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Picture of Pocket Size Spinthariscope

The spinthariscope was invented by William Crookes in 1903. While observing the apparently uniform fluorescence on a zinc sulfide screen created by the radioactive emissions (mostly alpha radiation) of a sample of radium bromide, he spilled some of the sample, and, owing to its extreme rarity and cost, he was eager to find and recover it.

Upon inspecting the zinc sulfide screen under a microscope, he noticed separate flashes of light created by individual alpha particle collisions with the screen. Crookes took his discovery a step further and invented a device specifically intended to view these scintillations.

It consisted of a small screen coated with zinc sulfide affixed to the end of a tube, with a tiny amount of radium salt suspended a short distance from the screen and a lens on the other end of the tube for viewing the screen. Crookes named his device from Greek σπινθήρ (spinth´ēr) "spark".


What's the difference between the upgraded, and regular version? The previous version used a reflection based fixed scintillation screen, while this version uses a transmission based adjustable scintillation screen. Compared to the previous version this one offers an increased scintillation rate, and the ability to set the distance between the source and the screen.

Step 1: Safety First

Picture of Safety First

To build this device you'll need to deal with a radioactive substance: Americium 241.

In the process of radioactive decay, americium releases alpha particles and gamma rays. Alpha particles are relatively high energy particles, but travel only extremely short distances and do not penetrate the skin.

However, if americium is taken into the body and enters body tissues, alpha particles may produce damage to nearby cells.

The radiation from americium is the primary cause of adverse health effects from absorbed americium. Upon entering the body by any route of exposure, americium moves relatively rapidly through the body and is deposited on the surfaces of the bones where it remains for a long time.

The dose from this alpha and gamma radiation can cause changes in the genetic material of these cells that could result in health effects such as bone cancers.

Gamma rays can travel much greater distances and can penetrate the entire body. Since alpha particles do not penetrate the skin and the gamma rays released from americium sources are relatively low in energy, external exposure to americium is not usually considered to be a danger to your health.

Anyway you must use at least eye protection, dust mask and rubber gloves when dealing with Americium 241.

Nice. I'm gonna have to do this one day.
almateus6 days ago
Do you think that if you attach a webcam to the microscope it would show the scintillations? That would make it easier to show what happens to the students. Thanks for the instructable. No smoke alarms here in Brazil, but I do have an Americium source at school, maybe I will try this sometime.
Remove the lens and filter from the webcam and just put the Americium near the ccd sensor. No need for ZnS. If you google for 'Americium webcam', you'll find examples.
hombremagnetico (author)  almateus6 days ago
Hi almateus, the new version is more suitable to be used with a USB microscope. The scintillations are brighter using the scotch tape screen, but I don't know if a normal webcam is sensitive enough. Putting the scotch tape directly in contact with the CCD (powder side facing outwards) should do the job though...
The webcam on a microscope is an awesome idea! Or, go to ebay and search for "USB Microscope" You can get a 1.3 megapixel USB microscope with > 100x magnification for just over $10 to $12 (including shipping.)
Thanks for reminding me that I have one of those already. It basically is a webcam with a lens in front of it. Don´t know if it can magnify 100X, or if the sensor is sensitive enough for low light conditions, but it is worth a try.
Olá, no Mercado Livre você acha alguns modelos, Não sei se usam o Americium. Grato
SHOE00074 days ago
Well, Amercium 241 is cheap to get and you can get old smoke alarms on ebay for that or a smoke detector. I like this type of project. I bet other ore like Pitchblade which is 80 percent UO2 would not work since it not powerful enough alpha particles It 8000 cpm were Alpha can be 100,000 CPM in alpha.
RobertS7705 days ago
What's the difference between the upgraded, and regular version?
hombremagnetico (author)  RobertS7705 days ago
Hi RobertS770, the previous version used a reflection based fixed scintillation screen, while this version uses a transmission based adjustable scintillation screen. Compared to the previous version this one offers an increased scintillation rate, and the ability to set the distance between the source and the screen.
tercero9 days ago
I LOVE this instructable. It's very cool. My wife teaches elementary school, I wonder if it would be considered safe enough for her to bring into the school to give a demonstration if I build this.
Thanks again for this instructables.
Hi Tercero, Your wife and you probably realize this already, but considering how some people are these days, I would suggest that she run this experiment by the Principal, write up exactly what she will be doing and how the ingredients work and have the parents sign off on letting the children "participate". Accidents do happen and some kids just have an overwhelming need to touch and know why. There is always the one or two kids that have earplugs in when the word dangerous is said. Kids sometimes have no concept of danger (we were all there once :) ) and this can go terribly wrong. Good luck.
I finished building this, and instead used an adapter for my Nikon Z6 FX to take some pretty amazing shots.
She showed the results to her class and explained what exactly they were looking at.
Pretty amazing.
hombremagnetico (author)  tercero9 days ago
Thanks! :) Well... as long as the source is not ingested or touched with bare hands it should be pretty safe. But the better people to ask for info and authorization should be school's health and safety representatives. Every country has is own laws...
We're in Ontario, Canada btw.
hombremagnetico (author)  tercero6 days ago
I'm afraid I can't help... :)
As a demo
You need to hold it against your eye

