I placed 10 thorium laced lantern mantles into a wide mouth glass jar 5.25 inches diameter x 6 inches tall, filled with tap water to just below the threaded neck portion of the jar. The jar mouth opening internal diameter is 3.75 inches. The measured liquid volume is 1.5 liters of 70 degree tap water, assume no dissolved antibacterial chlorine left after sitting for several days w/no lid. The dissolved solids content is probably fairly high (fairly hard water is found in KC Missouri following water treatment processing of Missouri river water source).

The thorium (thoria) laced lantern mantles were manufactured by Aladdin Industries, Inc. Mantle Division / Nashville, Tennessee. These mantles fit standard popular yard, patio, commercial gaslights, and most Coleman Lanterns. They are of two ply construction, and claim to produce up to 15% more light than other similar competition mantles.

These mantles will make a hand held geiger counter sound like a radio tuned for interstation static. I believe the primary emission from thorium dioxide (Tho2) are beta particles. Wikipedia states "The band gap of thoria is about 6 eV." and also reports the use in gas mantle of lanterns, which were frequently composed of 99 percent ThO2 and 1% cerium(IV) oxide". Wikipedia further explains (see isotopes of thorium) "Although thorium (Th), with atomic number 90, has 6 naturally occurring isotopes, none of these isotopes are stable; however, one isotope, 232Th, is relatively stable, with a half-life of 14.05 billion years, considerably longer than the age of the earth, and even slightly longer than the generally accepted age of the universe."(?!!) emphasis mine "This isotope makes up nearly all natural thorium. As such, thorium is considered to be mononuclidic. It has a characteristic terrestrial isotopic composition and thus an atomic mass can be given. Relative atomic mass: 232.03806(2)". Furthermore Wikipedia states "232Th is the only primordial isotope of thorium and makes up effectively all of natural thorium, with other isotopes of thorium appearing only in trace amounts as relatively short-lived decay products of uranium and thorium".[17]

"232Th decays by alpha decay with a half-life of 1.405×1010 years, over three times the age of the earth and more than the age of the universe. Its decay chain is the thorium series eventually ending in lead-208. The remainder of the chain is quick; the longest half-lives in it are 5.75 years for radium-228 and 1.91 years for thorium-228, with all other half-lives totaling less than 5 days."[18] Thorium appears to have many decay states, Th-228 through Th-234. I think most decay by alpha emission.

With all this in mind, my experiment was to see if I could visually detect the presence of Cherenkov radiation inside the glass jar, either looking directly down through the open mouth of the container, or looking through the glass body of it. To my dismay, I was unable to detect even the faintest blue light "glow". I thought the thorium material would likely produce via Cherenkov radiation explanation. I allowed my eyes to accommodate in darkness conditions, but possibly I did not wait long enough?

I based the ignorance of my unsatisfactory quest for the mysterious blue "fire" on the information gleaned from another Wikipedia article: "Cherenkov radiation". I quote this source: "Cherenkov radiation, also known as Vavilov–Cherenkov radiation,[a] is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. The characteristic blue glow of an underwater nuclear reactor is due to Cherenkov radiation. It is named after Soviet scientist Pavel Alekseyevich Cherenkov, the 1958 Nobel Prize winner who was the first to detect it experimentally.[1] A theory of this effect was later developed within the framework of Einstein's special relativity theory by Igor Tamm and Ilya Frank, who also shared the Nobel Prize. Cherenkov radiation had been theoretically predicted by the English polymath Oliver Heaviside in papers published in 1888–89.[2]

Furthermore the same article states the following: While electrodynamics holds that the speed of light in a vacuum is a universal constant (c), the speed at which light propagates in a material may be significantly less than c. For example, the speed of the propagation of light in water is only 0.75c. Matter can be accelerated beyond this speed (although still to less than c) during nuclear reactions and in particle accelerators. Cherenkov radiation results when a charged particle, most commonly an electron, travels through a dielectric (electrically polarizable) medium with a speed greater than that at which light propagates in the same medium.

Moreover, the velocity that must be exceeded is the phase velocity of light rather than the group velocity of light. The phase velocity can be altered dramatically by employing a periodic medium, and in that case one can even achieve Cherenkov radiation with no minimum particle velocity, a phenomenon known as the Smith-Purcell effect.

So, here is another ignorant question, what is a "periodic medium", and does my tap water qualify as being one? If not, is there some kind of salt or acid I can easily procure to add to my tap water so as to make it behave like a "periodic medium"??

Thank you for reading this hopefully stimulating and thought provoking information and inform me as to why my experiment failed, and what I can do to the water make it work?

