lens is not ok for prolonged periods, then 8x as far away it's 1/1024 as much exposure at 2.4 meters? If so, the cabinets are about 2 meters from the desk and 4 meters from bed, but having that many lenses is having the average radiation * 100 (# lenses), and by being close in a room I spend 10 hours a day+, that's about 40+ more time exposed what I spend shooting with lenses during the year...That's about 4000 more dose than the average assumption with one lens. So the single lens used occasionally doesn't worry me, but this other case has me saying, don't worry, do the test and if it bothers me, move the outliers out.

With the detector, I will check the lenses, and any outliers, I can put in a different location, or inside the right metal box...

Click to expand...

Or you could just compare the background radiation itself and if significantly higher than do something about it. There's radiation everywhere.

I would be surprised if a significant number of your lenses were radioactive, just being old doesn't imply that they will be radioactive.

Click to expand...

Hello!

Been there - done that (with the model I linked below). Currently I do own 14 lenses that kicked the counter.

Im case you are interested, I can share some findings.

Best,

Alex

Click to expand...

Yes, I'd be interested. I reported that I only saw 3 really kick it out of the ones I tried, with only one being a concern.

As I wrote, A Shutterbug article showed the fogging a Takumar lens produced when placed in a Polaroid Film pack. I think they left it in place overnight and the film is bout ISO 200. There was a very clear fogged disk when the lens had been.

It was the type of film pack used in cut film holders and the lens was over the paper light shield. They then ran pack though the processing roller system.

The radioactive lens was not in direct contact. The stood the lens on its mount so it was inches from the film, about the same distance as a mounted lens. ISO of about 200 for 12 hours is not that far from a few minutes at ISO 16,000 for silicon.

Dr JLW said:

As I wrote, A Shutterbug article showed the fogging a Takumar lens produced when placed in a Polaroid Film pack.

Click to expand...

I see no trace of that article... do you have a citation? It was very common 50+ years ago to check radioactivity by placing whatever object on a sheet of printing paper for a week, and I did find a reference to a late 1990s Shutterbug article repeating that suggestion.

Dr JLW said:

I think they left it in place overnight and the film is bout ISO 200. There was a very clear fogged disk when the lens had been.

Click to expand...

That would imply the image is from Betas. Alphas shouldn't do anything and Gammas will spread without being impeded by a metal lens barrel, so I would expect you'd see a diffuse pattern rather than a spot.

Dr JLW said:

It was the type of film pack used in cut film holders and the lens was over the paper light shield. They then ran pack though the processing roller system.

The radioactive lens was not in direct contact. The stood the lens on its mount so it was inches from the film, about the same distance as a mounted lens.

Click to expand...

Stood the lens on what "inches-long" mount? If it could fog film from inches away, then you'd certainly have film sitting in a Spotmatic 45mm away from the Takumar for days/weeks very visibly fogged. That most assuredly did NOT happen.

If that shows a disc, it would have to be Betas... but I wouldn't expect Betas to penetrate the light shield very well. Are you sure about this?

Dr JLW said:

ISO of about 200 for 12 hours is not that far from a few minutes at ISO 16,000 for silicon.

Click to expand...

It's also far from clear that CMOS sensors have similar response. Neither would I assume that ISO has anything whatsoever to do with it. In fact, boosting ISO on most modern CMOS sensors mostly boosts noise -- that's what that whole ISO-less/ISO-invariant discussion is about. Exposures of minutes also involve a lot of sensor heating, etc., that corrupt the noise floor.

You'd really want to do something that only blocks part of the sensor from the radiation so the fogging is self-referenced. If it's Betas, a piece of pretty much any material a few mm thick will stop 'em (although the act of stopping them can cause bremsstrahlung radiation that might even increase fogging -- in fact, I'd expect that would be the most likely cause of fogging in the experiment you describe). Anyway, you'd need a differential exposure to reliably detect such low-level fogging....

ProfHankD said:

Dr JLW said:

As I wrote, A Shutterbug article showed the fogging a Takumar lens produced when placed in a Polaroid Film pack.

Click to expand...