Not a good idea when it cannot be guaranteed to be sealed or uncontaminated.

Even at senior physics classes this has been not a good idea.

Biggest issue was eye infections from the eye piece..
garybau7 days ago
Illegal in Australia as well.
Not to be encouraged.
hombremagnetico (author)  garybau6 days ago
Thanks for your comment! I added a "legal bit" section as well.
Great instructable. I sure wish all these 'Safety Pups' had been around when humans entered the atomic age. Oh wait, we probably wouldn't have. I wish government would keep us all safer.
I do have to say that this instructable was well written about a subject and device few know about; where it falls down a bit is in it's cavalier attitude on handling a radioactive source, and the ignoring of laws that exist in almost every country about handling such sources.

It does do some diligence in noting to use some safety equipment to extract the Americium source from a smoke detector, I will give the author that. It also notes the elevated danger such a source possesses should it be ingested. But it might have gone further to warn people that what they are doing may be subject to laws in their country, and that proceeding could open them to legal liability.

Regarding your assertion that humans would not have "entered the atomic age" had the dangers been known, I would dispute that. I think, had we known the dangers, we would have proceeded far more cautiously than we did, and many of the accidents that were suffered by researchers and others throughout the early to post-WW2 years may have been avoided.

There's also the (slim) possibility we, as a species, would have not proceeded with the development of nuclear weapons; one can hardly say we have developed socially or responsibly enough to handle weapons which can cause an existential crisis to our species should they be used en-masse. While so far, their existence have seemed to have deterred wars of the scale we have seen in the past, less than a century is not anywhere near long enough of a time to know if the reasoning of MAD holds true long-term. Given that our current POTUS has in the past ruminated on why we shouldn't be able to use such weapons, it seems clear that it is only a matter of time before some country actually does so. This would seem to indicate that we have learned little to nothing regarding these weapons as a species, unfortunately.

The government regulations we have in place currently for handling radioactive material were arrived at precisely because such material is now known to be dangerous in the hands of those who either do not or can not handle it responsibly. Whether that is individuals, companies, or nation-states does not matter; these regulations seek to try to control such proliferation in order to help, in whatever manner, to keep people safe.

That is part of the role of government; it is why government as a concept exists, period - it is power, willingly or unwillingly ceded to an entity in the idea and hope that such entity will keep the "citizens" from harm. One can argue that there is a point where doing so does in fact constitute a harm to the citizens; but you need to make such an argument for it to be considered, which you haven't.

I'd argue that in this case, the laws and regulations that surround the handling of nuclear material from our governments around the world have been an attempt to keep the citizenry safer, and that such regulation does not rise to a harm itself.
hombremagnetico (author)  AndrewA1676 days ago
Thanks for your comment! I added a "legal bit" section as well.
RGrimmer7 days ago
I speak as a physics teacher (secondary school, UK) who has looked into the safety of smoke detectors both for use as a demonstration in class, and so as to give advice at CPD workshops I run for the Institute of Physics.