Steve Cummins NOTE Several days later I came to the realization that I needed to make some additional comments based on the responses to my above questions.

In the following section I have asked probably a lot of "plebeian" questions. Stuff I should have learned in HS, but didn't. Most of my questions below I have prefixed with the letter (Q). A lot of them might be as simple as a yes or no response. If you could insert your answers between the text in a different color font type it will simplify the process of making your explanations understandable to me, as they will be in context with whatever question I have asked. With that said, onto the rest of the story.

I am kind of embarrassed to admit to the fact that I don't know pretty much anything about the radioactive decay process. So, I may not have asked my questions properly.

My whole reason for performing this experiment is because I wanted to have the visual experience of seeing the Cherenkov radiation effect.

At least that was what it was in the beginning. But after searching these and many other subjects: thorium, thorium dioxide, actinide, gas mantle, nuclear transmutation, radioactive decay, alpha particles, thorianite (ThO2), thorite (ThSiO4) and monazite, ((Th,Ca,Ce)PO4) I now realize my very serious lack of knowledge (ignorance) about these and a great deal more about a lot of other related subjects.

I guess I could setup some sort of cloud chamber thing, use blank film, or hook up one of my PMT's (which by the way I don't know how to do) all are good suggestions, and all are impressive solutions, but for me, they are sorta "beside the point".

Question (Q) I want to know why my experiment failed to produce the intended visual effect? To this end I have added what I hope will be helpful information that you can refer back and forth on without going elsewhere to search for information. I hope this stuff will help jog your memory cells back into a frame of reference, the same one that I used to formulate and ask my questions.

Let us begin: The measured radioactive decay of what I assume are alpha particles emanating from my gas-light (unburned) mantles will set a geiger counter popping off hits like popcorn on a hot stove. This tells me that it has detected the presence of some kind of decay emissions, and based on their audible signatures, are present in fairly significant numbers.

(Q) Is my experimental failure because the alpha decay of the thorium, produces particles that are too weak, slow or whatever, to penetrate through the water any appreciable distance so as to propagate the Cherenkov effect?

Wikipedia see: alpha decay "Alpha particles have a typical kinetic energy of 5 MeV (or ≈ 0.13% of their total energy, 110 TJ/kg) and have a speed of about 15,000,000 m/s, or 5% of the speed of light.(emphasis mine).

"There is surprisingly small variation around this energy, due to the heavy dependence of the half-life of this process on the energy produced (see equations in the Geiger–Nuttall law). Because of their relatively large mass, +2 electric charge and relatively low velocity, alpha particles are very likely to interact with other atoms and lose their energy, and their forward motion can be stopped by a few centimeters of air".

I did a headcount on the number of mantles I placed in the jar, there are 14 mantles. These mantles have a globular shape, I expanded them when I put them into the jar and they are holding that shape fairly well. I have an additional 16 mantles I could place into the jar, but that would not leave very much free space between the mantles and the wall of the jar.

If my lack of retinal perceptual acuity turns out to be a limiting factor (more mantles = higher numbers of disintegrations) I can add the rest of them into the jar if this is determined necessary.

According to Wikipedia: Scintillation scintillation:" is a flash of light produced in a transparent material by the passage of a particle (an electron, an alpha particle, an ion, or a high-energy photon). See: Scintillator and scintillation counter for practical applications.[1][2]" Source: Wikipedia.

Also, Wikipedia states: "The process of scintillation is one of luminescence whereby light of a characteristic spectrum is emitted following the absorption of radiation. The emitted radiation is usually less energetic than that absorbed. Scintillation is an inherent molecular property in conjugated and aromatic organic molecules and arises from their electronic structures. Scintillation also occurs in many inorganic materials, including salts, gases, and liquids". Source: Wikipedia emphasis mine.

(Q) Is Cherenkov radiation a type of scintillation effect?

(Q) In the text of my original question, I asked for assistance in determining what possible additions could be made to the aqueous media, such as salts, acids or as stated above aromatic organic molecules, so as to promote the luminescence response. This request is sort of related to my other question below.

In another question I asked for help identifying what a periodic medium is, and how I can make one. Re: "The phase velocity can be altered dramatically by employing a periodic medium, and in that case one can even achieve Cherenkov radiation with no minimum particle velocity, a phenomenon known as the Smith-Purcell effect". Source: Wikipedia: see Cherenkov radiation. emphasis mine throughout

This question was kind of important, and also begs an answer to the Smith-Purcell effect. (Q) "no minimum particle velocity", what does "no minimum particle velocity" mean, and how is it associated with a "periodic medium"? Inquiring minds still want to know.

