FAQ - More on test sources for calibration and testing

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Richard Hull
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FAQ - More on test sources for calibration and testing

Post by Richard Hull » Wed Jun 19, 2019 9:39 pm

I have already dealt with the acquisition, use and storage of test and calibration sources in a previous FAQ.

I wish to now give insightful data on the decay chains and dangers involved with handling, accidental inhalation and even ingestion of common sources allowed under NCR regulations.

First and foremost..... never allow food or drink near any activities involving unsealed sources. This usually applies only to Uranium or Thorium ore or their related chemicals.

Second....Always wear latex disposable gloves when handling radioactive ore and minerals as well as any open, unsealed radioactive source.

Third...... always wash your hands after touching any radioactive mineral or source accidentally. Take a reading with a good mica windowed Gm counter to verify that your hands are not above normal background levels after washing. Many re-washings might be needed!

Sealed test sources

These might be the best all around bet, even if a bit expensive. These are totally safe to handle with the bare hands and can be had in a number of isotopes as they are sold under an NRC general license as unlicensed quantities of source material. They are typically used to calibrate radiation detection instruments such as Geiger counters and Gamma Ray spectrometers. They are usually distributed sealed in plastic disks. Never
attempt to open these or defeat their holders!!!

Uranium Ore issues

Under the NCR general license you are allowed to hold, store and transfer limited amounts of uranium ore. This allows mineral collectors, mineral dealers, geologists and museums to have this material in their possession without having the NRC generate millions of needless licenses. The proviso in the general license, which we all have as U.S. citizens, is that the ore not be processed in any manner!! In other words, it must remain as rock! You may not process it to obtain uranium in chemical or metallic form. These ores, in their words, are considered an unimportant form of source material.

All ore rocks have some radioactivity. The bulk of the U ore that will come into your possession will have 95% of its radiation blocked due to internal shielding of all of the alpha and beta radiation with only a small amount of internal gamma radiation leaving the specimen. Thus, you will only have access to surface radiation. This should be most adequate for your purposes in calibration, especially in the case of aligning the gain for a gamma ray spectrometer as there are a whole bunch of nice, well known gamma ray signatures in U ore that is in full equilibrium. All ore is in equilibrium!

As such, radon in constantly emitted from the surface of the ore rock and any significant amount of ore should be placed in a tightly sealed container and preferably never stored in a living space. A separate outdoor shed is ideal. Old surplus military metal ammo cans have a superb gasket seal and are a first choice for storage. Harbor Freight sells a heavy duty plastic version with an equally good seal.

Uranium ore also has daughter products all over its surface that can and will transfer to bare hands leaving them radioactive. This is why the admonition given above about wearing disposable gloves is of paramount importance.

Uranium Chemicals

These are rare but have been found at flea markets, but are very rare to non-existent and nearly impossible to obtain in the commercial markets.
Avoid these as they are worthless for gamma spec alignment as no real gamma rays will be found in them. Why? When U ore is purified to a pure uranium chemical, it will not produce any good gamma rays until about 2 million years after it is purified and in equilibrium with all of its daughters. Uranium chemicals will never emit radon, ever! (well 2 million years from now they will). With no worries about radon, the big worry is only direct ingestion via mouth. No one eats uranium chemicals. Still, be careful as they are a great alpha and beta emitter about 5 months after being manufactured.

Thorium ore

Thorium ore, such as monazite and many others, is much less encountered, albeit, in far greater abundance in the Earth's crust than Uranium. Thorium minerals are traditionally far less radioactive as many of the daughters are alpha emitters and many GM counters will not pick up alpha particles, thus the average counter will show a weaker count in many cases. All thorium minerals will also give off radon. It used to be called Thoron gas. The radon from thorium minerals is much more dangerous to inhale than radon from uranium minerals due to its 54 second half life. As you inhale thoron a far greater number of atoms will decay in your lungs. Radon from U ore has a half life of 3.8 days and only a tiny amount will decay in your lungs before you exhale.

The only advantage of thorium minerals are the huge energies of 10 mev alphas emitted by Po212 and the high energy Gamma emitted in the 2.6 mev range by Tl208! As with Uranium, all Thorium minerals are in full equilibrium and have the same storage suggestions.

Thorium chemicals

Thorium chemicals are even rarer than U chemicals and are tightly regulated. Still, you might find an ancient bottle of thorium nitrate from an old lab for sale. Thorium gas lantern mantles were once common and could be purchased in hardware, sports and department stores. Not anymore!
Thorium in such mantles was removed many years ago. However, these mantles are still manufactured by the millions in third world countries. These contain thorium nitrate in a silk mesh. When a new mantle is installed and fired up, the thorium nitrate is instantly turned into thorium oxide to produce the brilliant white light. The silk is also consumed and only a web of powdered thorium oxide remains. This is easily damaged and powdered to dust if the lantern suffers a sharp blow in handling. This dust can be inhaled when replacing the mantle. Nasty!!

A big issue exists regarding thorium equilibrium. Unlike Uranium taking 2 million years to reach full equilibrium with its many daughters. Fresh thorium chemicals including mantles can rip through to full equilibrium in about 36 years giving off immense quantities of Radon gas, far more than one might imagine if the chemicals or mantles are of that age. Very, very dangerous. Remember. it must be old Thorium.

These are the only sources available to the fusioneer. For the gamma spec guys you might invest in a Cs137 limited quantity isotope disc and a good hot sample of Uranium ore.

All of the above would also be good for gamma/neutron discrimination when setting up a neutron counter electronics.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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