[MossyRocks]

Hmm, not true, watch the videos above. Beta can travel through a whole book. Unless that's the gammas. From what I've read most betas are stopped by a few milimetres of aluminium, not a sheet of paper.

Alpha particles (helium nucli) are the ones stopped by a bit of thin paper and the outer layer of dead skin cells on your body. Beta particles can travel further but are stopped when they encounter any metal or a bit more material unless they are really high energy in which case you should be concerned as to why you have an electron gun running unshielded near you. Gamma rays are typically the ones that go really far into things requiring a bunch of lead or other dense material, however the decay chain for thorium produces fairly low power gamma rays and I think only one is capable of pair production, and most being in the medical x-ray range for a single photon. It looks like most of the gamma emissions are from the Tl208 decay but those photons have energies from .277MeV to 2.614Mev. Gamma rays sound scary especially since the term is rather nebulous but they are just part of the electromagnetic spectrum but these photons often originate from nuclear processes instead of other means and a lot of what people class as gamma rays are actually x-rays of similar energy to those used in medicine. They are measured in eV and to figure out where in the electromagnetic spectrum that emission falls you can look up the energy and see where they fall in the spectrum. So looking at the gamma emissions on the low end of .277MeV that is in the hard X-ray range but that is a single photon of hard x-ray. On the high end there is an emission at 2.614MeV which is clearly into the gamma ray range capable of pair production, but all of the rest are well below 1MeV so they are also in the hard X-ray range. Also not every thorium atom will decay through Tl208 as there is a split that happens in the decay of Bi212 where some become Tl208 and some becomes Po212. When you get an x-ray at the doctors office you get blasted with a bunch of hard x-rays because they do a really good job of going through material.

[AntonioS]

Hmm, not true, watch the videos above. Beta can travel through a whole book. Unless that's the gammas. From what I've read most betas are stopped by a few milimetres of aluminium, not a sheet of paper.

Yes my fault, I studied this 30 years ago, sorry

Just for curiosity (not a lesson in any way !)



Thin paper will block ALPHA

Thin aluminum foil, thick cardboard will block BETA

Almost nothing will block gamma unless it hits an atom. Most of the matter structure are "holes" for this wavelenghts.

If BETA has enough energy and hits high Z elements like lead, those elements can radiate X-Rays due the bremsstrahlung (seconday X-Ray emission). That's why old cathode ray tubes emiited X-Rays (very high energy electrons hitting matter). With less energy they would just cause the phospor to glow.






Again, it's a matter of the energy associated to the Beta emission, A 1 MeV beta particle can travel approximately 3.5 meters in air.
The maximum energy associated with the Thorium series beta decay is about 4 MeV for the Th-232 but the emission is very low due the extreme long half life, about 10ˆ10 years. all the other beta decays on this series are lower in energy Some alphas are high in energy.


take a look:



Thorium decay is slow and the quantities of subproducts are very low, unless you wait for eons.
Again the radioactive emission is not that different from the average background, this is layman paranoid and some untold things.
Don't worry too much with this.

[stevebrot]

That's the problem when layman people starts to think about some things they don't have a clue of how they work.

Don't assume that the people on this thread or similar threads on this site are laymen or uninformed.


Steve

(...btw...you are wrong...)

[AntonioS]

Alpha particles (helium nucli) are the ones stopped by a bit of thin paper and the outer layer of dead skin cells on your body. Beta particles can travel further but are stopped when they encounter any metal or a bit more material unless they are really high energy in which case you should be concerned as to why you have an electron gun running unshielded near you. Gamma rays are typically the ones that go really far into things requiring a bunch of lead or other dense material, however the decay chain for thorium produces fairly low power gamma rays and I think only one is capable of pair production, and most being in the medical x-ray range for a single photon. It looks like most of the gamma emissions are from the Tl208 decay but those photons have energies from .277MeV to 2.614Mev. Gamma rays sound scary especially since the term is rather nebulous but they are just part of the electromagnetic spectrum but these photons often originate from nuclear processes instead of other means and a lot of what people class as gamma rays are actually x-rays of similar energy to those used in medicine. They are measured in eV and to figure out where in the electromagnetic spectrum that emission falls you can look up the energy and see where they fall in the spectrum. So looking at the gamma emissions on the low end of .277MeV that is in the hard X-ray range but that is a single photon of hard x-ray. On the high end there is an emission at 2.614MeV which is clearly into the gamma ray range capable of pair production, but all of the rest are well below 1MeV so they are also in the hard X-ray range. Also not every thorium atom will decay through Tl208 as there is a split that happens in the decay of Bi212 where some become Tl208 and some becomes Po212. When you get an x-ray at the doctors office you get blasted with a bunch of hard x-rays because they do a really good job of going through material.