So, in the immortal words of Strother Martin & Paul Newman "What we've got here is failure to communicate" (1967, Movie: "Cool Hand Luke").

The fault primarily lies in my choice of communication style, which is scattered I admit, and probably contains a lot of extraneous quoted information, some are likely to be irrelevant. I am sorry that I was not as concise and succinct as I should have been (this is probably a gross understatement)?

The fact that I am clouded in my thinking about many basic concepts, things like how the process of radioactive decay takes place in the primordial Thorium and in the source material used in the manufacture of my mantles, which was probably derived by-- "It (thorium dioxide) is produced mainly as a by-product of lanthanide and uranium production." Source Wikipedia: see Thorium Dioxide.

If it takes 14.4 billion years for the half life of thorium (dioxide?) to degrade, and our Universe is less than or equal to this number, and the earth is only 5+ billion years old, then does this mean that all the other unstable forms of thorium in/on this planet are of pre-big bang extraterrestrial origin, originating as the decay products left over from some other previous "universe"? Probably a stupid question, but "stupid is as stupid does", and I duz a lot of stupid things.

(Q) Did all thorium (including its daughter products, everywhere in the Universe) initially start out as primordial thorium?

Unstable: Primordial thorium (ThO2?) --> Th-232--> Ra-228--> Ra-224?--> Rn-220--> Po-216--> Pb-212 stable.

I don't really have any kind of fundamental intuitive grasp of the process of radioactive-decay. (Q) Is it a quantum step-like function, like photonic emissions? (Q) Is there a certain number of alpha-particle emissions that must be released before the thorium dioxide in my mantles decays, and then "quantum-leaps" into becoming say radium-228? Or, (Q) is the process of decay a more linear type function, where it transforms based of the absolute number of alpha particles (becquerels) released, gradually, progressively then "transmutates" (Soddy later recalled, he shouted out: "Rutherford, this is transmutation!" Rutherford snapped back, "For Christ's sake, Soddy, don't call it transmutation. They'll have our heads off as alchemists."[5]) (physics joke) from one element into another. (Q) Why do these nuclear phase-transition times vary all over the map, wildly different for each different daughter isotope compound created, some lasting only seconds while others a millennium or more? (Q) The "amount" of radioactive decay produced per second, seem to be "species dependent" and the becquerel factor (abbreviated Bq) for each species are quantitatively rate limited for that species. (Q) Why is this so, what is it (what property) makes a certain daughter isotope emit alpha particles faster or slower than other isotopes within that same series? Why don't they just continually spew off alpha particles left and right, always in the process of transitioning, one element into another, and always at the same rate?

One respondent stated that the rate of thorium decay may only produce single digit Bq. I have difficulty understanding this, based on the geiger counters ecstatic response when I scanned the thorium mantles.

I guestimate these mantles were made in the late 60's based on their original packaging materials. The guy I got them from retired from the Gas Service Company probably 20 years before I got them, which was in the early 90's.

(Q) Is the thorium in my mantles still thorium, or has it transitioned into something else?

Below is a link to a diagram https://commons.wikimedia.org/wiki/File:Radioactive_decay_chains_diagram.svg#/media/File:Radioactive_decay_chains_diagram.svg

A diagram of the thorium decay chain (Wikipedia) See link below.


The chart below gives half-life times for the various nuclides. Thorium-232 is the heaviest. (Q) Is thorium-232 of primordial origin, clocking in at around 14.4 billion years half life. If it is not of primordial origin, then what form of thorium is?. I don't understand the implied meanings behind the numbers reported in these decay tables.

"The 4n chain of Th-232 is commonly called the "thorium series" or "thorium cascade". Beginning with naturally occurring thorium-232, this series includes the following elements: actinium, bismuth, lead, polonium, radium,radon and thallium. All are present, at least transiently, in any natural thorium-containing sample, whether metal, compound, or mineral. The series terminates with lead-208.

Sorry about the butchered table below, I don't have enough "points" to allow me to insert links to click on. It looks completely different while I am in the "edit" mode. I am too slow in my understanding as to how to properly compose readable text in this format. Please See the above references for how to get to the online version of the table shown below. They look completely different, they are understandable and are in a properly laid out format.