I see no trace of that article... do you have a citation? It was very common 50+ years ago to check radioactivity by placing whatever object on a sheet of printing paper for a week, and I did find a reference to a late 1990s Shutterbug article repeating that suggestion.

ProfHankD said:

I think they left it in place overnight and the film is bout ISO 200. There was a very clear fogged disk when the lens had been.

Click to expand...

That would imply the image is from Betas. Alphas shouldn't do anything and Gammas will spread without being impeded by a metal lens barrel, so I would expect you'd see a diffuse pattern rather than a spot.

ProfHankD said:

It was the type of film pack used in cut film holders and the lens was over the paper light shield. They then ran pack though the processing roller system.

The radioactive lens was not in direct contact. The stood the lens on its mount so it was inches from the film, about the same distance as a mounted lens.

Click to expand...

Stood the lens on what "inches-long" mount? If it could fog film from inches away, then you'd certainly have film sitting in a Spotmatic 45mm away from the Takumar for days/weeks very visibly fogged. That most assuredly did NOT happen.

If that shows a disc, it would have to be Betas... but I wouldn't expect Betas to penetrate the light shield very well. Are you sure about this?

ProfHankD said:

ISO of about 200 for 12 hours is not that far from a few minutes at ISO 16,000 for silicon.

Click to expand...

It's also far from clear that CMOS sensors have similar response. Neither would I assume that ISO has anything whatsoever to do with it. In fact, boosting ISO on most modern CMOS sensors mostly boosts noise -- that's what that whole ISO-less/ISO-invariant discussion is about. Exposures of minutes also involve a lot of sensor heating, etc., that corrupt the noise floor.

You'd really want to do something that only blocks part of the sensor from the radiation so the fogging is self-referenced. If it's Betas, a piece of pretty much any material a few mm thick will stop 'em (although the act of stopping them can cause bremsstrahlung radiation that might even increase fogging -- in fact, I'd expect that would be the most likely cause of fogging in the experiment you describe). Anyway, you'd need a differential exposure to reliably detect such low-level fogging....

Click to expand...

@ProfHankD

I remember that Shutterbug article, also remember a two-part article in the British Journal of Photography, several decades ago. Might even have a copy buried around here somewhere in my files, paper or digital, but impossible to find. Sorry, don't have a citation for either.

Have you seen this:

"An Analysis of Residual Radiation in Thoriated Camera Lenses - DiVA"

Just to be clear,

ZilverHaylide said:

ProfHankD said:

ZilverHaylide said:

The radioactive lens was not in direct contact. The stood the lens on its mount so it was inches from the film, about the same distance as a mounted lens.

Click to expand...

Stood the lens on what "inches-long" mount? If it could fog film from inches away, then you'd certainly have film sitting in a Spotmatic 45mm away from the Takumar for days/weeks very visibly fogged. That most assuredly did NOT happen.

Click to expand...

Click to expand...

This is the strongly suggestive evidence you wouldn't get a spot on a Polaroid from a Takumar at a reasonable distance. My Dad's Spotmatic was a backup camera for me (I shot mostly Minoltas) and hence would often have a roll in it at the same frame for weeks between uses. Cloth shutter + mirror in the way -- similar to light shield on Polaroid, no? I never saw any sign of differential fogging of the frame behind the radioactive Takumar.

BTW, you can get a spot on a Polaroid by simply sitting a non-radioactive weight on it.

ZilverHaylide said:

@ProfHankD

I remember that Shutterbug article, also remember a two-part article in the British Journal of Photography, several decades ago. Might even have a copy buried around here somewhere in my files, paper or digital, but impossible to find. Sorry, don't have a citation for either.

Click to expand...

I actually found several references to an article in Shutterbug, all vague, and all in disagreement about details of the test. I didn't find any actual Shuterbug article.

ZilverHaylide said:

Have you seen this:

"An Analysis of Residual Radiation in Thoriated Camera Lenses - DiVA"

https://www.diva-portal.org/smash/get/diva2:652338/FULLTEXT01.pdf

Click to expand...

Hadn't seen it. Interesting how specific they are about eye exposure....

petrochemist said:

MHshooter said:

SiFu said:

sensiblename99 said:

Which (inexpensive) Geiger counter for lenses?