Exactly. Matter of energy, half life and different pathways.

For example, Bi-212 decays in two forms, by beta to Po-212 (64%) and to Ta-208 by alpha (36%).

More easy reading here: NRC: Radiation Basics

---------- Post added 04-22-19 at 02:55 PM ----------

Don't assume that the people on this thread or similar threads on this site are laymen or uninformed.


Steve

(...btw...you are wrong...)

Never assumed this. I was talking in general about what people say in the Internet.
And I'm not wrong, I studied this kind of stuff for some good years at the University.
It's not my intention to escalate this, I was just trying to clarify some misconceptions.

Cheers!

[mccririck]

Again the radioactive emission is not that different from the average background, this is layman paranoid and some untold things.
Don't worry too much with this.

Did you watch the youtube videos with the geyger counter tests. The radiation emitted from these lenses is clearly well above background.

[AntonioS]

Did you watch the youtube videos with the geyger counter tests. The radiation emitted from these lenses is clearly well above background.

Yes but at a very short distance. This makes all the difference. The effective danger will be greatly decreased by absorption and scattering.

[mccririck]

Yes but at a very short distance. This makes all the difference. The effective danger will be greatly decreased by absorption and scattering.

It's well above background! Well above!

[AntonioS]

It's well above background! Well above!

At what distance ? Less than 1 inch ? It's ok to hear all that popping at contact distance. At 2 inches it will drop dramatically, by the square of the distance, and from a few inches it will be at the background level.

Again, you have the distance of more than one inch from the lens back to you, and you have the metal camera back. You won't be harmed.

If this lens was so dangerous like people like to say, it would completely fog film ! I dare someone to show (and prove) that a film was fogged this way.

Lots of things in your house are also radioactive like concrete, cement, granite... You don't need to worry.

Digging here in my old papers I found some actual scientific studies about this:

Taylor et al. (1983) measured the absorbed dose rate at the back of a camera and the thorium content of the lens. The thorium in the lens was estimated to be 13 kBq (0.36 Ci). Using the 3–290 methodology described in Appendix A.4 for sources close to the body, the dose rate at 10 cm depth in the body was determined to be 1×10-4 mSv/h (0.01 mrem/h).

A serious outdoor photographer is assumed to spend 30 days/yr in the field (average photographers-10 days/yr) and to carry a camera next to the body for 6 hours per day during that time. This exposure time should be conservative for most photographers. Based on the assumed exposure time and the absorbed dose rate, the annual EDE would be 0.02 mSv (2 mrem). For an average photographer the EDE would be 0.007 mSv (0.7 mrem)

Note that 0.007 mSv is 0.2% of what you get annual from normal background radiation (3 mSv).
A more pertinent question might be what the dose rate to the eye is. Radiation exposure can lead to cataracts, and of course a camera lens is going to be very close to one's eye. From the same publication, they measured the dose rate at the surface of the camera lens to be 0.48 mrad/h, or about 5 micro-Sv/hr. The dose limit to the lens of the eye for members of the public is 15 mSv per year, so you would need to hold this lens against your eye for 3,000 hours to exceed that. With the lens attached to a camera, the dose rate dropped by a factor of 5 (due to blocking the electrons and alphas). At this level, one couldn't exceed the dose limit even if they continually held the camera to their eye for an entire year. Also note that dose limits to members of the public are already pretty conservative in terms of preventing effects.
So to summarize, there is almost no way to exceed the dose limits while using a camera of this type. Furthermore, the radiation you would receive is only a small fraction of the background radiation.

Here, another lecture from an old U.S. Army study (http://www.irpa.net/irpa3/cdrom/VOL.3B/W3B_13.PDF)
I love this lecture. Read the introduction on page 883 (specially paragraph 4). Note the statement about the only potential problem is IF the ocular lens was highly thoriated.
Also take a look at the summary on the last page.