The total energy released from thorium-232 to lead-208, including the energy lost to neutrinos, is 42.6 MeV. (mega electron volts?) nuclide historic name(short) historic name(long) decay mode half-life (a=year) energy released, MeV product of decay 252Cf α 2.645 a 6.1181 248Cm 248Cm α 3.4×105 a 5.162 244Pu 244Pu α 8×107 a 4.589 240U 240U β− 14.1 h .39 240Np 240Np β− 1.032 h 2.2 240Pu 240Pu α 6561 a 5.1683 236U 236U α 2.3×107 a 4.494 232Th 232Th Th Thorium α 1.405×1010 a 4.081 228Ra 228Ra MsTh1 Mesothorium 1 β− 5.75 a 0.046 228Ac 228Ac MsTh2 Mesothorium 2 β− 6.25 h 2.124 228Th 228Th RdTh Radiothorium α 1.9116 a 5.520 224Ra 224Ra ThX Thorium X α 3.6319 d 5.789 220Rn 220Rn Tn Thoron, Thorium Emanation α 55.6 s 6.404 216Po 216Po ThA Thorium A α 0.145 s 6.906 212Pb 212Pb ThB Thorium B β− 10.64 h 0.570 212Bi 212Bi ThC Thorium C β− 64.0 α 35.94%

                                               60.55 min    2.252 6.208 212Po

208Tl 212Po ThC′ Thorium C′ α 299 ns 8.955 208Pb 208Tl ThC″ Thorium C″ β− 3.053 min 4.999 208Pb 208Pb ThD Thorium D stable . . .

There you have it all now. I won't claim to know most of what are contained in the borrowed charts and diagrams above. Hopefully you will and can use them to tell me where I have gone astray.

Disclaimer: If the scope of this inquiry is outside the parameters of this physics forum, then I apologize for its content and ask for your forgiveness of my ineptitude.

Steve Cummins.

  • $\begingroup$ The principal means of radioactive decay in thorium is through alpha emission, not beta emission as I incorrectly stated in the above article/questions. $\endgroup$ Feb 4, 2016 at 6:11
  • $\begingroup$ Steve, you can edit your question to correct any mistakes. $\endgroup$ Feb 4, 2016 at 6:13
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    $\begingroup$ I would guess the Cherenkov radiation is there but it's too faint to be seen. The blue glow seen in pictures of nuclear storage pools comes from very intense radiation many orders of magnitude higher than your thorium mantles can produce. $\endgroup$ Feb 4, 2016 at 6:15
  • 1
    $\begingroup$ You should be able to detect it with a photomultiplier tube, which is still well within the reach of a do-it-yourself physics experiment. I don't think you ever want to see radiation with your own eyes under anything but extremely controlled conditions... if you see it, and it's not properly shielded, you would be seriously exposed. You can buy surplus photomultiplier tubes for less than $100. A high voltage power supply and a base are easy to make (or you can try to buy one, too). The rest is careful construction of a dark box and... lots of patience with the calibration and controls. $\endgroup$
    – CuriousOne
    Feb 4, 2016 at 6:47
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    $\begingroup$ You know what, I think I still have the two Hamamatsu PMT's I salvaged out of an inductively coupled mass spectrometer that was antiquated and headed for the bone yard. With my kind of luck, I would probably get run over by a horseless carriage, sort of like what happened to Pierre Curie, before I died from what little radiation poisoning I'd get from thorium laced lantern mantles. Hmm, I wonder if my teeth glow in the dark from the strontium blown into the midwest from all the atmospheric testing done out west in Alamogordo, NM and all around Frenchman's Flat, NV in the 50's and 60's? $\endgroup$ Feb 4, 2016 at 9:24

3 Answers 3


As the lifetime of the thorium you have available is so long , the probability of an atom decaying is very small . In addition the transit velocity of an electron which is traveling with a velocity higher than the phase velocity of light in water, will be in a time frame undetectable to the eye, so the cerenkov radiation from that single electron will be in a very small delta(t) . You need a very great number of such electrons to see by the naked eye the radiation as the glow in the water reactors.

As you were told in the comments a photomultiplier would detect it. I am suggesting here a simpler experiment. Prepare a light tight box for your experiment. Take two pieces of unexposed film. In a dark room as complete as possible,( I think photographers use red light which does not register on the film), wrap one film around the water container, and close the whole in the light tight box. In a second light tight box do the same with the other piece of film, which will be your control for light leakage and may be cosmic rays . Leave it for 24 hours.

You should have the radiation sources on one side of the glass jar. I expect you will get images of the thorium locations in your water container while the control film will be generally fuzzy. If the first film is over exposed this will also be proof, if under exposed try for a week. ( have not calculated anything).

Not relevant , but it is what made me think of the film:

Back when I was a graduate student, we had been using a gun camera to get pictures from a spark chamber for cosmic rays. Gun cameras were used in WWII to take a photo of the target area when gunning with airplanes. We found it cheap at the flee market :). It is designed to always have a fresh film available, after the first shot.