Please, NEVER dismantle a smoke detector. Every syllabus I have seen states that alpha particles cannot go through paper, so you might assume that they will never penetrate their metal ionisation chamber within the smoke alarm, nor the plastic body of the smoke alarm itself. However, if you hold a school Geiger counter near a smoke detector, you WILL detect radiation, above background level, coming from it. If it can penetrate the ionisation chamber and the body of the smoke alarm, it can certainly penetrate your gloves!

CLEAPPS (Consortium of Local Education Authorities for the Provision of Science Services) publication L93: "Ionising Radiations and Radioactive Substances" advises that "The plastic cover of the smoke alarm may be opened for observation, to detect ionising radiation and to insert the battery. Under no circumstances should the metal ionisation chamber be opened."

This is a very interesting Instructable, but my advice is to look at these things on the web, and not to do them yourself.

I just found another possibility regarding your geiger counter and higher readings than background radiation. The long and the skinny is that geiger counters are not useful for accurately measuring low dose sources of radiation. here's the quote and the link to the page. "... when it comes to understanding some of the limitations of Geiger counters – it helps to understand that alpha particles have a lot more energy than do beta particles. It also helps to understand that radiation dose is a measure of the amount of energy that’s deposited by radiation in an object – more energy means more dose. So looking at this graph, we can see that high-energy radiation hitting a detector leaves a bigger signal than does low-energy radiation. Now look to the right, in the Geiger-Muller region – in this region the high-energy radiation produces exactly the same signal as the low-energy radiation. So we can’t tell the difference between high-energy and low-energy radiation, which means that we can’t necessarily tell how much radiation dose a person was exposed to if we’re just measuring with a Geiger counter. This is one reason that we can’t always use a Geiger counter to measure radiation dose rate accurately. If a Geiger counter, for example, is calibrated to measure radiation dose rate from the radionuclide Cs-137 it will be right on the money as long as you’re trying to measure radiation dose from this nuclide. But what if you’re trying to measure radiation from cobalt-60 (Co-60)? Well, then you’re in a bit of trouble – radiation from Co-60 is twice the energy as radiation from Cs-137 so whatever your detector reads will be only half the actual radiation dose rate. On the other hand, a lot of radionuclides are lower-energy; in this case, your meter is going to read a higher dose-rate than is actually the case. The bottom line is that a Geiger counter will only give an accurate radiation dose-rate reading if it’s measuring the same radioactive material it was calibrated with. This is why Geiger counters aren’t always the best instruments to use to measure radiation dose rates." link here:
Interesting. here's what the Canadian Government has to say about Radiation from smoke detectors. "The radiation source in ionization chamber smoke detectors is sandwiched between metal foils, which keep the radioactive material well contained.
The tiny amount of radiation that can be measured outside the unit does not pose any health risk. In fact, the average annual radiation dose a person receives from a smoke detector is 0.01 percent of the dose they receive from natural background radiation."
I would pose that if you have detected amounts of radiation from an Ionization chamber smoke detector, I would report it immediately to your government for them to take action. My government strictly regulates all radioactive materials and perform over a hundred tests on these devices to make sure they are safe. the detector you tested should be reported immediately it might be a breech of the regulations the UK has on them. either that, or the Geiger counter you used is out of calibration, and they need to be calibrated. Also, Geiger counters have a limited service life and it is not recommended to use them after that date. myself, having used several geiger counters at University (Nuclear Medicine), it is highly likely that the latter is the case rather than the former, Since Americium is so expensive and labor intensive to retrieve from Nuclear reactors, I don't think someone is going to deliberately nor accidentally put too much Americium in a source for a smoke detector. Most School Geiger counters don't need calibration since the lessons taught are of a empirical nature, meaning it's just good enough to show that there is radiation coming from whatever it is they are testing. Things like that are heavily regulated and when rules a breached, it means laws have been broken and usually prison time enues, so no one is going to be negligent when metering out minute amounts of radioactive Americium 241. Most people I know also do not wish to harm others and when in such positions of employ, take extra precaution when working. Much like Nurses, doctors, Surgeons etc. do when they work to improve people's health.
Rolls eyes. When I was your age, we did Macho Science. We "played" with highly corrosive, highly poisonous and highly explosive materials - AND WE LIKED IT! occasionally a finger or an eye was lost - so what? That's the price of freedom bitches!! Don't be a pussy! I did 4 tours in Iraq - if I want to suck some alpha particles, I earned the right to do it... (USACE, 416th Engineer Command.)
The radiation source in ionization chamber smoke detectors is sandwiched between metal foils, which keep the radioactive material well contained.
The tiny amount of radiation that can be measured outside the unit does not pose any health risk. In fact, the average annual radiation dose a person receives from a smoke detector is 0.01 percent of the dose they receive from natural background radiation. This is an excerpt from the Canadian Nuclear Safety Commission's webpage. further information can be found here:
I'm just going to leave this information here and a link to where it came from, in lieu of all the posts and concern about Radiation from Smoke detectors. This is what is said in the link:
"Ionization chamber and photoelectric smoke detectors are the two most common types. Both work very well and are safe to use.
There are no health concerns with photoelectric smoke detectors because no radiation is involved. Photoelectric smoke detectors sound an alarm when smoke particles scatter a beam of light in the detection chamber. They respond quickly to fires with lots of smoke.
Ionization chamber smoke detectors contain a small amount of americium-241, a radioactive material. Smoke particles disrupt the low, steady electrical current produced by radioactive particles and trigger the detector's alarm. They react quickly to fires that give off little smoke. Ionization smoke detectors expose people to a tiny amount of radiation—about 1/100 of a millirem per year. This is well below the background radiation level of about 360 millirems a year. If a smoke detector contains radioactive materials, a printed notice on the packaging will say so.
Because of the long half-life of americium-241, the amount of radioactive material in an ionization chamber smoke detector at the end of its useful life will be about the same as when it was purchased. State and local requirements for disposal of ionization smoke alarms vary. Some States conduct an annual roundup of ionization smoke detectors similar to that for hazardous household chemicals. Others allow ionization smoke detectors to be thrown out with ordinary trash but recommend that used smoke alarms be returned to the supplier. Some States require that used smoke detectors be returned to the supplier. Check with your local solid waste district, hazardous waste program, or health department to find out the procedures in your area. All manufacturers of ionization smoke detectors must accept returns—when in doubt, return the detector. Return addresses are listed in the product warranty or use instructions.
Smoke detector batteries should be disposed of as explained in What should I do with dead batteries?
Health Issues: Radiation can cause cancer and other problems, including defects in unborn children. Radiation produced during normal use of ionization smoke detectors is so low it has no noticeable effect. If the ceramic chamber containing the radioactive material is removed and swallowed, exposure is about six times the desirable yearly exposure—still too low to cause acute health effects."
BarryB146 days ago
Herbivore1 thank for your honestly, but like I always say check with the professionals before myself making a comment. This is not an attack on you, I am just saying this because of what I do for myself. My friend.
fred_6 days ago
Cool be looking for that post.
the nrc considered a teacher using the source in the classroom.