This page condensates some of the NRC conclusions about the same situation: Thoriated Camera Lens (ca. 1970s)
According to the NRC the average background radiation dose in the US is about 360 mrem/yr, WAY MORE than you will ever receive from a thorium glass lens.

We live in a radioactive world, and radiation has always been all around us as a part of our natural environment. As explained above, the annual average dose per person from all sources is about 360 mrem, but it is not uncommon for any of us to receive more than that average dose in a given year (largely as a result of medical procedures). To find your personal annual radiation dose, use the interactive Personal Annual Radiation Dose Calculator or this printer friendly worksheet. (source: NRC)

There are plenty of studies with the same conclusions. If you like, read this enormous NUREG document: http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1717/nureg-1717.pdf (section 3.19)

Just for curiosity, there is a rule of thumb to estimate the beta range by energy and material density: For low density materials, it's about 2mm/MeV and for medium density materials, about 1mm/MeV. (for air, 3.5m/MeV ; glass 2.1mm ; aluminum 1.8mm ; copper 0.45mm, water 4.5mm)

A 5 MeV alpha is stopped by: 3.7 cm of air / 53 micrometers of paper / 45 micrometers of water and will not penetrate the skin.





The way some people spread information is simlpy bad science, no scientific methodology and lots of misconceptions.

Please don't panic and enjoy your marvelous vintage lenses !

[stevebrot]

The way some people spread information is simlpy bad science, no scientific methodology and lots of misconceptions.

The most common misinformation is that thorium decay produces no gamma. The second is that the amount there is is too low to do harm. That last depends on where one lives and cumulative occupational and environmental exposure from all sources. One form of misinformation is to quote multiple sources using multiple disparate measurements of radioactivity followed by a blanket statement that all are too low for concern.

It is probably enough to note:

• Thoriated glass disappeared from camera optics long before widespread public awareness of its existence. Whether it was because of public health concerns or increased regulation of raw materials or increased cost of production is not clear.
• Many of us have heightened awareness of radiation risks due to known environmental exposures in our regions*
• Ionizing radiation is, well, ionizing radiation

Please don't panic and enjoy your marvelous vintage lenses !

I own several lenses having thoriated glass. I used one (M42 Auto Rikenon 55/1.4) yesterday and it is still attached to my K-3 on the counter behind me. Rumors are that it may not be good for the camera sensor. I do know that the radiation may have been strong enough to create additional noise, though I have no inclination to do any testing. By coincidence, I store my gear in areas of the house where they provide almost no exposure risk. I also don't cuddle with my lenses.


Steve

* Many people I know had downwind exposure to atmospheric releases from the Hanford Reservation in Washington State during the 50's and 60's and resulting thyroid damage and increased cancer risk. Some on this site take care when exploring the deserts near their homes due to uranium mine tailings at some locations.

[AntonioS]

I own several lenses having thoriated glass. I used one (M42 Auto Rikenon 55/1.4) yesterday and it is still attached to my K-3 on the counter behind me. Rumors are that it may not be good for the camera sensor. I do know that the radiation may have been strong enough to create additional noise, though I have no inclination to do any testing. By coincidence, I store my gear in areas of the house where they provide almost no exposure risk. I also don't cuddle with my lenses.

Simple to check. Take an old digital camera you don't use anymore and fit the lens. Let it there for one year, then check for dead pixels.

Second way is to get a 4x5 film sheet, like a Tri-X. Place it inside a thick envelope and put the lens resting over it with the rear element down. Better, place two lenses, one in a fixed position and another one that you will move and wait for different times for each place, line 1 day, one week and 1 month. Then develop the film and check. This is the basic dosimeter and will always work for gamma, x-rays and high energy beta. Low energy beta may not pass a thick envelope.

Cheers

[les3547]

Not mentioned are lenses using lanthanum, like some of the old Voigtlanders. I'm not sure if the modern "Lanthar" Voigtlanders (Cosina) I own actually contain lanthanum or if it's just been left in the name. In any case lanthanum is said to be "only 1/10,000th as radioactive as thorium."

There's a long list of lenses that test radioactive found here.

[photoptimist]

The most common misinformation is that thorium decay produces no gamma. The second is that the amount there is is too low to do harm. That last depends on where one lives and cumulative occupational and environmental exposure from all sources. One form of misinformation is to quote multiple sources using multiple disparate measurements of radioactivity followed by a blanket statement that all are too low for concern.

