Easy polonium-beryllium neutron source: assembly, disassembly, and discussion

[priisdk]

Even if you don't need your neutron detector in the Chadwick experient (Chadwick didn't have one!) it could be interesting to see if there are really detectable neutrons moving in the 'backwards' direction.

[priisdk]

I find your video(s) extremely interesting!

However, I would be even more excited if you would make a video reproducing Chadwicks origimal experiment. Put the piece of Beryllium between the Polonium source and a Geiger tube. Prepare a small piece of plastic (or paraffin) to put between the Beryllium and the Geiger tube.

Chadwick had a vacuum chamber but your experiment shows that this is not really necessary for producing neutrons.

Poul Riis, physics teacher, Denmark

priisdk@gmail.com

[Thallium208]

@priisdk Thanks for your interest. The challenge in repeating Chadwick's experiment with this setup has to do with the exceedingly small neutron flux available from the 5 mCi source, and the low efficiency of Chadwick's recoil detection process. Your Geiger tube would have a background countrate that is high relative to any observed recoil protons, just because of natural background. Chadwick had relatively large neutron sources at his disposal.

[priisdk]

@Thallium208

Thank you for your quick and clarifying response to my (apparently rather naive) suggestion!

Do you happen to know how strong Chadwicks polonium source was?

Poul Riis

[Thallium208]

@priisdk One can only guess on the basis of other sources of "beryllium radiation" that were common at the time, since Chadwick didn't mention source strength in his paper. It was probably a large fraction of a curie of radium (D+E+F), that is, Po-210 and its parents, deposited on a silver disk. Chadwick mounted this disk facing a piece of beryllium in a ~40 mm steel pipe, essentially identical to a standard 2-3/4" CF nipple with a quarter-inch side tubulation for pumping.

[radumotisan]

You should place the neutron source (Alfa emitter+Be) OUTSIDE the plastic blocks. The reason for having those blocks is to Slow down the fast neutrons, so you can detect them with the long detector tube. What you're doing in this video is to only detect a small amount of the neutrons you're producing. Nice demonstration, but very dangerous, you shouldn't provide such explicit instructions on how to replicate it!

[Thallium208]

@radumotisan Disagree that the best place for the source is outside the blocks. Disagree with your assessment that anything is "very dangerous".

[radumotisan]

@Thallium208 Would you explain what is the purpose of the plastic blocks then? This is "pseudo science" with radioactive materials, so yes, it is very dangerous. Feel free to disagree.

[Thallium208]

@radumotisan The plastic is a moderator, a material to slow neutrons by elastic scattering (as explained in the video). The slow neutron flux in this moderated geometry peaks in the immediate vicinity of the source. I'm sorry if you're not familiar with neutron behavior, but this video illustrates basic and accepted phenomena. If you have specific questions, I'll try to answer.

[ActinideChemist]

@radumotisan How or why is this dangerous to those who are trained to handle apparatus and material, as demonstrated here? As I think has been mentioned several times, this is all generally licensed and the safest form of material--sealed sources. The advice regarding the moderator is just wrong.Do you have any questions? Wish Chadwick were alive for you to tell him your ideas on this being pseudo-science.

[KarbineKyle]

VERY NICE Demonstration! Wow! 5mCi of Po-210! That's a lot to experiment with! Nice sample of Beryllium too! I really like your He-3 probe! I know that has to be expensive. I've never seen a Ludlum with that type of probe before. I've seen them with the sperical body, but not like this probe. I've been trying to figure out how to obtain Cf-252, but no luck so far. Also, it would cost a fortune. Nevertheless, I would love to try it! This is a great experiment! Thanks for making this video! =D

[ryanlak1234]

This assembly reminds me of the demon core experiment that killed two scientists.

[ElGordoUno]

@ryanlak1234 I was thinking the same thing. Kept wait for the flash of blue

[bionerd23]

thanks a lot for this awesome demonstration! =)

very interesting that you can just lease these sources in the USA. is there an "exempt quantity" for neutron sources (in general)?

here, when you turn one thing into something else, it may sometimes put that item under different laws. for example, there's no limit for the possession of uranium ore (falls under some chemicals law, ChemVerbotsV), but if you process it with acids, you have to closely follow the rad. law (StrSchV).

[bionerd23]

@bionerd23

then again, processing uranium ore with acid is "permanent", while this neutron source isnt. hmmm.

well, the exempt quantity for Po-210 is just 10 kBq here, anyway (no matter if leased or not), too bad. my only current option seems to be Cf-254, but that's really horribly expensive.

[Thallium208]

@bionerd23 The way I see it, classifying this ad-hoc arrangement of beryllium and a sealed alpha source as a "neutron source" for legal purposes puts one on a slippery slope. After all, some small number of neutrons already occur incidental to ordinary operation (presumably mostly from O(a,n) in the air). It's a trace neutron source, but not being "manufactured" in any meaningful sense. If I get a call from the authorities, I'll let you know!

[teslafredde]

Very educational and interesting!

It would be interesting to experiment with other alpha targets other than beryllium and observe how the neutron counts would very. I´ve heard that both lithium and aluminium will emmit neutrons when struck by a alpha particle. They are both alot cheaper and more easily obtained than beryllium but ofcourse they are not nearly as efficient as beryllium. But one might ask what is the second best material to use?

[Thallium208]

@teslafredde Hi, and thanks for your comment. The (a,n) neutrons from elemental boron powder and from fluorine in Fluorinert solvents and solid PTFE are easy to detect using weak alpha sources; my own experience entails Am-241 and Ra-226 sealed sources in contact with these materials. Boron is most certainly the next-best after beryllium.

[AScannerClearly]

Neat video, as always! Would have been neat if that were capable of activating other elements, alas I guess I'll have to build a fusor someday to fulfill that dream after all! I must ask, is that source strong enough to observe the blue glow from the ionization of the air in darkness? And how does it do scintillating against various phosphors?

[Thallium208]

@AScannerClearly Yep, you won't get anywhere close to fusor levels with homebrew Be(a,n) sources, but they're still useful for some activation, scattering, and neutron capture experiments. One of my other videos treats the production of Mn-56 using an AmBe source, and I have posted on my blog and on the "fusor forum" about experiments to detect activation as well as prompt scattering and capture radiations using weak neutron sources like this.

[TheOpticalFreak]

Thank you very much for your reply!

Although i am a bit disappointed that americium gives such a poor result.

i had higher hopes for it.

[10mintwo]

Your very own Urchin initiator! :D

[ALARAiswise]

Carl, your videos are very impressive and a great education. Thank you for posting.

[Thallium208]

@ALARAiswise Thanks! 

[TheOpticalFreak]

great demo!

but i am wondering can you also generate neutrons with that peas of beryllium and an alpha source out of an smoke-detector, or is that two weak.

[Thallium208]

@TheOpticalFreak You can generate detectable neutrons with smoke detector sources on beryllium, but by detectable I mean count times on the order of a day, with background subtraction, with careful statistics. In other words, not visually impressive or a quick test.

[RockSteadyRus]

Hello From Russia =)

[MucusFelidae]

A wonderful demo indeed.

Thank you for spending that much money teaching us :-)