In the case of misuse, the following scenarios are considered: (1) exposure to a teacher who
removes an 241Am source from a smoke detector for use in classroom demonstrations about
radioactivity, and (2) exposure to a person who removes an 241Am source from a smoke
detector and subsequently swallows it by accident. To estimate the potential radiation dose to
the teacher, it is assumed that the teacher stores the 241Am source in a convenient location in a
classroom and is exposed at an average distance of about 1 meter from the source for
1000 h/yr. The EDE rate at 1 meter from a 37-kBq (1-Ci) source of 241Am without regard for
shielding by other materials is about 0.09 nSv/h (9 nrem/h) (see Section 2.15.3) and the annual
EDE to the teacher could be 9×105
mSv (0.009 mrem). Also, the teacher handles the 241Am
source for 10 h/yr during classroom demonstrations at a nominal 1 cm distance (due to the size
of the disk upon which the source is mounted) then the dose equivalent to a small area of skin
on the hand is about 0.3 mSv (30 mrem), based on a calculation using photon fluence and
tissue (skin) energy absorption. Assuming a 10 cm2
exposed skin area out of a total skin area
of 1.8×104
(ICRP 26) and a skin weighting factor of 0.01 (ICRP 60), the calculated EDE
would be less than 1×105
mSv (< 0.001 mrem).

so like about spending a day in Denver.