I'm looking to buy a fairly cheap (the cheaper the better) Geiger counter for measuring the radiation from lenses but not sure what I should be looking at.

What kind of radiation do you need to consider with lenses (Alpha, Beta, Gamma, obviously not electromagnetic)?

There are plenty of inexpensive options on eBay but not sure if they will be useful.
Any suggestions or experience to share?

Click to expand...

Hello!

I bought this one (via Amazon):

https://www.gqelectronicsllc.com/comersus/store/comersus_viewItem.asp?idProduct=5629

It does not show alpha though, but this is fine with me, since this is the one I am not concerned about.

Best,

Alex

Click to expand...

All counters will show gamma (most penetrating) and beta (electrons). Many counters do not detect alpha since alpha (helium nucleus) will only penetrate saran wrap, not skin or a sheet of paper. For that, the geiger counter must have an "alpha window" which is usually seen as a screen or grid on an opening in the counter allowing the alpha particles access to the geiger tube interior. If the counter has an exposed alpha window (no screen protection) do NOT touch it as it will shatter, it is very thin and brittle. Also, alpha particles will only travel about 1 inch in air and be stopped so no alpha will be detected beyond that no matter what geiger counter you use.

Click to expand...

Actually the pancake G-M tube used is our contamination monitors as work have very little sensitivity to gamma. They are sensitive to alpha (our main issue) & beta.

For ultra budget radiation detection I suspect a solid state type will be the answer. Buying cheap used GM tubes you'll probably end up with one with a cracked window...

Click to expand...

They don't all have windows. Russians sell hundreds on ebay that are just steel tubes. Solid state detectors aren't bad, just not sensitive. They sold some that were about 1 inch long and plugged into a phone or tablet mic jack. Can remember the name. They were pretty cheap, but only suitable for close-in measurement. The best thing is a scintillation counter, or a geiger-type "pancake" detector (large surface area) but they tend to be expensive.

MHshooter said:

petrochemist said:

MHshooter said:

SiFu said:

sensiblename99 said:

Which (inexpensive) Geiger counter for lenses?

I'm looking to buy a fairly cheap (the cheaper the better) Geiger counter for measuring the radiation from lenses but not sure what I should be looking at.

What kind of radiation do you need to consider with lenses (Alpha, Beta, Gamma, obviously not electromagnetic)?

There are plenty of inexpensive options on eBay but not sure if they will be useful.
Any suggestions or experience to share?

Click to expand...

Hello!

I bought this one (via Amazon):

https://www.gqelectronicsllc.com/comersus/store/comersus_viewItem.asp?idProduct=5629

It does not show alpha though, but this is fine with me, since this is the one I am not concerned about.

Best,

Alex

Click to expand...

All counters will show gamma (most penetrating) and beta (electrons). Many counters do not detect alpha since alpha (helium nucleus) will only penetrate saran wrap, not skin or a sheet of paper. For that, the geiger counter must have an "alpha window" which is usually seen as a screen or grid on an opening in the counter allowing the alpha particles access to the geiger tube interior. If the counter has an exposed alpha window (no screen protection) do NOT touch it as it will shatter, it is very thin and brittle. Also, alpha particles will only travel about 1 inch in air and be stopped so no alpha will be detected beyond that no matter what geiger counter you use.

Click to expand...

Actually the pancake G-M tube used is our contamination monitors as work have very little sensitivity to gamma. They are sensitive to alpha (our main issue) & beta.

For ultra budget radiation detection I suspect a solid state type will be the answer. Buying cheap used GM tubes you'll probably end up with one with a cracked window...

Click to expand...

They don't all have windows. Russians sell hundreds on ebay that are just steel tubes. Solid state detectors aren't bad, just not sensitive. They sold some that were about 1 inch long and plugged into a phone or tablet mic jack. Can remember the name. They were pretty cheap, but only suitable for close-in measurement. The best thing is a scintillation counter, or a geiger-type "pancake" detector (large surface area) but they tend to be expensive.

Click to expand...