Edit after edit of question:

Too many questions are asked in the edited version, whereas the site answers one question or so at a time.

what does "no minimum particle velocity" mean, and how is it associated with a "periodic medium"? Inquiring minds still want to know.

If you looked further in the wiki Cerenkov link for the Purcel effect you would find:

they sent an energetic beam of electrons very closely parallel to the surface of a ruled optical diffraction grating,

In a nutshell they changed the phase velocity of light built up by the grating. If they say no velocity limit it is because the phase velocity of light in the beam generated by the electrons is changed independent of the velocity of the electron because the light is generated by the grazing interaction of the electron with the grating and depends on the angle of scatter , not on the particular velocity of the electron .

If you do not know what a diffraction grating is , hit on the link in the link above.

So no, you cannot have one in a jar.

Now alpha particles ionize heavily in water and pick up electrons and disappear into helium gas . It is the electrons that survive in water enough , so only those isotopes in your thorium sample will contribute to the cerenkov effect.

Counts in Geiger counters in air, are different than counts in water, so the noise your counter makes is not relevant as far as observing radiation products in water. Why do you think they made water surrounded reactors? to absorb the radiation. The blue light C effect is a side product from beta decays that survive in water.

  • $\begingroup$ Great suggestion, a heck of alot easier than trying to figure the pin-out configuration at the bottom of my PMT. Film? what is film? $\endgroup$ Feb 4, 2016 at 10:08
  • $\begingroup$ Aren't you supposed to place a copper cross in front of the film? $\endgroup$ Feb 5, 2016 at 6:32
  • $\begingroup$ @KeithMcClary as a control? I have suggested a second film for a control away from the radiation sources. $\endgroup$
    – anna v
    Feb 5, 2016 at 6:40

No. If $v \approx 0.05c$ then you need an index of refraction on the order of 20. That's not going to work with water.

Note that Cherenkov detection is pretty much a 1 parameter system: the index of refraction $n$ controls everything:

Threshold: $v = c/n$

Cone Angle: $\cos{\theta_C} = c/(vn)$

Photons per cm: $490Z^2 \sin{\theta_C} $.

Spectrum: $\frac{dN}{dE} \propto E$.

The penultimate formula means you get 0 photons right at the threshold--you need margin in choosing $n$.

The last formula means UV photons are preferred, and most of the energy will be where your PMT can see them (esp. if you deposit pTP on them), but your eye's can't.

  • 1
    $\begingroup$ If I removed the coating used inside fluorescent tubes and suspended this particulate in a suitably clear medium along with my thorium laced lantern mantles, would there be enough decay energy present to make some of the suspended material fluoresce? If this is possible, what would the ideal suspension media be? $\endgroup$ Nov 28, 2017 at 6:43
  • $\begingroup$ @SteveCummins Vegetable glycerin is (relatively) cheap, and non-toxic. It is clear, and thick enough it might stop descending particles. Plus if your residue is fine enough it won't go anywhere, adhering to the glycerin. $\endgroup$
    – Mark C
    Apr 21, 2018 at 21:46
  • $\begingroup$ @SteveCummins If you want a fluorescence, use a plastic or other organic. To test it: hold it in sunlight (or black light). Do the edges turn purple? If yes, then it is converting UV to visible. The plastic seal on gatorade sports bottles is a good example. $\endgroup$
    – JEB
    Apr 21, 2018 at 22:52

You might be able to see it if you remain in a totally dark room for a number of hours so your eyesight is fully dark adapted. The eye can register as few as 10 photons per second.

The hard bit is the "totally dark room". By that I mean not a single photon enters. In practice you would have to do this underground, probably in a cave.

  • $\begingroup$ I do suppose I could wear a pair of those funky red-goggles that radiologists wear when outside the darkroom. I happen to have such an item, gotta find them though, this could take a while. $\endgroup$ Feb 4, 2016 at 10:11
  • $\begingroup$ @SteveCummins Nowhere near good enough. Your face and skull will be transparent to significant numbers of visible light photons. $\endgroup$
    – user56903
    Feb 4, 2016 at 10:23
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    $\begingroup$ The vitreous humor generates Cerenkov radiation every time a cosmic muon passes through the eyeball itself. Alas, given the size of the eye, the middling QE of the light sensitive pigments and the need for multiple nearby hits to register consciously, the vast majority will never register. To try it, go far enough into a shallow cave to find complete darkness, wait for adaption, lay on your back. Depending on depth you might expect as many as 1 cosmic muon with good geometry in each eye every 20 seconds or so. But I think that you will register only a few percent at best and without color. $\endgroup$ Feb 4, 2016 at 15:23

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