It is probably enough to note:

• Thoriated glass disappeared from camera optics long before widespread public awareness of its existence. Whether it was because of public health concerns or increased regulation of raw materials or increased cost of production is not clear.
• Many of us have heightened awareness of radiation risks due to known environmental exposures in our regions*
• Ionizing radiation is, well, ionizing radiation

I own several lenses having thoriated glass. I used one (M42 Auto Rikenon 55/1.4) yesterday and it is still attached to my K-3 on the counter behind me. Rumors are that it may not be good for the camera sensor. I do know that the radiation may have been strong enough to create additional noise, though I have no inclination to do any testing. By coincidence, I store my gear in areas of the house where they provide almost no exposure risk. I also don't cuddle with my lenses.


Steve

* Many people I know had downwind exposure to atmospheric releases from the Hanford Reservation in Washington State during the 50's and 60's and resulting thyroid damage and increased cancer risk. Some on this site take care when exploring the deserts near their homes due to uranium mine tailings at some locations.

Precaution is wise if one is facing an unknown exposure to harm from an invisible source of danger.

However, if one learns about the nature of the risk, the level of exposure and the corresponding level of risk, then precaution can be replaced by informed acceptance of the risk relative to the benefits.
The biggest factor of this risk are:

• Merely being in the proximity of a radioactive object is much safer than inhaling or ingesting a radioactive substance
• Even modest distances from a radioactive object strongly attenuate the radiation
• The total health risk from natural background radiation is very low*
• The incremental radiation from using a thoriated lens is a tiny fraction of the normal daily exposure and many other sources of exposure.

Roughly speaking, one hour of using a thoriated lens is roughly the equivalent to: eating 1 banana; about 1 week of living in a stone, brick, or concrete house; about 2 hours visiting a mountainous area; about 1 minute of jet airliner flying time. In the rogues gallery of risks to human life, using a thoriated lens adds miniscule risks. The average landscape photographer gets far more radiation flying to visit and photograph a mountain than from the lens and the total added risk is very very low. I'd not be surprised if worrying about thoriated lenses may be more harmful to a person's health (through high blood pressure and ignoring other far larger controllable risks such as diet, exercise, and safe driving) than using these lenses.


* NOTE: it's not entirely clear that radiation has no safe dose for the average person. Some studies find the opposite effect -- some exposure to radiation might stimulate self-repair mechanisms and reduce rates of cancer. Called radiation hormesis (Radiation hormesis - Wikipedia Radiation Hormesis: The Good, the Bad, and the Ugly ), it's just a hypothesis with lots of conflicting data. And the data is conflicting because it's virtually impossible to do good controlled studies on large enough sample sizes to detect this subtle effect. (And it's virtually impossible to get good data because the health risks of low levels of radiation are so minuscule that other health risks swamp the effects of radiation.)

[mccririck]

I guess the important thing is not to look into the lens close up. Don't hold it up to your eye and stare into it!

Has anyone measure the radiation from the front of the lens, from the rear, from the sides, and then from the rear when it is attached to a camera? It would be interesting to see the differences.

[stevebrot]

Roughly speaking, one hour of using a thoriated lens is roughly the equivalent to: eating 1 banana;...

Ha! Ha! I chuckle when I come across the B.E.D. (Banana Equivalent Dose) which is conveniently about 1% of background and is traceable to the relatively high concentration of potassium found in bananas, potatoes, and many other vegetables. The chuckle is because eating a banana does not appreciably increase one's exposure. The radioactive potassium (40K) is incidental to the total potassium in the banana and is present in the same percentages as potassium already inside us. Homeostasis results in the total amount of dosage from potassium being essentially constant regardless of how many bananas one might eat. There is a transient "bump" in body potassium after eating the banana with a return to previous levels an hour or so later, with the extra going out in the urine.

That aside, I tend to agree with your conclusions as far as reasonable diligence is concerned.


Steve

[stevebrot]

Has anyone measure the radiation from the front of the lens, from the rear, from the sides, and then from the rear when it is attached to a camera? It would be interesting to see the differences.

There is at least one video where the presenter has done just that and some other reports regarding a few lenses where the radiation is strongest towards the front.


Steve