I bought a GQ GMC-600 Plus digital Geiger Counter installed with a high sensitive Pancake Geiger tube LND 7317 for Alpha, Beta, Gamma and X-Ray radiation detection.

It’s not so cheap though.

My question is... if a counter measures 27,000 CPM Beta+Gamma in the rear, is any precaution needed? I did not see a single person address this, but I measured 17000 close to the rear and other measurements by others were 27,000 CPM.

fferreres said:

MHshooter said:

petrochemist said:

MHshooter said:

SiFu said:

sensiblename99 said:

Which (inexpensive) Geiger counter for lenses?

I'm looking to buy a fairly cheap (the cheaper the better) Geiger counter for measuring the radiation from lenses but not sure what I should be looking at.

What kind of radiation do you need to consider with lenses (Alpha, Beta, Gamma, obviously not electromagnetic)?

There are plenty of inexpensive options on eBay but not sure if they will be useful.
Any suggestions or experience to share?

Click to expand...

Hello!

I bought this one (via Amazon):

https://www.gqelectronicsllc.com/comersus/store/comersus_viewItem.asp?idProduct=5629

It does not show alpha though, but this is fine with me, since this is the one I am not concerned about.

Best,

Alex

Click to expand...

All counters will show gamma (most penetrating) and beta (electrons). Many counters do not detect alpha since alpha (helium nucleus) will only penetrate saran wrap, not skin or a sheet of paper. For that, the geiger counter must have an "alpha window" which is usually seen as a screen or grid on an opening in the counter allowing the alpha particles access to the geiger tube interior. If the counter has an exposed alpha window (no screen protection) do NOT touch it as it will shatter, it is very thin and brittle. Also, alpha particles will only travel about 1 inch in air and be stopped so no alpha will be detected beyond that no matter what geiger counter you use.

Click to expand...

Actually the pancake G-M tube used is our contamination monitors as work have very little sensitivity to gamma. They are sensitive to alpha (our main issue) & beta.

For ultra budget radiation detection I suspect a solid state type will be the answer. Buying cheap used GM tubes you'll probably end up with one with a cracked window...

Click to expand...

They don't all have windows. Russians sell hundreds on ebay that are just steel tubes. Solid state detectors aren't bad, just not sensitive. They sold some that were about 1 inch long and plugged into a phone or tablet mic jack. Can remember the name. They were pretty cheap, but only suitable for close-in measurement. The best thing is a scintillation counter, or a geiger-type "pancake" detector (large surface area) but they tend to be expensive.

Click to expand...

I bought a GQ GMC-600 Plus digital Geiger Counter installed with a high sensitive Pancake Geiger tube LND 7317 for Alpha, Beta, Gamma and X-Ray radiation detection.

It’s not so cheap though.

My question is... if a counter measures 27,000 CPM Beta+Gamma in the rear, is any precaution needed? I did not see a single person address this, but I measured 17000 close to the rear and other measurements by others were 27,000 CPM.

Click to expand...

Nice unit, counter per min aren't the typical dose measurement, sieverts are, your counter will read out in micro sieverts per hour. Micro is 1/millionth of a sievert. A chest x-ray is equivalent to 5.8 milli-sieverts or 5800 micro sieverts. Maximum dose per year is now set as 50 milli-sieverts. Also, radiation works the same as light, it is governed by the "inverse square law" where if you double the distance from the source, it is reduce by 4 times. A 100u(micro) sievert per hour reading at 1 inch, should be 25u at 2 inches, 6.125 at 4 inches, and so on. All you have to do to find maximum exposure is take a reading and say divide it into 50 milli-sieverts for a year, divide that by 365 for a day, and 24 for an hour. It's not likely any lens could give any kind of dose to make you ill or exceed the recommended limit. Full-body exposure is a bit different, you body is larger than the sensor in your geiger counter so you will absorb more radiation than the counter indicates for its surface-area. This is all for gamma radiation because it is the most penetrating and travels the furthest distance in air. Exposing skin however to direct contact with a beta or alpha source for a prolonged period could result in area damage to the skin. Depends on the strength of the source. BTW, 8-10 seiverts will result in death.